Seedling-stage drought responses of two endemic pear and oak species inform climate-adaptive management approaches in Hyrcanian forests

Seedling-stage drought responses of two endemic pear and oak species inform climate-adaptive management approaches in Hyrcanian forests | 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 Seedling-stage drought responses of two endemic pear and oak species inform climate-adaptive management approaches in Hyrcanian forests Masoud Tabari, Yadollah Davoudi, Seyed Ehsan Sadati, Martin Karl-Friedrich Bader This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7250378/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The diverse Hyrcanian relic forests are increasingly threatened by more frequent and severe climate change-related droughts. This study investigated morpho-physiological and biochemical responses to drought in two endemic tree species of the Hyrcanian forests, Pyrus boisseriana Buhse and Quercus atropatena Schwarz. In a 120-day greenhouse experiment, seedlings of each species were exposed to two different irrigation treatments (FC100 and FC40, indicating percentage of field capacity). Under FC100 conditions, all morphological characteristics of Q. atropatena were significantly greater compared to those of P. boisseriana . FC40-exposed P. boisseriana and Q. atropatena seedlings exhibited statistically significant declines in photosynthesis (-55, -49.6%), transpiration (-11.8, -21.7%), intercellular CO 2 concentration ( C i ) (-54.8, -8.3%), mesophyll conductance ( g m ) (-58.5, -49.5%), RWC (only Q. atropatena : -22%), and water use efficiency (-95.3, -57.3%), respectively, and an increase in leaf temperature. Likewise, FC40-treated P. boisseriana and Q. atropatena seedlings displayed an increase in proline (+ 390.8, + 46.5%), and a decline in carotenoids (-19.9, -14.5%), respectively. Drought stress had smaller impacts on radial and height growth, photosynthesis, C i , g m , carotenoids, EL and MDA, in Q. atropatena compared to P. boisseriana , indicating greater drought tolerance in the former. These findings imply a prioritization of Q. atropatena in forest management and conservation planning in arid and semi-arid Hyrcanian forests, especially given future climate scenarios. Our results also offer valuable insights for nursery managers facing water scarcity and for stakeholders in afforestation and reforestation projects, thus contributing to the broader discussion on tree species resilience to drought during the critical seedling stage. Electrolyte leakage Height growth Malondialdehyde Proline Relative water content Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Severe droughts are expected to increase in frequency, magnitude, and spatial extent in the coming decades posing significant risks to the supply of essential resources such as water, food, and energy (Alencar et al. , 2024; Teutschbein et al., 2023 ). The frequency of drought events has grown over the past century, particularly in the last fifty years (Cai et al., 2021 ). Recent projections from the World Climate Research Program indicate that global warming will impact the hydrological cycle, leading to heightened risks and intensified drought conditions in certain regions by the century's end. Concurrently, soil drying is expected to become increasingly widespread and intense with rising temperatures (Cook et al., 2020 ). The distribution of plant species will be profoundly affected by environmental changes. However, the degree of these consequences will vary based on the ability of each species to withstand water scarcity (Zia et al., 2021 ). Approximately 50% of the Earth's surface is covered by forests in which keystone tree species play a pivotal role in ecosystem structure and functioning by providing essential habitats, food sources, and symbiotic relationships for a variety of microorganisms, fungi, animals, and other plant species (Aitken et al., 2008 ). Comprehending how trees cope with drought and its consequences on tree health and functioning is essential for the effective management of forest resources, the identification of suitable species and origins in reforested regions, and the conservation of forest ecosystems (Robakowski et al. , 2020). Plants cannot migrate from environments with unfavorable conditions like animals, and are therefore more susceptible to extreme weather conditions (Seleiman et al., 2021 ). Water deficit is considered one of the most important environmental stresses with negative effects on plant growth, development and intracellular processes (Trenberth et al., 2014 ). Drought represents a significant constraint on plant growth, as the process of cell expansion –driven by the hydrostatic pressure within the newly forming cells – requires adequate water availability in the cambium (Peters et al., 2021 ). Water scarcity impedes essential physiological processes such as photosynthesis, respiration, and the movement of stomata, ultimately influencing overall plant growth and metabolic functions (Yang et al., 2021 ). Drought-induced impairment of photosystem II (PSII) I (PSI) activity restricts photosynthetic electron transport, which leads to an accumulation of surplus energy in the reaction centers and thus the formation of reactive oxygen species (ROS) and increased oxidative damage (Zhang et al., 2020 ). The net photosynthetic rate is indicative of the biomass productivity per unit leaf area, thus serving as a dependable metric for assessing the overall production capacity of plants under otherwise non-limiting conditions. The closure of stomata leads to a reduction in CO 2 absorption, resulting in a diminished net photosynthetic rate. In tree seedlings that lack large carbon reserves, prolonged stomatal closure may lead to carbon limitation, which not only reduces biomass productivity but may also hasten drought-related mortality (Reddy et al., 2019 ; Liu et al., 2022 ). This phenomenon is strongly influenced by the intensity and duration of drought events, as well as the developmental stage of the plant (Tardieu et al., 2018 ). Overall, drought stress results in a decrease in survival (Engelbecht and Kursar, 2003), growth (Xiaoqin et al., 2009 ), leaf area (Wang et al., 2024 ), and plant biomass (Abbaspour et al., 2012 ). Depending on the level of drought adaptation, plant water relations deteriorate more or less rapidly (Fang et al., 2015; Shivakrishna et al., 2018 ; Farooq et al., 2012 ), and, at the same time, oxidative damage indicated by oxidative stress markers increases (e.g., malondialdehyde, hydrogen peroxide, and electrolyte leakage, Anjum et al., 2011 ), which is often accompanied by a rise in antioxidants and osmoregulants (Sachan et al., 2020 ). Pyrus boissieriana Buhse (Rosaceae) is the second most widely distributed wild pear species across Iran. It primarily thrives in the Hyrcanian Forest (Zakavi et al., 2016 ), which is distinguished by a range of ecological conditions, including annual precipitation levels between 213 and 2045 mm and elevations from 12 m below sea level to 2400 m a.s.l., contributing to its extensive biodiversity (Heidari et al., 2019 ). Various researchers have classified wild pear species as xerophytic woody plants due to their comparatively low reliance on soil moisture (Boucek, 1954 ; Zakavi et al., 2016 ). Previous studies revealed that P. boissiriana specimens originating from semi-arid environments exhibit greater tolerance to drought stress compared to specimens from semi-humid populations (Zarafshar et al., 2014 ) and these more drought hardy individuals may thus serve as valuable rootstock resources for more drought-sensitive commercial wild pear scions in agricultural settings (Zakavi et al., 2016 ). It has been reported that wild pear trees under drought stress experiences a decrease in photosynthetic pigment concentration (Sattarian et al., 2015 ), leaf relative water content and water potential, and an increase in electrolyte leakage (Zarafshar et al., 2018 ). Quercus atropatena O. Schwarz & Hess is a tree of the oak family native to the Hyrcanian forests of Iran, which is of great ecological importance. Although reports on the characteristics of this species are few, studies have shown that the oak genus is generally tolerant to water deficit stress (Khosravi et al., 2022 ; Hernandez and Park, 2022 ). However, despite the wealth of oak-related drought studies, there are no reports on the physiological and biochemical responses of Q. atropatena to drought conditions. In recent decades, increasing population growth and water demand have highlighted the importance of water resources management in arid and semi-arid regions, including Iran, where low rainfall and irregular distribution cause these types of climates (Tabari and Talaee, 2011 ). To thrive in these harsh conditions, plants require powerful resistance and/or tolerance mechanisms (Zerga, 2015 ). In arid and semi-arid regions, expanding forests and increasing afforestation is hindered by limited water resources, which makes the selection of drought-resistant species crucial. Therefore, screening for drought tolerance traits and assessing water requirements is one of the most effective approaches to water management and ensuring success in seedling planting projects in these regions. There is a lack of information on the drought sensitivity of P. boissieriana and Q. atropatena , which are potential candidates for reforestation initiatives. The aim of this study was to assess the morphological, physiological, and biochemical responses of P. boissieriana and Q. atropatena seedlings to drought stress to inform forest managers and other stakeholders about their potential in future forest planning and decision-making. In this study, we seek to answer the following questions. 1) How do the morphological, physiological and biochemical responses differ between these two species under drought stress conditions? 2) What promise do P. boissieriana and Q. atropatena hold as drought-tolerant species for future-proofing forest regeneration in this increasingly dry region? 2. Materials and Methods 2.1. Experimental design In this study, two-year-old seedlings of P. boissieriana and Q. atropatena , growing in 5-liter pots, were analyzed under greenhouse conditions at Lajim Nursery, north of Iran. For this purpose, after three months of initial seedling growth, 192 healthy seedlings with approximately the same diameter (8 ± 2 mm) and height (40 ± 3 cm) were selected and maintained in greenhouse conditions. This investigation was performed using a factorial experimental approach, structured as a randomized complete block design, with three replications conducted for six months. The first factor was the water deficit treatment including FC100 (100% field capacity) as a control and FC40 (40% field capacity), and the second factor was the tree species identity. The determination of the field capacity of the soil and the irrigation process were carried out following Zarik et al., ( 2016 ). 2.2. Morphological characteristics Morphological characteristics, including root diameter and seedling height, were measured at the beginning and end of the period. Root diameter was measured using a digital caliper (with an accuracy of one-hundredth of a millimeter) and height was measured using a graduated ruler (with an accuracy of one cm). From the difference between diameter and height at the end and beginning of the period, diameter growth and height growth were obtained, respectively. Then, three seedlings were randomly chosen from each treatment combination, removed from the soil and after carefully washing off rhizosphere soil, the root length was measured using a ruler (Parad et al., 2016 ). Leaf, root, and stem samples were oven-dried at 70°C for 48 hours. Subsequently, biomass was determined using a digital scale with a precision of 0.0001 g. The total biomass for the seedlings was calculated by combining the dry weights of their roots, leaves, and shoots. A leaf area meter (Model LI-3000, Li-Cor, Lincoln, NE, USA) was employed to assess the leaf area of six fully developed leaves from the upper section of each seedling. The specific leaf area (SLA) was determined by calculating the ratio of the leaf area to the dry weight of the leaves (Zarafshar et al., 2014 ). 2.3. Physiological characteristics We assessed leaf net photosynthetic rate ( A ), transpiration (E), stomatal conductance (gs), leaf temperature, and intercellular CO 2 concentration ( C i ). Measurements were taken following treatments in an outdoor environment, under natural conditions of temperature, light, and relative humidity between 9:30 and 11:00 AM, utilizing a portable gas exchange measurement device (Model LCpro+, ADC BioScientific Ltd., Hertfordshire, UK). For this analysis, 3–6 fully expanded, mature leaves were chosen from each replicate, located at the upper sections of the seedlings (Ghanbary et al., 2020 ). Water use efficiency (WUE) was calculated by the ratio of A/E (net photosynthetic rate/transpiration), while mesophyll conductance ( g m ) was derived from the ratio of photosynthesis to C i . In order to determine the relative leaf water content (RWC), three healthy and fully developed leaves were taken from the top of each seedling. The initial fresh weight (FW) of the leaves was documented. Subsequently, the leaves were submerged in distilled water in a dark environment for 24 hours to facilitate water absorption and swelling (SW). After this period, the fully hydrated leaves were weighed again followed by oven-drying at 70 ° C for 48 hours, and subsequent dry weight (DW) determination. The relative leaf water content (RWC) was then calculated using Eq. 1 (Yang et al., 2007 ). RWC = [(FW-DW) / (SW-DW)] ×100 (1) 2.4. Measurement of biochemical characteristics The assessment of electrolyte leakage (EL) was conducted following the protocol outlined by Campos et al., ( 2003 ). Small leaf segments, each measuring 0.25 cm², were excised from 100 mg of fresh leaf tissue and placed into 50 mL falcon tubes filled with 15 mL of double distilled water. The tubes were then subjected to a boiling water bath at 80°C for 12 hours. After 2 hours, the initial electrical conductivity (EC1) was measured using an electrical conductivity meter. The samples were then transferred to a non-ventilated oven set at 120°C for 120 minutes. After cooling to 25°C, the final electrical conductivity (EC 2 ) was recorded. The EL was calculated using the following Eq. 2: EL= [EC1/EC2] ×100 (2) To assess the pigment amount, 0.1 g of frozen leaf discs was mixed with 0.1 g of calcium carbonate and 4 mL of 80% acetone. This mixture was then extracted in the dark at − 80°C. The resulting solution was transferred to a separate test tube and centrifuged at 4000 rpm for 10 minutes at 4°C. After the supernatant was separated, absorbance measurements were recorded spectrophotometrically at wavelengths of 470, 645, and 663 nm (PG Instruments T60, Wibtoft, Leicestershire, UK). The concentrations of chlorophyll a, chlorophyll b, and carotenoids were calculated using Equations (3, 4 and 5) (Arnon et al., 1949). Proline was measured following Bates et al., ( 1973 ). For this purpose, 0.5 g of frozen leaves from each species and treatment level were extracted using 5 mL of 3% sulfosalicylic acid. The resulting extract was then centrifuged for 15 minutes at 6000 rpm and 4°C. Following this, 2 mL of the supernatant was combined with 2 mL of ninhydrin reagent, 30 mL of glacial acetic acid, and 2 mL of acetic acid, and the mixture was incubated in a hot water bath at 95°C for one hour. After cooling on ice, 4 mL of toluene was introduced to the samples, which were then vortexed for 15 minutes after being kept in the dark for 20 minutes. The absorption of the pink upper phase containing toluene and proline was measured at 520 nm using a spectrophotometer (PG Instruments T60, Wibtoft, Leicestershire, UK), and the concentration of proline was determined by referencing a standard curve prepared with concentrations of 50, 40, 30, 20, 10, 5, 2.5, and 0 µM of pure proline. In order to assess the malondialdehyde (MDA) concentration, 0.2 g of frozen leaf discs from each species were mixed with 4 mL of trichloroacetic acid (TCA) buffer solution and subsequently subjected to centrifugation at 1500 rpm for 15 minutes. Following this step, 2 mL of the supernatant was extracted, and 2.5 mL of a 5% thiobarbituric acid (TBA) solution was added to it. The mixture was incubated in a hot water bath at 95°C for 50 minutes, followed by centrifugation at 10,000 rpm for 10 minutes. The mixture was cooled in ice water for 10 minutes, and the absorbance was measured spectrophotometrically at 532 nm (PG Instruments T60, Wibtoft, Leicestershire, UK). The concentration of MDA was determined using an extinction coefficient of 155 mm − 1 cm − 1 (Heath and Packer, 1968 ). 