Effects of Plant Growth Promoting Bacteria on chlorophyll a fluorescence parameters of Lolium perenne grown with microclover in drought conditions

Effects of Plant Growth Promoting Bacteria on chlorophyll a fluorescence parameters of Lolium perenne grown with microclover in drought conditions | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of Plant Growth Promoting Bacteria on chlorophyll a fluorescence parameters of Lolium perenne grown with microclover in drought conditions Milena Truba, Jakub Dobrzyński, Jacek Sosnowski This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6520497/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract Background Turf surface is a dominant element of green areas located within rural buildings or in cities. In recent years, mainly lawn varieties of grasses have been used to plant green areas, but microclover ( Trifolium repe ns L.) has been increasingly popular. In addition, microclover can be effective in reducing irrigation costs. Drought is one of the main factors inhibiting the growth and development of plants. In modern agriculture some bacteria are used to promote plant growth and development ie. Plant growth promoting rhizobacteria (PGPR) increase systemic resistance of plants to biotic and abiotic stress. Chlorophyll fluorescence is used to measure the physiological condition and stress level of plants. Fluorescence analysis at O-J-I-P points (OJIP test) is a method used for the examination of plant vitality. Results The presence of microclover in the mixture contributed to the improvement of many chlorophyll a fluorescence parameters of Lolium perenne. Statistically, the maximum fluorescence (Fm), the maximum photochemical efficiency of PSII (Fv/Fm), and the maximum water-splitting efficiency on the donor side of PSII (Fv/Fo) increased significantly. The number of active reaction centers also increased, which translated into better energy flux absorbed by one reaction center (ABS/RC). In addition, there were upward tendencies of such parameters as the area above the induction curve (Area) and the density of reaction centers (RC/CSo). The use of Plant Growth Promoting Bacteria increased the maximum chlorophyll a fluorescence (Fm), the area above the induction curve (Area), and the density of reaction centers (RC/CSo). Conclusion Due to the above effects, microclover can be recommended to be used in lawn mixtures. The positive effect of the plant-promoting PGPB microbial vaccine on the Lolium perenne lawn variety suggests that more studies should be conducted on other plant species subjected to other kinds of abiotic stress. Growing plants exposed to drought stress with the substrate moisture level of 40% FWC did not affect the photosynthesis process. The parameter most sensitive to low substrate moisture was the rate of electron transport through one active reaction center (ETo/RC). Therefore, the ETo/RC parameter should be recommended for further research on drought stress. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Background Drought is one of the main factors inhibiting the growth and development of plants [1]. Despite numerous studies on its mechanism, drought stress impact on plants is relevant as a topic and still frequently discussed [2-7]. A lack of soil moisture significantly inhibits photosynthesis, preventing the effective use of light energy, which in effect is dissipated as fluorescence or heat; these changes occur before the plant shows visible signs of turgor loss. That is why to measure drought stress, methods of chlorophyll a fluorescence determination have been used [8]. In modern agriculture some bacteria are used to promote plant growth and development. According to Furtak [9], the effects of using PGPB (plant growth-promoting bacteria) containing Bacillus spp. bacteria include greater resistance to long-term stress, accelerated seed germination, and the improved growth and extent of the root system. Furthermore, Consentino et al. [10] argue that PGPB are among the effective products reducing the use of mineral fertilizers. Those bacteria stimulate plant growth by producing various biologically active substances, such as phytohormones (IAA, gibberellins and cytokinins) and enzymes (ACC deaminase). Some of their enzymes are involved in biomass breakdown (cellulase, ligninase, and chitinase), in fixing atmospheric nitrogen (nitrogenase), and dissolving forms of phosphorus unavailable to plants [11, 12]. Bacillus bacteria are also included into the PGPR (plant growth promoting rhizobacteria) group, not only because they positively affect plant growth by producing hormones, but also because they increase the content of available nutrients in the soil and produce 1-aminocyclopropane-1-carboxylate deaminase to reduce ethylene concentration in plant tissues [13]. PGPR increase systemic resistance of plants to biotic and abiotic stress [14]. Bacillus strains are ubiquitous and can survive biotic and abiotic stress for long periods of time, forming spores in vivo. Some species of Bacillus have been successfully used as safe biological fertilizers and pesticides, due to their high survivability and as the most prominent rhizobacteria [15]. Chlorophyll fluorescence is used to measure the physiological condition and stress level of plants. Fluorescence analysis at O-J-I-P points (OJIP test) is a method used for the examination of plant vitality [16]. Developed by Strasser et al. [16], the test is applied to analyze photosynthetic apparatus condition during specific types of stress. It is used to determine the impact of stress on specific factors affecting the absorption of light and its conversion into biochemical energy. During the test, within the first second of illumination of the plant sample, previously kept in the dark, chlorophyll a fluorescence increases from the initial value (Fo) to the maximum (Fm) one [17, 18]. The results of the test, presented as a curve on a logarithmic scale, allow determining changes in the flow of excited electrons through the photosynthetic apparatus. The O step in the curve represents an increase in chlorophyll a fluorescence emission from the initial level and reflects the gradual accumulation of QA, i.e. the primary quinone electron acceptor of Photosystem II (PSII) in its reduced form. The O–J phase of the curve represents the reduction of the acceptor side of PSII [2]. The J–I phase represents the process of the reduction of the plastoquinone (PQ) pool. The I-P phase, on the other hand, is the slowest and involves the transfer of electrons through Photosystem I (PSI) and is attributed to the reduction of the acceptor side of PSI [19]. The chlorophyll fluorescence induction curve and the maximum photochemical yield (Fv/Fm) are used as leading parameters detecting stress of various origins, affecting PSII [20, 21]. Another parameter is the maximum water-splitting efficiency (Fv/Fo), which, unlike Fv/Fm, is not an indicator of carbon assimilation but allows for faster detection of stress in the plant. In addition, the Fv/Fo ratio is used to calculate OJIP parameters. These parameters describe the energy fluxes inside and around the reaction center (RC) of PSII, i.e., specific energy fluxes per active reaction center (RC) and phenomenological energy fluxes per excited cross section (CS) of the sample [4, 22]. According to Olsen et al. [21], the absorption components (ABS/RC – energy absorbed per reaction center), trapped energy (TRo/RC – trapped energy flux per reaction center), and electron transport (ETo/RC- electron transport flux per reaction center) should be studied to analyze the location of interference within the photosynthetic apparatus. Pollastrini et al. [23] found that chlorophyll a fluorescence parameters were useful for analyzing plant responses to a variety of environmental stress factors and for phenotyping. According to Baker [24], drought stress can alter the steps of the OJIP test and reduce the intensity of fluorescence at the JIP phase. In negative environmental conditions, on the basis of the chlorophyll a fluorescence technique, it is possible to measure plant vigor, closely related to the functioning of PSII [25]. Additionally, the impairment of the photosynthetic activity affects CO2 fixation [26]. Turf surface is a dominant element of green areas located within rural buildings or in cities. Promoting biodiversity, green areas used for recreation play an underestimated role in the functioning of villages and cities. Additionally, as natural retention reservoirs they soak up rainwater. However, because of low soil moisture or a lack of irrigation, green areas often fail to fulfill their aesthetic function. In the literature there are reports on how drought can be mitigated by microbiological consortia and by using synthetic or natural water absorbents [27-30]. In recent years, mainly lawn varieties of grasses have been used to plant green areas, but microclover ( Trifolium repens L.) has been increasingly popular. According to the literature, in a mixture with grass it fixes atmospheric nitrogen, introducing it to the soil through mineralization, which has a positive effect on the functional and aesthetical value of the lawn [31]. In addition, according to the research by Saeedipooya et al. [32], as a short plant, microclover can be effective in reducing irrigation costs. The present paper examines the effect of PGPB and microclover on minimizing the current problem of drought and insufficient irrigation of green areas. In the research, the following research hypotheses were proposed: 1. Microclover grown in lawn mixtures will have a positive effect on mitigating the effects of drought. 2. The PGPB bacterial strain will minimize drought stress in Lolium perenne grown with microclover and in pure stand. Material and methods Plant growth conditions and experimental design The pot experiment was conducted from the beginning of November 2023 to mid-January 2024 in a phytotron, ensuring constant growing conditions. The air temperature in the light and dark-adapted stage was 22°C, with the light intensity of 200 μmol m −2 s −1 (obtained with high-pressure sodium lamps) and the photoperiod of 16 h in light. The 1.5L pots were filled with soil, which, according to the Bouyoucos–Casagrande aerometric method modified by Prószyński, was light clay [33]. The following plants were used in the experiment: Lolium perenne 2N lawn Boxer, seeds produced by the Granum Seed Company, Wodzierady, Poland, as certified seed material; Trifolium repens L. (microclover) cv. Pipolina seeds purchased from Eco Deco, Kraków, Poland as certified seed material. The seeds of Lolium perenne were sown into some pots , with the seeding rate of 36 g m -2 (Lp1). Other plots were planted with Lolium perenne (34.9 g m -2 ) together with microclover (1.1 g m -2 ), with the latter constituting a 3% share in the mixture (Lp2). The above Lp1 and Lp2 plots were the main research factor. The second factor was drought stress, achieved by maintaining the soil moisture levels of 40% FWC (Field Water Capacity), while FWC in other pots was 60%. The third research factor was the strain of Bacillus spp. N188 producing ACC deaminase – referred to as PGPB in this paper. PGPB were not applied to control pots. The experiment was conducted in four replications. Combinations of experimental factors are presented in Table 1. Table 1 Methodological data Type of crop Field Water Capacity 40% FWC 60% FWC Soil treatment Control PGPB Control PGPB Lp1 Lolium perenne 100% Lp1 40% FWC Lp1 40%FWC/PGPB Lp1 60% FWC Lp1 60%FWC/PGPB Lp2 Lolium perenne 97 % Microclover 3% Lp2 40% FWC Lp2 40%FWC/PGPB Lp2 60% FWC Lp2 60%FWC/PGPB Microbiological material When plants germinated, the Bacillus spp. strain producing ACC deaminase (PGPB) was applied to the soil with a pipette, in the amount of 5mL per pot. The N188 strain was isolated from the soil by the Institute of Technology and Life Sciences - National Research Institute in Falenty (Poland). Approximately 100 bacterial strains were isolated from various soils, including both rhizosphere and bulk soil. Bacterial colonies were selected and passaged until pure strains were obtained. Then the strains were inoculated, according to Patil et al. [34], onto ACC minimal media with bromothymol blue (BTB). The N188 strain was selected, with phenol red as a marker, and grown at 30°C for 24 hours with shaking at 150 rpm in 5 mL of Lysogeny Broth (LB). Then, the strain was inoculated onto Dworkin and Foster medium amended with 3 mM ACC (instead of (NH 4 ) 2 SO 4 ) as the sole nitrogen source [35,36]. After incubation, the bacterial culture was centrifuged at 6000 rpm for 10 minutes. The resulting pellet was suspended in 1 ml of 0.1 M Tris-HCl buffer at pH 7.6, and then the process was continued according to the method described by Penrose and Glick [36]. ACC deaminase activity was calculated by measuring alpha-ketobutyric acid formed by the cleavage of ACC by the ACC deaminase enzyme. Then the selected bacterial strain was identified by sequencing the 16S rRNA gene. To amplify the 16S rRNA genes, universal primers 27F (5′-AGAGTTTGATCCTGGCTCAG-3′) and 1492R (5′-GGTTACCTTGTTACGACTT-3′) were used. The PCR (polymerase chain reaction) products were sequenced by the Sanger technique (NEXBIO, Lublin, Poland). The obtained sequences were assembled to contig (BioEdit) and compared with the sequences from GenBank, EMBL (European Molecular Biology Laboratory), using BLAST (the Basic Local Alignment Search Tool). The 16S rRNA gene sequences of the bacterial strain were deposited in GenBank under accession number PP500625. Chlorophyll a fluorescence After the sample was adapted in the dark, measurements on flag leaf blades were made with the OS30p+ fluorometer (plant stress meter), using a clip. Each measurement was preceded by 30 minutes of adaptation in the dark. Then OJIP measurements were made. As a result of the OJIP test measurement, the chlorophyll a fluorescence parameters presented in Table 2 were obtained. Table 