Rice straw biochar mitigates metal stress in maize and assists in the phytoattenuation of a slag-contaminated soil

Rice straw biochar mitigates metal stress in maize and assists in the phytoattenuation of a slag-contaminated soil | 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 Rice straw biochar mitigates metal stress in maize and assists in the phytoattenuation of a slag-contaminated soil Venâncio Lima Veloso, Fernando Bruno Vieira Silva, Paula Renata Muniz Araújo, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4252712/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 Soils polluted by heavy metals soils pose a high risk to human health and must be remediated. Applying biochar to such soils can reduce metal bioavailability and phytotoxicity, improving phytoremediation techniques. This work aimed to assess the effects of rice straw biochar (RSB) on mitigating metal stress and accumulation of Si, Cd, Pb, and Zn in maize plants grown in soil contaminated by metallurgy slag. The soil in pots was amended with RSB rates equivalent to 0.0, 5.0, 10.0, 20.0, and 30.0 t ha -1 and grown with maize for 45 days. Chlorophyll fluorescence, photosynthetic pigment contents, and gas exchange parameters were evaluated as metal toxicity indicators. The RSB rates significantly increased Si uptake while reducing Cd, Pb, and Zn accumulation in maize shoots. The addition of 30.0 t ha -1 RSB promoted 18, 34, and 37% reductions for Zn, Cd, and Pb in the plants. Photosynthetic rate, transpiration, and stomatal conductance increased by 68%, 67%, and 55%, while chlorophyll a, b, and carotenoid contents increased by 77%, 57%, and 42%, correspondingly. Chlorophyll fluorescence measurements showed a linear and positive relationship between photosystem II energy consumption efficiency (Fv/Fm) and RSB rates. Applying RSB associated with maize cultivation can assist in the phytoattenuation of Cd, Pb, and Zn contamination in soils since RSB increases biomass and the plant's tolerance to metal stress. potentially toxic element soil remediation photosynthesis abiotic stress gas exchange Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. INTRODUCTION Heavy metal-polluted soils pose high risk to human and animal health, being one of the most concerning environmental problems worldwide. The anthropogenic input of heavy metals in the environment affects soil ecosystem functions, threatens food quality, and poses a risk to human health due to the high persistence, phytotoxicity, non-biodegradability, and transfer of these elements to the food chain (Peng et al., 2017 ; Zhang et al., 2022 ). Metallurgy is a primary anthropogenic source of metals to the environment (da Silva et al., 2017 ; Wang et al., 2020 ). The accumulation of large volumes of slag rich in heavy metals in abandoned smelter plants can contaminate soils and water resources (Izydorczyk et al., 2021 ; Król et al., 2020 ). For example, in the city of Santo Amaro in Bahia, in the northeast region of Brazil, Pb smelting activities between the 1960s and 1980s resulted in thousands of tons of abandoned slag and the most severe case of Pb soil pollution in the country. Thousands of workers and residents around the Pb smelter plant showed neurological and renal damage and genotoxicity (de Andrade Lima and Bernardez, 2011 ; Niemeyer et al., 2015 ; Santos et al., 2015 ; Silvany Neto et al., 1996 ). Even after three decades of inactivity at the smelter plant, the soils in this region still have high concentrations of heavy metals with a potential risk to human health (da Silva et al., 2017 ). In this scenario, actions to remove or reduce the availability of metals in the soil are mandatory to guarantee the functionality of the ecosystem and the health of animals and humans. Among the polluted soil remediation techniques using plants, the so-called phytotechnologies, phytoattenuation aims to gradually decrease the concentrations of heavy metals in soils over time, mitigating environmental risks and providing income during the remediation process through valuable plants (Cundy et al., 2016 ; de Lima Veloso et al., 2022 ; Zhu et al., 2016 ). Phytoattenuation promotes synergies with energy crops, biodiversity, watershed management, carbon sequestration, and soil erosion reduction, making the remediation process socially, economically, and environmentally attractive (Burges et al., 2018 ; Cundy et al., 2016 ). One of the phytoattenuation strategies includes using plant biomass for energy production (e.g., conversion into biogas by anaerobic digestion) (Ahmad et al. 2018 ; de Lima Veloso et al. 2022 ). Maize ( Zea mays L.) is a bioenergetic crop cultivated in many regions of the world; besides, it is easy to manage and has fast growth, high biomass, and an extensive root system (Ahmad et al., 2018 ). In addition, maize is a species relatively tolerant to heavy metals (da Silva et al., 2017 ; Haider et al., 2022a ; Irfan et al., 2021 ; Murakami and Ae, 2009 ). These characteristics make this crop promising for the phytoattenuation of soils polluted by metals. Heavy metals in soils can be immobilized by organic materials such as manure, compost, and biochar (Ahmad et al., 2018 ). Biochar is an eco-friendly amendment to retain heavy metals in the soil system and decrease metal uptake and toxicity to plants (Cui et al., 2016 ; Meng et al., 2018 ). Biochar is a material rich in pyrogenic carbon, highly recalcitrance, porous, and originated from the organic wastes pyrolysis (Lu et al., 2014 ; Meng et al., 2018 ). Biochars can immobilize the most labile fraction of metals in the soil and reduce their plant uptake through precipitation, ion exchange, complexation, and chemisorption (Wang et al., 2021 ). Furthermore, biochar can be a source of nutrients (e.g., N, P, and micronutrients) and silicon (Si) for plants (Chew et al., 2022 ), as in the case of biochar produced from straw or rice husks (K and S, 2020; Li et al., 2019 ; Wang et al., 2019 ; Yao et al., 2022 ). Si is a beneficial element for plants and a mitigating agent of soil pollution by heavy metals (Li et al., 2022 ; Yadav et al., 2023 ). Si mitigates heavy metal toxicity through mechanisms external and internal to the plants and can act from the immobilization of the metal in the soil to the regulation of the absorption and translocation of the contaminant in the plant (Adrees et al., 2015 ; Bhat et al., 2019 ; Li et al., 2022 ). Cadmium and Pb are toxic even at low content in the soil and are not essential elements to plants; Zn, on the other hand, is a micronutrient that can be toxic to plants when in high concentrations in the soil, usually due to anthropogenic contamination (Kabata-Pendias, 2010 ; Zhang et al., 2018 ). Metal phytotoxicity can inhibit root growth (Huang et al., 2021 ), affect water and nutrient uptake (Singh et al., 2023 ), and inhibit metabolic processes such as chlorophyll synthesis (Zhang et al., 2020 ), photosynthesis and respiration (Peršić et al., 2019 ); in addition, heavy metals can cause oxidative damage in plants due to the excessive accumulation of reactive oxygen species (ROS) (Rusinowski et al., 2019 ). Physiological processes such as photosynthesis are susceptible to heavy metal stress (Chu et al., 2018 ; Duarte et al., 2023 ; Hou et al., 2018 ; Zhang et al., 2018 ). Damage to the photosynthetic apparatus is related to (i) the direct interaction of metal ions with the thiol–, histidine– and carboxyl– groups of proteins; (ii) the formation of ROS; and (iii) the replacement of essential cations in the active centers of proteins (e.g., the exchange of Mg 2+ for Cd 2+ or Zn 2+ in the chlorophyll molecule, resulting in the formation of the chlorophyll-metal complex with lower quantum efficiency in photosystem II (PSII) (Żurek et al., 2014 ). Chlorophyll fluorescence measurements, photosynthetic pigments, and gas exchange parameters are indicators of heavy metal stress in plants (Ren et al., 2021 ; Rusinowski et al., 2019 ; Zhang et al., 2020 ). For instance, chlorophyll fluorescence analysis provides information about changes in photochemical efficiency. The Fv/Fm index derived from the relationship between variable and maximum fluorescence evaluates the performance of the photosynthetic apparatus, indicating the plant's ability to tolerate metal stress (Dezhban et al., 2015 ). Other physiological indicators of stress are chlorophyll content and gas exchange. Chlorophyll a and b contents are important indexes of the effects of soil pollution on plants (Chu et al., 2018 ; Moradi and Ehsanzadeh, 2015 ), as well as changes in stomatal conductance, CO 2 assimilation, and photosynthetic rate (Feng et al., 2010 ; Silva Gonzaga et al., 2019 ). We hypothesize that applying rice straw biochar (RSB) in heavy metal-polluted soils can help mitigate metal toxicity in plants, stabilize metals in the soil, and phytoattenuate the contamination. Therefore, the study assessed the effects of RSB rates on biomass yield and accumulation of Si, Cd, Pb, and Zn in maize cultivated in soil polluted by slag. We also evaluated the photosynthetic apparatus functioning, the production of photosynthetic pigments, and the gas exchange parameters. Our results may indicate the technical viability of the combined use of RSB and plants in the remediation of heavy metal-polluted soils. 