2.5. Statistical analysis All statistical analyses were performed with SAS version 9.1 statistical software (SAS Institute Inc. 2023). Initially, the data's homogeneity and normality were evaluated using the Levene test and the Kolmogorov-Smirnov test, respectively. A two-way ANOVA was then conducted to examine the interaction effects between species type and water deficit stress. We used graphical model validation tools to check the underlying assumptions. A plot of the standardized residuals vs. fitted values indicated no gross violation of the variance homogeneity assumption and a quantile-quantile plot of the residuals showed no strong deviation from normality. Duncan's multiple range test was utilized to compare the means at both the 5% and 1% confidence levels. Structural equation modeling (SEM) was conducted utilizing Amos 24.0 software to assess the impact of species type and water deficit stress on various morphological, physiological and biochemical parameters. This approach was employed as it facilitates the exploration and comprehension of intricate connections among different morphological, physiological, and biochemical factors in relation to drought stress, offering insights into both the direct and indirect impacts of drought on two species: oak and pear. In this research, a general structural equation model was utilized, linking observed variables to latent variables. The model was assessed through path coefficients to measure the strength and direction of these connections, where positive coefficients signify direct and beneficial relationships, while negative coefficients denote inverse relationships. Furthermore, Gephi 0.10 software served as a network modeling tool for constructing, visualizing and analyzing the network model. 3. Results 3.1. Morphological characteristics The results of the two-way analysis of variance (Table 1 ) demonstrated that the interaction of species and water deficit had a significant effect (P < 0.05 ) on the morphological characteristics of Q. atropatena and P. boisseriana seedlings (except for survival, height growth, root biomass and root volume). The impact of species on the morphological traits of seedlings (except for survival and height growth) was significant ( P < 0.01 ). Also, water deficit stress had a considerable influence ( P < 0.05 ) on the morphological traits (except for survival, height growth, diameter growth, and root biomass) (Table 1 ). At the FC100 and FC40 field capacities, the survival rates of wild pear seedlings were 97% and 93%, and for oak seedlings 95% and 93%, respectively (Fig. 1 ). The greatest and smallest diameter growth (examined for 6 months) occurred in wild pear seedlings at FC100 and FC40 with averages of 10 mm and 6 mm, respectively. Under stress conditions (FC40), diameter growth experienced a decline of 38.4% in wild pear and 9.6% in oak when compared to well-watered seedlings (FC100) (Fig. 2 A). This means that under drought conditions, radial growth losses in oak were four times lower than in wild pear. Table 1 Two-way analysis of variance of the effect of species type, water deficit and their interaction on morphological, physiological and biochemical characteristics of P. boissieriana and Q. atropatena seedlings Characteristic Species Water deficit Water stress × Species df MS F value df MS F value df MS F value Morphological Survival 1 8.333 0.10ns 1 102.083 1.24ns 3 8.333 0.10ns Diameter growth 1 0.070 0.15ns 1 1.077 2.27ns 3 2.664 5.62* Height growth 1 162.803 13.73** 1 0.316 0.03ns 3 15.526 1.31ns Root biomass 1 280.381 80.7** 1 0.698 0.2ns 3 2.895 0.83ns Stem biomass 1 168.330 79.51** 1 31.857 15.05** 3 57.630 27.22** Leaf biomass 1 196.222 76.98** 1 18.612 7.30** 3 39.440 15.47** Total biomass 1 1912.033 131.20** 1 83.225 5.71* 3 148.106 10.16** Root volume 1 1321.425 458.03** 1 69.432 24.07** 3 0.0099 2.544* Leaf area 1 1030.360 220.93** 1 47.262 10.13** 3 44.409 9.52** Specific leaf area 1 24184.387 65.30** 1 2696.651 7.28** 3 2545.622 6.87* Physiochemical Photosynthesis (A) 1 558.319 263.2** 1 1953.111 920.7** 3 27.563 12.99** Transpiration (E) 1 82.19 263.79** 1 0.009 0.03ns 3 3.658 75.93** Stomatal conductance (gs) 1 253891.5 46.35** 1 11172.8 2.04ns 3 91935.0 16.79** temperature 1 370.84 11.42** 1 0.823 0.03ns 3 1282.9 39.52** Mesophilic conductance (gm) 1 0.004 258.2** 1 0.016 1013.62** 3 0.0001 5.05* Intracellular CO2 concentration (Ci) 1 8473.06 1.73ns 1 54885.59 11.18** 3 24535.26 5.00* Relative water content (RWC) 1 1809.089 41.08** 1 636.563 14.45** 3 806.224 18.31** Water use efficiency (WUE) 1 475.96 510.15** 1 601.75 644.97** 3 92.294 98.92** Biochemical Chlorophyll a 1 0.554 33.23** 1 0.202 12.15** 3 0.001 0.10 ns Chlorophyll b 1 0.482 30.41** 1 0.518 32.73** 3 0.018 1.19 ns Chl a/b ratio 1 0.004 0.15ns 1 0.252 10.51** 3 0.113 4.69* Total chl 1 2.070 36.04** 1 1.370 23.85** 3 0.009 0.16 ns Carotenoid 1 0.034 2.72ns 1 0.147 11.76** 3 0.002 0.17ns Total chl/ Carotenoid 1 9.363 146.29** 1 0.289 4.52* 3 0.410 6.41* Proline 1 0.003 0.04ns 1 0.203 2.61ns 3 0.610 7.83* Malondialdehyde (MDA) 1 2.509 7.06* 1 0.897 0.17ns 3 0.739 0.17ns Electrolyte leakage (EL) 1 101.036 46.35ns 1 584.924 6.06** 3 579.213 6.00* ns = nonsignificant * and **= significant at level of 0.05 and 0.01 percent. The height growth of both species was not significantly influenced by irrigation or the interaction between species and irrigation. Nonetheless, species identity had a significant impact on height growth with oak seedling height surpassing that of wild pear seedlings by 76.6%, irrespective of the irrigation treatment (Fig. 2 B). Root biomass in both species remained unaffected by drought and overall, the root biomass of oak seedlings was 2–3 times higher than that of wild pear seedlings (Table 1 , Fig. 2 C). Under water deficit conditions, a significant reduction in stem biomass was only observed in oak (-22.6%), resulting in a significant species × drought interaction (Table 1 , Fig. 2 D). However, oak seedlings had significantly greater biomass than pear to start with. Leaf biomass declined by 13.8% in wild pear and by 32.5% in oak in response to drought conditions, which also gave rise to a significant species × drought interaction (Table 1 , Fig. 2 E). The pattern seen in above-ground biomass compartments was also evident in the total biomass with stronger losses in oak (-25%) relative to pear (-14%), reflected in a significant species × drought interaction (Table 1 , Fig. 2 F). Oak root volume was roughly 4.7 times larger than that of wild pear. Furthermore, in both irrigation regimes, oak seedlings consistently exhibited a greater root volume compared to wild pear seedlings (3 times and 2.4 times at FC100 and FC40, respectively) (Fig. 2 G). Both total leaf area and specific leaf area (SLA) remained largely unaffected by drought in pear but showed steep declines in oak (leaf area: − 22%, SLA: -28%) resulting in a significant species x drought interaction (Table 1 , Fig. 2 H, Fig. 2 I). Overall, at each soil field capacity, the specific leaf area was significantly greater in oak than in wild pear (Fig. 2 I). 3.2. Physiological characteristics The results of the two-way analysis of variance demonstrated that the interaction of water deficit stress and species type had a significant effect on all physiological characteristics of oak and wild pear seedlings (Table 1 ). Under water deficit stress, photosynthesis rates in wild pear and oak diminished by 55% and 49.6%, respectively, while oak consistently exhibited higher photosynthetic carbon uptake than wild pear across both water conditions (Fig. 3 A). Additionally, leaf temperature increased under water deficit stress in both species (Fig. 3 B). Furthermore, drought conditions led to a reduction in transpiration rates in both species, with wild pear experiencing an 11.8% decrease and oak a 21.7% decrease (Fig. 3 C). Stomatal conductance did not change significantly under drought conditions in oak seedlings, while drought-exposed pear seedlings showed a significant reduction by 19.7% (Fig. 3 D). Mesophyll conductance was generally greater in oak compared to pear but declined under drought in both species, with wild pear experiencing a 58.5% decrease and oak a 49.5% decrease (Fig. 3 E). In the FC40 treatment, oak exhibited higher C i levels than wild pear. The drought-related decrease in C i in wild pear was significantly more pronounced (-54.8%) compared to oak, which only showed a slight decrease of -8% under stress conditions (Fig. 3 F). Relative water content (RWC) remained unaffected by drought conditions in wild pear but decreased by 22% in oak (Fig. 3 G). Oak seedlings had significantly greater WUE than pear seedlings (Table 1 ). At FC40, a significant decrease was observed in both species, with the decrease being 52% in pear and 54.9% in oak (Fig. 3 H). 3.3. Biochemical characteristics There were no significant species × drought interactions on chlorophyll a or b, total chlorophyll, carotenoids or MDA (Table 1 ). Nonetheless all these parameters were significantly affected by the two main effects, except for carotenoids which were similar among species but declined significantly under water deficit (wild pear: -19.9%, oak: -14.5%). However, MDA levels in oak were significantly greater by about 32% compared to wild pear but remained unaffected by the water deficit (Table 1 , Fig. 4 ). Regardless of species identity, the amounts of chlorophyll a, chlorophyll b, and total chlorophyll were 30.4%, 27.5%, and 28.9% higher in wild pear than in oak, respectively (Fig. 4 A, 4 B, and 4 D). We detected significant species × drought interactions on the chlorophyll a/b ratio, the chlorophyll/carotenoid ratio, proline content and electrolyte leakage (El) (Table 1 , Fig. 4 ). More specifically, the chlorophyll a/b ratio remained largely unaffected by water deficit in wild pear but increased by ca. 24% under water deficit in oak seedlings (Fig. 4 C). The chlorophyll/carotenoid ratio did not change significantly under water deficit in wild pear but decreased by ca. 18% in oak (Fig. 4 F). Under water deficit, proline levels rose about 4.9-fold in wild pear but only 32% in oak (Fig. 4 G). EL was unresponsive to water deficit in wild pear but increased by 20.4% in FC40-exposed oak seedlings (Fig. 4 I). The structural equation model indicated that both species identity and water deficit stress significantly influenced the variations in physiological and biochemical parameters by affecting morphological traits. These traits were carefully chosen and incorporated into the SEM (Fig. 5 ). The results from the network model reveal that the roles of species identity and water deficit stress substantially impact the traits under investigation (Fig. 6 ). Notably, species identity exerts a more pronounced influence on biochemical traits, while water deficit stress primarily affects physiological and morphological traits. 4. Discussion 4.1. Morphological characteristics This research examined morphological, physiological and biochemical drought responses of seedlings of two prevalent tree species from the Hyrcanian forests to provide guidance to stakeholders concerned with nursery propagation and ecosystem management. Generally, the ability to survive periods of water scarcity and minimize growth losses associated with water deficit stress is essential for understanding plant drought tolerance (Engelbrecht and Kursar, 2003 ). In our study, the average survival rates across treatments exceeded 90% in both species, which, along with the relatively small losses in height and diameter growth under drought, indicates a remarkable drought tolerance. Numerous studies have shown that water scarcity often has a negative impact on plant survival rates. For instance, drought experiments conducted on Robinia pseudoacacia seedlings by Norouzi Harouni et al., (2015) and on pine seedlings by Gou et al., (2010) showed that elevated drought stress, caused reduced soil water availability and resulted in about 20% lower survival rates in these plants. Under drought conditions, plants typically prioritize resource allocation to belowground sinks, i.e. increasing root volume and length to improve water uptake, thereby enhancing drought tolerance (Rooki et al., 2018 ). Indeed, in our study root volume increased in both species under drought but since this occurred without concomitant increases in root biomass, we can confidently conclude that root expansion was facilitated by a reduction in root density. Typically, the earliest morphological indicators of drought stress include decreases in seedling height growth, stem diameter growth, and total biomass production, since growth processes become increasingly impaired as drought conditions intensify (Monclus et al., 2006 ). Reduced growth during drought stress is primarily linked to a decrease in turgor pressure in the cambium and inadequate cell development (Lockhart 1965 ; Peters et al., 2021 ), ultimately leading to a reduction in shoot growth in diameter and/or height. In our study, significant drought-induced radial growth losses only occurred in wild pear while height growth showed no significant reductions in either species. The observed decrease in diameter growth of wild pear by 38% is consistent with the results reported for Cupressus arizonica and Cupressus sempervirens var. fastigiata (Rooki et al., 2018 ), Pinus nigra (Dehghan et al., 2016 ), and Cercis siliquastrum (Norouzi Haroni et al., 2017 ). The smaller diameter growth in drought-stressed wild pear seedlings was not accompanied by a reduction in stem biomass. Together with the small but statistically insignificant reduction in height growth, this suggests an increase in wood density, as reported previously for other woody species growing under water deficit (Lambers et al., 1998; Eliyani et al.,., 2005). Our findings showed drought stress-induced reductions in stem biomass (oak: -22.6%), leaf biomass (oak: -32.5%, wild pear: -13.8%) and total biomass (oak: -30.2%, wild pear: -12.2%) of seedlings. These results are consistent with the study of Jafarnia et al., ( 2018 ) on seedlings