2 The description of fluorescence parameters (in relative value) The data obtained in the OJIP test and other parameters calculated Abbreviation Description O Fluorescence at 20 μs K Fluorescence at 300 μs J Fluorescence at 2 ms I Fluorescence at 30 ms P = Fm Fluorescence at 3s (with maximum fluorescence measured) Fo Minimum fluorescence Fv/Fm Maximum photochemical efficiency of PSII Fv/Fo Maximum water-splitting efficiency on the donor side of PSII Area The area between the OJIP curve and Fm ABS/RC Energy absorbed by one active reaction center TRo/RC Energy flux trapped by one active reaction center (RC) ETo/RC Electron transport flux per one active reaction center (RC) DIo/CS Thermal dissipation of excitation energy by PSII of a photosynthetic sample ETo/CSo Electron transport flux per cross section (CS) of a sample RC/CSo Density of reaction centers (QA reducing PSII reaction centers) Statistics The results of the research were processed using the Statistica 13 program (TIBCO Soft-ware Inc., PaloAlto, CA, USA). The data were analyzed at the significance level of p<0.05. The differences between means were assessed with ANOVA and Tukey’s HSD test (Honest Significant Difference). In the tables the significance of the differences between means is indicated by lowercase and uppercase letters. Results and discussion Chlorophyll a fluorescence induction curve (OJIP curve) Chlorophyll a fluorescence induction curves presented in Figure 1 illustrate the plants’ physiological condition for each experimental unit. The lowest chlorophyll a fluorescence was recorded in control Lolium perenne grown in pure stand (Lp1) on the soil with 60% moisture. On the other hand, the highest values were noted for the grass grown in a mixture with microclover (Lp2) on the soil with the 60% moisture. The fact that curves for Lolium perenne grown together with microclover on the soil with 60% moisture (Lp2/60%) were higher than the others might be attributed to the presence of the legume plant in the mixture. Due to its ability to fix atmospheric nitrogen, microclover introduced its additional amount into the soil. In effect plants in the mixture were nourished better and chlorophyll a fluorescence reached greater values. Similarly, Kalaji et al. [37] confirmed that the supply of plants with nitrogen resulted in an increase in fluorescence. The induction curve of Lolium perenne grown in pots with 40% FWC did not change so dynamically. However, there were clear differences between the Lp1 and Lp2 curves, with the latter reaching greater values than the former, both for 40% WFC and 60% WFC. The absence of a distinct K-point on all chlorophyll fluorescence induction curves indicated that the photosynthesis process of plants grown on both 40 and 60% FWC soil was not disturbed. According to the literature, the K-peak can be used as a potential indicator of physiological instability under drought stress even before the appearance of visible signs on plants [5, 18]. The K-point on the chlorophyll a fluorescence curve is caused by the inactivation of the oxygen-releasing complex or by the inhibition of electron transport on the donor and acceptor side of PSII [18]. The multivariate analysis of variance showed no statistically significant effect of either FWC or PGPB or their interaction on chlorophyll fluorescence (Table 3). On the other hand, the effects of the crop type and its interaction with PGPB or FWC were statistically significant. Similarly, statistically significant differences were also noted in the triple interaction of all factors on the O-J fragment of the induction curve. Table 3 Chlorophyll fluorescence assessed by the OJIP test Crop type FWC PGPB Crop type x PGPB %FWC x PGPB Crop type x %FWC Crop type x PGPB x %FWC O 44.25* ns ns 74.17* ns 88.50* 89.00* K 59.75* ns ns 91.16* ns 113.17* 112.67* J 78.17* ns ns 117.34* ns 87.00* 147.34* I 165.88* ns ns 221.97* ns 267.33* ns P 193.12* ns ns ns ns 312.13* ns HSD values from three-way analysis of variance for the effects of crop type, i.e. Lp1 and Lp2; field water capacity (FWC) i.e. 40% and 60%; treatment, i.e. control and PGPB on OJIP parameters. *p≤0.05; ns p>0.05 The results indicated that the application of PGPB significantly increased chlorophyll a fluorescence both for plants grown in Lp1 and Lp2 pots, with Lp2 values being visibly greater (Figure 2a). Chlorophyll a fluorescence for Lp1 plants was greater when soil FWC was 40%, while in Lp2 pots it was greater at 60% FWC (Fig. 2b). It can be assumed that optimal moisture content and the presence of microclover in the mixture contributed to the intensification of the chlorophyll a fluorescence process. According to Digrado et al. [38], low soil moisture had a small effect on PSII performance, but it increased the PSII sensitivity of Lolium perenne to heat stress. Chlorophyll a fluorescence parameters assessed by the OJIP test Compared to control, PGPB increased the minimum fluorescence (Fo) to a large extent (Table 4). Additionally, a 9% increase in Fo indicated an interaction between the type of crop and PGPB. The literature reports that plants react with a chlorophyll a fluorescence increase after the application of plant supporting products [39, 40]. In the present experiment no significant differences were found between the minimum fluorescence (Fo) values for Lolium perenne grown in pure stand and in the mixture. There was a slight difference between pots with different FWC values, for non-irrigated pots this value was on average 1.6% greater. The Fo value was measured with plant receptors open in the dark-adapted state. The measurements were taken in a faint red light so as not to excite the photosynthetic process. According to the literature, greater values indicate lower efficiency of excitation energy transfer between pigment molecules in the PSII energy antenna [41]. On the other hand, photoprotection or an increase in CO 2 fixation can contribute to a Fo decrease. Table 4 Minimum chlorophyll a fluorescence of dark-adapted state (Fo) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 319.00±1.00Bb 389.33±8.08Aa 354.17A 60% FWC 308.33±5.51Bb 340.33±5.51Ba 324.33 A Lp2 40% FWC 312.33±14.15Bb 342.33±5.69Ba 327.33 A 60% FWC 347.67±10.41Aa 344.00±3.61Ba 345.83 A Mean for moisture 40% FWC 315.67Ab 365.83Aa 340.75 A 60% FWC 328.00Aa 340.17Aa 335.08 A Mean for type of crop Lp1 313.67From 364.83Aa 339.25A Lp2 330.00Aa 343.17Aa 336.58A Mean 321.83 b 354.00 a The means in columns marked with the same uppercase letters do not differ significantly. The means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria The maximum fluorescence values varied (Table 5). It was observed that Lolium perenne plants growing with the leguminous plant (Lp2) had a much greater Fm value than Lolium perenne in pure stand (Lp1). According to Kalaji et al. [37], even small doses of nitrogen increased Fm in spring barley. Kalaji and Łoboda [42] stated that nitrogen reduction in relation to the control sample indicated the occurrence of stress, as a result of which not all electron acceptors in PSII were completely reduced. Table 5 Maximum chlorophyll a fluorescence (Fm) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 991.33±240.58 Aa 1090.7±129,68 Aa 1041.0AB 60% FWC 902.33±241.47 Aa 916.00±135.52 Aa 909.17B Lp2 40% FWC 1052.0±135.84 Aa 1178.0±175.45 Aa 1115.0AB 60% FWC 1207.0±113.85 Aa 1235.7±137.17 Aa 1221.0A Mean for moisture 40% FWC 1021.7 Aa 1134.3 Aa 1078.0A 60% FWC 1054.7 Aa 1075.8 Aa 1065.3A Mean for type of crop Lp1 946.83 Aa 1003.3 Aa 975.08B Lp2 1129.5 Aa 1206.8 Aa 1168.2A Mean 1038.2a 1105.1a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Wang et al. [43] observed that in a Bothriochloa ischaemum and Lespedeza davurica mixture, Fm increased with an increasing nitrogen dose. In the present experiment there was no significant effect of substrate moisture on Fm. There was a slight tendency for the PGPB plants to have a 6% greater Fm value compared to control. It is possible that there was an interaction between microclover plants and PGPB Bacillus microorganisms, which increased the Fm value in Lolium perenne growing together with the leguminous plant . The Fv/Fm parameter varied within the experiment and ranged from 0.6 to 0.7 (Table 6). Its values differed significantly between Lolium perenne from Lp1 and Lp2 pots. Lolium perenne grown with microclover had about 9.5% greater value of the maximum photochemical efficiency of PSII. Table 6 Maximum photochemical efficiency of PSII (Fv/Fm) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 0.665±0.080Aa 0.639±0.048 Aa 0.652A 60% FWC 0.642±0.088 Aa 0.623±0.053 Aa 0.632A Lp2 40% FWC 0.698±0.050 Aa 0.704±0.046 Aa 0.701A 60% FWC 0.709±0.033 Aa 0.719±0.032 Aa 0.714A Mean for moisture 40% FWC 0.682Aa 0.671 Aa 0.677A 60% FWC 0.676 Aa 0.671 Aa 0.673A Mean for type of crop Lp1 0.653 Aa 0.631 Aa 0.642B Lp2 0.704 Aa 0.711 Aa 0.708A Mean 0.679 a 0.671 a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria According to Angelini et al. [44], in optimal plant growth conditions, its value should be about 0.85 relative units, and its decrease indicates the occurrence of stress. In the present research, the parameter did not change with the change in soil moisture, which proves it is not sensitive to drought stress. Kalaji et al. [22] also reported that some kinds of stress, e.g. drought, did not affect Fv/Fm value. Digrado et al. [38] obtained the highest Fv/Fm in Lolium perenne in autumn, with average values of approx. 0.75, which indicated a high PSII efficiency. In summer, on the other hand, values as low as 0.15 were noted. Lower Fv/Fm values in summer indicated a reduced photochemical efficiency of PSII and stronger energy dissipation, but the plant returned to its full photochemical activity after the stress subsided. The greatest value of the maximum efficiency of water splitting on the PSII donor side was noted for Lolium perenne plants grown in the mixture (Table 7). According to Aazami et al. [45], plant stress caused by adverse conditions can lead to temporary photoinhibition or damage of photosynthetic organs, resulting in a decrease in chlorophyll fluorescence parameters. This was confirmed by Li et al. [46], who observed that drought stress combined with high temperature resulted in Fv/Fo values falling sharply. Olsen et al. [21] observed that when Fo increased in stressed plants, the Fv/Fo ratio decreased. Table 7 Maximum water-splitting efficiency on the PSII donor side (Fv/Fo) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 2.108±0.761Aa 1.806±0.388 Aa 1.957A 60% FWC 1.924±0.774 Aa 1.690±0.383 Aa 1.807A Lp2 40% FWC 2.385±0.597 Aa 2.446±0.566 Aa 2.416A 60% FWC 2.479±0.423 Aa 2.594±0.431 Aa 2.536A Mean for moisture 40% FWC 2.247 Aa 2.126 Aa 2.186A 60% FWC 2.201 Aa 2.142 Aa 2.172A Mean for type of crop Lp1 2.016 Aa 1.748 Aa 1.882B Lp2 2.432 Aa 2.520 Aa 2.476A Mean 2.224a 2.134a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Statistical analysis of the Area parameter did not show any significant differences between different experimental units, but some tendencies were notable (Table 8). The area above the Lp2 Lolium perenne curves was on average 25% greater, which meant that for those units the number of electron acceptors of photosynthetic electron transport chain (PETC) was also greater. A visible difference was also noticed between the average values of the Area parameter for pots with and without PGPB. Plants with PGPB had a 13% greater number of PETC electron acceptors. Soil moisture content did not significantly affect the Area parameter, and the difference in the average values between 40%FWC and 60%FWC was about 5%. Schansker et al. [47] argue that there is a relationship between the area over the OJIP transients and the number of electrons transported through the PETC before the Fm value is reached. Strasser et al. [16] and Khan et al. [48] stated that this area was proportional to the number of PETC electron acceptors. Table 8 Area over OJIP Induction Curve Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 8379.3±4671.4Aa 9640.7±3429.5 Aa 9010.0 A 60% FWC 7429.3±2982.3 Aa 7401.0±2954.6 Aa 7415.3 A Lp2 40% FWC 9210.7±2650.5 Aa 10545.0±3978.4 Aa 9879.0 A 60% FWC 9700.0±1721.8 Aa 11603.0±2756.9 Aa 10652.0 A Mean for moisture 40% FWC 8795.0 Aa 10094.0 Aa 9444.5A 60% FWC 8564.8 Aa 9502.0 Aa 9033.4A Mean for type of crop Lp1 7904.5 Aa 8520.8 Aa 8212.7A Lp2 9455.3 Aa 11075.0 Aa 10265.0A Mean 8679.9a 9798.0a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Figures 3, 4, and 5 present the differences in percentage between the effects of experimental factor. The pot with Lolium perenne grown in pure stand at optimal field water capacity and without the microbiological vaccine (Lp1/60% FWC) was used as a reference value (100%). Figure 3 presents the effects of experimental factors on Fo, Fm, Fv/Fv, Fv/Fm, and Area parameters. They took greater values for Lp2 pots than for Lp1 ones, which meant that microclover affected the growth and physiological functions of Lolium perenne . A beneficial effect of PGPB was also recorded for pots with plants in drought stress (40% FWC/PGPB), where Fm and Area increased on average by approx. 