2. MATERIAL AND METHODS 2.1. Soil and biochar characterization The soil utilized in this research, classified as Acrisol according to the WRB-FAO ( 2015 ), exhibited significant contamination resulting from the deposition of a slag enriched with Cd, Pb, and Zn near an abandoned lead smelting facility in Santo Amaro, Brazil (12° 32′ 21.6′′ S, 38° 43′ 41′′ W). A representative soil sample was air-dried and sieved through a 2.0 mm mesh sieve. Subsequently, three subsamples were used for comprehensive chemical and physical characterization, as well as the determination of total, semi-total, and bioavailable concentrations of metals in the soil (Table 1 ). Table 1 Chemical, physicochemical and physical characteristics of soil and rice straw biochar (RSB 400 ºC) used in the experiment Soil attributes IV Soil values Biochar attributes Biochar values pH (1:2.5) in CaCl 2 --- 6.5 ± 0.8 pH (1:5) in H 2 O 7.3 ± 0.1 SOC (g kg − 1 ) --- 11.4 ± 2.1 EC (dS m − 1 ) 222.4 ± 41.3 SOM (g kg − 1 ) --- 19.6 ± 1.8 CEC (cmolc kg − 1 ) 44.5 ± 2.4 CEC (cmol c dm − 3 ) --- 23.2 ± 3.0 SSA (m 2 g − 1 ) 1.4 ± 0.3 Ca 2+ (cmol c dm − 3 ) --- 17.1 ± 3.2 Humidity (%) 7.5 ± 0.1 Mg 2+ (cmol c dm − 3 ) --- 4.9 ± 0.7 Fixed carbon (%) 49.3 ± 5.9 K + (cmol c dm − 3 ) --- 0.4 ± 0.1 Ash (%, w/w) 33.1 ± 0.7 H + Al (cmol c dm − 3 ) --- 2.8 ± 0.6 C (%, w/w) 66.0 ± 3.1 P available (mg dm − 3 ) --- 4.4 ± 0.7 N (%, w/w) 2.9 ± 0.1 Sand (g kg − 1 ) --- 153.5 ± 10.8 O (%, w/w) 10.7 ± 1.8 Silt (g kg − 1 ) --- 381.5 ± 8.7 Si (%, w/w) 3.7 ± 0.9 Clay (g kg − 1 ) --- 654.0 ± 12.3 P (g kg − 1 ) 11.7 ± 0.2 Zn total (mg kg − 1 ) * --- 566.0 ± 28.3 K (g kg − 1 ) 6.0 ± 0.1 Zn semi–total (mg kg − 1 ) ** 450.0 366.3 ± 29.2 Ca (g kg − 1 ) 2.1 ± 0.1 Zn available (mg kg − 1 ) *** --- 65.1 ± 6.7 Mg (g kg − 1 ) 0.8 ± 0.1 Pb total (mg kg − 1 ) * --- 1991.8 ± 58.4 Fe (mg kg − 1 ) 747.5 ± 9.6 Pb semi–total (mg kg − 1 ) ** 180.0 1392.8 ± 32.9 Mn (mg kg − 1 ) 917.5 ± 4.2 Pb available (mg kg − 1 ) *** --- 855.6 ± 51.3 Cu (mg kg − 1 ) 20.2 ± 0.4 Cd total (mg kg − 1 ) * --- 24.9 ± 3.0 Zn (mg kg − 1 ) 37.8 ± 1.8 Cd semi–total (mg kg − 1 ) ** 3.0 19.3 ± 1.6 Pb (mg kg − 1 ) < LOQ Cd available (mg kg − 1 ) *** --- 19.2 ± 2.9 Cd (mg kg − 1 ) < LOQ IV investigation values for the agricultural scenario (CONAMA 2009); SOM soil organic carbon; CEC cation exchange capacity; EC electric conductivity; SA specific surface area; * acid dissolution with HF + HNO3 + HClO4 + HCl (2:1:1:1); **method EPA 3051a; ***DTPA pH 7.3; LOQ quantification limit (0.07 and 0.78 mg kg − 1 for Cd and Pb, respectively). (Table 1 ) The biochar tested was obtained from pyrolysis of rice straw at 400°C. The biochar was characterized following the procedures described by Singh et al. ( 2017 ) and the results are presented in Table 1 . The total concentrations of P, Zn, Cd, and Pb were obtained from the extract of the biochar digestion using the 3051A method (USEPA, 2007 ) followed by metal measurements by ICP-OES (Optima 7000 Perkin Elmer, USA). 2.2. Pot experiment The soil was fertilized with (mg kg − 1 ) 250.0 N (Urea), 240.0 P (MAP), 150.0 K (KCl), 160.0 S (K 2 SO 4 ), 2.0 Fe (FeSO 4 .7H 2 O), 4.0 Mn (MnCl 2 .4H 2 O), 1.3 Cu (CuSO 4 ), 1.0 B (H 3 BO 3 ), and 0.2 Mo (Na 2 MoO 4 .2H 2 O) (da Silva et al., 2017 ). The RSB was applied to 5 kg pots at five rates (equivalents to 0.0, 5.0, 10.0, 20.0, and 30.0 t ha − 1 ) replicated four times in a randomized block design. In each pot, five maize seeds were initially planted, and post-germination, only two plants were kept for biomass collection. Maize was selected for testing due to its potential for bioenergy production through harvest. Throughout the experiment, control was maintained to sustain the soil at 80% of its maximum water retention capacity. 2.3. Plant physiological analyses Leaf gas exchange (photosynthetic rate, transpiration, and stomatal conductance) were evaluated at 45 days of cultivation using a portable gas exchange system (model LI–6400XT, LI–COR Bioscences, Lincoln, NE, USA). Measurements were carried out on two leaves of the upper third of the plant. All parameters were measured between 9 am and 11 am, when the plants were physiologically functional. During the measurements, the intensity of the photosynthetic photon flux was maintained at 1800 µmol m 2 s –1 (Dourado et al., 2022 ). The initial fluorescence (Fo), variable fluorescence (Fv), maximum fluorescence (Fm), and maximum quantum yield index (Fv/Fm) were determined simultaneously, immediately following the gas exchange measurements, using a portable fluorometer (FluorPen, model F100, Photon Systems Instruments). Measurements were carried out on two leaves of the upper third of the plant, which previously had a leaf blade section kept in the dark for 30' (de Souza et al., 2021 ). To analyze chlorophyll a and b (Chl a and Chl b) and carotenoid contents, 0.1 g of fresh material from two leaves was extracted with 8 mL of 95% acetone solution for 24 hours at 4ºC in the dark. Subsequently, the extracts were measured in a spectrophotometer at 663.2 nm (Chl a), 646.8 nm (Chl b), and 470 nm (carotenoids); the contents of each pigment were estimated according to Lichtenthaler & Buschmann (2001) and expressed in mg g –1 of fresh mass. After these analyses, the plants were collected. The shoots were washed with tap and distilled water, dried at 60°C, and weighed, obtaining the shoots biomass; then, the samples were ground in a knife mill. 2.4. Chemical analyses and quality control The concentration of the metals Cd, Pb, and Zn were determined in the extracts of maize shoots after digestion in a microwave system (USEPA 1996) in an acid solution with HNO 3 + H 2 O 2 at 180°C for 10’. Silicon concentration in shoots was obtained according to Elliott & Snyder ( 1991 ). The heavy metal (Cd, Pb, and Zn) and Si contents in maize shoots were obtained by multiplying the elemental concentrations and the shoots' dry biomass. Blank samples and plant reference material (SRM 1570a Spinach leaves) with multielement concentrations certified by the National Institute of Standards and Technology (NIST) were analyzed. The element concentrations recovered in the certified sample varied between 90% and 110%. All analyses were carried out in duplicate. 2.5. Statistical analyses Mean and standard deviation values were computed for all variables subjected to analysis. The normality of the data was assessed using the Shapiro–Wilk test, and, when necessary, logarithmic or square root transformations were applied to the dataset. Each variable under scrutiny underwent analysis of variance (ANOVA) at a significance level of p < 0.05. Regression models (p < 0.05) were then tailored to the dependent variables based on the biochar rates applied to the soil, with the goodness of fit determined by the regression coefficient (r2). Additionally, Pearson's linear correlation analysis (p < 0.05) was conducted to explore relationships between physiological parameters and the concentrations of Si and metals in the plant shoots. All statistical analyses were executed using STATISTICA (v. 10) and OriginPro 2022b software. 3. RESULTS AND DISCUSSION 3.1. Silicon, cadmium, lead, and zinc uptake by maize plants The addition of RSB significantly increased Si accumulation in the plant (Fig. 1 ). At the rate of 30.0 Mg ha –1 , the Si content in the shoots was 98% higher than in control. Yao et al. ( 2022 ) observed that the Si concentration in the rice shoots increased, on average, by 105% with the application of 0.3% RSB compared to the control (–Si). Si concentration in rice straw biochar can vary between 55.0 and 185.0 mg kg –1 ; therefore, RSB can increase the Si bioavailability in the soil and the accumulation of this element in crops (K and S, 2020; Li et al., 2019 ; Wang et al., 2019 ). (Fig. 1 ) The application of RSB significantly diminished the concentrations of Cd, Pb and Zn in the maize shoots (Fig. 2 A – 2 C). Cd accumulation ranged from 0.29 mg pot –1 (control) to 0.27(–7%), 0.25(–14%), 0.22(–24%) and 0.19(–34%) mg pot –1 ; for Pb, the reduction was from 0.38 mg pot –1 (control) to 0.35(–8%), 0.33(–13%), 0.28(–26%) and 0.24(–37%) mg pot –1 ; while Zn reduced 3, 6, 12 and 18% in the treatments 5.0, 10.0, 20.0, and 30.0 Mg ha –1 RSB, respectively. Other works also reported that applying biochar in soils polluted by metals reduced their concentrations in plants (Ahmad et al., 2018 ; Irfan et al., 2021 ; Mansoor et al., 2021 ; Nie et al., 2018 ; Nzediegwu et al., 2019 ; Wang et al., 2019 ). A meta-analysis with 1298 data demonstrated that biochar applied to soils contaminated by metals was able to promote a reduction of 38, 39 and 17% in the concentrations of Cd, Pb and Zn, respectively, in several crops (Chen et al., 2018 ); these results were similar to the 30.0 Mg ha –1 RSB rate teste here. (Fig. 2 ) The lower Cd, Pb, and Zn concentrations in maize is likely related to reduced bioavailability in the soil amended with biochar. De Lima Veloso et al. ( 2022 ) found that applying 30.0 Mg ha –1 RSB, in the same soil used in this experiment, promoted a reduction of 34, 32 and 33% in the bioavailability of Cd, Pb, and Zn assessed by DTPA, respectively. The immobilization of metals in the soil by biochar can take