of oak species (Q. libani ) with two different seed provenances showing a 15–35% reduction in total dry biomass, Dehmardy et al., ( 2018 ) on olive seedlings ( Olea europaea ), Ashkavand et al., ( 2016 ) on hawthorn seedlings ( Crataegus aronia L.) and mahaleb cherry ( Prunus mahaleb L.), and Saeidi Abueshaghi et al., ( 2023 ) on Judas seedlings ( Cercis siliquastrum L.) with a ca. 46%, and 45% reduction in total fresh and dry biomass, respectively. As outlined above, the reduction in plant shoot biomass observed during drought conditions is probably primarily due to a decline in turgor pressure, which adversely affects the growth and proliferation of plant cells (Ashkavand et al., 2016 ). Another contributing factor is the decrease in transpiration levels, which plants reduce to manage drought stress, ultimately leading to less shoot growth (Yang, 2007). During periods of drought stress, oak and wild pear seedlings undergo specific physiological changes, which help them survive in their environment. This starts with a tighter stomatal control over transpiration. When water is scarce, the seedlings retain more of the water taken up by the roots within the root system to promote stronger root growth or root volume. In other words, during periods of water deficit, plants tend to extend their roots deeper into the deeper soil layers to tap into soil moisture reserves and thus mitigate drought stress (Norouzi Haroni et al., 2017 ), which contributes to an increase in root volume and root weight. In our study, the root volume increased significantly (33% for wild pear and 13% for oak), although this was not associated with significant changes in root weight under drought conditions, translating into a decrease in root tissue density. Similarly, a study involving seedlings of Pistacia lentiscus L. and Quercus coccifera found that heightened drought conditions do not necessarily promote the development of plant root systems, i.e. greater root biomass (Vilagrosa et al., 2003 ). In the present study, under drought conditions, leaf area and specific leaf area in oak decreased by 22% and 28%, respectively, which is consistent with the findings reported for Cercis siliquastrum (Norouzi Haroni et al., 2017 ), Pistacia atlantica (Mirzaei, 2015 ), Celtis Caucasica L. (Sepahvand et al.,, 2021), Populus euphratica (Zhao et al., 2021 ), and Ligustrum obtusifolium (Wang et al., 2024 ). Leaf area is primarily determined by leaf tissue turgor, temperature, and various growth factors, which tend to decline under conditions of water deficit stress (Wang et al., 2020 ). This leads to a reduction in leaf area, primarily due to decreased transpiration, cell division, and the elongation of cells during periods of water scarcity (Yang et al., 2025 ). Generally, based on various morphological traits our findings indicated that oak and wild pear seedlings exhibit significant drought stress tolerance. In reality, similar to other oak and pear species, the high drought tolerance of Q. atropatena and Pyrus boisseriana appear to be primarily attributed to the ability to develop an extensive and deep root system for absorb of water and nutrient in lower soil layers (Abrams 1990 ; Thomas and Gosling, 2000; Zarafshar et al., 2014 ). 4.2. Physiological characteristics The present study indicated that the photosynthesis rate was greater in oak seedlings compared to wild pear both under high and low water availability. Also, consistent with previous findings in both species, the rate of photosynthesis declined with decreasing water deficit (from FC100 to FC40) (Jafarnia et al., 2018 ; Xiong et al., 2022 ). Stomatal conductance in our oak seedlings remained unchanged by water scarcity, which has also been reported by Thomas and Gausling ( 2000 ) for seedlings of two European oak species ( Q. robur, Q. petraea ) and the same water use behaviour has recently been reported for mature individuals of the same oak species (Bader et al., 2022 ). Essentially, under water deficit, the leaf water potential diminishes, leading to stomatal closure, which subsequently lowers stomatal conductance. This reduction in stomatal conductance results in decreased CO 2 availability, thereby impairing the rate of photosynthesis and ultimately hindering growth (Yang et al., 2007 ; Yang et al., 2021 ). In the current study, transpiration decreased with increasing water deficit, which is consistent with the results of Mirzaei et al., (2015) on Pistacia atlantica seedlings and Rooki et al., ( 2018 ) on Cupressus arizonica and Cupressus sempervirens . The decline in transpiration rates observed in stressed wild pear seedlings is likely attributed to the closure of stomata and consequently a reduction in stomatal conductance and transpiration rate. Such a stomatal restriction of transpiration is likely co-regulated by hydraulic cues at the leaf-level and long-distance signaling from the roots via the abscisic acid pathway. Reduced transpiration rates during periods of drought stress are an effective strategy to preserve a favorable leaf water status, thereby helping to avert plant mortality under such conditions (Fang et al., 2015). By contrast, the diminished transpiration in oak under water deficit must be due to non-stomatal limitations (e.g. xylem embolism) since stomatal conductance remained unchanged. Leaf surface temperature in both species increased with decreasing soil water availability, which is consistent with the findings of Mirzaei et al., (2015) and Rooki et al., ( 2018 ) and reflects the reduced transpirational cooling associated with (non-) stomatal downregulation of transpiration (Scherrer et al., 2011 ). Under drought conditions, mesophyll conductance exhibited a decline, a finding corroborated by previous research (Hosseinian et al., 2018 ). Our findings further indicate a reduction in C i under water deficit conditions in both species, which was quite dramatic in wild pear but only minor in oak. In wild pear the large drop in C i seems more closely linked to the observed decrease in stomatal conductance, resulting in diminished CO 2 absorption. In oak, the rather high C i , coinciding with unaltered stomatal conductance, may result from increased photorespiration and, as a direct consequence, an accumulation of CO 2 in the mesophyll. This sequence of events disrupts leaf gas-exchange processes and lowers the water use efficiency of the plant (Anjum et al., 2011 ). Reducing the soil water availability from field capacity to 40% thereof, caused a decrease in leaf RWC of oak, while the unaltered leaf RWC in wild pear suggests a more effective maintenance of leaf hydration status through tighter stomatal control and probably osmotic adjustment as indicated by the strongly elevated levels of proline, which, among other functions, also serves as an osmoregulant (see below). The RWC response to drought seen in oak, is consistent with the results of Dehghan et al., (2015) on Pinus nigra seedlings, Ashkavand et al., ( 2016 ) on Crataegus aronia seedlings. Leaf RWC is a very good indicator of the water status of the plant cell (Schonfeld et al., 1988 ). During periods of drought, reduced moisture within the leaves leads to reduced cell expansion, which subsequently reduces leaf biomass. In our investigation, WUE was significantly reduced in drought-stressed pear and oak seedlings. Similar findings were reported for other woody and non-woody species. For instance, Norouzi and Tabari (2015) reported diminished WUE in drought-exposed Robinia pseudoacacia and Rooki et al., ( 2018 ) for Cupressus arizonica , Katerji et al., ( 2009 ) in Triticum durum and Hordeum vulgare and Mashilo et al., ( 2017 ) in Lagenaria siceraria . In our study, the WUE of both species was roughly halved under drought, which resulted from changes in both photosynthesis and stomatal conductance in wild pear, while the decline in oak was solely driven by a decrease in photosynthesis. Interestingly, the WUE of drought-stressed oak seedlings was similar to the WUE of wild pear seedlings growing under favorable soil water conditions. This finding contrasts with the largely unchanged WUE under drought in Quercus infectoria and Q. libani (Ghanbary et al., 2021 ). 4.3. Biochemical characteristics Our findings indicate notable differences in the biochemical characteristics examined under conditions of water deficit stress, with the exception of carotenoid and malondialdehyde. A degradation of photosynthetic pigments due to drought stress is a typical response observed in numerous plant species (Farooq et al., 2012 ). Most plants exhibit a decline in chlorophyll content as drought stress intensifies. Similar to the present study, Liu et al., ( 2022 ), reported a decrease in chlorophyll content under drought stress conditions in three Juglans species. Variations in chlorophyll content are often associated with the plant's water availability (Gitelson et al., 2003 ). Consistent with the results conducted on Q. infectoria and Q. libani (Ghanbary et al., 2021 ) and Olea europaea (Dehmardy et al., 2018 ), in the present study, a decrease in carotenoid content was observed under drought conditions. Drought stress also impairs photosynthetic performance by degrading photosynthetic pigments, leading to a decline in chlorophyll and carotenoid content (Tatari et al., 2020 ). This reduction may result from inhibited or halted synthesis of photosynthetic pigments under water-deficit conditions (Wang et al., 2021 ). In addition, ROS accumulating under drought stress can directly oxidize pigments or cause oxidative damage to cell membranes, thus affecting the structural integrity of chloroplasts and pigment-binding proteins. In the present study, proline accumulated in both species under drought stress conditions, but the increase was greater in wild pear than in oak. This drought-related increase in proline is in line with the responses observed in other tree species ( Pinus eldarica : Delfan Azari et al., 2018; Cercis siliquastrum : Saeidi Abueshaghi et al., 2023 ; Lagerstroemia indica : Wang et al., 2021 ), especially in Quercus brantii (Jafarnia et al., 2018 )d infectoria (Ghanbary et al., 2020 ), which are native to the Zagros forest region in Iran. However, no increase in proline was reported under water deficit for the more drought-sensitive Quercus libani , which co-occurs in the Zagros forests (Ghanbary et al., 2020 ). The extent of proline accumulation in plant cells depends on the type of species and the severity of stress (Claussen, 2005). The observed rise in proline content could result from either enhanced synthesis (increased anabolism) or reduced breakdown (decreased catabolism) of proline. In the case of Persian oak ( Quercus brantii ), severe drought conditions resulted in an increase in proline and MDA levels, as well as elevated electrolyte leakage (Jafarnia et al., 2018 ). Although in the present study, MDA levels did not change significantly with irrigation regime, oak showed a greater content than pear. By contrast, the two native oaks from the Zagros forests, Q. infectoria and Q. libani , both showed a substantial increase in MDA in response to drought (Ghanbary et al., 2020 ). Similar findings were reported by Wang et al., ( 2021 ) for Lagerstroemia indica , Lim et al., ( 2017 ) for Quercus acutissima , and Saeidi Abueshaqi et al., (2023) for Cercis siliquastrum , indicating that the amount of MDA increases with the intensity of drought in many woody species. Indeed, most plants exhibit a common response to oxidative stress in their biological membranes through lipid membrane peroxidation, which is indicated by a rise in malondialdehyde (Jafarnia et al., 2018 ). Specifically, during periods of drought stress, the overproduction of ROS leads to oxidative damage, potentially culminating in plant death. This finding reinforces the notion that MDA content is directly linked to the stress sensitivity of various plant species (Zhang et al., 2020 ). In our study, EL was markedly raised in our oak seedlings under drought, which is consistent with the findings for Persian oak ( Quercus brantii ; Jafarnia et al., 2018 ), Aleppo oak ( Q. infectoria ) and Lebanon oak ( Q. libani ) (Ghanbary et al., 2021 ), the three prevailing oak species in the Zagros forests, the other major forest zone of Iran. Under drought conditions, the plasma membrane of plant cells is one of the first structures to become damaged, which increases EL through the loss of the selective permeability property of the cell (Farooq et al., 2012 ) and is accompanied by an increase in the production and accumulation of ROS (such as superoxide radicals, hydrogen peroxide, and hydroxyl radicals) (Wang et al., 2024 ). Of course, an increase in lipid peroxidation, along with a decrease in the stability index of cell membranes, has been identified as a contributing factor to the rise in EL under-drought stress, too (Fayyaz et al., 2013 ). 5. Conclusion Based on this study, both species demonstrated high viability and significant drought stress tolerance, under water-deficit conditions. Notably, species identity exerts a more pronounced influence on biochemical traits, while water deficit stress primarily affects physiological and morphological traits. The analysis of various morphological traits showed that oak and wild pear seedlings possess considerable tolerance to drought stress. Severe drought conditions led to changes in the rate of physiological parameters (e.g., net photosynthesis, intracellular CO 2 concentration, mesophyll conductance and relative water content of leaves) in both species. Drought stress influenced notable modifications in most biochemical parameters in the two species (except proline and malondialdehyde). Furthermore, most physiological and biochemical traits were higher in oak seedling compared to wild pear seedling, both under water deficit and non-stress conditions. The findings of this study indicated that both species exhibited high viability and demonstrated good tolerance to drought stress. In the case of drought, the diameter growth in pear was diminished, whereas oak showed no significant change. Under drought conditions, the stem and leaf biomass, total biomass, leaf area, and specific leaf area remained relatively stable in pear, but experienced a decrease in oak. The insights gained from this research can be valuable for nursery managers dealing with water scarcity and for those involved in afforestation initiatives within the arid and semi-arid regions of the Hyrcanian forests, aligning with the best practices in seedling production and planting for these two species. Because tree species selection is essential to maintaining forest sustainability, our research adds to the ongoing discussion about the resilience of tree species against drought during the critical stage of seedling, particularly in the context of climate change. The outcomes of this research will aid in the selection of species for afforestation initiatives and the creation of sustainable forests, particularly focusing on drought-resistant species, in response to the rising frequency and severity of droughts in semi-arid regions. Declarations Author Contributions: Conceptualization, Y.D. and M.T.; methodology, Y.D. and M.T.; software, Y.D.; validation, M.T. and M.K.-F.B.; formal analysis, Y.D.; investigation, Y.D.; resources, E.S.; data curation, Y.D. and E.S.; writing—original draft preparation, Y.D.; writing—review and editing, M.T. and M.K.-F.B.; visualization, Y.D. and M.K.