25% compared to the reference value (Lp1/60% FWC). Specific energy flux per one active reaction center (RC) of PSII The energy absorbed by one active reaction center (ABS/RC) was significantly greater, by 12%, in Lolium perenne plants in pure stand than in Lolium perenne grown with microclover (Table 9). No statistically significant differences were noted between the effects of the other experimental factors, but some trends were observed. A 5% increase in the flux of energy absorbed by one active reaction center was noted for 40% FWC pots compared to 60% FWC ones. Table 9 Energy absorbed by one active reaction center (ABS/RC) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 2.828±0.569 Aa 2.5153±0.343 Aa 2.6718A 60% FWC 2.463±0.405 Aa 2.6107±0.404 Aa 2.5368A Lp2 40% FWC 2.2350±0.206 Aa 2.3920±0.290 Aa 2.3135A 60% FWC 2.2937±0.210 Aa 2.2523±0.395 Aa 2.2730A Mean for moisture 40% FWC 2.5317 Aa 2.4537 Aa 2.4927A 60% FWC 2.3783 Aa 2.4315 Aa 2.4049A Mean for type of crop Lp1 2.6457 Aa 2.5630 Aa 2.6043A Lp2 2.2643 Aa 2.3222 Aa 2.2933B Mean 2.4550a 2.4426a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Monneveux et al. [49] noted an increase in the ABS/RC parameter in plants during drought stress and argued that that indicated that some reaction centers were inactive and the yield per reaction center increased. The ABS/RC parameter also reflects the effective antenna size of the active reaction centers; as the parameter increases, the antenna size of the active reaction centers decreases [50]. Therefore, in the present studies, the antenna of the active reaction centers was larger in the case of Lolium perenne plants on soil with the substrate moisture of 60% FWC and in those grown with microclover. The values of the energy flux trapped by one active reaction center (TRo/RC) did not vary across research factors, ranging on average from 1.59 to 1.67 (Table 10). Using P. scutellarioides plants, Meng et al. [18] observed that the TRo/RC parameter increased in response to drought stress only for the first 10 days, and then it began to decrease. The authors concluded that to resist drought stress and to maintain their growth, plants inhibited electron transport and reduced the PSII photochemical activity at an earlier stage of stress. Table 10 Energy flux trapped by one active reaction center (RC), at time 0 (TRo/RC) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 1.7845±0.130 Aa 1.5605±0.176 Aa 1.6725A 60% FWC 1.6174±0.066 Aa 1.6582±0.154 Aa 1.6378A Lp2 40% FWC 1.5821±0.074 Aa 1.7161±0.165 Aa 1.6491A 60% FWC 1.6009±0.150 Aa 1.5758±0.182 Aa 1.5884A Mean for moisture 40% FWC 1.6833 Aa 1.6383 Aa 1.6608A 60% FWC 1.6092 Aa 1.6170 Aa 1.6131A Mean for type of crop Lp1 1.7010 Aa 1.6093 Aa 1.6551A Lp2 1.5915 Aa 1.6460 Aa 1.6187A Mean 1.6462a 1.6277a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria In the present experiment no statistically significant effect of experimental factors on the electron transport flux through one active reaction center (ETo/RC) was noted. However, this parameter was 6.5% greater for plants in drought stress, growing on substrate with 40% FWC (Table 11). According to the literature [51, 52], in waterlogged conditions plants reduce the ETo/RC parameter value because there are fewer active RCs and more QA reduction. The reoxidation of reduced QA through electron transport in the active RC is also reduced, indicating a decrease in ETo/RC. Table 11 Rate of electron transport through one active reaction center, at time 0 (ETo/RC) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 6.4554±0.753 Aa 5.6524±0.745 Aa 6.0539A 60% FWC 5.8205±0.869Aa 5.7484±0.518 Aa 5.7845A Lp2 40% FWC 6.1488±0.241 Aa 6.6594±0.606 Aa 6.4041A 60% FWC 5.6624±1.164 Aa 5.9708±0.09 Aa 5.8166A Mean for moisture 40% FWC 6.3021 Aa 6.1559 Aa 6.2290A 60% FWC 5.7415 Aa 5.8596 Aa 5.8006A Mean for type of crop Lp1 6.1380 Aa 5.7004 Aa 5.9192A Lp2 5.9056 Aa 6.3151 Aa 6.1103A Mean 6.0218a 6.0078a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Figure 4 present the effects of experimental factors on ABS/RC, TRo/RC, and ETo/RC parameters. Their highest values were recorded for Lolium perenne in pure stand, not treated with PGBG and subjected to drought stress (Lp1/40% WFC). The values for the 40% FWC pots with PGPB were nearly the same as the reference value (Lp1/60% FWC). On the other hand, the lowest values of ABS/RC, TRo/RC, and ETo/RC parameters were recorded in Lolium perenne plants growing in a mixture with microclover, with substrate moisture content of 60% FWC and without PGPB (L2/60% FWC). Fig. 4 The effect of experimental factors on ABS/RC, TRo/RC, and ETo/RC parameters. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Phenomenological energy fluxes per excited cross section of the photosynthetic sample (CS) Density of active reaction centers (RCs) of PSII The results (Table 12, 13, 14) did not show any significant effects of the crop type, %FWC, or PGPB, or their double or triple interactions on the reaction center density (RC/CSo), electron transport by PSII (Eto/CSo), and thermal dissipation of excitation energy by PSII (DIo/CS). Despite the lack of statistically significant differences, many downward or upward tendencies in the above-mentioned parameters were observed. Thus, in the case of the RC/CSo parameter, the number of reaction center densities for Lolium perenne growing in the mixture with microclover was about 10% greater than for Lolium perenne in pure stand (Table 12). In addition, the use of PGPB also resulted in an increase in the RC/CSo parameter by approx. 9%. Table 12 Density of plastoquinone QA reducing reaction centers (RC/CSo) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 112.26±24.31 Aa 136.96±18.80 Aa 124.61A 60% FWC 131.74±20.71Aa 151.05±18.99 Aa 141.40A Lp2 40% FWC 156.20±11.04 Aa 145.12±16.76 Aa 150.66A 60% FWC 136.66±9.86 Aa 155.08±26.75 Aa 145.87A Mean for moisture 40% FWC 134.23 Aa 141.04 Aa 137.64A 60% FWC 134.20 Aa 153.07 Aa 143.63A Mean for type of crop Lp1 122.00 Aa 144.01 Aa 133.00A Lp2 146.43 Aa 150.10 Aa 148.27A Mean 134.21a 147.05a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria The results indicated that the electron transport per cross section of the photosynthetic sample (ETo/CSo) had similar values for both 40 and 60 % FWC. Minor differences were noted between the average ETo/CSo results for Lolium perenne growing in a mixtu re with microclover and in pure stand (Table 13). For the former the value was about 13% greater than for the latter. Similarly, the use of PGPB increased the electron transport flux by about 8%. Table 13 Electron transport flux per cross section (ETo/CS) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 778.14±234.09 Aa 870.68±159.57 Aa 824.41A 60% FWC 735.63±234.13 Aa 778.69±184.41 Aa 757.16A Lp2 40% FWC 772.29±160.21 Aa 925.44±156.50 Aa 848.87A 60% FWC 962.14±104.55 Aa 964.82±123.87 Aa 963.48A Mean for moisture 40% FWC 775.21 Aa 898.06 Aa 836.64A 60% FWC 848.88 Aa 871.76 Aa 860.32A Mean for type of crop Lp1 756.88 Aa 824.69 Aa 790.78A Lp2 867.21 Aa 945.13 Aa 906.17A Mean 812.05a 884.91a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria No major differences for the thermal dissipation of excitation energy by PSII of the photosynthetic sample (DIo/CS) between the experimental units were observed (Table 14). Table 14 Thermal dissipation of excitation energy by PSII of a photosynthetic sample (DIo/CS) Type of crop Moisture Soil treatment Mean Control PGPB Lp1 40% FWC 1.0442±0.44331 Aa 0.95530±0.22540 Aa 0.99970A 60% FWC 0.84627±0.33953 Aa 0.95303±0.26371 Aa 0.89965A Lp2 40% FWC 0.69317±0.14294 Aa 0.67697±0.21421 Aa 0.68507A 60% FWC 0.65307±0.13287 Aa 0.67647±0.14323 Aa 0.66477A Mean for moisture 40% FWC 0.84862 Aa 0.81585 Aa 0.83223A 60% FWC 0.76972 Aa 0.81500 Aa 0.79236A Mean for type of crop Lp1 0.94522 Aa 0.95413 Aa 0.94967A Lp2 0.67312 Aa 0.67672 Aa 0.67492A Mean 0.80917a 0.81542a Means in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 – Lolium perenne in pure stand; LP2 - Lolium perenne in a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria Figure 5 presents the effect of experimental factors on of RC/CSo, ETo/CSo, and DIo/CS parameters. The thermal dissipation of excitation energy by PSII of the sample (DIo/CS) was more beneficial for units with Lolium perenne grown in the mixture (20% lower than for Lp1). On the other hand, its values for Lolium perenne in pure stand were greater than for Lp2 plants, both on 40% and 60% FWC substrate or whether PGPB was used or not. Electron transport flux per cross section (ETo/CSo) was the greatest in Lolium perenne grown with microclover on substrate with optimal field water capacity (Lp2/60% FWC). Increased values of this parameter were also noted for the Lp2 and Lp1 plants grown on substrate with 40% FWC and with PGPB. Density of reaction centers (RC/CSo) was greater in Lolium perenne grown with microclover, with PGPB and 60% FWC (L2/60% FWC/PGPB). The RC/CSo and ETo/CSo parameters are often used to determine damage to the PSII reaction center, caused by adverse environmental conditions [53]. However, as the results indicated, drought stress caused by the moisture level of 40% FWC did not significantly affect the functioning of the PSII and no damage occurred. According to Zhao et al. [6], with low soil water content (<29.7%), the PSII reaction center absorbed significantly more light energy, but the ability to capture and transmit it was significantly reduced; therefore, the accumulation of excess light energy eventually reduced photosynthetic efficiency, with a significant decrease in RC/CSo and ETo/CSo values. Chen et al. [54] and Zhang et al. [55] stated that this indicated that excessive excitation energy was stored at the reaction center, causing the electron transfer on the PSII acceptor side to be interrupted, with the photosynthetic apparatus further damaged. A tendency to decrease RC/CSo, ETo/CSo and increase DIo/CS as a result of subjecting the plant to drought stress was also noted by Contreras-Porcia et al. [56] and Olsen et. al. [21]. Conclusions The presence of microclover in the mixture contributed to the improvement of many chlorophyll a fluorescence parameters of Lolium perenne . Statistically, the maximum fluorescence (Fm), the maximum photochemical efficiency of PSII (Fv/Fm), and the maximum water-splitting efficiency on the donor side of PSII (Fv/Fo) increased significantly. The number of active reaction centers also increased, which translated into better energy flux absorbed by one reaction center (ABS/RC). In addition, there were upward tendencies of such parameters as the area above the induction curve (Area) and the density of reaction centers (RC/CSo). Due to the above effects, microclover can be recommended to be used in lawn mixtures. The use of Plant Growth Promoting Bacteria increased the maximum chlorophyll a fluorescence (Fm), the area above the induction curve (Area), and the density of reaction centers (RC/CSo). The positive effect of the plant-promoting PGPB microbial vaccine on the Lolium perenne lawn variety suggests that more studies should be conducted on other plant species subjected to other kinds of abiotic stress. As the results indicated, growing plants exposed to drought stress with the substrate moisture level of 40% FWC did not affect the photosynthesis process. The parameter most sensitive to low substrate moisture was the rate of electron transport through one active reaction center (ETo/RC). Therefore, the ETo/RC parameter should be recommended for further research on drought stress. Declarations Abbreviations Not applicable. Availability of data and materials The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. Authors' contributions M.T. - study design; J.D. - preparation of microbiological formula; M.T. and J.S. - data collection; M.T. - statistical analysis, M.T. - data interpretation; M.T., J.D. and J.S. - manuscript preparation; M.T., J.D. and J.S. - literature search. Acknowledgements Not applicable. Funding This research was supported by Ministry of Science and Higher Education – Poland, Grant No. 161/23/B. Ethics declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare no competing interests. References Farooq M, Wahid A, Kabayashi N, Fujita D, Basra SMA. 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J Plant Physiol. 2003;160:657-666. https://doi.org/10.1078/0176-1617-00772 Mehta P, Jajoo A, Mathur S, Bharti S. Chlorophyll a fluorescence study revealing effects of high salt stress on Photosystem II in wheat leaves. Plant Physiol Biochem. 2010;48:16-20. https://doi.org/10.1016/j.plaphy.2009.10.006 Tsimilli-Michael M, Strasser R. The energy flux theory 35 years later: formulations and applications. Photosynth Res. 2013;117:289–320. https://doi.org/10.1007/s11120-013-9895-1 Sharma S, Bhatt U, Sharma J, Darkalt A, Mojski J, Soni V. Effect of different waterlogging periods on biochemistry, growth, and chlorophyll a fluorescence of Arachis hypogaea L. Front Plant Sci. 2022;13. https://doi.org/10.3389/fpls.2022.1006258 Jia H, Hao JB, Cao HB, Han Y, Li D, Chen HJ. Effects of shading on fast chlorophyll fuorescence induction dynamics of ‘Baojiahong’ peach leaves. Acta Bot Boreal -Occid Sin. 2015;35:1861–1867. https://doi.org/10.7606/j.issn.1000-4025.2015.09.1861 Chen SG, Yin CY, Dai XB, Sheng Q, Xu XM. Action of tenuazonic acid, a natural phytotoxin, on photosystem II of spinach. Environ Exp Bot. 2008;62:279–289. https://doi.org/10.1016/j.envex pbot.2007.10.002 Zhang DY, Pan XL, Mu GJ, Wang JL. Toxic effects of antimony on photosystem II of Synechocystis sp. as probed by in vivo chlorophyll fluorescence. J Appl Phycol. 