place through direct mechanisms (e.g., adsorption, ion exchange, complexation, and precipitation reactions) and indirect (increases in pH, organic matter, electrical conductivity, and cation exchange capacity) that will inhibit the absorption of metals by plants (Cao et al., 2009 ; Chen et al., 2018 ; Ding et al., 2014 ; Lu et al., 2012 ; Qiu et al., 2021 ). Other works with RSB at the same pyrolysis temperature reported more significant adsorption of metals compared to biochar produced at different temperatures (Ding et al., 2014 ; Jiang et al., 2012 ). Another determining factor for reducing heavy metals in maize may be the higher Si uptake due to RSB addition. Linear and negative relationships were observed between the accumulations of Si and heavy metals in shoots (Fig. 2 D – 2 F). With the addition of 30.0 Mg ha –1 RSB, the accumulation of 100 µg Si in maize promoted a reduction of 39, 39, and 22% in the Cd, Pb, and Zn accumulations in the crop, respectively. Other studies have observed that Si nutrition reduced the uptake of heavy metals in plants (Bhat et al., 2019 ; Debona et al., 2017 ; El-Saadony et al., 2021 ; Etesami and Jeong, 2018 ; Imtiaz et al., 2016 ; Pereira et al., 2018 ; Silva et al., 2021 ; Vaculík et al., 2020 ). Silicon induces internal mechanisms in the plant that can reduce the absorption and transport of metals from roots to shoots. These effects may occur due to (i) a physical barrier of amorphous silica in the apoplast (biosilicification), hindering the influx of metals into the symplast and/or transpiration flow (Guerriero et al., 2016 ), (ii) reduced cell wall porosity in roots, decreasing the metal loading into the xylem and its translocation towards shoots (Keller et al., 2015 ), (iii) the decrease in the transport of metals via the apoplast due to adsorption reactions in the cell wall (Ye et al., 2012 ) and (iv) (co)precipitation of heavy metals with Si in the roots (Adrees et al., 2015 ; da Cunha and do Nascimento, 2009 ; Ma et al., 2015 ). 3.2. Leaf photochemical traits, pigment profile and gas exchange Plants treated with RSB showed a better physiological status due to reduced metal accumulation and possibly lower oxidative stress. In the 30.0 Mg ha –1 RSB treatment, photosynthetic rate, transpiration, and stomatal conductance increased by 68, 67, and 55% compared to the control (Fig. 3 A – 3 C). Regarding photosynthetic pigments, Chla contents rose from 0.69 to 1.22 mg g –1 (+ 77%); for Chlb, the increase was from 0.49 to 0.77 mg g –1 (+ 57%); for total carotenoids, there was an increase from 0.71 to 1.01 mg g –1 (+ 42%) when the results between control (no Si) and 30.0 Mg ha –1 were compared (Fig. 3 D – 3 F). Studies have confirmed that the addition of biochar in soils polluted by heavy metals can have a positive effect on the content of photosynthetic pigments and, consequently, on the photosynthetic capacity of plants (García et al., 2020 ; Haider et al., 2022b ; Kamran et al., 2020 ; Zhen et al., 2022 ). (Fig. 3 ) Ren et al. ( 2021 ) found improvements in gas exchange parameters and a significant increase in the photosynthetic pigments in tobacco grown in soil contaminated with 20.0 mg kg –1 of Cd and treated with 1.0% peanut shell biochar. The authors reported that in biochar-treated plants, Chla, Chlb, and carotenoid contents were 9.9, 12.6, and 10.3% higher than in the treatment without adding biochar, respectively. There was also an increase of 11% in the photosynthetic rate and stomatal conductance in the treatment with biochar. The authors suggested that biochar can mitigate the Cd phytotoxic effects by protecting the chloroplast structure in leaves and increasing the levels of photosynthetic pigments. Chlorophyll fluorescence is a physiological parameter that reflects photoinhibition (Kalaji et al., 2018 ; Zhang et al., 2020 ). Various works found significant inhibition in the photosystem II (PSII) (e.g., decrease in maximum quantum yield values - Fv/Fm) in metal-stressed plants (Chu et al., 2018 ; Hou et al., 2018 ; Paunov et al., 2018 ; Rajput et al., 2021 ). In this study, initial, variable and maximum fluorescence in corn leaves decreased by 23, 15 and 22% at the rate of 30.0 Mg ha –1 RSB (Fig. 4 A – 4 C); on the other hand, Fv/Fm varied from 0.69 (control) to 0.71 (+ 3%), 0.73 (+ 6%), 0.76 (+ 10%) and 0.80 (+ 16%) at doses of 5.0; 10.0; 20.0 and 30.0 Mg ha –1 RSB, respectively (Fig. 4 D). This behavior is similar to that reported by Rajput et al. ( 2021 ), where the maximum quantum yield of barley leaves increased from 0.68 to 0.71 (+ 4%) by applying 2.5% biochar in soil polluted by heavy metals. The reduction in fluorescence intensity (Fo, Fv, and Fm) and the increase in maximum quantum yield in plants treated with RSB indicate a lower energy expenditure in electron transport in photosystem II and, therefore, greater photosynthetic activity (Zhang et al., 2020 ). It can be observed that there is maximum efficiency in the conversion of luminous energy into chemical energy in PSII when the Fv/Fm ratio results in values close to 0.8. In this state, PSII is absorbing enough light for energy transfer to occur to produce energy compounds, essential for the synthesis of carbohydrates (Bjorkman and Demmig, 1987 ; Martins et al., 2020 ). (Fig. 4 ) The Si supply to maize in treatments with RSB contributed to the alleviation of physiological stress. Significant correlations were obtained between Si and parameters related to photosynthesis (Fig. 5 ). Previous studies confirmed the impacts of Si on chlorophyll biosynthesis and photosynthetic mechanisms of species such as cucumber (Feng et al., 2010 ), maize (Mihaličová Malčovská et al., 2014 ), wheat (Hussain et al., 2015 ), rice (Song et al., 2014 ), barley (Shen et al., 2014 ) and cotton (Bharwana, 2013 ) exposed to heavy metals. According to Rastogi et al. ( 2021 ), Si can inhibit the abiotic stress caused by heavy metals through improved photosynthesis by (i) protecting the photosynthetic structure, (ii) increasing water use efficiency, (iii) improving electron transport, (iv) preventing the photosynthetic machinery from reactive oxygen species (ROS) damages, and (v) regulating genes and interaction with physiological processes, such as nutrient uptake and production of phytohormones that influence photosynthetic activity. (Fig. 5 ) 4. CONCLUSION Applying rice straw biochar (RSB) in the soil polluted by Cd, Pb, and Zn efficiently reduced metal stress to maize plants. The 30.0 Mg ha –1 rate supplied Si to the plants and significantly reduced the metal accumulation in the maize shoots. Furthermore, RSB promoted improvements in the photosynthetic apparatus, including greater gas exchange efficiency, production of photosynthetic pigments, and optimization of the use of free electron energy in photosystem II (PSII). Applying RSB associated with maize cultivation can phytoattenuate Cd, Pb, and Zn contamination since RSB increases the biomass and maize tolerance to metal stress. This phytotechnology can be applied in areas where resources available for remediation are scarce, enabling an income for the stakeholder while reducing environmental and human health risks. Declarations Disclosure statement No potential conflict of interest was reported by the author(s). Funding No funding. Contributions Study conception and design: C.W.A.N., V.L.V; data collection: V.L.V., F.B.V.S., T.S.P.; analysis and interpretation of results: C.W.A.N., V.L.V; F.B.V.S., E.R.S., P.R.M.A.; draft manuscript preparation: C.W.A.N., V.L.V; F.B.V.S., E.R.S., P.R.M.A., T.S.P.; manuscript revision and approval: C.W.A.N., V.L.V; F.B.V.S., E.R.S., P.R.M.A., T.S.P. Availability of data and material The data that support the findings of this study are available from the corresponding author, C.W.A.N., upon reasonable request. Consent for publication All authors have approved the manuscript and consent to publish it in Environmental Monitoring and Assessment. References Adrees M, Ali S, Rizwan M, Zia-ur-Rehman M, Ibrahim M, Abbas F, Farid M, Qayyum MF, Irshad MK (2015) Mechanisms of silicon-mediated alleviation of heavy metal toxicity in plants: A review. Ecotoxicol Environ Saf 119:186–197. https://doi.org/10.1016/j.ecoenv.2015.05.011 Ahmad M, Usman ARA, Al-Faraj AS, Ahmad, Mahtab, Sallam A, Al-Wabel MI (2018) Phosphorus-loaded biochar changes soil heavy metals availability and uptake potential of maize (Zea mays L.) plants. Chemosphere 194:327–339. https://doi.org/10.1016/j.chemosphere.2017.11.156 Bharwana S (2013) Alleviation of Lead Toxicity by Silicon is Related to Elevated Photosynthesis, Antioxidant Enzymes Suppressed Lead Uptake and Oxidative Stress in Cotton. J Bioremediat Biodegrad 04:10–4172. https://doi.org/10.4172/2155-6199.1000187 Bhat JA, Shivaraj SM, Singh P, Navadagi DB, Tripathi DK, Dash PK, Solanke AU, Sonah H, Deshmukh R (2019) Role of Silicon in Mitigation of Heavy Metal Stresses in Crop Plants. Plants 8:71. https://doi.org/10.3390/plants8030071 Bjorkman O, Demmig B (1987) Photon yield of O2 evolution and chlorophyll fluorescence characteristics at 77 K among vascular plants of diverse origins. Planta 170:489–504. https://doi.org/10.1007/BF00402983 Burges A, Alkorta I, Epelde L, Garbisu C (2018) From phytoremediation of soil contaminants to