-F.B.; supervision, M.T.; project administration, M.T.; funding acquisition, M.T. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Tarbiat Mordares University. Data Availability Statement: Data is available upon request from the corresponding authors. 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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-7250378","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":497806310,"identity":"3a843163-b74e-48bf-9b68-a5109f9981b2","order_by":0,"name":"Masoud Tabari","email":"","orcid":"","institution":"Tarbiat Modares University","correspondingAuthor":false,"prefix":"","firstName":"Masoud","middleName":"","lastName":"Tabari","suffix":""},{"id":497806311,"identity":"4c5e7a37-8b23-4f6d-81c7-677fad264d64","order_by":1,"name":"Yadollah Davoudi","email":"","orcid":"","institution":"Tarbiat Modares University","correspondingAuthor":false,"prefix":"","firstName":"Yadollah","middleName":"","lastName":"Davoudi","suffix":""},{"id":497806312,"identity":"0dad30c8-39b0-4880-9b13-7f9adfdbbab1","order_by":2,"name":"Seyed Ehsan Sadati","email":"","orcid":"","institution":"Mazandaran Agricultural and Natural Resources Research and Education Center, AREEO","correspondingAuthor":false,"prefix":"","firstName":"Seyed","middleName":"Ehsan","lastName":"Sadati","suffix":""},{"id":497806313,"identity":"67d26fd5-226b-406b-a99b-0f249c4a613d","order_by":3,"name":"Martin Karl-Friedrich Bader","email":"data:image/png;base64,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","orcid":"","institution":"Maastricht University","correspondingAuthor":true,"prefix":"","firstName":"Martin","middleName":"Karl-Friedrich","lastName":"Bader","suffix":""}],"badges":[],"createdAt":"2025-07-30 08:23:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7250378/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7250378/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88816971,"identity":"2f673ed5-e526-4de7-984f-0cc9d61c9a4d","added_by":"auto","created_at":"2025-08-11 16:36:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":82158,"visible":true,"origin":"","legend":"\u003cp\u003eMeans of seedling survival of \u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz. and \u003cem\u003ePyrus boisseriana\u003c/em\u003eBuhse. seedlings under water deficit. The different lowercase letters on the columns indicate the significance of means among the 4 treatment combinations. The different uppercase letters on the columns indicate the significance of the means between two species, regardless of the irrigation treatment.\u003c/p\u003e","description":"","filename":"Figures111.png","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/3f1cd45fd4953ff0b11ddbba.png"},{"id":88816587,"identity":"b0ff96b6-a0b4-4c89-9426-85fccbf991c1","added_by":"auto","created_at":"2025-08-11 16:28:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":204471,"visible":true,"origin":"","legend":"\u003cp\u003eMeans of A- root volume, B- diameter growth, C- height growth D- root biomass, E- stem biomass, F- leaf biomass, G- total biomass, H- leaf area and I- specific leaf area of \u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz. and \u003cem\u003ePyrus boisseriana\u003c/em\u003e Buhse. seedlings under water deficit. The different lowercase letters on the columns indicate the significance of means among the 4 treatment combinations. The different uppercase letters on the columns indicate the significance of the means between two species, regardless of the irrigation treatment.\u003c/p\u003e","description":"","filename":"Figures112.png","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/e3fa545281d52cfd296b1fa7.png"},{"id":88817702,"identity":"448608db-2097-41f3-bb90-92454f21c591","added_by":"auto","created_at":"2025-08-11 16:44:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":287148,"visible":true,"origin":"","legend":"\u003cp\u003eMeans of A- photosynthesis, B- temperature, C- transpiration, D- stomatal conductance, E- intracellular CO\u003csub\u003e2\u003c/sub\u003e concentration, F- mesophilic conductance and G- WUE and G- RWC and H- water use efficiency of \u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz. and \u003cem\u003ePyrus boisseriana\u003c/em\u003e Buhse. seedlings under water deficit. The different lowercase letters on the columns indicate the significance of means among the 4 treatment combinations. The different uppercase letters on the columns indicate the significance of the means between two species, regardless of the irrigation treatment\u003c/p\u003e","description":"","filename":"Figures113.png","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/8e832f850f182fffd347a1e5.png"},{"id":88816592,"identity":"1da83fb3-0d68-4392-9afc-bfa9606eef42","added_by":"auto","created_at":"2025-08-11 16:28:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":319024,"visible":true,"origin":"","legend":"\u003cp\u003eMeans of A- carotenoid, B- proline, C- malondialdehyde and D- electrolyte leakage of \u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz. and \u003cem\u003ePyrus boisseriana\u003c/em\u003eBuhse. seedlings under water deficit. The different lowercase letters on the columns indicate the significance of means among the 4 treatment combinations. The different uppercase letters on the columns indicate the significance of the means between two species, regardless of the irrigation treatment.\u003c/p\u003e","description":"","filename":"Figures114.png","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/ca91cab510bd8f943d971ba4.png"},{"id":88817707,"identity":"b4e4d8cd-0ff5-4624-b1ee-7faf9ce310b0","added_by":"auto","created_at":"2025-08-11 16:44:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":293308,"visible":true,"origin":"","legend":"\u003cp\u003eStructural equation model (SEM) evaluating the direct and indirect effects of drought stress on some morphological, physiological, and biochemical traits in oak (\u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz.) and wild pear (\u003cem\u003ePyrus boisseriana\u003c/em\u003e Buhse) seedlings. The numbers on the rectangular boxes and directions represent the standardized variance and the standardized regression weights, respectively. Abbreviations are detailed in the parentheses (Rootvol: Root volume; Dgrowth: Diameter growth; Hgrowth: Height growth; Rmass: Root biomass; Smass: Stem biomass; Lmass: Leaf biomass; Tmass: Total biomass; LAI: Leaf Area; SLA: Specific leaf area; Photosyn: Photosynthesis; Transp: transpiration; Stomcon: Stomata conductance; Temp: temperature; IntercCO\u003csub\u003e2\u003c/sub\u003e: Intercellular CO\u003csub\u003e2\u003c/sub\u003e concentration; Mesocan: Mesophilic conductance; RWC: Relative water content; WUE: Water use efficiency; Chla: Chlorophyll a; Chlb:Chlorophyll b; Chla/b: Chlorophyll a / Chlorophyll b; Tchl: Total chlorophyll; Caro: Carotenoid; TchlCaro: Total chlorophyll/ Carotenoid; Malon: Malondialdehyde; El: Electrolyte leakage).\u003c/p\u003e","description":"","filename":"Figures115.png","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/3879e57d08eed8ed6a6cdedc.png"},{"id":88817704,"identity":"bbc3ec0b-d555-4a73-b474-7e51baf36fc5","added_by":"auto","created_at":"2025-08-11 16:44:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":318164,"visible":true,"origin":"","legend":"\u003cp\u003eA network model generated using drought stress in oak (\u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz.) and wild pear \u003cem\u003e(Pyrus boisseriana\u003c/em\u003e Buhse) seedlings and 24 morphological, physiological, and biochemical traits. Each node (circle) represents a property, and each edge (connection) indicates significant correlations among properties and samples. Node colors reflect the identified modules (groups), and the size and label of each node is proportional to the eigenvector centrality. The thickness of each edge (line) between two nodes is proportional to the standardized regression weights. The size and color density of the lines reflects the varying strength of relationship between the 24 morphological, physiological, and biochemical traits, i.e., thicker lines indicate stronger relationships and the direction of the arrows shows the influence of the factors on each other. Some variables are more central and have more connections than others. Abbreviations are detailed as follow.\u003c/p\u003e","description":"","filename":"Figures116.png","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/5e4b07d2f3e6b8a1dd79281a.png"},{"id":90336934,"identity":"9a5f7ddc-ff6c-4976-af60-712f5e08bdb4","added_by":"auto","created_at":"2025-09-01 14:23:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2365855,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7250378/v1/89df028d-bbcc-4a98-aece-5f22dda8a63c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Seedling-stage drought responses of two endemic pear and oak species inform climate-adaptive management approaches in Hyrcanian forests","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSevere droughts are expected to increase in frequency, magnitude, and spatial extent in the coming decades posing significant risks to the supply of essential resources such as water, food, and energy (Alencar \u003cem\u003eet al.\u003c/em\u003e, 2024; Teutschbein et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The frequency of drought events has grown over the past century, particularly in the last fifty years (Cai et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Recent projections from the World Climate Research Program indicate that global warming will impact the hydrological cycle, leading to heightened risks and intensified drought conditions in certain regions by the century's end. Concurrently, soil drying is expected to become increasingly widespread and intense with rising temperatures (Cook et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The distribution of plant species will be profoundly affected by environmental changes. However, the degree of these consequences will vary based on the ability of each species to withstand water scarcity (Zia et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Approximately 50% of the Earth's surface is covered by forests in which keystone tree species play a pivotal role in ecosystem structure and functioning by providing essential habitats, food sources, and symbiotic relationships for a variety of microorganisms, fungi, animals, and other plant species (Aitken et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Comprehending how trees cope with drought and its consequences on tree health and functioning is essential for the effective management of forest resources, the identification of suitable species and origins in reforested regions, and the conservation of forest ecosystems (Robakowski \u003cem\u003eet al.\u003c/em\u003e, 2020).\u003c/p\u003e\u003cp\u003ePlants cannot migrate from environments with unfavorable conditions like animals, and are therefore more susceptible to extreme weather conditions (Seleiman et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Water deficit is considered one of the most important environmental stresses with negative effects on plant growth, development and intracellular processes (Trenberth et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Drought represents a significant constraint on plant growth, as the process of cell expansion \u0026ndash;driven by the hydrostatic pressure within the newly forming cells \u0026ndash; requires adequate water availability in the cambium (Peters et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Water scarcity impedes essential physiological processes such as photosynthesis, respiration, and the movement of stomata, ultimately influencing overall plant growth and metabolic functions (Yang et al., \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Drought-induced impairment of photosystem II (PSII) I (PSI) activity restricts photosynthetic electron transport, which leads to an accumulation of surplus energy in the reaction centers and thus the formation of reactive oxygen species (ROS) and increased oxidative damage (Zhang et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The net photosynthetic rate is indicative of the biomass productivity per unit leaf area, thus serving as a dependable metric for assessing the overall production capacity of plants under otherwise non-limiting conditions. The closure of stomata leads to a reduction in CO\u003csub\u003e2\u003c/sub\u003e absorption, resulting in a diminished net photosynthetic rate. In tree seedlings that lack large carbon reserves, prolonged stomatal closure may lead to carbon limitation, which not only reduces biomass productivity but may also hasten drought-related mortality (Reddy et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This phenomenon is strongly influenced by the intensity and duration of drought events, as well as the developmental stage of the plant (Tardieu et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Overall, drought stress results in a decrease in survival (Engelbecht and Kursar, 2003), growth (Xiaoqin et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), leaf area (Wang et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), and plant biomass (Abbaspour et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Depending on the level of drought adaptation, plant water relations deteriorate more or less rapidly (Fang et al., 2015; Shivakrishna et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Farooq et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and, at the same time, oxidative damage indicated by oxidative stress markers increases (e.g., malondialdehyde, hydrogen peroxide, and electrolyte leakage, Anjum et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), which is often accompanied by a rise in antioxidants and osmoregulants (Sachan et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cem\u003ePyrus boissieriana\u003c/em\u003e Buhse (Rosaceae) is the second most widely distributed wild pear species across Iran. It primarily thrives in the Hyrcanian Forest (Zakavi et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), which is distinguished by a range of ecological conditions, including annual precipitation levels between 213 and 2045 mm and elevations from 12 m below sea level to 2400 m a.s.l., contributing to its extensive biodiversity (Heidari et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Various researchers have classified wild pear species as xerophytic woody plants due to their comparatively low reliance on soil moisture (Boucek, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1954\u003c/span\u003e; Zakavi et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Previous studies revealed that \u003cem\u003eP. boissiriana\u003c/em\u003e specimens originating from semi-arid environments exhibit greater tolerance to drought stress compared to specimens from semi-humid populations (Zarafshar et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and these more drought hardy individuals may thus serve as valuable rootstock resources for more drought-sensitive commercial wild pear scions in agricultural settings (Zakavi et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). It has been reported that wild pear trees under drought stress experiences a decrease in photosynthetic pigment concentration (Sattarian et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), leaf relative water content and water potential, and an increase in electrolyte leakage (Zarafshar et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). \u003cem\u003eQuercus atropatena\u003c/em\u003e O. Schwarz \u0026amp; Hess is a tree of the oak family native to the Hyrcanian forests of Iran, which is of great ecological importance. Although reports on the characteristics of this species are few, studies have shown that the oak genus is generally tolerant to water deficit stress (Khosravi et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Hernandez and Park, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, despite the wealth of oak-related drought studies, there are no reports on the physiological and biochemical responses of \u003cem\u003eQ. atropatena\u003c/em\u003e to drought conditions.