2010;22:479–488. https://doi. org/10.1007/s10811-009-9482-1 Contreras-Porcia L, Thomas D, Flores V, Correa JA.Tolerance to oxidative stress induced by desiccation in Porphyra columbina (Bangiales, Rhodophyta). J Exp Bot. 2011;62:1815-1829. https://doi. org/10.1093/jxb/erq364 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 29 Dec, 2025 Reviewers agreed at journal 10 Dec, 2025 Reviews received at journal 02 Jun, 2025 Reviewers agreed at journal 27 May, 2025 Reviewers invited by journal 27 May, 2025 Editor assigned by journal 15 May, 2025 Submission checks completed at journal 15 May, 2025 First submitted to journal 15 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6520497","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":462433971,"identity":"e31dc4e3-e8cc-4e42-ba2c-1a40551c50f2","order_by":0,"name":"Milena Truba","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYDACZuYGKIuHgeEDhGUAxBZ4tDCCtUiAtDDOQGiRwGMNkhZmHmK06LYzNj4uqGGoM5+Re/Czbdthewb25m0SjDtwazE7zNhsPOMYg4TMjbxk6dy2w4kNPMfKJBjP4NXSJs3DxiAhIZFjANRyO4FBIsdMgrENr5b23zz/wFqMf1u23bZnkH9DUEsbM28bWIuZNGPbbcYGCR6CWpqlefskJGfwvEuz7Dn3P7GNJ63YIhGfX84fPviZ55sNvwR77uEbP8rS7PnZD2+88XGHDU4tUIBkJhuISGwgpAMDMJKuZRSMglEwCoYvAAC99UdHyR3YUgAAAABJRU5ErkJggg==","orcid":"","institution":"University of Siedlce","correspondingAuthor":true,"prefix":"","firstName":"Milena","middleName":"","lastName":"Truba","suffix":""},{"id":462433972,"identity":"ffadcc26-67b1-4646-9bd9-51fae1a4d65d","order_by":1,"name":"Jakub Dobrzyński","email":"","orcid":"","institution":"Institute of Technology and Life Sciences—National Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Jakub","middleName":"","lastName":"Dobrzyński","suffix":""},{"id":462433973,"identity":"0152c001-ea7f-4ba0-9763-56388cafd374","order_by":2,"name":"Jacek Sosnowski","email":"","orcid":"","institution":"University of Siedlce","correspondingAuthor":false,"prefix":"","firstName":"Jacek","middleName":"","lastName":"Sosnowski","suffix":""}],"badges":[],"createdAt":"2025-04-24 11:53:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6520497/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6520497/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":83588726,"identity":"14fb41e3-96cd-4c2a-ba97-15a6e31bdee2","added_by":"auto","created_at":"2025-05-29 05:11:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":96466,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of experimental factors on chlorophyll a fluorescence induction curve. Abbreviations: Lp1 – \u003cem\u003eLolium perenne\u003c/em\u003ein pure stand; Lp2 - \u003cem\u003eLolium perenne\u003c/em\u003ein a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6520497/v1/2c6483669b6f7e03533dccc6.png"},{"id":83588286,"identity":"e0c7003d-326c-4d77-a26c-e92424e830e4","added_by":"auto","created_at":"2025-05-29 05:03:18","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":229761,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of a) PGPB on chlorophyll a fluorescence assessed by the OJIP test; b) substrate moisture on chlorophyll fluorescence assessed by the OJIP test. Abbreviations: O ,K, J, I, P – points on the chlorophyll a fluorescence induction curve; Lp1 - \u003cem\u003eLolium perene\u003c/em\u003e grown in pure stand; Lp2 – \u003cem\u003e\u0026nbsp;Lolium perene\u003c/em\u003e grown in a mixture with microclover\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6520497/v1/d5fee35ab5f773b2b1e3e6d3.png"},{"id":83588283,"identity":"bc5d7044-d4c6-4ba1-a42d-b45b0a931da6","added_by":"auto","created_at":"2025-05-29 05:03:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":98370,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of experimental factors on of Fo, Fm, Fv/Fo, Fv/Fm and Area parameters. Abbreviations: Lp1 – \u003cem\u003eLolium perenne\u003c/em\u003ein pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003ein a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6520497/v1/77ecdd2cc7c1b5302ed6e8be.png"},{"id":83588728,"identity":"96d9a5cf-935c-42fb-9b6b-f3337fd5b29a","added_by":"auto","created_at":"2025-05-29 05:11:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":79224,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of experimental factors on ABS/RC, TRo/RC, and ETo/RC parameters. Abbreviations: Lp1 – \u003cem\u003eLolium perenne\u003c/em\u003ein pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003ein a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6520497/v1/42e483e652bc8117f673b937.png"},{"id":83588285,"identity":"85d39161-e46c-4df8-8a89-80dbf903d591","added_by":"auto","created_at":"2025-05-29 05:03:18","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":102350,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of experimental factors on of RC/CSo, ETo/CSo, and DIo/CS parameters. Abbreviations: Lp1 – \u003cem\u003eLolium perenne\u003c/em\u003ein pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003ein a mixture with microclover; 40% FWC – 40% field water capacity; 60% FWC – 60% field water capacity; PGPB – Plant Growth Promoting Bacteria\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6520497/v1/4e75c4ca31d77e9b96806b69.png"},{"id":83589363,"identity":"ce49bd6c-b7e5-47ac-90b1-f5eddeb88bef","added_by":"auto","created_at":"2025-05-29 05:35:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1598753,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6520497/v1/4be3429c-4919-4312-876d-302cf8f7cc92.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of Plant Growth Promoting Bacteria on chlorophyll a fluorescence parameters of Lolium perenne grown with microclover in drought conditions","fulltext":[{"header":"Background","content":"\u003cp\u003eDrought is one of the main factors inhibiting the growth and development of plants [1]. Despite numerous studies on its mechanism, drought stress impact on plants is relevant as a topic and still frequently discussed [2-7]. A lack of soil moisture significantly inhibits photosynthesis, preventing the effective use of light energy, which in effect is dissipated as fluorescence or heat; these changes occur before the plant shows visible signs of turgor loss. That is why to \u0026nbsp;measure drought stress, methods of chlorophyll a fluorescence determination have been used [8].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn modern agriculture some bacteria are used to promote plant growth and development. According to Furtak [9], the effects of using PGPB (plant growth-promoting bacteria) containing \u003cem\u003eBacillus\u003c/em\u003e spp. bacteria include greater resistance to long-term stress, accelerated seed germination, and the improved growth and extent of the root system. Furthermore, Consentino et al. [10] argue that PGPB are among the effective products reducing the use of mineral fertilizers. Those bacteria stimulate plant growth by producing various biologically active substances, such as phytohormones (IAA, gibberellins and cytokinins) and enzymes (ACC deaminase). Some of their enzymes are involved in biomass breakdown (cellulase, ligninase, and chitinase), in fixing atmospheric nitrogen (nitrogenase), and dissolving forms of phosphorus unavailable to plants [11, 12]. \u003cem\u003eBacillus\u0026nbsp;\u003c/em\u003ebacteria are also included into the PGPR (plant growth promoting rhizobacteria) group, not only because they positively affect plant growth by producing hormones, but also because they increase the content of available nutrients in the soil and produce 1-aminocyclopropane-1-carboxylate deaminase to reduce ethylene concentration in plant tissues [13]. PGPR increase systemic resistance of plants to biotic and abiotic stress [14]. Bacillus strains are ubiquitous and can survive biotic and abiotic stress for long periods of time, forming spores in vivo. Some species of \u003cem\u003eBacillus\u003c/em\u003e have been successfully used as safe biological fertilizers and pesticides, due to their high survivability and as the most prominent rhizobacteria [15].\u003c/p\u003e\n\u003cp\u003eChlorophyll fluorescence is used to measure the physiological condition and stress level of plants. Fluorescence analysis at O-J-I-P points (OJIP test) is a method used for the examination of plant vitality [16]. Developed by Strasser et al. [16], the test is applied to analyze photosynthetic apparatus condition during specific types of stress. It is used to determine the impact of stress on specific factors affecting the absorption of light and its conversion into biochemical energy. During the test, within the first second of illumination of the plant sample, previously kept in the dark, chlorophyll a fluorescence increases from the initial value (Fo) to the maximum (Fm) one [17, 18]. The results of the test, presented as a curve on a logarithmic scale, allow determining changes in the flow of excited electrons through the photosynthetic apparatus. The O step in the curve represents an increase in chlorophyll a fluorescence emission from the initial level and reflects the gradual accumulation of QA, i.e. the primary quinone electron acceptor of Photosystem II (PSII) in its reduced form. The O\u0026ndash;J phase of the curve represents the reduction of the acceptor side of PSII [2]. The J\u0026ndash;I phase represents the process of the reduction of the plastoquinone (PQ) pool. The I-P phase, on the other hand, is the slowest and involves the transfer of electrons through Photosystem I (PSI) and is attributed to the reduction of the acceptor side of PSI [19].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe chlorophyll fluorescence induction curve and the maximum photochemical yield (Fv/Fm) are used as leading parameters detecting stress of various origins, affecting PSII [20, 21]. Another parameter is the maximum water-splitting efficiency (Fv/Fo), which, unlike Fv/Fm, is not an indicator of carbon assimilation but allows for faster detection of stress in the plant. In addition, the Fv/Fo ratio is used to calculate OJIP parameters. These parameters describe the energy fluxes inside and around the reaction center (RC) of PSII, i.e., specific energy fluxes per active reaction center (RC) and phenomenological energy fluxes per excited cross section\u0026nbsp;(CS) of the sample [4, 22]. According to Olsen et al. [21], the absorption components (ABS/RC \u0026ndash; energy absorbed per reaction center), trapped energy (TRo/RC \u0026ndash; trapped energy flux per reaction center), and electron transport (ETo/RC- electron transport flux per reaction center) should be studied to analyze the location of interference within the photosynthetic apparatus. Pollastrini et al. [23] found that chlorophyll a fluorescence parameters were useful for analyzing plant responses to a variety of environmental stress factors and for phenotyping. According to Baker [24], drought stress can alter the steps of the OJIP test and reduce the intensity of fluorescence at the JIP phase. In negative environmental conditions, on the basis of the chlorophyll a fluorescence technique, it is possible to measure plant vigor, closely related to the functioning of PSII [25]. Additionally, the impairment of the photosynthetic activity affects CO2 fixation [26].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTurf surface is a dominant element of green areas located within rural buildings or in cities. Promoting biodiversity, green areas used for recreation play an underestimated role in the functioning of villages and cities. Additionally, as natural retention reservoirs they soak up rainwater. However, because of low soil moisture or a lack of irrigation, green areas often fail to fulfill their aesthetic function. In the literature there are reports on how drought can be mitigated by microbiological consortia and by using synthetic or natural water absorbents [27-30]. In recent years, mainly lawn varieties of grasses have been used to plant green areas, but microclover (\u003cem\u003eTrifolium repens L.)\u0026nbsp;\u003c/em\u003ehas been increasingly popular. According to the literature, in a mixture with grass it fixes atmospheric nitrogen, introducing it to the soil through mineralization, which has a positive effect on the functional and aesthetical value of the lawn [31]. In addition, according to the research by Saeedipooya et al. [32], as a short plant, microclover can be effective in reducing irrigation costs.\u003c/p\u003e\n\u003cp\u003eThe present paper examines the effect of PGPB and microclover on minimizing the current problem of drought and insufficient irrigation of green areas. In the research, the following research hypotheses were proposed:\u003c/p\u003e\n\u003cp\u003e1. Microclover grown in lawn mixtures will have a positive effect on mitigating the effects of drought.\u003c/p\u003e\n\u003cp\u003e2. The PGPB bacterial strain will minimize drought stress in \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003egrown with microclover and in pure stand.\u0026nbsp;\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cp\u003e\u003cstrong\u003ePlant growth conditions and experimental design\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe pot experiment was conducted from the beginning of November 2023 to mid-January 2024 in a phytotron, ensuring constant growing conditions. The air temperature in the light and dark-adapted stage was 22\u0026deg;C, with the light intensity of 200 \u0026mu;mol m\u003csup\u003e\u0026minus;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;1\u003c/sup\u003e (obtained with high-pressure sodium lamps) and the photoperiod of 16 h in light. The 1.5L pots were filled with soil, which, according to the Bouyoucos\u0026ndash;Casagrande aerometric method modified by Pr\u0026oacute;szyński, was light clay [33].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe following plants were used in the experiment:\u003cem\u003e\u0026nbsp;Lolium perenne\u003c/em\u003e 2N lawn Boxer, seeds produced by the Granum Seed Company, Wodzierady, Poland, as certified seed material; \u003cem\u003eTrifolium repens\u003c/em\u003e L. (microclover) cv. Pipolina seeds purchased from Eco Deco, Krak\u0026oacute;w, Poland as certified seed material. The seeds of \u003cem\u003eLolium perenne\u003c/em\u003e were sown into some pots\u003cem\u003e,\u003c/em\u003e with the seeding rate of 36 g m\u003csup\u003e-2\u003c/sup\u003e (Lp1). Other plots were planted with \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003e (34.9 g m\u003csup\u003e-2\u003c/sup\u003e) together with microclover (1.1 g m\u003csup\u003e-2\u003c/sup\u003e), with the latter constituting a 3% share in the mixture (Lp2). The above Lp1 and Lp2 plots were the main research factor. The second factor was drought stress, achieved by maintaining the soil moisture levels of 40% FWC (Field Water Capacity), while \u0026nbsp;FWC in other pots was 60%. The third research factor was \u0026nbsp;the strain of \u003cem\u003eBacillus\u003c/em\u003e spp. N188 producing ACC deaminase \u0026ndash; referred to as PGPB in this paper. PGPB were not applied to control pots. The experiment was conducted in four replications. Combinations of experimental factors are presented in Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 1 Methodological data\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 156px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 448px;\"\u003e\n \u003cp\u003eField Water Capacity\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 213px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 235px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\" style=\"width: 448px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eLolium perenne\u003c/em\u003e100%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003cp\u003e40%FWC/PGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003cp\u003e60%FWC/PGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eLolium perenne 97\u003c/em\u003e%\u003c/p\u003e\n \u003cp\u003eMicroclover 3%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003cp\u003e40%FWC/PGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003cp\u003e60%FWC/PGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eMicrobiological material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWhen plants germinated, the Bacillus spp. strain producing ACC deaminase (PGPB) was applied to the soil with a pipette, in the amount of 5mL per pot. The N188 strain was isolated from the soil by the Institute of Technology and Life Sciences - National Research Institute in Falenty (Poland).