phytomanagement of ecosystem services in metal contaminated sites. Int J Phytorem 20:384–397. https://doi.org/10.1080/15226514.2017.1365340 Cao X, Ma L, Gao B, Harris W (2009) Dairy-Manure Derived Biochar Effectively Sorbs Lead and Atrazine. Environ Sci Technol 43:3285–3291. https://doi.org/10.1021/es803092k Chen D, Liu X, Bian R, Cheng K, Zhang X, Zheng J, Joseph S, Crowley D, Pan G, Li L (2018) Effects of biochar on availability and plant uptake of heavy metals – A meta-analysis. J Environ Manage 222:76–85. https://doi.org/10.1016/j.jenvman.2018.05.004 Chew J, Joseph S, Chen G, Zhang Y, Zhu L, Liu M, Taherymoosavi S, Munroe P, Mitchell DRG, Pan G, Li L, Bian R, Fan X (2022) Biochar-based fertiliser enhances nutrient uptake and transport in rice seedlings. Sci Total Environ 826:154174. https://doi.org/10.1016/j.scitotenv.2022.154174 Chu J, Zhu F, Chen X, Liang H, Wang R, Wang X, Huang X (2018) Effects of cadmium on photosynthesis of Schima superba young plant detected by chlorophyll fluorescence. Environ Sci Pollut Res 25:10679–10687. https://doi.org/10.1007/s11356-018-1294-x Cui L, Pan G, Li L, Bian R, Liu X, Yan J, Quan G, Ding C, Chen T, Liu, Yang L, Yuming, Yin C, Wei C, Yang Y, Hussain Q (2016) Continuous immobilization of cadmium and lead in biochar amended contaminated paddy soil: A five-year field experiment. Ecol Eng 93:1–8. https://doi.org/10.1016/j.ecoleng.2016.05.007 Cundy AB, Bardos RP, Puschenreiter M, Mench M, Bert V, Friesl-Hanl W, Müller I, Li XN, Weyens N, Witters N, Vangronsveld J (2016) Brownfields to green fields: Realising wider benefits from practical contaminant phytomanagement strategies. J Environ Manage 184:67–77. https://doi.org/10.1016/j.jenvman.2016.03.028 da Cunha KPV, do Nascimento CWA (2009) Silicon Effects on Metal Tolerance and Structural Changes in Maize (Zea mays L.) Grown on a Cadmium and Zinc Enriched Soil. Water Air Soil Pollut 197:323–330. https://doi.org/10.1007/s11270-008-9814-9 da Silva WR, da Silva FBV, Araújo PRM, do Nascimento CWA (2017) Assessing human health risks and strategies for phytoremediation in soils contaminated with As, Cd, Pb, and Zn by slag disposal. Ecotoxicol Environ Saf 144:522–530. https://doi.org/10.1016/j.ecoenv.2017.06.068 de Lima A, Bernardez LRP, L.A (2011) Characterization of the lead smelter slag in Santo Amaro, Bahia, Brazil. J Hazard Mater 189:692–699. https://doi.org/10.1016/j.jhazmat.2011.02.091 de Lima Veloso V, da Silva FBV, dos Santos NM, do Nascimento CWA (2022) Phytoattenuation of Cd, Pb, and Zn in a Slag-contaminated Soil Amended with Rice Straw Biochar and Grown with Energy Maize. Environ Manage 69:196–212. https://doi.org/10.1007/s00267-021-01530-6 de Souza AAB, do Nascimento CWA, de Souza ER (2021) Mineral composition, chlorophyll fluorescence and zinc biofortification in Vigna unguiculata fertilized with bulk and nanoparticulate zinc oxides. Acta Physiol Plant 43:159. https://doi.org/10.1007/s11738-021-03333-y Debona D, Rodrigues FA, Datnoff LE (2017) Silicon’s Role in Abiotic and Biotic Plant Stresses. Annu Rev Phytopathol 55:85–107. https://doi.org/10.1146/annurev-phyto-080516-035312 Dezhban A, Shirvany A, Attarod P, Delshad M, Matinizadeh M, Khoshnevis M (2015) Cadmium and lead effects on chlorophyll fluorescence, chlorophyll pigments and proline of Robinia pseudoacacia. J Res 26:323–329. https://doi.org/10.1007/s11676-015-0045-9 Ding W, Dong X, Ime IM, Gao B, Ma LQ (2014) Pyrolytic temperatures impact lead sorption mechanisms by bagasse biochars. Chemosphere 105:68–74. https://doi.org/10.1016/j.chemosphere.2013.12.042 Dourado PRM, de Souza ER, Santos MA, dos, Lins CMT, Monteiro DR, Paulino MKSS, Schaffer B (2022) Stomatal Regulation and Osmotic Adjustment in Sorghum in Response to Salinity. Agriculture 12:658. https://doi.org/10.3390/agriculture12050658 Duarte B, Pires V, Carreiras J, de Carvalho RC, Ferreira R, Pereira MFC, Maurício AM, Martins-Dias S, Caçador I (2023) Cistus ladanifer metal uptake and physiological performance in biochar amended mine soils. South Afr J Bot 153:246–257. https://doi.org/10.1016/j.sajb.2023.01.002 El-Saadony MT, Desoky E-SM, Saad AM, Eid RSM, Selem E, Elrys AS (2021) Biological silicon nanoparticles improve Phaseolus vulgaris L. yield and minimize its contaminant contents on a heavy metals-contaminated saline soil. J Environ Sci 106:1–14. https://doi.org/10.1016/j.jes.2021.01.012 Elliott CL, Snyder GH (1991) Autoclave-induced digestion for the colorimetric determination of silicon in rice straw. J Agric Food Chem 39:1118–1119. https://doi.org/10.1021/jf00006a024 Etesami H, Jeong BR (2018) Silicon (Si): Review and future prospects on the action mechanisms in alleviating biotic and abiotic stresses in plants. Ecotoxicol Environ Saf 147:881–896. https://doi.org/10.1016/j.ecoenv.2017.09.063 Feng J, Shi Q, Wang X, Wei M, Yang F, Xu H (2010) Silicon supplementation ameliorated the inhibition of photosynthesis and nitrate metabolism by cadmium (Cd) toxicity in Cucumis sativus L. Sci Hortic (Amsterdam) 123:521–530. https://doi.org/10.1016/j.scienta.2009.10.013 García AC, Tavares OCH, de Oliveira DF (2020) Biochar as agricultural alternative to protect the rice plant growth in fragile sandy soil contaminated with cadmium. Biocatal Agric Biotechnol 29:101829. https://doi.org/10.1016/j.bcab.2020.101829 Guerriero G, Hausman J-F, Legay S (2016) Silicon and the Plant Extracellular Matrix. Front. Plant Sci 7:463. https://doi.org/10.3389/fpls.2016.00463 Haider FU, Farooq M, Naveed M, Cheema SA, Ain Nul, Salim MA, Liqun C, Mustafa A (2022a) Influence of biochar and microorganism co-application on stabilization of cadmium (Cd) and improved maize growth in Cd-contaminated soil. Front Plant Sci 13:983830. https://doi.org/10.3389/fpls.2022.983830 Haider FU, Wang X, Farooq M, Hussain S, Cheema SA, Ain Nul, Virk AL, Ejaz M, Janyshova U, Liqun C (2022b) Biochar application for the remediation of trace metals in contaminated soils: Implications for stress tolerance and crop production. Ecotoxicol Environ Saf 230:113165. https://doi.org/10.1016/j.ecoenv.2022.113165 Hou X, Han H, Cai L, Liu A, Ma X, Zhou C, Wang G, Meng F (2018) Pb stress effects on leaf chlorophyll fluorescence, antioxidative enzyme activities, and organic acid contents of Pogonatherum crinitum seedlings. Flora 240:82–88. https://doi.org/10.1016/j.flora.2018.01.006 Huang S, Tan L, Zhu H, Sheng GD (2021) Root damages induced by extended phytotoxic effects of cadmium pre-exposure against subsequent lindane uptake in rice seedlings. Environ Exp Bot 189:104553. https://doi.org/10.1016/j.envexpbot.2021.104553 Hussain I, Ashraf MA, Rasheed R, Asghar A, Sajid MA, Iqbal M (2015) Exogenous application of silicon at the boot stage decreases accumulation of cadmium in wheat (Triticum aestivum L.) grains. Brazilian J Bot 38:223–234. https://doi.org/10.1007/s40415-014-0126-6 Imtiaz M, Rizwan MS, Mushtaq MA, Ashraf M, Shahzad SM, Yousaf B, Saeed DA, Rizwan M, Nawaz MA, Mehmood S, Tu S (2016) Silicon occurrence, uptake, transport and mechanisms of heavy metals, minerals and salinity enhanced tolerance in plants with future prospects: A review. J Environ Manage 183:521–529. https://doi.org/10.1016/j.jenvman.2016.09.009 Irfan M, Mudassir M, Khan MJ, Dawar KM, Muhammad D, Mian IA, Ali W, Fahad S, Saud S, Hayat Z, Nawaz T, Khan SA, Alam S, Ali B, Banout J, Ahmed S, Mubeen S, Danish S, Datta R, Elgorban AM, Dewil R (2021) Heavy metals immobilization and improvement in maize (Zea mays L.) growth amended with biochar and compost. Sci Rep 11:18416. https://doi.org/10.1038/s41598-021-97525-8 Izydorczyk G, Mikula K, Skrzypczak D, Moustakas K, Witek-Krowiak A, Chojnacka K (2021) Potential environmental pollution from copper metallurgy and methods of management. Environ Res 197:111050. https://doi.org/10.1016/j.envres.2021.111050 Jiang J, Xu R, Jiang T, Li Z (2012) Immobilization of Cu(II), Pb(II) and Cd(II) by the addition of rice straw derived biochar to a simulated polluted Ultisol. J Hazard Mater 229–230. https://doi.org/10.1016/j.jhazmat.2012.05.086 K A, S, J.S (2020) Production and characterization of vermicompost and biochar from rice straw. J Pharmacogn Phytochem 9:1556–1562. https://doi.org/10.22271/phyto.2020.v9.i5v.12557 Kabata-Pendias A (2010) Trace Elements in Soils and Plants, 4th ed, Trace Elements in Soils and Plants, Fourth Edition. CRC Press, Boca Raton. https://doi.org/10.1201/b10158 Kalaji HM, Bąba W, Gediga K, Goltsev V, Samborska IA, Cetner MD, Dimitrova S, Piszcz U, Bielecki K, Karmowska K, Dankov K, Kompała-Bąba A (2018) Chlorophyll fluorescence as a tool for nutrient status identification in rapeseed plants. Photosynth Res 136:329–343. https://doi.org/10.1007/s11120-017-0467-7 Kamran M, Malik Z, Parveen A, Huang L, Riaz M, Bashir S, Mustafa A, Abbasi GH, Xue B, Ali U (2020) Ameliorative Effects of Biochar on Rapeseed (Brassica napus L.) Growth and Heavy Metal Immobilization in Soil Irrigated with Untreated Wastewater. J Plant Growth Regul 39:266–281. https://doi.org/10.1007/s00344-019-09980-3 Keller C, Rizwan M, Davidian J-C, Pokrovsky OS, Bovet N, Chaurand P, Meunier J-D (2015) Effect of silicon on wheat seedlings (Triticum turgidum L.) grown in hydroponics and exposed to 0 to 30 µM Cu. Planta 241:847–860. https://doi.org/10.1007/s00425-014-2220-1 Król