\u003c/p\u003e\u003cp\u003eIn recent decades, increasing population growth and water demand have highlighted the importance of water resources management in arid and semi-arid regions, including Iran, where low rainfall and irregular distribution cause these types of climates (Tabari and Talaee, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). To thrive in these harsh conditions, plants require powerful resistance and/or tolerance mechanisms (Zerga, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In arid and semi-arid regions, expanding forests and increasing afforestation is hindered by limited water resources, which makes the selection of drought-resistant species crucial. Therefore, screening for drought tolerance traits and assessing water requirements is one of the most effective approaches to water management and ensuring success in seedling planting projects in these regions. There is a lack of information on the drought sensitivity of \u003cem\u003eP. boissieriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e, which are potential candidates for reforestation initiatives. The aim of this study was to assess the morphological, physiological, and biochemical responses of \u003cem\u003eP. boissieriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e seedlings to drought stress to inform forest managers and other stakeholders about their potential in future forest planning and decision-making. In this study, we seek to answer the following questions. 1) How do the morphological, physiological and biochemical responses differ between these two species under drought stress conditions? 2) What promise do \u003cem\u003eP. boissieriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e hold as drought-tolerant species for future-proofing forest regeneration in this increasingly dry region?\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Experimental design\u003c/h2\u003e\u003cp\u003eIn this study, two-year-old seedlings of \u003cem\u003eP. boissieriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e, growing in 5-liter pots, were analyzed under greenhouse conditions at Lajim Nursery, north of Iran. For this purpose, after three months of initial seedling growth, 192 healthy seedlings with approximately the same diameter (8\u0026thinsp;\u0026plusmn;\u0026thinsp;2 mm) and height (40\u0026thinsp;\u0026plusmn;\u0026thinsp;3 cm) were selected and maintained in greenhouse conditions. This investigation was performed using a factorial experimental approach, structured as a randomized complete block design, with three replications conducted for six months. The first factor was the water deficit treatment including FC100 (100% field capacity) as a control and FC40 (40% field capacity), and the second factor was the tree species identity. The determination of the field capacity of the soil and the irrigation process were carried out following Zarik et al., (\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Morphological characteristics\u003c/h2\u003e\u003cp\u003eMorphological characteristics, including root diameter and seedling height, were measured at the beginning and end of the period. Root diameter was measured using a digital caliper (with an accuracy of one-hundredth of a millimeter) and height was measured using a graduated ruler (with an accuracy of one cm). From the difference between diameter and height at the end and beginning of the period, diameter growth and height growth were obtained, respectively. Then, three seedlings were randomly chosen from each treatment combination, removed from the soil and after carefully washing off rhizosphere soil, the root length was measured using a ruler (Parad et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Leaf, root, and stem samples were oven-dried at 70\u0026deg;C for 48 hours. Subsequently, biomass was determined using a digital scale with a precision of 0.0001 g. The total biomass for the seedlings was calculated by combining the dry weights of their roots, leaves, and shoots. A leaf area meter (Model LI-3000, Li-Cor, Lincoln, NE, USA) was employed to assess the leaf area of six fully developed leaves from the upper section of each seedling. The specific leaf area (SLA) was determined by calculating the ratio of the leaf area to the dry weight of the leaves (Zarafshar et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Physiological characteristics\u003c/h2\u003e\u003cp\u003eWe assessed leaf net photosynthetic rate (\u003cem\u003eA\u003c/em\u003e), transpiration (E), stomatal conductance (gs), leaf temperature, and intercellular CO\u003csub\u003e2\u003c/sub\u003e concentration (\u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e). Measurements were taken following treatments in an outdoor environment, under natural conditions of temperature, light, and relative humidity between 9:30 and 11:00 AM, utilizing a portable gas exchange measurement device (Model LCpro+, ADC BioScientific Ltd., Hertfordshire, UK). For this analysis, 3\u0026ndash;6 fully expanded, mature leaves were chosen from each replicate, located at the upper sections of the seedlings (Ghanbary et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Water use efficiency (WUE) was calculated by the ratio of A/E (net photosynthetic rate/transpiration), while mesophyll conductance (\u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e) was derived from the ratio of photosynthesis to \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e. In order to determine the relative leaf water content (RWC), three healthy and fully developed leaves were taken from the top of each seedling. The initial fresh weight (FW) of the leaves was documented. Subsequently, the leaves were submerged in distilled water in a dark environment for 24 hours to facilitate water absorption and swelling (SW). After this period, the fully hydrated leaves were weighed again followed by oven-drying at 70\u003csup\u003e\u0026deg;\u003c/sup\u003eC for 48 hours, and subsequent dry weight (DW) determination. The relative leaf water content (RWC) was then calculated using Eq.\u0026nbsp;1 (Yang et al., \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eRWC = [(FW-DW) / (SW-DW)] \u0026times;100 (1)\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e2.4. Measurement of biochemical characteristics\u003c/em\u003e\u003c/h2\u003e\u003cp\u003eThe assessment of electrolyte leakage (EL) was conducted following the protocol outlined by Campos et al., (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Small leaf segments, each measuring 0.25 cm\u0026sup2;, were excised from 100 mg of fresh leaf tissue and placed into 50 mL falcon tubes filled with 15 mL of double distilled water. The tubes were then subjected to a boiling water bath at 80\u0026deg;C for 12 hours. After 2 hours, the initial electrical conductivity (EC1) was measured using an electrical conductivity meter. The samples were then transferred to a non-ventilated oven set at 120\u0026deg;C for 120 minutes. After cooling to 25\u0026deg;C, the final electrical conductivity (EC\u003csub\u003e2\u003c/sub\u003e) was recorded. The EL was calculated using the following Eq.\u0026nbsp;2:\u003c/p\u003e\u003cp\u003eEL= [EC1/EC2] \u0026times;100 (2)\u003c/p\u003e\u003cp\u003eTo assess the pigment amount, 0.1 g of frozen leaf discs was mixed with 0.1 g of calcium carbonate and 4 mL of 80% acetone. This mixture was then extracted in the dark at \u0026minus;\u0026thinsp;80\u0026deg;C. The resulting solution was transferred to a separate test tube and centrifuged at 4000 rpm for 10 minutes at 4\u0026deg;C. After the supernatant was separated, absorbance measurements were recorded spectrophotometrically at wavelengths of 470, 645, and 663 nm (PG Instruments T60, Wibtoft, Leicestershire, UK). The concentrations of chlorophyll a, chlorophyll b, and carotenoids were calculated using Equations (3, 4 and 5) (Arnon et al., 1949).\u003c/p\u003e\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img1754929562.png\" style=\"width: 639px;\"\u003e\u003c/p\u003e\u003cp\u003eProline was measured following Bates et al., (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1973\u003c/span\u003e). For this purpose, 0.5 g of frozen leaves from each species and treatment level were extracted using 5 mL of 3% sulfosalicylic acid. The resulting extract was then centrifuged for 15 minutes at 6000 rpm and 4\u0026deg;C. Following this, 2 mL of the supernatant was combined with 2 mL of ninhydrin reagent, 30 mL of glacial acetic acid, and 2 mL of acetic acid, and the mixture was incubated in a hot water bath at 95\u0026deg;C for one hour. After cooling on ice, 4 mL of toluene was introduced to the samples, which were then vortexed for 15 minutes after being kept in the dark for 20 minutes. The absorption of the pink upper phase containing toluene and proline was measured at 520 nm using a spectrophotometer (PG Instruments T60, Wibtoft, Leicestershire, UK), and the concentration of proline was determined by referencing a standard curve prepared with concentrations of 50, 40, 30, 20, 10, 5, 2.5, and 0 \u0026micro;M of pure proline.\u003c/p\u003e\u003cp\u003eIn order to assess the malondialdehyde (MDA) concentration, 0.2 g of frozen leaf discs from each species were mixed with 4 mL of trichloroacetic acid (TCA) buffer solution and subsequently subjected to centrifugation at 1500 rpm for 15 minutes. Following this step, 2 mL of the supernatant was extracted, and 2.5 mL of a 5% thiobarbituric acid (TBA) solution was added to it. The mixture was incubated in a hot water bath at 95\u0026deg;C for 50 minutes, followed by centrifugation at 10,000 rpm for 10 minutes. The mixture was cooled in ice water for 10 minutes, and the absorbance was measured spectrophotometrically at 532 nm (PG Instruments T60, Wibtoft, Leicestershire, UK). The concentration of MDA was determined using an extinction coefficient of 155 mm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Heath and Packer, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1968\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Statistical analysis\u003c/h2\u003e\u003cp\u003eAll statistical analyses were performed with SAS version 9.1 statistical software (SAS Institute Inc. 2023). Initially, the data's homogeneity and normality were evaluated using the Levene test and the Kolmogorov-Smirnov test, respectively. A two-way ANOVA was then conducted to examine the interaction effects between species type and water deficit stress. We used graphical model validation tools to check the underlying assumptions. A plot of the standardized residuals vs. fitted values indicated no gross violation of the variance homogeneity assumption and a quantile-quantile plot of the residuals showed no strong deviation from normality. Duncan's multiple range test was utilized to compare the means at both the 5% and 1% confidence levels. Structural equation modeling (SEM) was conducted utilizing Amos 24.0 software to assess the impact of species type and water deficit stress on various morphological, physiological and biochemical parameters. This approach was employed as it facilitates the exploration and comprehension of intricate connections among different morphological, physiological, and biochemical factors in relation to drought stress, offering insights into both the direct and indirect impacts of drought on two species: oak and pear. In this research, a general structural equation model was utilized, linking observed variables to latent variables. The model was assessed through path coefficients to measure the strength and direction of these connections, where positive coefficients signify direct and beneficial relationships, while negative coefficients denote inverse relationships. Furthermore, Gephi 0.10 software served as a network modeling tool for constructing, visualizing and analyzing the network model.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Morphological characteristics\u003c/h2\u003e\u003cp\u003eThe results of the two-way analysis of variance (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) demonstrated that the interaction of species and water deficit had a significant effect \u003cem\u003e(P\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/em\u003e) on the morphological characteristics of \u003cem\u003eQ. atropatena\u003c/em\u003e and \u003cem\u003eP. boisseriana\u003c/em\u003e seedlings (except for survival, height growth, root biomass and root volume). The impact of species on the morphological traits of seedlings (except for survival and height growth) was significant (\u003cem\u003eP\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/em\u003e). Also, water deficit stress had a considerable influence (\u003cem\u003eP\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/em\u003e) on the morphological traits (except for survival, height growth, diameter growth, and root biomass) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). At the FC100 and FC40 field capacities, the survival rates of wild pear seedlings were 97% and 93%, and for oak seedlings 95% and 93%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The greatest and smallest diameter growth (examined for 6 months) occurred in wild pear seedlings at FC100 and FC40 with averages of 10 mm and 6 mm, respectively. Under stress conditions (FC40), diameter growth experienced a decline of 38.4% in wild pear and 9.6% in oak when compared to well-watered seedlings (FC100) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). This means that under drought conditions, radial growth losses in oak were four times lower than in wild pear.