\u0026nbsp;Approximately 100 bacterial strains were isolated from various soils, including both rhizosphere and bulk soil. Bacterial colonies were selected and passaged until pure strains were obtained. Then the strains were inoculated, according to Patil et al. [34], onto ACC minimal media with bromothymol blue (BTB). The N188 strain was selected, with phenol red as a marker, and grown at 30\u0026deg;C for 24 hours with shaking at 150 rpm in 5 mL of Lysogeny Broth (LB). Then, the strain was inoculated onto Dworkin and Foster medium amended with 3 mM ACC (instead of (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e\u0026nbsp;\u003c/sub\u003eas the sole nitrogen source [35,36]. After incubation, the bacterial culture was centrifuged at 6000 rpm for 10 minutes. The resulting pellet was suspended in 1 ml of 0.1 M Tris-HCl buffer at pH 7.6, and then the process was continued according to the method described by Penrose and Glick [36]. ACC deaminase activity was calculated by measuring alpha-ketobutyric acid formed by the cleavage of ACC by the ACC deaminase enzyme. Then the selected bacterial strain was identified by sequencing the 16S rRNA gene. To amplify the 16S rRNA genes, universal primers 27F (5\u0026prime;-AGAGTTTGATCCTGGCTCAG-3\u0026prime;) and 1492R (5\u0026prime;-GGTTACCTTGTTACGACTT-3\u0026prime;) were used. The PCR (polymerase chain reaction) products were sequenced by the Sanger technique (NEXBIO, Lublin, Poland). The obtained sequences were assembled to contig (BioEdit) and compared with the sequences from GenBank, EMBL (European Molecular Biology Laboratory), using BLAST (the Basic Local Alignment Search Tool). The 16S rRNA gene sequences of the bacterial strain were deposited in GenBank under accession number PP500625.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eChlorophyll a fluorescence\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter the sample was adapted in the dark, measurements on flag leaf blades were made with the OS30p+ fluorometer (plant stress meter), using a clip. Each measurement was preceded by 30 minutes of adaptation in the dark. Then OJIP measurements were made. As a result of the OJIP test measurement, the chlorophyll a fluorescence parameters presented in Table 2 were obtained.\u003c/p\u003e\n\u003cp\u003eTable 2 The description of fluorescence parameters (in relative value)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 604px;\"\u003e\n \u003cp\u003eThe data obtained in the OJIP test and other parameters calculated\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eAbbreviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eDescription\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eFluorescence at 20\u0026nbsp;\u0026mu;s\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eFluorescence at 300\u0026nbsp;\u0026mu;s\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eJ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eFluorescence at 2 ms\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eFluorescence at 30 ms\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eP = Fm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eFluorescence at 3s (with maximum fluorescence measured)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eFo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eMinimum fluorescence\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eFv/Fm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eMaximum photochemical efficiency of PSII\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eFv/Fo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eMaximum water-splitting efficiency on the donor side of PSII\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eArea\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eThe area between the OJIP curve and Fm\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eABS/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eEnergy absorbed by one active reaction center\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eTRo/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eEnergy flux trapped by one active reaction center (RC)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eETo/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eElectron transport flux per one active reaction center (RC)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eDIo/CS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eThermal dissipation of excitation energy by PSII of a photosynthetic sample\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eETo/CSo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eElectron transport flux per cross section (CS) of a sample\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eRC/CSo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 482px;\"\u003e\n \u003cp\u003eDensity of reaction centers (QA reducing PSII reaction centers)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eStatistics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe results of the research were processed using the Statistica 13 program (TIBCO Soft-ware Inc., PaloAlto, CA, USA). The data were analyzed at the significance level of p\u0026lt;0.05. The differences between means were assessed with ANOVA and Tukey\u0026rsquo;s HSD test (Honest Significant Difference). In the tables the significance of the differences between means is indicated by lowercase and uppercase letters.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003eChlorophyll a fluorescence induction curve (OJIP curve)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eChlorophyll a fluorescence induction curves presented in Figure 1 illustrate the plants\u0026rsquo; physiological condition for each experimental unit. \u0026nbsp;The lowest chlorophyll a fluorescence was recorded in control \u003cem\u003eLolium perenne\u003c/em\u003e grown in pure stand (Lp1) on the soil with 60% moisture.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOn the other hand, the highest values were noted for the grass grown in a mixture with microclover (Lp2) on the soil with the 60% moisture. The fact that curves for \u003cem\u003eLolium perenne\u003c/em\u003e grown together with microclover on the soil with 60% moisture (Lp2/60%) were higher than the others might be attributed to the presence of the legume plant in the mixture. Due to its ability to fix atmospheric nitrogen, microclover introduced its additional amount into the soil. In effect plants in the mixture were nourished better and chlorophyll a fluorescence reached greater values. Similarly, Kalaji et al. [37] confirmed that the supply of plants with nitrogen resulted in an increase in fluorescence.\u003c/p\u003e\n\u003cp\u003eThe induction curve of \u003cem\u003eLolium perenne\u003c/em\u003e grown in pots with 40% FWC did not change so dynamically. However, there were clear differences between the Lp1 and Lp2 curves, with the latter reaching greater values than the former, both for 40% WFC and 60% WFC. The absence of a distinct K-point on all chlorophyll fluorescence induction curves indicated that the photosynthesis process of plants grown on both 40 and 60% FWC soil was not disturbed. According to the literature, the K-peak can be used as a potential indicator of physiological instability under drought stress even before the appearance of visible signs on plants [5, \u0026nbsp;18]. The K-point on the chlorophyll a fluorescence curve is caused by the inactivation of the oxygen-releasing complex or by the inhibition of electron transport on the donor and acceptor side of PSII [18]. The multivariate analysis of variance showed no statistically significant effect of either FWC or PGPB or their interaction on chlorophyll fluorescence (Table 3). On the other hand, the effects of the crop type and its interaction with PGPB or FWC were statistically significant. Similarly, statistically significant differences were also noted in the triple interaction of all factors on the O-J fragment of the induction curve.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 3 Chlorophyll fluorescence assessed by \u0026nbsp;the OJIP test\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 47px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eCrop type\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eFWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCrop type x PGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e%FWC x\u003c/p\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCrop type x %FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCrop type x PGPB\u0026nbsp;\u003c/p\u003e\n \u003cp\u003ex %FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 47px;\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e44.25*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e74.17*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e88.50*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e89.00*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 47px;\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e59.75*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e91.16*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e113.17*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e112.67*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 47px;\"\u003e\n \u003cp\u003eJ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e78.17*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e117.34*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e87.00*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e147.34*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 47px;\"\u003e\n \u003cp\u003eI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e165.88*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e221.97*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e267.33*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 47px;\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e193.12*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e312.13*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003ens\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eHSD values from three-way analysis of variance for the effects of crop type, i.e. Lp1 and Lp2; field water capacity (FWC) i.e. 40% and 60%; treatment, i.e. control and PGPB on OJIP parameters. *p\u0026le;0.05; ns p\u0026gt;0.05\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe results indicated that the application of PGPB significantly increased chlorophyll a fluorescence both for plants grown in Lp1 and Lp2 pots, with Lp2 values being visibly greater (Figure 2a). Chlorophyll a fluorescence for Lp1 plants was greater when soil FWC was 40%, while in Lp2 pots it was greater at 60% FWC (Fig. 2b). It can be assumed that optimal moisture content and the presence of microclover in the mixture contributed to the intensification of the chlorophyll a fluorescence process. According to Digrado et al. [38], low soil moisture had a small effect on PSII performance, but it increased the PSII sensitivity of \u003cem\u003eLolium perenne\u003c/em\u003e\u0026nbsp; to heat stress.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eChlorophyll a fluorescence parameters assessed by the OJIP test\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCompared to control, PGPB increased the minimum fluorescence (Fo) to a large extent (Table 4). Additionally, a 9% increase in Fo indicated an interaction between the type of crop and PGPB. The literature reports that plants react with a chlorophyll a fluorescence increase after the application of plant supporting products [39, 40]. In the present experiment no significant differences were found between the minimum fluorescence (Fo) values for \u003cem\u003eLolium perenne\u003c/em\u003e grown in pure stand and in the mixture. There was a slight difference between pots with different FWC values, for non-irrigated pots this value was on average 1.6% greater. The Fo value was measured with plant receptors open in the dark-adapted state. The measurements were taken in a faint red light so as not to excite the photosynthetic process. According to the literature, greater values indicate lower efficiency of excitation energy transfer between pigment molecules in the PSII energy antenna [41]. On the other hand, photoprotection or an increase in CO\u003csub\u003e2\u003c/sub\u003e fixation can contribute to a Fo decrease.