A, Mizerna K, Bożym M (2020) An assessment of pH-dependent release and mobility of heavy metals from metallurgical slag. J Hazard Mater 384:121502. https://doi.org/10.1016/j.jhazmat.2019.121502 Li Z, Song Z, Singh BP, Wang H (2019) The impact of crop residue biochars on silicon and nutrient cycles in croplands. Sci Total Environ 659:673–680. https://doi.org/10.1016/j.scitotenv.2018.12.381 Li Z, Yuan Y, Xiang L, Su Q, Liu Z, Wu W, Huang Y, Tu S (2022) Silicon-Rich Biochar Detoxify Multiple Heavy Metals in Wheat by Regulating Oxidative Stress and Subcellular Distribution of Heavy Metal. Sustainability 14:16417. https://doi.org/10.3390/su142416417 Lichtenthaler HK, Buschmann C (2005) Chlorophylls. Handbook of Food Analytical Chemistry. John Wiley & Sons, Inc., Hoboken, NJ, USA, pp 153–199. https://doi.org/10.1002/0471709085.ch21 Lu H, Zhang W, Yang Y, Huang X, Wang S, Qiu R (2012) Relative distribution of Pb2 + sorption mechanisms by sludge-derived biochar. Water Res 46:854–862. https://doi.org/10.1016/j.watres.2011.11.058 Lu K, Yang X, Shen J, Robinson B, Huang H, Liu D, Bolan N, Pei J, Wang H (2014) Effect of bamboo and rice straw biochars on the bioavailability of Cd, Cu, Pb and Zn to Sedum plumbizincicola. Agric Ecosyst Environ 191:124–132. https://doi.org/10.1016/j.agee.2014.04.010 Ma J, Cai H, He C, Zhang W, Wang L (2015) A hemicellulose-bound form of silicon inhibits cadmium ion uptake in rice (Oryza sativa) cells. New Phytol 206:1063–1074. https://doi.org/10.1111/nph.13276 Mansoor S, Kour N, Manhas S, Zahid S, Wani OA, Sharma V, Wijaya L, Alyemeni MN, Alsahli AA, El-Serehy HA, Paray BA, Ahmad P (2021) Biochar as a tool for effective management of drought and heavy metal toxicity. Chemosphere 271:129458. https://doi.org/10.1016/j.chemosphere.2020.129458 Martins JB, Santos Júnior JA, Leal LY, de Paulino C, de Souza MKSS, Gheyi ER, H.R (2020) Fluorescence emission and photochemical yield of parsley under saline waters of different cationic nature. Sci Hortic (Amsterdam) 273:109574. https://doi.org/10.1016/j.scienta.2020.109574 Meng J, Tao M, Wang L, Liu X, Xu J (2018) Changes in heavy metal bioavailability and speciation from a Pb-Zn mining soil amended with biochars from co-pyrolysis of rice straw and swine manure. Sci Total Environ 633:300–307. https://doi.org/10.1016/j.scitotenv.2018.03.199 Mihaličová Malčovská S, Dučaiová Z, Maslaňáková I, Bačkor M (2014) Effect of Silicon on Growth, Photosynthesis, Oxidative Status and Phenolic Compounds of Maize (Zea mays L.) Grown in Cadmium Excess. Water, Air, Soil Pollut. 225, 2056. https://doi.org/10.1007/s11270-014-2056-0 Moradi L, Ehsanzadeh P (2015) Effects of Cd on photosynthesis and growth of safflower (Carthamus tinctorius L.) genotypes. Photosynthetica 53:506–518. https://doi.org/10.1007/s11099-015-0150-1 Murakami M, Ae N (2009) Potential for phytoextraction of copper, lead, and zinc by rice (Oryza sativa L.), soybean (Glycine max [L.] Merr.), and maize (Zea mays L). J Hazard Mater 162:1185–1192. https://doi.org/10.1016/j.jhazmat.2008.06.003 Nie C, Yang X, Niazi NK, Xu X, Wen Y, Rinklebe J, Ok YS, Xu S, Wang H (2018) Impact of sugarcane bagasse-derived biochar on heavy metal availability and microbial activity: A field study. Chemosphere 200:274–282. https://doi.org/10.1016/j.chemosphere.2018.02.134 Niemeyer JC, Moreira-Santos M, Ribeiro R, Rutgers M, Nogueira MA, da Silva EM, Sousa JP (2015) Ecological Risk Assessment of a Metal-Contaminated Area in the Tropics. Tier II: Detailed Assessment. PLoS ONE 10:e0141772. https://doi.org/10.1371/journal.pone.0141772 Nzediegwu C, Prasher S, Elsayed E, Dhiman J, Mawof A, Patel R (2019) Effect of biochar on heavy metal accumulation in potatoes from wastewater irrigation. J Environ Manage 232:153–164. https://doi.org/10.1016/j.jenvman.2018.11.013 Paunov M, Koleva L, Vassilev A, Vangronsveld J, Goltsev V (2018) Effects of Different Metals on Photosynthesis: Cadmium and Zinc Affect Chlorophyll Fluorescence in Durum Wheat. Int J Mol Sci 19:787. https://doi.org/10.3390/ijms19030787 Peng X, Shi G, Liu G, Xu J, Tian Y, Zhang Y, Feng Y, Russell AG (2017) Source apportionment and heavy metal health risk (HMHR) quantification from sources in a southern city in China, using an ME2-HMHR model. Environ Pollut 221:335–342. https://doi.org/10.1016/j.envpol.2016.11.083 Pereira TS, Pereira Thaís, Soares, Souza CLF, de Lima C, Batista EJA, Lobato BL (2018) A.K. da S. Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants. Physiol. Mol. Biol. Plants 24, 99–114. https://doi.org/10.1007/s12298-017-0494-z Peršić V, Đerđ T, Varga M, Hackenberger BK (2019) Real-time CO2 uptake/emission measurements as a tool for early indication of toxicity in Lemna-tests. Aquat Toxicol 206:154–163. https://doi.org/10.1016/j.aquatox.2018.11.013 Qiu B, Tao X, Wang H, Li W, Ding X, Chu H (2021) Biochar as a low-cost adsorbent for aqueous heavy metal removal: A review. J Anal Appl Pyrol 155:105081. https://doi.org/10.1016/j.jaap.2021.105081 Rajput VD, Gorovtsov AV, Fedorenko GM, Minkina TM, Fedorenko AG, Lysenko VS, Sushkova SS, Mandzhieva SS, Elinson MA (2021) The influence of application of biochar and metal-tolerant bacteria in polluted soil on morpho-physiological and anatomical parameters of spring barley. Environ Geochem Health 43:1477–1489. https://doi.org/10.1007/s10653-019-00505-1 Rastogi A, Yadav S, Hussain S, Kataria S, Hajihashemi S, Kumari P, Yang X, Brestic M (2021) Does silicon really matter for the photosynthetic machinery in plants… Plant Physiol. Biochem 169:40–48. https://doi.org/10.1016/j.plaphy.2021.11.004 Ren T, Chen N, Mahari W, Xu WA, Feng C, Ji H, Yin X, Chen Q, Zhu P, Liu S, Liu H, Li G, Lam L, S.S (2021) Biochar for cadmium pollution mitigation and stress resistance in tobacco growth. Environ Res 192:110273. https://doi.org/10.1016/j.envres.2020.110273 Rusinowski S, Krzyżak J, Sitko K, Kalaji HM, Jensen E, Pogrzeba M (2019) Cultivation of C4 perennial energy grasses on heavy metal contaminated arable land: Impact on soil, biomass, and photosynthetic traits. Environ Pollut 250:300–311. https://doi.org/10.1016/j.envpol.2019.04.048 dos Santos NM, Accioly AM, de Nascimento A, do CWA, Silva IR, Santos JAG (2015) Bioavailability of lead using chemical extractants in soil treated with humic acids and activated carbon. Rev CIÊNCIA AGRONÔMICA 46:663–668. https://doi.org/10.5935/1806-6690.20150052 Shen X, Xiao X, Dong Z, Chen Y (2014) Silicon effects on antioxidative enzymes and lipid peroxidation in leaves and roots of peanut under aluminum stress. Acta Physiol Plant 36:3063–3069. https://doi.org/10.1007/s11738-014-1676-8 Silva Gonzaga MI, Oliveira da Silva PS, Carlos de Jesus Santos J, Junior GdeO, L.F (2019) Biochar increases plant water use efficiency and biomass production while reducing Cu concentration in Brassica juncea L. in a Cu-contaminated soil. Ecotoxicol Environ Saf 183:109557. https://doi.org/10.1016/j.ecoenv.2019.109557 Silva JR, Veloso VdeL, Silva FBV, da, Nascimento CWA (2021) do Cadmium, silicon and nutrient accumulation by maize plants grown on a contaminated soil amended with a diatomaceous Earth fertilizer. Ciência Rural 51. https://doi.org/10.1590/0103-8478cr20190804 Silvany Neto AM, Carvalho FM, Tavares TM, Guimaraes GC, Amorim CJB, Peres MFT, Lopes RS, Rocha CM, Raña MC (1996) Lead poisoning among children of Santo Amaro, Bahia, Brazil in 1980, 1985, and 1992. Bull. Pan Am. Heal. Organ. (PAHO); 30 (1), mar. 1996 Singh B, Camps-Arbestain M, Lehmann J (2017) Biochar: a guide to analytical methods. Csiro Publishing Singh R, Kumar V, Tewari RK, Pratap SG, Singh PK (2023) Hazardous waste leachates induced changes in plant water relation, photosynthetic pigments, heavy metal accumulation and yield of mustard (Brassica juncea L.) plant. J Hazard Mater Adv 10:100306. https://doi.org/10.1016/j.hazadv.2023.100306 Song A, Li P, Fan F, Li Z, Liang Y (2014) The Effect of Silicon on Photosynthesis and Expression of Its Relevant Genes in Rice (Oryza sativa L.) under High-Zinc Stress. PLoS ONE 9:e113782. https://doi.org/10.1371/journal.pone.0113782 USEPA (United States Environmental Protection Agency) (1996) Method 3050B: Acid Digestion of Sediments, Sludges, and Soils. Z. Für Anal. Chem USEPA E (2007) Method 3051: Microwave assisted acid digestion of sediments, sludges, soils, and oils. Test Methods Eval Solid Waste 1–30 Vaculík M, Lukačová Z, Bokor B, Martinka M, Tripathi DK, Lux A (2020) Alleviation mechanisms of metal(loid) stress in plants by silicon: a review. J Exp Bot 71:6744–6757. https://doi.org/10.1093/jxb/eraa288 Wang J, Wang L, Wang Y, Tsang DCW, Yang X, Beiyuan J, Yin M, Xiao T, Jiang Y, Lin W, Zhou Y, Liu J, Wang, Liang, Zhao M (2021) Emerging risks of toxic metal(loid)s in soil-vegetables influenced by steel-making activities and isotopic source apportionment. Environ Int 146:106207. https://doi.org/10.1016/j.envint.2020.106207 Wang M, Wang JJ, Tafti ND, Hollier CA, Myers G, Wang X (2019) Effect of alkali-enhanced biochar on silicon uptake and suppression of gray leaf spot development in perennial ryegrass. Crop Prot 119:9–16. https://doi.org/10.1016/j.cropro.2019.01.013 Wang Y, Duan X, Wang L (2020) Spatial distribution and source analysis of heavy metals in soils influenced by industrial enterprise distribution: Case study in Jiangsu Province. Sci Total Environ 710:134953. https://doi.org/10.1016/j.scitotenv.2019.134953 WRB-FAO IWG (2015) IUSS Working Group WRB. 2015. World Reference Base for Soil Resources 2014, update 2015 International soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports N o . 