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eTwo-way analysis of variance of the effect of species type, water deficit and their interaction on morphological, physiological and biochemical characteristics of \u003cem\u003eP. boissieriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e seedlings\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"15\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCharacteristic\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eSpecies\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c11\" namest=\"c9\"\u003e\u003cp\u003eWater deficit\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c15\" namest=\"c13\"\u003e\u003cp\u003eWater stress \u0026times; Species\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003edf\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eMS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eF value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003edf\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eMS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eF value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003edf\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c14\"\u003e\u003cp\u003eMS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c15\"\u003e\u003cp\u003eF value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eMorphological\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSurvival\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e8.333\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.10ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e102.083\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e1.24ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e8.333\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e0.10ns\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiameter growth\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.070\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.15ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.077\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e2.27ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e2.664\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e5.62*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHeight growth\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e162.803\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e13.73**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.316\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.03ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e15.526\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e1.31ns\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRoot biomass\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e280.381\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e80.7**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.698\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.2ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e2.895\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e0.83ns\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStem biomass\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e168.330\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e79.51**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e31.857\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e15.05**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e57.630\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e27.22**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLeaf biomass\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e196.222\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e76.98**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e18.612\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e7.30**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e39.440\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e15.47**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal biomass\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e1912.033\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e131.20**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e83.225\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e5.71*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e148.106\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e10.16**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRoot volume\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e1321.425\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e458.03**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e69.432\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e24.07**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.0099\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e2.544*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLeaf area\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e1030.360\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e220.93**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e47.262\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e10.13**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e44.409\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e9.52**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecific leaf area\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e24184.387\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e65.30**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e2696.651\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e7.28**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e2545.622\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e6.87*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003ePhysiochemical\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhotosynthesis (A)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e558.319\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e263.2**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1953.111\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e920.7**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e27.563\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e12.99**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTranspiration (E)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e82.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e263.79**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.009\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.03ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e3.658\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e75.93**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStomatal conductance (gs)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e253891.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e46.35**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e11172.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e2.04ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e91935.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e16.79**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003etemperature\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e370.84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e11.42**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.823\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.03ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e1282.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e39.52**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMesophilic conductance (gm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e258.2**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.016\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e1013.62**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e5.05*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIntracellular CO2 concentration (Ci)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8473.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e1.73ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e54885.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e11.18**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e24535.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e5.00*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRelative water content (RWC)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e1809.089\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e41.08**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e636.563\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e14.45**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e806.224\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e18.31**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWater use efficiency (WUE)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e475.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e510.15**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e601.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e644.97**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e92.294\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e98.92**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eBiochemical\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChlorophyll a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.554\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e33.23**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.202\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e12.15**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e0.10\u003csup\u003ens\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChlorophyll b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.482\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e30.41**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.518\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e32.73**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.018\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e1.19\u003csup\u003ens\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChl a/b ratio\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.15ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.252\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e10.51**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.113\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e4.69*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal chl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e2.070\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e36.04**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.370\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e23.85**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.009\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e0.16\u003csup\u003ens\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCarotenoid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.034\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e2.72ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.147\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e11.76**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e0.17ns\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal chl/ Carotenoid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e9.363\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e146.29**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.289\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e4.52*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.410\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e6.41*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eProline\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.04ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.203\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e2.61ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.610\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e7.83*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMalondialdehyde (MDA)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e2.509\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e7.06*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.897\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.17ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e0.739\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e0.17ns\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eElectrolyte leakage (EL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e101.036\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e46.35ns\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e584.924\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e6.06**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e579.213\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e6.00*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"15\"\u003ens\u0026thinsp;=\u0026thinsp;nonsignificant * and **= significant at level of 0.05 and 0.01 percent.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe height growth of both species was not significantly influenced by irrigation or the interaction between species and irrigation. Nonetheless, species identity had a significant impact on height growth with oak seedling height surpassing that of wild pear seedlings by 76.6%, irrespective of the irrigation treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). Root biomass in both species remained unaffected by drought and overall, the root biomass of oak seedlings was 2\u0026ndash;3 times higher than that of wild pear seedlings (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). Under water deficit conditions, a significant reduction in stem biomass was only observed in oak (-22.6%), resulting in a significant species \u0026times; drought interaction (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD). However, oak seedlings had significantly greater biomass than pear to start with. Leaf biomass declined by 13.8% in wild pear and by 32.5% in oak in response to drought conditions, which also gave rise to a significant species \u0026times; drought interaction (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE). The pattern seen in above-ground biomass compartments was also evident in the total biomass with stronger losses in oak (-25%) relative to pear (-14%), reflected in a significant species \u0026times; drought interaction (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF). Oak root volume was roughly 4.7 times larger than that of wild pear. Furthermore, in both irrigation regimes, oak seedlings consistently exhibited a greater root volume compared to wild pear seedlings (3 times and 2.4 times at FC100 and FC40, respectively) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG). Both total leaf area and specific leaf area (SLA) remained largely unaffected by drought in pear but showed steep declines in oak (leaf area: \u0026minus;\u0026thinsp;22%, SLA: -28%) resulting in a significant species x drought interaction (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI). Overall, at each soil field capacity, the specific leaf area was significantly greater in oak than in wild pear (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Physiological characteristics\u003c/h2\u003e\u003cp\u003eThe results of the two-way analysis of variance demonstrated that the interaction of water deficit stress and species type had a significant effect on all physiological characteristics of oak and wild pear seedlings (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Under water deficit stress, photosynthesis rates in wild pear and oak diminished by 55% and 49.6%, respectively, while oak consistently exhibited higher photosynthetic carbon uptake than wild pear across both water conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Additionally, leaf temperature increased under water deficit stress in both species (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). Furthermore, drought conditions led to a reduction in transpiration rates in both species, with wild pear experiencing an 11.8% decrease and oak a 21.7% decrease (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). Stomatal conductance did not change significantly under drought conditions in oak seedlings, while drought-exposed pear seedlings showed a significant reduction by 19.7% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMesophyll conductance was generally greater in oak compared to pear but declined under drought in both species, with wild pear experiencing a 58.5% decrease and oak a 49.5% decrease (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE). In the FC40 treatment, oak exhibited higher \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e levels than wild pear. The drought-related decrease in \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e in wild pear was significantly more pronounced (-54.8%) compared to oak, which only showed a slight decrease of -8% under stress conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF). Relative water content (RWC) remained unaffected by drought conditions in wild pear but decreased by 22% in oak (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eG). Oak seedlings had significantly greater WUE than pear seedlings (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). At FC40, a significant decrease was observed in both species, with the decrease being 52% in pear and 54.9% in oak (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eH).