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 4 Minimum chlorophyll a fluorescence of dark-adapted state (Fo)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 323px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e319.00\u0026plusmn;1.00Bb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e389.33\u0026plusmn;8.08Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e354.17A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e308.33\u0026plusmn;5.51Bb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e340.33\u0026plusmn;5.51Ba\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e324.33 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e312.33\u0026plusmn;14.15Bb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e342.33\u0026plusmn;5.69Ba\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e327.33 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e347.67\u0026plusmn;10.41Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e344.00\u0026plusmn;3.61Ba\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e345.83 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e315.67Ab\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e365.83Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e340.75 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e328.00Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e340.17Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e335.08 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e313.67From\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e364.83Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e339.25A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e330.00Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e343.17Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e336.58A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e321.83 b\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 163px;\"\u003e\n \u003cp\u003e354.00 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe means in columns marked with the same uppercase letters do not differ significantly. The means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe maximum fluorescence values varied (Table 5). It was observed that \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003eplants \u0026nbsp;growing with the leguminous plant (Lp2) had a much greater Fm value than \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003ein pure stand (Lp1). According to Kalaji et al. [37], even small doses of nitrogen increased Fm in spring barley. Kalaji and Łoboda [42] stated that nitrogen reduction in relation to the control sample indicated the occurrence of stress, as a result of which not all electron acceptors in PSII were completely reduced. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 5 Maximum chlorophyll a fluorescence (Fm)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 332px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e991.33\u0026plusmn;240.58 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1090.7\u0026plusmn;129,68 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1041.0AB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e902.33\u0026plusmn;241.47 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e916.00\u0026plusmn;135.52 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e909.17B\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1052.0\u0026plusmn;135.84 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1178.0\u0026plusmn;175.45 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1115.0AB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1207.0\u0026plusmn;113.85 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1235.7\u0026plusmn;137.17 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1221.0A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1021.7 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1134.3 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1078.0A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1054.7 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1075.8 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1065.3A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e946.83 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1003.3 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e975.08B\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1129.5 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1206.8 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1168.2A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1038.2a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e1105.1a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWang et al. [43] observed that in a \u003cem\u003eBothriochloa ischaemum\u003c/em\u003e and \u003cem\u003eLespedeza davurica\u003c/em\u003e mixture, Fm increased with an increasing nitrogen dose. In the present experiment there was no significant effect of substrate moisture on Fm. There was a slight tendency for the PGPB plants to have a 6% greater Fm value compared to control. It is possible that there was an interaction between microclover plants and PGPB \u003cem\u003eBacillus\u0026nbsp;\u003c/em\u003emicroorganisms, which increased the Fm value in \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003egrowing together with the leguminous plant\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe Fv/Fm parameter varied within the experiment and ranged from 0.6 to 0.7 (Table 6). Its values differed significantly between \u003cem\u003eLolium perenne\u003c/em\u003e from Lp1 and Lp2 pots. \u003cem\u003eLolium perenne\u003c/em\u003e grown with microclover had about 9.5% greater value of the maximum photochemical efficiency of PSII. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 6 Maximum photochemical efficiency of PSII (Fv/Fm)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 323px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.665\u0026plusmn;0.080Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.639\u0026plusmn;0.048 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.652A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.642\u0026plusmn;0.088 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.623\u0026plusmn;0.053 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.632A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.698\u0026plusmn;0.050 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.704\u0026plusmn;0.046 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.701A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.709\u0026plusmn;0.033 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.719\u0026plusmn;0.032 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.714A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.682Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.671 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.677A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.676 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.671 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.673A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.653 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.631 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.642B\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.704 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.711 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.708A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.679 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.671 a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAccording to Angelini et al. [44], in optimal plant growth conditions, its value should be about 0.85 relative units, and its decrease indicates the occurrence of stress. In the present research, the parameter did not change with the change in soil moisture, which proves it is not sensitive to drought stress. Kalaji et al. [22] also reported that some kinds of stress, e.g. drought, did not affect Fv/Fm value. Digrado et al. [38] obtained the highest Fv/Fm in \u003cem\u003eLolium perenne\u003c/em\u003e in autumn, with average values of approx. 0.75, which indicated a high PSII efficiency. In summer, on the other hand, values as low as 0.15 were noted. Lower Fv/Fm values in summer indicated a reduced photochemical efficiency of PSII and stronger energy dissipation, but the plant returned to its full photochemical activity after the stress subsided.\u003c/p\u003e\n\u003cp\u003eThe greatest value of the maximum efficiency of water splitting on the PSII donor side was noted for \u003cem\u003eLolium perenne\u003c/em\u003e plants grown in the mixture (Table 7). According to Aazami et al. [45], plant stress caused by adverse conditions can lead to temporary photoinhibition or damage of photosynthetic organs, resulting in a decrease in chlorophyll fluorescence parameters. This was confirmed by Li et al. [46], who observed that drought stress combined with high temperature resulted in Fv/Fo values falling sharply. Olsen et al. [21] observed that when Fo increased in stressed plants, the Fv/Fo ratio decreased. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 7 Maximum water-splitting efficiency on the PSII donor side (Fv/Fo)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 95px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 313px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.108\u0026plusmn;0.761Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e1.806\u0026plusmn;0.388 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.957A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.924\u0026plusmn;0.774 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e1.690\u0026plusmn;0.383 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.807A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.385\u0026plusmn;0.597 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e2.446\u0026plusmn;0.566 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.416A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.479\u0026plusmn;0.423 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e2.594\u0026plusmn;0.431 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.536A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 170px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.247 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e2.126 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.186A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 170px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.201 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e2.142 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.172A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 170px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.016 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e1.748 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.882B\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 170px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.432 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e2.520 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.476A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 170px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.224a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e2.134a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eStatistical analysis of the Area parameter did not show any significant differences between different experimental units, but some tendencies were notable (Table 8). The area above the Lp2 \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003ecurves was on average 25% greater, which meant that for those units the number of electron acceptors of photosynthetic electron transport chain (PETC) was also greater. A visible difference was also noticed between the average values of the Area parameter for pots with and without PGPB. Plants with PGPB had a 13% greater number of PETC electron acceptors. Soil moisture content did not significantly affect the Area parameter, and the difference in the average values between 40%FWC and 60%FWC was about 5%. Schansker et al. [47] argue that there is a relationship between the area over the OJIP transients and the number of electrons transported through the PETC before the Fm value is reached. Strasser et al. [16] and Khan et al. [48] stated that this area was proportional to the number of PETC electron acceptors. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 8 Area over OJIP Induction Curve\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 332px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e8379.3\u0026plusmn;4671.4Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e9640.7\u0026plusmn;3429.5 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e9010.0 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e7429.3\u0026plusmn;2982.3 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e7401.0\u0026plusmn;2954.6 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e7415.3 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e9210.7\u0026plusmn;2650.5 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e10545.0\u0026plusmn;3978.4 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e9879.0 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e9700.0\u0026plusmn;1721.8 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e11603.0\u0026plusmn;2756.9 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e10652.0 A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e8795.0 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e10094.0 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e9444.5A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e8564.8 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e9502.0 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e9033.4A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e7904.5 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e8520.8 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e8212.7A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e9455.3 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e11075.0 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e10265.0A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e8679.9a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e9798.0a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigures 3, 4, and 5 present the differences in percentage between the effects of experimental factor. The pot with \u003cem\u003eLolium perenne\u003c/em\u003e grown in pure stand at optimal field water capacity and without the microbiological vaccine (Lp1/60% FWC) was used as a reference value (100%). Figure 3 presents the effects of experimental factors on Fo, Fm, Fv/Fv, Fv/Fm, and Area parameters. They took greater values for Lp2 pots than for Lp1 ones, which meant that microclover affected the growth and physiological functions of \u003cem\u003eLolium perenne\u003c/em\u003e. A beneficial effect of PGPB was also recorded for pots with plants in drought stress (40% FWC/PGPB), where Fm and Area increased on average by approx. 