106 Yadav M, George N, Dwibedi V (2023) Emergence of toxic trace elements in plant environment: Insights into potential of silica nanoparticles for mitigation of metal toxicity in plants. Environ Pollut 333:122112. https://doi.org/10.1016/j.envpol.2023.122112 Yao D, Wu J, Gao H, Wu D, Wei Z (2022) Changes in soil silicon forms and availability as affected by rice straw and its biochar. Eur J Soil Sci 73:e13316. https://doi.org/10.1111/ejss.13316 Ye J, Yan C, Liu J, Lu H, Liu T, Song Z (2012) Effects of silicon on the distribution of cadmium compartmentation in root tips of Kandelia obovata (S., L.) Yong. Environ Pollut 162:369–373. https://doi.org/10.1016/j.envpol.2011.12.002 Zhang H, Xu Z, Guo K, Huo Y, He G, Sun H, Guan Y, Xu N, Yang W, Sun G (2020) Toxic effects of heavy metal Cd and Zn on chlorophyll, carotenoid metabolism and photosynthetic function in tobacco leaves revealed by physiological and proteomics analysis. Ecotoxicol Environ Saf 202:110856. https://doi.org/10.1016/j.ecoenv.2020.110856 Zhang R-H, Xie, Yanlan, Zhou G, Li Z, Ye A, Huang X, Xie, Yanfeng, Shi L, Cao X, Zhang J, Lin C (2022) The effects of short-term, long-term, and reapplication of biochar on the remediation of heavy metal-contaminated soil. Ecotoxicol Environ Saf 248:114316. https://doi.org/10.1016/j.ecoenv.2022.114316 Zhang S, Yao H, Lu Y, Shan D, Yu X (2018) Reclaimed Water Irrigation Effect on Agricultural Soil and Maize (Zea mays L.) in Northern China. CLEAN - Soil Air Water 46:1800037. https://doi.org/10.1002/clen.201800037 Zhen K, Zhu Q, Zhai S, Gao Y, Cao H, Tang X, Wang C, Li J, Tian L, Sun H (2022) PPCPs and heavy metals from hydrothermal sewage sludge-derived biochar: migration in wheat and physiological response. Environ Sci Pollut Res 29:83234–83246. https://doi.org/10.1007/s11356-022-21432-2 Zhu S, Ma X, Guo R, Ai S, Liu B, Zhang W, Zhang Y (2016) A field study on heavy metals phytoattenuation potential of monocropping and intercropping of maize and/or legumes in weakly alkaline soils. Int J Phytorem 18:1014–1021. https://doi.org/10.1080/15226514.2016.1183570 Żurek G, Rybka K, Pogrzeba M, Krzyżak J, Prokopiuk K (2014) Chlorophyll a Fluorescence in Evaluation of the Effect of Heavy Metal Soil Contamination on Perennial Grasses. PLoS ONE 9:e91475. https://doi.org/10.1371/journal.pone.0091475 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4252712","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":290906000,"identity":"60d7e2f6-98e1-4a3e-becd-90ba71fdcd18","order_by":0,"name":"Venâncio Lima Veloso","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABDklEQVRIiWNgGAWjYPACCRDBeABIyBmABQwsiNLCANJibMDADNIiQZxdIC2JG8BaGHBrMTjee/BzQY2FHINE8oEDH/7YpG9n7z+64UeBBAN/e3cCVi1nziVLzzgmYcwgkZZwcGZbWu7OnsNsN3uADpM4c3YDNi2SM3IMpHkbJBIbeM4YHOZtOJy74UYy2w0eoBYDiVzsWua/Mf4N0XL+w2GeP4fTDYBabv7Bo4VfgscMYgt7D8NhHrbDCSAtt/HZws+TY2bNA/QLG3ubAcgvhhvOHDa7LWMgwYPLL2zsZ4xv89TUyfEzMz98AAwxeYPjjc9uvvljI8ff3otVC0IvugAPXuWjYBSMglEwCvACAFRBXPqADTQ/AAAAAElFTkSuQmCC","orcid":"","institution":"Federal Rural University of Pernambuco","correspondingAuthor":true,"prefix":"","firstName":"Venâncio","middleName":"Lima","lastName":"Veloso","suffix":""},{"id":290906001,"identity":"894b8463-126a-4097-a942-746d9a46ab2a","order_by":1,"name":"Fernando Bruno Vieira Silva","email":"","orcid":"","institution":"Federal Rural University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Fernando","middleName":"Bruno Vieira","lastName":"Silva","suffix":""},{"id":290906005,"identity":"1533e5ab-237b-4dde-9223-0ad9ab015c46","order_by":2,"name":"Paula Renata Muniz Araújo","email":"","orcid":"","institution":"Federal Rural University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Paula","middleName":"Renata Muniz","lastName":"Araújo","suffix":""},{"id":290906006,"identity":"aea21fec-24ba-4ab3-b007-520a022bb6c0","order_by":3,"name":"Taciana Silva Paraizo","email":"","orcid":"","institution":"Federal Rural University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Taciana","middleName":"Silva","lastName":"Paraizo","suffix":""},{"id":290906007,"identity":"e038a484-2dff-40c6-accb-b5dd427e9c1a","order_by":4,"name":"Edivan Rodrigues Souza","email":"","orcid":"","institution":"Federal Rural University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Edivan","middleName":"Rodrigues","lastName":"Souza","suffix":""},{"id":290906008,"identity":"aa528032-51ec-46e5-8563-4680509273fa","order_by":5,"name":"Clístenes Williams Araújo Nascimento","email":"","orcid":"","institution":"Federal Rural University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Clístenes","middleName":"Williams Araújo","lastName":"Nascimento","suffix":""}],"badges":[],"createdAt":"2024-04-11 13:23:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4252712/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4252712/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54758580,"identity":"9b168f67-2e73-43a1-a55b-7bcd94fa20de","added_by":"auto","created_at":"2024-04-16 10:37:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":43766,"visible":true,"origin":"","legend":"\u003cp\u003eMean values (± standard deviation) silicon content of the shoot of maize plants cut for 45 days in a soil polluted by slag from a Pb metallurgy and subjected to doses of rice straw biochar. \u003cem\u003ep \u003c/em\u003e\u0026lt; 0.01 significant at 1% probability by ANOVA.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4252712/v1/d7987e444f38d15cbda76767.png"},{"id":54759122,"identity":"5b3a73d4-29b2-4467-97f5-92a9faf48c74","added_by":"auto","created_at":"2024-04-16 10:45:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":132352,"visible":true,"origin":"","legend":"\u003cp\u003eMean content (± standard deviation) of Cd, Pb and Zn in the shoot of maize plants cultivated for 45 days in a soil polluted by slag from a Pb metallurgy and submitted to doses of rice straw biochar (A–C); cause-effect relationship between Si and heavy metal contents in the shoot of maize plants (D–F). \u003cem\u003ep \u0026lt; \u003c/em\u003e0.01 and \u003cem\u003ep \u0026lt; \u003c/em\u003e0.05\u003cem\u003e \u003c/em\u003esignificant at 1 and 5% probability by ANOVA, respectively.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4252712/v1/0efa2d22c8a56a21f54819bb.png"},{"id":54758581,"identity":"e3c48734-6863-4421-a710-d287ea2eb62c","added_by":"auto","created_at":"2024-04-16 10:37:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":148559,"visible":true,"origin":"","legend":"\u003cp\u003eMean values (± standard deviation) of physiological parameters (A–C) and of photosynthetic pigment content (D–F) of maize plants cultivated for 45 days in a soil polluted by slag from a Pb metallurgy and submitted to doses of rice straw biochar. \u003cem\u003ep \u0026lt; \u003c/em\u003e0.01 and \u003cem\u003ep \u0026lt; \u003c/em\u003e0.05\u003cem\u003e \u003c/em\u003esignificant at 1 and 5% probability by ANOVA, respectively.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4252712/v1/0d61500ff7de486acf210dbb.png"},{"id":54759123,"identity":"ab2816b7-1082-47a1-a043-9afc1f81907d","added_by":"auto","created_at":"2024-04-16 10:45:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":98015,"visible":true,"origin":"","legend":"\u003cp\u003eMean values (± standard deviation) Fo (minimal chlorophyll a fluorescence), Fv (variable chlorophyll a fluorescence), Fm (maximum chlorophyll a fluorescence) and Fv/Fm (photosystem II photochemical efficiency) of maize plants cultivated for 45 days in a soil polluted by slag from a Pb metallurgy and submitted to doses of rice straw biochar. \u003cem\u003ep \u0026lt; \u003c/em\u003e0.01 and \u003cem\u003ep \u0026lt; \u003c/em\u003e0.05\u003cem\u003e \u003c/em\u003esignificant at 1 and 5% probability by ANOVA, respectively.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4252712/v1/0dbb4144a6b8893683beec74.png"},{"id":54758579,"identity":"e1b8de56-24fa-4934-8afe-0db8913ced10","added_by":"auto","created_at":"2024-04-16 10:37:59","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":73992,"visible":true,"origin":"","legend":"\u003cp\u003ePearson’s correlation coefficients (\u003cem\u003ep \u003c/em\u003e\u0026lt; 0.05) of the contents of silicon and physiological parameters of maize plants cultivated for 45 days in a soil polluted by slag from a Pb metallurgy and submitted to doses of rice straw biochar. \u003cem\u003eChl a \u003c/em\u003echlorophyll a, \u003cem\u003eChl b\u003c/em\u003echlorophyll b, \u003cem\u003eTC \u003c/em\u003etotal carotenoids, \u003cem\u003ePR \u003c/em\u003ephotosynthetic rate, \u003cem\u003eTR \u003c/em\u003etranspiration rate, \u003cem\u003eSC \u003c/em\u003estomatal conductance, \u003cem\u003eFo \u003c/em\u003eminimal chlorophyll a fluorescence, \u003cem\u003eFv \u003c/em\u003evariable chlorophyll a fluorescence, \u003cem\u003eFm \u003c/em\u003emaximum chlorophyll a fluorescence and Fv/Fm (photosystem II photochemical efficiency).