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Biochemical characteristics\u003c/h2\u003e\u003cp\u003eThere were no significant species \u0026times; drought interactions on chlorophyll a or b, total chlorophyll, carotenoids or MDA (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Nonetheless all these parameters were significantly affected by the two main effects, except for carotenoids which were similar among species but declined significantly under water deficit (wild pear: -19.9%, oak: -14.5%). However, MDA levels in oak were significantly greater by about 32% compared to wild pear but remained unaffected by the water deficit (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Regardless of species identity, the amounts of chlorophyll a, chlorophyll b, and total chlorophyll were 30.4%, 27.5%, and 28.9% higher in wild pear than in oak, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB, and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). We detected significant species \u0026times; drought interactions on the chlorophyll a/b ratio, the chlorophyll/carotenoid ratio, proline content and electrolyte leakage (El) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). More specifically, the chlorophyll a/b ratio remained largely unaffected by water deficit in wild pear but increased by ca. 24% under water deficit in oak seedlings (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). The chlorophyll/carotenoid ratio did not change significantly under water deficit in wild pear but decreased by ca. 18% in oak (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF). Under water deficit, proline levels rose about 4.9-fold in wild pear but only 32% in oak (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eG). EL was unresponsive to water deficit in wild pear but increased by 20.4% in FC40-exposed oak seedlings (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eI).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe structural equation model indicated that both species identity and water deficit stress significantly influenced the variations in physiological and biochemical parameters by affecting morphological traits. These traits were carefully chosen and incorporated into the SEM (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The results from the network model reveal that the roles of species identity and water deficit stress substantially impact the traits under investigation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Notably, species identity exerts a more pronounced influence on biochemical traits, while water deficit stress primarily affects physiological and morphological traits.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e4.1. Morphological characteristics\u003c/h2\u003e\u003cp\u003eThis research examined morphological, physiological and biochemical drought responses of seedlings of two prevalent tree species from the Hyrcanian forests to provide guidance to stakeholders concerned with nursery propagation and ecosystem management. Generally, the ability to survive periods of water scarcity and minimize growth losses associated with water deficit stress is essential for understanding plant drought tolerance (Engelbrecht and Kursar, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). In our study, the average survival rates across treatments exceeded 90% in both species, which, along with the relatively small losses in height and diameter growth under drought, indicates a remarkable drought tolerance. Numerous studies have shown that water scarcity often has a negative impact on plant survival rates. For instance, drought experiments conducted on \u003cem\u003eRobinia pseudoacacia\u003c/em\u003e seedlings by Norouzi Harouni et al., (2015) and on pine seedlings by Gou et al., (2010) showed that elevated drought stress, caused reduced soil water availability and resulted in about 20% lower survival rates in these plants.\u003c/p\u003e\u003cp\u003eUnder drought conditions, plants typically prioritize resource allocation to belowground sinks, i.e. increasing root volume and length to improve water uptake, thereby enhancing drought tolerance (Rooki et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Indeed, in our study root volume increased in both species under drought but since this occurred without concomitant increases in root biomass, we can confidently conclude that root expansion was facilitated by a reduction in root density. Typically, the earliest morphological indicators of drought stress include decreases in seedling height growth, stem diameter growth, and total biomass production, since growth processes become increasingly impaired as drought conditions intensify (Monclus et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Reduced growth during drought stress is primarily linked to a decrease in turgor pressure in the cambium and inadequate cell development (Lockhart \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1965\u003c/span\u003e; Peters et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), ultimately leading to a reduction in shoot growth in diameter and/or height. In our study, significant drought-induced radial growth losses only occurred in wild pear while height growth showed no significant reductions in either species. The observed decrease in diameter growth of wild pear by 38% is consistent with the results reported for \u003cem\u003eCupressus arizonica\u003c/em\u003e and \u003cem\u003eCupressus sempervirens\u003c/em\u003e var. \u003cem\u003efastigiata\u003c/em\u003e (Rooki et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), \u003cem\u003ePinus nigra\u003c/em\u003e (Dehghan et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), and \u003cem\u003eCercis siliquastrum\u003c/em\u003e (Norouzi Haroni et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The smaller diameter growth in drought-stressed wild pear seedlings was not accompanied by a reduction in stem biomass. Together with the small but statistically insignificant reduction in height growth, this suggests an increase in wood density, as reported previously for other woody species growing under water deficit (Lambers et al., 1998; Eliyani et al.,., 2005). Our findings showed drought stress-induced reductions in stem biomass (oak: -22.6%), leaf biomass (oak: -32.5%, wild pear: -13.8%) and total biomass (oak: -30.2%, wild pear: -12.2%) of seedlings. These results are consistent with the study of Jafarnia et al., (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) on seedlings of oak species (Q. \u003cem\u003elibani\u003c/em\u003e) with two different seed provenances showing a 15\u0026ndash;35% reduction in total dry biomass, Dehmardy et al., (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) on olive seedlings (\u003cem\u003eOlea europaea\u003c/em\u003e), Ashkavand et al., (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) on hawthorn seedlings (\u003cem\u003eCrataegus aronia\u003c/em\u003e L.) and mahaleb cherry (\u003cem\u003ePrunus mahaleb\u003c/em\u003e L.), and Saeidi Abueshaghi et al., (\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) on Judas seedlings (\u003cem\u003eCercis siliquastrum\u003c/em\u003e L.) with a ca. 46%, and 45% reduction in total fresh and dry biomass, respectively. As outlined above, the reduction in plant shoot biomass observed during drought conditions is probably primarily due to a decline in turgor pressure, which adversely affects the growth and proliferation of plant cells (Ashkavand et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Another contributing factor is the decrease in transpiration levels, which plants reduce to manage drought stress, ultimately leading to less shoot growth (Yang, 2007). During periods of drought stress, oak and wild pear seedlings undergo specific physiological changes, which help them survive in their environment. This starts with a tighter stomatal control over transpiration. When water is scarce, the seedlings retain more of the water taken up by the roots within the root system to promote stronger root growth or root volume. In other words, during periods of water deficit, plants tend to extend their roots deeper into the deeper soil layers to tap into soil moisture reserves and thus mitigate drought stress (Norouzi Haroni et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), which contributes to an increase in root volume and root weight. In our study, the root volume increased significantly (33% for wild pear and 13% for oak), although this was not associated with significant changes in root weight under drought conditions, translating into a decrease in root tissue density. Similarly, a study involving seedlings of \u003cem\u003ePistacia lentiscus\u003c/em\u003e L. and \u003cem\u003eQuercus coccifera\u003c/em\u003e found that heightened drought conditions do not necessarily promote the development of plant root systems, i.e. greater root biomass (Vilagrosa et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn the present study, under drought conditions, leaf area and specific leaf area in oak decreased by 22% and 28%, respectively, which is consistent with the findings reported for \u003cem\u003eCercis siliquastrum\u003c/em\u003e (Norouzi Haroni et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), \u003cem\u003ePistacia atlantica\u003c/em\u003e (Mirzaei, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), \u003cem\u003eCeltis Caucasica\u003c/em\u003e L. (Sepahvand et al.,, 2021), \u003cem\u003ePopulus euphratica\u003c/em\u003e (Zhao et al., \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and \u003cem\u003eLigustrum obtusifolium\u003c/em\u003e (Wang et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Leaf area is primarily determined by leaf tissue turgor, temperature, and various growth factors, which tend to decline under conditions of water deficit stress (Wang et al., \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This leads to a reduction in leaf area, primarily due to decreased transpiration, cell division, and the elongation of cells during periods of water scarcity (Yang et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Generally, based on various morphological traits our findings indicated that oak and wild pear seedlings exhibit significant drought stress tolerance. In reality, similar to other oak and pear species, the high drought tolerance of \u003cem\u003eQ. atropatena\u003c/em\u003e and \u003cem\u003ePyrus boisseriana\u003c/em\u003e appear to be primarily attributed to the ability to develop an extensive and deep root system for absorb of water and nutrient in lower soil layers (Abrams \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; Thomas and Gosling, 2000; Zarafshar et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e4.2. Physiological characteristics\u003c/h2\u003e\u003cp\u003eThe present study indicated that the photosynthesis rate was greater in oak seedlings compared to wild pear both under high and low water availability. Also, consistent with previous findings in both species, the rate of photosynthesis declined with decreasing water deficit (from FC100 to FC40) (Jafarnia et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Xiong et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Stomatal conductance in our oak seedlings remained unchanged by water scarcity, which has also been reported by Thomas and Gausling (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) for seedlings of two European oak species (\u003cem\u003eQ. robur, Q. petraea\u003c/em\u003e) and the same water use behaviour has recently been reported for mature individuals of the same oak species (Bader et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Essentially, under water deficit, the leaf water potential diminishes, leading to stomatal closure, which subsequently lowers stomatal conductance. This reduction in stomatal conductance results in decreased CO\u003csub\u003e2\u003c/sub\u003e availability, thereby impairing the rate of photosynthesis and ultimately hindering growth (Yang et al., \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In the current study, transpiration decreased with increasing water deficit, which is consistent with the results of Mirzaei et al., (2015) on \u003cem\u003ePistacia atlantica\u003c/em\u003e seedlings and Rooki et al., (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) on \u003cem\u003eCupressus arizonica\u003c/em\u003e and \u003cem\u003eCupressus sempervirens\u003c/em\u003e. The decline in transpiration rates observed in stressed wild pear seedlings is likely attributed to the closure of stomata and consequently a reduction in stomatal conductance and transpiration rate. Such a stomatal restriction of transpiration is likely co-regulated by hydraulic cues at the leaf-level and long-distance signaling from the roots via the abscisic acid pathway. Reduced transpiration rates during periods of drought stress are an effective strategy to preserve a favorable leaf water status, thereby helping to avert plant mortality under such conditions (Fang et al., 2015). By contrast, the diminished transpiration in oak under water deficit must be due to non-stomatal limitations (e.g. xylem embolism) since stomatal conductance remained unchanged.\u003c/p\u003e\u003cp\u003eLeaf surface temperature in both species increased with decreasing soil water availability, which is consistent with the findings of Mirzaei et al., (2015) and Rooki et al., (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and reflects the reduced transpirational cooling associated with (non-) stomatal downregulation of transpiration (Scherrer et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Under drought conditions, mesophyll conductance exhibited a decline, a finding corroborated by previous research (Hosseinian et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Our findings further indicate a reduction in \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e under water deficit conditions in both species, which was quite dramatic in wild pear but only minor in oak. In wild pear the large drop in \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e seems more closely linked to the observed decrease in stomatal conductance, resulting in diminished CO\u003csub\u003e2\u003c/sub\u003e absorption. In oak, the rather high \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, coinciding with unaltered stomatal conductance, may result from increased photorespiration and, as a direct consequence, an accumulation of CO\u003csub\u003e2\u003c/sub\u003e in the mesophyll. This sequence of events disrupts leaf gas-exchange processes and lowers the water use efficiency of the plant (Anjum et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Reducing the soil water availability from field capacity to 40% thereof, caused a decrease in leaf RWC of oak, while the unaltered leaf RWC in wild pear suggests a more effective maintenance of leaf hydration status through tighter stomatal control and probably osmotic adjustment as indicated by the strongly elevated levels of proline, which, among other functions, also serves as an osmoregulant (see below). The RWC response to drought seen in oak, is consistent with the results of Dehghan et al., (2015) on \u003cem\u003ePinus nigra\u003c/em\u003e seedlings, Ashkavand et al., (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) on \u003cem\u003eCrataegus aronia\u003c/em\u003e seedlings. Leaf RWC is a very good indicator of the water status of the plant cell (Schonfeld et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). During periods of drought, reduced moisture within the leaves leads to reduced cell expansion, which subsequently reduces leaf biomass.