25% compared to the reference value\u0026nbsp;(Lp1/60% FWC).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSpecific energy flux per one active reaction center (RC) of PSII\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe energy absorbed by one active reaction center (ABS/RC) was significantly greater, by 12%, in \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003eplants \u0026nbsp;in pure stand than in \u003cem\u003eLolium perenne\u003c/em\u003e grown with microclover (Table 9). No statistically significant differences were noted between the effects of the other experimental factors, but some trends were observed. A 5% increase in the flux of energy absorbed by one active reaction center was noted for 40% FWC pots compared to 60% FWC ones. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 9\u0026nbsp;Energy absorbed by one active reaction center (ABS/RC)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 332px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.828\u0026plusmn;0.569 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.5153\u0026plusmn;0.343 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.6718A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.463\u0026plusmn;0.405 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.6107\u0026plusmn;0.404 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.5368A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.2350\u0026plusmn;0.206 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.3920\u0026plusmn;0.290 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.3135A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.2937\u0026plusmn;0.210 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.2523\u0026plusmn;0.395 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.2730A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.5317 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.4537 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.4927A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.3783 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.4315 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.4049A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.6457 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.5630 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.6043A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.2643 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.3222 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e2.2933B\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e2.4550a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e2.4426a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMonneveux et al. [49] noted an increase in the ABS/RC parameter in plants during drought stress and argued that that indicated that some reaction centers were inactive and the yield per reaction center increased. The ABS/RC parameter also reflects the effective antenna size of the active reaction centers; as the parameter increases, the antenna size of the active reaction centers decreases [50]. Therefore, in the present studies, the antenna of the active reaction centers was larger in the case of \u003cem\u003eLolium perenne\u003c/em\u003e plants on soil with the substrate moisture of 60% FWC and in those grown with microclover.\u003c/p\u003e\n\u003cp\u003eThe values of the energy flux trapped by one active reaction center (TRo/RC) did not vary across research factors, ranging on average from 1.59 to 1.67 (Table 10). Using \u003cem\u003eP. scutellarioides\u0026nbsp;\u003c/em\u003eplants, Meng et al. [18] observed that the TRo/RC parameter increased in response to drought stress only for the first 10 days, and then it began to decrease. The authors concluded that to resist drought stress and to maintain their growth, plants inhibited electron transport and reduced the PSII photochemical activity at an earlier stage of stress.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 10 Energy flux trapped by one active reaction center (RC), at time 0 (TRo/RC)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 332px;\"\u003e\n \u003cp\u003eSoil treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.7845\u0026plusmn;0.130 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.5605\u0026plusmn;0.176 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6725A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.6174\u0026plusmn;0.066 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.6582\u0026plusmn;0.154 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6378A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.5821\u0026plusmn;0.074 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.7161\u0026plusmn;0.165 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6491A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.6009\u0026plusmn;0.150 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.5758\u0026plusmn;0.182 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.5884A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.6833 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.6383 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6608A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.6092 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.6170 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6131A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.7010 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.6093 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6551A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.5915 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.6460 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e1.6187A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e1.6462a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e1.6277a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the present experiment no statistically significant effect of experimental factors on the electron transport flux through one active reaction center (ETo/RC) was noted. However, this parameter was 6.5% greater for plants in drought stress, growing on substrate with 40% FWC (Table 11). According to the literature [51, 52], in waterlogged conditions plants reduce the ETo/RC parameter value because there are fewer active RCs and more QA reduction. The reoxidation of reduced QA through electron transport in the active RC is also reduced, indicating a decrease in ETo/RC.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 11 Rate of electron transport through one active reaction center, at time 0 (ETo/RC)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 332px;\"\u003e\n \u003cp\u003eSoil treatment\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e6.4554\u0026plusmn;0.753 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e5.6524\u0026plusmn;0.745 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e6.0539A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e5.8205\u0026plusmn;0.869Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e5.7484\u0026plusmn;0.518 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e5.7845A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e6.1488\u0026plusmn;0.241 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e6.6594\u0026plusmn;0.606 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e6.4041A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e5.6624\u0026plusmn;1.164 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e5.9708\u0026plusmn;0.09 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e5.8166A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e6.3021 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e6.1559 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e6.2290A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e5.7415 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e5.8596 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e5.8006A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e6.1380 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e5.7004 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e5.9192A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e5.9056 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e6.3151 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e6.1103A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 151px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e6.0218a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e6.0078a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 4 present the effects of experimental factors on ABS/RC, TRo/RC, and ETo/RC parameters. Their highest values were recorded for \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand, not treated with PGBG and subjected to drought stress (Lp1/40% WFC). The values for the 40% FWC pots with PGPB were nearly the same as the reference value (Lp1/60% FWC). On the other hand, the lowest values of ABS/RC, TRo/RC, and ETo/RC parameters were recorded in \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003eplants \u0026nbsp;growing in a mixture with microclover, with substrate moisture content of 60% FWC and without PGPB (L2/60% FWC). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig. 4 The effect of experimental factors on ABS/RC, TRo/RC, and ETo/RC parameters. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhenomenological energy fluxes per excited cross section of the photosynthetic sample (CS) Density of active reaction centers (RCs) of PSII\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe results (Table 12, 13, 14) did not show any significant effects of the crop type, %FWC, or PGPB, or their double or triple interactions on the reaction center density (RC/CSo), electron transport by PSII (Eto/CSo), and thermal dissipation of excitation energy by PSII (DIo/CS). Despite the lack of statistically significant differences, many downward or upward tendencies in the above-mentioned parameters were observed. Thus, in the case of the RC/CSo parameter, the number of reaction center densities for \u003cem\u003eLolium perenne\u003c/em\u003e growing in the mixture with microclover was about 10% greater than for \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand (Table 12). In addition, the use of PGPB also resulted in an increase in the RC/CSo parameter by approx. 9%. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 12\u0026nbsp;Density of plastoquinone QA reducing reaction centers (RC/CSo)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 325px;\"\u003e\n \u003cp\u003eSoil treatment\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 119px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e112.26\u0026plusmn;24.31 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e136.96\u0026plusmn;18.80 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e124.61A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e131.74\u0026plusmn;20.71Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e151.05\u0026plusmn;18.99 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e141.40A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e156.20\u0026plusmn;11.04 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e145.12\u0026plusmn;16.76 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e150.66A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e136.66\u0026plusmn;9.86 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e155.08\u0026plusmn;26.75 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e145.87A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e134.23 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e141.04 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e137.64A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e134.20 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e153.07 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e143.63A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e122.00 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e144.01 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e133.00A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e146.43 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e150.10 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e148.27A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 165px;\"\u003e\n \u003cp\u003e134.21a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e147.05a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u003c/p\u003e\n\u003cp\u003eThe results indicated that the electron transport per cross section of the photosynthetic sample (ETo/CSo) had similar values for both 40 and 60 % FWC. Minor differences were noted between the average ETo/CSo results for \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003egrowing in a mixtu\u003cem\u003ere\u0026nbsp;\u003c/em\u003ewith microclover and in pure stand (Table 13). For the former the value was about 13% greater than for the latter. Similarly, the use of PGPB increased the electron transport flux by about 8%.