\u003c/p\u003e","description":"","filename":"groupimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4252712/v1/1d00f01ab3cfa539babb47cd.jpeg"},{"id":55264662,"identity":"2a90180c-c393-4b4a-bc43-509d8ec528e6","added_by":"auto","created_at":"2024-04-25 01:46:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1054185,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4252712/v1/afc87f63-91c8-4041-bc05-5078e9565072.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Rice straw biochar mitigates metal stress in maize and assists in the phytoattenuation of a slag-contaminated soil","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eHeavy metal-polluted soils pose high risk to human and animal health, being one of the most concerning environmental problems worldwide. The anthropogenic input of heavy metals in the environment affects soil ecosystem functions, threatens food quality, and poses a risk to human health due to the high persistence, phytotoxicity, non-biodegradability, and transfer of these elements to the food chain (Peng et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMetallurgy is a primary anthropogenic source of metals to the environment (da Silva et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The accumulation of large volumes of slag rich in heavy metals in abandoned smelter plants can contaminate soils and water resources (Izydorczyk et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kr\u0026oacute;l et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For example, in the city of Santo Amaro in Bahia, in the northeast region of Brazil, Pb smelting activities between the 1960s and 1980s resulted in thousands of tons of abandoned slag and the most severe case of Pb soil pollution in the country. Thousands of workers and residents around the Pb smelter plant showed neurological and renal damage and genotoxicity (de Andrade Lima and Bernardez, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Niemeyer et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Santos et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Silvany Neto et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Even after three decades of inactivity at the smelter plant, the soils in this region still have high concentrations of heavy metals with a potential risk to human health (da Silva et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In this scenario, actions to remove or reduce the availability of metals in the soil are mandatory to guarantee the functionality of the ecosystem and the health of animals and humans.\u003c/p\u003e \u003cp\u003eAmong the polluted soil remediation techniques using plants, the so-called phytotechnologies, phytoattenuation aims to gradually decrease the concentrations of heavy metals in soils over time, mitigating environmental risks and providing income during the remediation process through valuable plants (Cundy et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; de Lima Veloso et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Zhu et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Phytoattenuation promotes synergies with energy crops, biodiversity, watershed management, carbon sequestration, and soil erosion reduction, making the remediation process socially, economically, and environmentally attractive (Burges et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Cundy et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). One of the phytoattenuation strategies includes using plant biomass for energy production (e.g., conversion into biogas by anaerobic digestion) (Ahmad et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; de Lima Veloso et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Maize (\u003cem\u003eZea mays\u003c/em\u003e L.) is a bioenergetic crop cultivated in many regions of the world; besides, it is easy to manage and has fast growth, high biomass, and an extensive root system (Ahmad et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In addition, maize is a species relatively tolerant to heavy metals (da Silva et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Haider et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e; Irfan et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Murakami and Ae, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These characteristics make this crop promising for the phytoattenuation of soils polluted by metals.\u003c/p\u003e \u003cp\u003eHeavy metals in soils can be immobilized by organic materials such as manure, compost, and biochar (Ahmad et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Biochar is an eco-friendly amendment to retain heavy metals in the soil system and decrease metal uptake and toxicity to plants (Cui et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Meng et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Biochar is a material rich in pyrogenic carbon, highly recalcitrance, porous, and originated from the organic wastes pyrolysis (Lu et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Meng et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Biochars can immobilize the most labile fraction of metals in the soil and reduce their plant uptake through precipitation, ion exchange, complexation, and chemisorption (Wang et al., \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, biochar can be a source of nutrients (e.g., N, P, and micronutrients) and silicon (Si) for plants (Chew et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), as in the case of biochar produced from straw or rice husks (K and S, 2020; Li et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Yao et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Si is a beneficial element for plants and a mitigating agent of soil pollution by heavy metals (Li et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Yadav et al., \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Si mitigates heavy metal toxicity through mechanisms external and internal to the plants and can act from the immobilization of the metal in the soil to the regulation of the absorption and translocation of the contaminant in the plant (Adrees et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Bhat et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCadmium and Pb are toxic even at low content in the soil and are not essential elements to plants; Zn, on the other hand, is a micronutrient that can be toxic to plants when in high concentrations in the soil, usually due to anthropogenic contamination (Kabata-Pendias, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Metal phytotoxicity can inhibit root growth (Huang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), affect water and nutrient uptake (Singh et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and inhibit metabolic processes such as chlorophyll synthesis (Zhang et al., \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), photosynthesis and respiration (Peršić et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); in addition, heavy metals can cause oxidative damage in plants due to the excessive accumulation of reactive oxygen species (ROS) (Rusinowski et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePhysiological processes such as photosynthesis are susceptible to heavy metal stress (Chu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Duarte et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Hou et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Damage to the photosynthetic apparatus is related to (i) the direct interaction of metal ions with the thiol\u0026ndash;, histidine\u0026ndash; and carboxyl\u0026ndash; groups of proteins; (ii) the formation of ROS; and (iii) the replacement of essential cations in the active centers of proteins (e.g., the exchange of Mg\u003csup\u003e2+\u003c/sup\u003e for Cd\u003csup\u003e2+\u003c/sup\u003e or Zn\u003csup\u003e2+\u003c/sup\u003e in the chlorophyll molecule, resulting in the formation of the chlorophyll-metal complex with lower quantum efficiency in photosystem II (PSII) (Żurek et al., \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eChlorophyll fluorescence measurements, photosynthetic pigments, and gas exchange parameters are indicators of heavy metal stress in plants (Ren et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Rusinowski et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For instance, chlorophyll fluorescence analysis provides information about changes in photochemical efficiency. The Fv/Fm index derived from the relationship between variable and maximum fluorescence evaluates the performance of the photosynthetic apparatus, indicating the plant's ability to tolerate metal stress (Dezhban et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Other physiological indicators of stress are chlorophyll content and gas exchange. Chlorophyll a and b contents are important indexes of the effects of soil pollution on plants (Chu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Moradi and Ehsanzadeh, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), as well as changes in stomatal conductance, CO\u003csub\u003e2\u003c/sub\u003e assimilation, and photosynthetic rate (Feng et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Silva Gonzaga et al., \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWe hypothesize that applying rice straw biochar (RSB) in heavy metal-polluted soils can help mitigate metal toxicity in plants, stabilize metals in the soil, and phytoattenuate the contamination. Therefore, the study assessed the effects of RSB rates on biomass yield and accumulation of Si, Cd, Pb, and Zn in maize cultivated in soil polluted by slag. We also evaluated the photosynthetic apparatus functioning, the production of photosynthetic pigments, and the gas exchange parameters. Our results may indicate the technical viability of the combined use of RSB and plants in the remediation of heavy metal-polluted soils.