\u003c/p\u003e\u003cp\u003eIn our investigation, WUE was significantly reduced in drought-stressed pear and oak seedlings. Similar findings were reported for other woody and non-woody species. For instance, Norouzi and Tabari (2015) reported diminished WUE in drought-exposed \u003cem\u003eRobinia pseudoacacia\u003c/em\u003e and Rooki et al., (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) for \u003cem\u003eCupressus arizonica\u003c/em\u003e, Katerji et al., (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) in \u003cem\u003eTriticum durum\u003c/em\u003e and \u003cem\u003eHordeum vulgare\u003c/em\u003e and Mashilo et al., (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) in \u003cem\u003eLagenaria siceraria\u003c/em\u003e. In our study, the WUE of both species was roughly halved under drought, which resulted from changes in both photosynthesis and stomatal conductance in wild pear, while the decline in oak was solely driven by a decrease in photosynthesis. Interestingly, the WUE of drought-stressed oak seedlings was similar to the WUE of wild pear seedlings growing under favorable soil water conditions. This finding contrasts with the largely unchanged WUE under drought in \u003cem\u003eQuercus infectoria\u003c/em\u003e and \u003cem\u003eQ. libani\u003c/em\u003e (Ghanbary et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e4.3. Biochemical characteristics\u003c/h2\u003e\u003cp\u003eOur findings indicate notable differences in the biochemical characteristics examined under conditions of water deficit stress, with the exception of carotenoid and malondialdehyde. A degradation of photosynthetic pigments due to drought stress is a typical response observed in numerous plant species (Farooq et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Most plants exhibit a decline in chlorophyll content as drought stress intensifies. Similar to the present study, Liu et al., (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), reported a decrease in chlorophyll content under drought stress conditions in three \u003cem\u003eJuglans\u003c/em\u003e species. Variations in chlorophyll content are often associated with the plant's water availability (Gitelson et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Consistent with the results conducted on \u003cem\u003eQ. infectoria and Q. libani\u003c/em\u003e (Ghanbary et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and \u003cem\u003eOlea europaea\u003c/em\u003e (Dehmardy et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), in the present study, a decrease in carotenoid content was observed under drought conditions. Drought stress also impairs photosynthetic performance by degrading photosynthetic pigments, leading to a decline in chlorophyll and carotenoid content (Tatari et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This reduction may result from inhibited or halted synthesis of photosynthetic pigments under water-deficit conditions (Wang et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition, ROS accumulating under drought stress can directly oxidize pigments or cause oxidative damage to cell membranes, thus affecting the structural integrity of chloroplasts and pigment-binding proteins.\u003c/p\u003e\u003cp\u003eIn the present study, proline accumulated in both species under drought stress conditions, but the increase was greater in wild pear than in oak. This drought-related increase in proline is in line with the responses observed in other tree species (\u003cem\u003ePinus eldarica\u003c/em\u003e: Delfan Azari et al., 2018; \u003cem\u003eCercis siliquastrum\u003c/em\u003e: Saeidi Abueshaghi et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; \u003cem\u003eLagerstroemia indica\u003c/em\u003e: Wang et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), especially in \u003cem\u003eQuercus brantii\u003c/em\u003e (Jafarnia et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)d \u003cem\u003einfectoria\u003c/em\u003e (Ghanbary et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), which are native to the Zagros forest region in Iran. However, no increase in proline was reported under water deficit for the more drought-sensitive \u003cem\u003eQuercus libani\u003c/em\u003e, which co-occurs in the Zagros forests (Ghanbary et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The extent of proline accumulation in plant cells depends on the type of species and the severity of stress (Claussen, 2005). The observed rise in proline content could result from either enhanced synthesis (increased anabolism) or reduced breakdown (decreased catabolism) of proline. In the case of Persian oak (\u003cem\u003eQuercus brantii\u003c/em\u003e), severe drought conditions resulted in an increase in proline and MDA levels, as well as elevated electrolyte leakage (Jafarnia et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Although in the present study, MDA levels did not change significantly with irrigation regime, oak showed a greater content than pear. By contrast, the two native oaks from the Zagros forests, \u003cem\u003eQ. infectoria\u003c/em\u003e and \u003cem\u003eQ. libani\u003c/em\u003e, both showed a substantial increase in MDA in response to drought (Ghanbary et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Similar findings were reported by Wang et al., (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) for \u003cem\u003eLagerstroemia indica\u003c/em\u003e, Lim et al., (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) for \u003cem\u003eQuercus acutissima\u003c/em\u003e, and Saeidi Abueshaqi et al., (2023) for \u003cem\u003eCercis siliquastrum\u003c/em\u003e, indicating that the amount of MDA increases with the intensity of drought in many woody species. Indeed, most plants exhibit a common response to oxidative stress in their biological membranes through lipid membrane peroxidation, which is indicated by a rise in malondialdehyde (Jafarnia et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Specifically, during periods of drought stress, the overproduction of ROS leads to oxidative damage, potentially culminating in plant death. This finding reinforces the notion that MDA content is directly linked to the stress sensitivity of various plant species (Zhang et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn our study, EL was markedly raised in our oak seedlings under drought, which is consistent with the findings for Persian oak (\u003cem\u003eQuercus brantii\u003c/em\u003e; Jafarnia et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), Aleppo oak (\u003cem\u003eQ. infectoria\u003c/em\u003e) and Lebanon oak (\u003cem\u003eQ. libani\u003c/em\u003e) (Ghanbary et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), the three prevailing oak species in the Zagros forests, the other major forest zone of Iran. Under drought conditions, the plasma membrane of plant cells is one of the first structures to become damaged, which increases EL through the loss of the selective permeability property of the cell (Farooq et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and is accompanied by an increase in the production and accumulation of ROS (such as superoxide radicals, hydrogen peroxide, and hydroxyl radicals) (Wang et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Of course, an increase in lipid peroxidation, along with a decrease in the stability index of cell membranes, has been identified as a contributing factor to the rise in EL under-drought stress, too (Fayyaz et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eBased on this study, both species demonstrated high viability and significant drought stress tolerance, under water-deficit conditions. Notably, species identity exerts a more pronounced influence on biochemical traits, while water deficit stress primarily affects physiological and morphological traits. The analysis of various morphological traits showed that oak and wild pear seedlings possess considerable tolerance to drought stress. Severe drought conditions led to changes in the rate of physiological parameters (e.g., net photosynthesis, intracellular CO\u003csub\u003e2\u003c/sub\u003e concentration, mesophyll conductance and relative water content of leaves) in both species. Drought stress influenced notable modifications in most biochemical parameters in the two species (except proline and malondialdehyde). Furthermore, most physiological and biochemical traits were higher in oak seedling compared to wild pear seedling, both under water deficit and non-stress conditions. The findings of this study indicated that both species exhibited high viability and demonstrated good tolerance to drought stress. In the case of drought, the diameter growth in pear was diminished, whereas oak showed no significant change. Under drought conditions, the stem and leaf biomass, total biomass, leaf area, and specific leaf area remained relatively stable in pear, but experienced a decrease in oak. The insights gained from this research can be valuable for nursery managers dealing with water scarcity and for those involved in afforestation initiatives within the arid and semi-arid regions of the Hyrcanian forests, aligning with the best practices in seedling production and planting for these two species. Because tree species selection is essential to maintaining forest sustainability, our research adds to the ongoing discussion about the resilience of tree species against drought during the critical stage of seedling, particularly in the context of climate change. The outcomes of this research will aid in the selection of species for afforestation initiatives and the creation of sustainable forests, particularly focusing on drought-resistant species, in response to the rising frequency and severity of droughts in semi-arid regions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e Conceptualization, Y.D. and M.T.; methodology, Y.D. and M.T.; software, Y.D.; validation, M.T. and M.K.-F.B.; formal analysis, Y.D.; investigation, Y.D.; resources, E.S.; data curation, Y.D. and E.S.; writing\u0026mdash;original draft preparation, Y.D.; writing\u0026mdash;review and editing, M.T. and M.K.-F.B.; visualization, Y.D. and M.K.-F.B.; supervision, M.T.; project administration, M.T.; funding acquisition, M.T. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research was funded by Tarbiat Mordares University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement:\u003c/strong\u003e Data is available upon request from the corresponding authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u003c/strong\u003e The authors declare no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbbaspour H, Saeidi-Sar S, Afshari H, Abdel-Wahhab MA (2012) Tolerance of Mycorrhiza infected pistachio (\u003cem\u003ePistacia vera\u003c/em\u003e L.) seedling to drought stress under glasshouse conditions. J. 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Microbiological research, p 126626\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Electrolyte leakage, Height growth, Malondialdehyde, Proline, Relative water content","lastPublishedDoi":"10.21203/rs.3.rs-7250378/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7250378/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe diverse Hyrcanian relic forests are increasingly threatened by more frequent and severe climate change-related droughts. This study investigated morpho-physiological and biochemical responses to drought in two endemic tree species of the Hyrcanian forests, \u003cem\u003ePyrus boisseriana\u003c/em\u003e Buhse and \u003cem\u003eQuercus atropatena\u003c/em\u003e Schwarz. In a 120-day greenhouse experiment, seedlings of each species were exposed to two different irrigation treatments (FC100 and FC40, indicating percentage of field capacity). Under FC100 conditions, all morphological characteristics of \u003cem\u003eQ. atropatena\u003c/em\u003e were significantly greater compared to those of \u003cem\u003eP. boisseriana\u003c/em\u003e. FC40-exposed \u003cem\u003eP. boisseriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e seedlings exhibited statistically significant declines in photosynthesis (-55, -49.6%), transpiration (-11.8, -21.7%), intercellular CO\u003csub\u003e2\u003c/sub\u003e concentration (\u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e) (-54.8, -8.3%), mesophyll conductance (\u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e) (-58.5, -49.5%), RWC (only \u003cem\u003eQ. atropatena\u003c/em\u003e: -22%), and water use efficiency (-95.3, -57.3%), respectively, and an increase in leaf temperature. Likewise, FC40-treated \u003cem\u003eP. boisseriana\u003c/em\u003e and \u003cem\u003eQ. atropatena\u003c/em\u003e seedlings displayed an increase in proline (+\u0026thinsp;390.8, +\u0026thinsp;46.5%), and a decline in carotenoids (-19.9, -14.5%), respectively. Drought stress had smaller impacts on radial and height growth, photosynthesis, \u003cem\u003eC\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e, carotenoids, EL and MDA, in \u003cem\u003eQ. atropatena\u003c/em\u003e compared to \u003cem\u003eP. boisseriana\u003c/em\u003e, indicating greater drought tolerance in the former. These findings imply a prioritization of \u003cem\u003eQ. atropatena\u003c/em\u003e in forest management and conservation planning in arid and semi-arid Hyrcanian forests, especially given future climate scenarios. Our results also offer valuable insights for nursery managers facing water scarcity and for stakeholders in afforestation and reforestation projects, thus contributing to the broader discussion on tree species resilience to drought during the critical seedling stage.\u003c/p\u003e","manuscriptTitle":"Seedling-stage drought responses of two endemic pear and oak species inform climate-adaptive management approaches in Hyrcanian forests","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-11 16:28:26","doi":"10.21203/rs.3.rs-7250378/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"48bc0100-8c40-48a6-a460-496a5d12e3d8","owner":[],"postedDate":"August 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-01T14:23:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-11 16:28:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7250378","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7250378","identity":"rs-7250378","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}