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 13 Electron transport flux per cross section \u0026nbsp;(ETo/CS)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 323px;\"\u003e\n \u003cp\u003eSoil treatment\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e778.14\u0026plusmn;234.09 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e870.68\u0026plusmn;159.57 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e824.41A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e735.63\u0026plusmn;234.13 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e778.69\u0026plusmn;184.41 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e757.16A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e772.29\u0026plusmn;160.21 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e925.44\u0026plusmn;156.50 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e848.87A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e962.14\u0026plusmn;104.55 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e964.82\u0026plusmn;123.87 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e963.48A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e775.21 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e898.06 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e836.64A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e848.88 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e871.76 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e860.32A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e756.88 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e824.69 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e790.78A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e867.21 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e945.13 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e906.17A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e812.05a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 181px;\"\u003e\n \u003cp\u003e884.91a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u003c/p\u003e\n\u003cp\u003eNo major differences for the thermal dissipation of excitation energy by PSII of the photosynthetic sample (DIo/CS) between the experimental units were observed (Table 14).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 14\u0026nbsp;Thermal dissipation of excitation energy by PSII of a photosynthetic sample (DIo/CS)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eType of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMoisture\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 323px;\"\u003e\n \u003cp\u003eSoil treatment\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 121px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003ePGPB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e1.0442\u0026plusmn;0.44331 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.95530\u0026plusmn;0.22540 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.99970A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.84627\u0026plusmn;0.33953 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.95303\u0026plusmn;0.26371 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.89965A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 66px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.69317\u0026plusmn;0.14294 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.67697\u0026plusmn;0.21421 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.68507A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.65307\u0026plusmn;0.13287 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.67647\u0026plusmn;0.14323 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.66477A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for moisture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e40% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.84862 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.81585 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.83223A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003e60% FWC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.76972 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.81500 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.79236A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 604px;\"\u003e\n \u003cp\u003eMean for type of crop\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.94522 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.95413 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.94967A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eLp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.67312 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.67672 Aa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e0.67492A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0.80917a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e0.81542a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMeans in columns marked with the same uppercase letters do not differ significantly. Means in lines marked with the same lowercase letters do not differ significantly. Abbreviations: Lp1 \u0026ndash; \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand; LP2 - \u003cem\u003eLolium perenne\u003c/em\u003e in a mixture with microclover; 40% FWC \u0026ndash; 40% field water capacity; 60% FWC \u0026ndash; 60% field water capacity; PGPB \u0026ndash; Plant Growth Promoting Bacteria\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 5 presents the effect of experimental factors on of RC/CSo, ETo/CSo, and DIo/CS parameters. The thermal dissipation of excitation energy by PSII of the sample (DIo/CS) was more beneficial for units with \u003cem\u003eLolium perenne\u003c/em\u003e grown in the mixture (20% lower than for Lp1). On the other hand, its values for \u003cem\u003eLolium perenne\u003c/em\u003e in pure stand were greater than for Lp2 plants, both on 40% and 60% FWC substrate or whether PGPB was used or not. Electron transport flux per cross section (ETo/CSo) was the greatest in \u003cem\u003eLolium perenne\u0026nbsp;\u003c/em\u003e grown with microclover on substrate with optimal field water capacity (Lp2/60% FWC). Increased values of this parameter were also noted for the Lp2 and Lp1 plants grown on substrate with 40% FWC and with PGPB. Density of reaction centers (RC/CSo) was greater in \u003cem\u003eLolium perenne\u003c/em\u003e grown with microclover, with PGPB and 60% FWC (L2/60% FWC/PGPB).\u003c/p\u003e\n\u003cp\u003eThe RC/CSo and ETo/CSo parameters are often used to determine damage to the PSII reaction center, caused by adverse environmental conditions [53]. However, as the results indicated, drought stress caused by the moisture level of 40% FWC did not significantly affect the functioning of the PSII and no damage occurred. According to Zhao et al. [6], with low soil water content (\u0026lt;29.7%), the PSII reaction center absorbed significantly more light energy, but the ability to capture and transmit it was significantly reduced; therefore, the accumulation of excess light energy eventually reduced photosynthetic efficiency, with a significant decrease in RC/CSo and ETo/CSo values. Chen et al. [54] and Zhang et al. [55] stated that this indicated that excessive excitation energy was stored at the reaction center, causing the electron transfer on the PSII acceptor side to be interrupted, with the photosynthetic apparatus further damaged. A tendency to decrease RC/CSo, ETo/CSo and increase DIo/CS as a result of subjecting the plant to drought stress was also noted by Contreras-Porcia et al. [56] and Olsen et. al. [21].\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe presence of microclover in the mixture contributed to the improvement of many chlorophyll a fluorescence parameters of \u003cem\u003eLolium perenne\u003c/em\u003e. Statistically, the maximum fluorescence (Fm), the maximum photochemical efficiency of PSII (Fv/Fm), and the maximum water-splitting efficiency on the donor side of PSII (Fv/Fo) increased significantly. The number of active reaction centers also increased, which translated into better energy flux absorbed by one reaction center (ABS/RC). In addition, there were upward tendencies of such parameters as the area above the induction curve (Area) and the density of reaction centers (RC/CSo). Due to the above effects, microclover can be recommended to be used in lawn mixtures. The use of Plant Growth Promoting Bacteria increased the maximum chlorophyll a fluorescence (Fm), the area above the induction curve (Area), and the density of reaction centers (RC/CSo). The positive effect of the plant-promoting PGPB microbial vaccine on the \u003cem\u003eLolium perenne\u003c/em\u003e lawn variety suggests that more studies should be conducted on other plant species subjected to other kinds of abiotic stress. As the results indicated, growing plants exposed to drought stress with the substrate moisture level of 40% FWC did not affect the photosynthesis process. The parameter most sensitive to low substrate moisture was the rate of electron transport through one active reaction center (ETo/RC). Therefore, the ETo/RC parameter should be recommended for further research on drought stress.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAbbreviations \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eM.T. \u0026nbsp;- study design; J.D. - preparation of microbiological formula; M.T. and J.S. - data collection; M.T. - statistical analysis, M.T. - data interpretation; M.T., J.D. and J.S. - manuscript preparation; M.T., J.D. and J.S. - literature search.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by Ministry of Science and Higher Education \u0026ndash; Poland, Grant No. 161/23/B.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eFarooq M, Wahid A, Kabayashi N, Fujita D, Basra SMA. 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J Exp Bot. 2011;62:1815-1829. https://doi. org/10.1093/jxb/erq364\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-plant-biology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pbio","sideBox":"Learn more about [BMC Plant Biology](http://bmcplantbiol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/pbio/default.aspx","title":"BMC Plant Biology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6520497/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6520497/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eTurf surface is a dominant element of green areas located within rural buildings or in cities. In recent years, mainly lawn varieties of grasses have been used to plant green areas, but microclover (\u003cem\u003eTrifolium repe\u003c/em\u003ens L.) has been increasingly popular. In addition, microclover can be effective in reducing irrigation costs. Drought is one of the main factors inhibiting the growth and development of plants. In modern agriculture some bacteria are used to promote plant growth and development ie. Plant growth promoting rhizobacteria (PGPR) increase systemic resistance of plants to biotic and abiotic stress. Chlorophyll fluorescence is used to measure the physiological condition and stress level of plants. Fluorescence analysis at O-J-I-P points (OJIP test) is a method used for the examination of plant vitality.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe presence of microclover in the mixture contributed to the improvement of many chlorophyll a fluorescence parameters of Lolium perenne. Statistically, the maximum fluorescence (Fm), the maximum photochemical efficiency of PSII (Fv/Fm), and the maximum water-splitting efficiency on the donor side of PSII (Fv/Fo) increased significantly. The number of active reaction centers also increased, which translated into better energy flux absorbed by one reaction center (ABS/RC). In addition, there were upward tendencies of such parameters as the area above the induction curve (Area) and the density of reaction centers (RC/CSo). The use of Plant Growth Promoting Bacteria increased the maximum chlorophyll a fluorescence (Fm), the area above the induction curve (Area), and the density of reaction centers (RC/CSo).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eDue to the above effects, microclover can be recommended to be used in lawn mixtures. The positive effect of the plant-promoting PGPB microbial vaccine on the Lolium perenne lawn variety suggests that more studies should be conducted on other plant species subjected to other kinds of abiotic stress. Growing plants exposed to drought stress with the substrate moisture level of 40% FWC did not affect the photosynthesis process. The parameter most sensitive to low substrate moisture was the rate of electron transport through one active reaction center (ETo/RC). Therefore, the ETo/RC parameter should be recommended for further research on drought stress.\u003c/p\u003e","manuscriptTitle":"Effects of Plant Growth Promoting Bacteria on chlorophyll a fluorescence parameters of Lolium perenne grown with microclover in drought conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-29 05:03:14","doi":"10.21203/rs.3.rs-6520497/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2025-12-29T13:30:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"83038160412963854105711489837848871275","date":"2025-12-10T08:47:12+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-02T20:12:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"301252882427577933842652702568616546039","date":"2025-05-27T10:19:49+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-27T08:54:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-16T03:58:47+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-15T20:49:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Plant Biology","date":"2025-05-15T20:48:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-plant-biology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pbio","sideBox":"Learn more about [BMC Plant Biology](http://bmcplantbiol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/pbio/default.aspx","title":"BMC Plant Biology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"577d3472-bf70-4bf2-937b-d8b908635bc7","owner":[],"postedDate":"May 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-05-29T05:03:14+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-29 05:03:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6520497","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6520497","identity":"rs-6520497","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}