\u003c/p\u003e"},{"header":"2. MATERIAL AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Soil and biochar characterization\u003c/h2\u003e \u003cp\u003eThe soil utilized in this research, classified as Acrisol according to the WRB-FAO (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), exhibited significant contamination resulting from the deposition of a slag enriched with Cd, Pb, and Zn near an abandoned lead smelting facility in Santo Amaro, Brazil (12\u0026deg; 32\u0026prime; 21.6\u0026prime;\u0026prime; S, 38\u0026deg; 43\u0026prime; 41\u0026prime;\u0026prime; W). A representative soil sample was air-dried and sieved through a 2.0 mm mesh sieve. Subsequently, three subsamples were used for comprehensive chemical and physical characterization, as well as the determination of total, semi-total, and bioavailable concentrations of metals in the soil (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\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\u003eChemical, physicochemical and physical characteristics of soil and rice straw biochar (RSB 400 \u0026ordm;C) used in the experiment\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoil attributes\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSoil values\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBiochar attributes\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBiochar values\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH (1:2.5) in CaCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003epH (1:5) in H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSOC (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEC (dS m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e222.4\u0026thinsp;\u0026plusmn;\u0026thinsp;41.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSOM (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCEC (cmolc kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e44.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCEC (cmol\u003csub\u003ec\u003c/sub\u003e dm\u003csub\u003e\u0026minus;\u0026thinsp;3\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSSA (m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e (cmol\u003csub\u003ec\u003c/sub\u003e dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHumidity (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMg\u003csup\u003e2+\u003c/sup\u003e (cmol\u003csub\u003ec\u003c/sub\u003e dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFixed carbon (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e49.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csup\u003e+\u003c/sup\u003e (cmol\u003csub\u003ec\u003c/sub\u003e dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAsh (%, w/w)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e33.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH\u0026thinsp;+\u0026thinsp;Al (cmol\u003csub\u003ec\u003c/sub\u003e dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eC (%, w/w)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e66.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP available (mg dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN (%, w/w)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSand (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e153.5\u0026thinsp;\u0026plusmn;\u0026thinsp;10.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eO (%, w/w)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilt (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e381.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSi (%, w/w)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eClay (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e654.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eP (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn total (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e566.0\u0026thinsp;\u0026plusmn;\u0026thinsp;28.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eK (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn semi\u0026ndash;total (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e450.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e366.3\u0026thinsp;\u0026plusmn;\u0026thinsp;29.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCa (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn available (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e***\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMg (g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePb total (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1991.8\u0026thinsp;\u0026plusmn;\u0026thinsp;58.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFe (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e747.5\u0026thinsp;\u0026plusmn;\u0026thinsp;9.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePb semi\u0026ndash;total (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e180.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1392.8\u0026thinsp;\u0026plusmn;\u0026thinsp;32.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMn (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e917.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePb available (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e***\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e855.6\u0026thinsp;\u0026plusmn;\u0026thinsp;51.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCu (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCd total (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eZn (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e37.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCd semi\u0026ndash;total (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePb (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt; LOQ\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCd available (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e***\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e---\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCd (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt; LOQ\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eIV\u003c/em\u003e investigation values for the agricultural scenario (CONAMA 2009); \u003cem\u003eSOM\u003c/em\u003e soil organic carbon; \u003cem\u003eCEC\u003c/em\u003e cation exchange capacity; \u003cem\u003eEC\u003c/em\u003e electric conductivity; \u003cem\u003eSA\u003c/em\u003e specific surface area; \u003csup\u003e*\u003c/sup\u003eacid dissolution with HF\u0026thinsp;+\u0026thinsp;HNO3\u0026thinsp;+\u0026thinsp;HClO4\u0026thinsp;+\u0026thinsp;HCl (2:1:1:1); **method EPA 3051a; ***DTPA pH 7.3; \u003cem\u003eLOQ\u003c/em\u003e quantification limit (0.07 and 0.78 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Cd and Pb, respectively).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e(Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe biochar tested was obtained from pyrolysis of rice straw at 400\u0026deg;C. The biochar was characterized following the procedures described by Singh et al. (\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and the results are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The total concentrations of P, Zn, Cd, and Pb were obtained from the extract of the biochar digestion using the 3051A method (USEPA, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) followed by metal measurements by ICP-OES (Optima 7000 Perkin Elmer, USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Pot experiment\u003c/h2\u003e \u003cp\u003eThe soil was fertilized with (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) 250.0 N (Urea), 240.0 P (MAP), 150.0 K (KCl), 160.0 S (K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e), 2.0 Fe (FeSO\u003csub\u003e4\u003c/sub\u003e.7H\u003csub\u003e2\u003c/sub\u003eO), 4.0 Mn (MnCl\u003csub\u003e2\u003c/sub\u003e.4H\u003csub\u003e2\u003c/sub\u003eO), 1.3 Cu (CuSO\u003csub\u003e4\u003c/sub\u003e), 1.0 B (H\u003csub\u003e3\u003c/sub\u003eBO\u003csub\u003e3\u003c/sub\u003e), and 0.2 Mo (Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e.2H\u003csub\u003e2\u003c/sub\u003eO) (da Silva et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The RSB was applied to 5 kg pots at five rates (equivalents to 0.0, 5.0, 10.0, 20.0, and 30.0 t ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) replicated four times in a randomized block design. In each pot, five maize seeds were initially planted, and post-germination, only two plants were kept for biomass collection. Maize was selected for testing due to its potential for bioenergy production through harvest. Throughout the experiment, control was maintained to sustain the soil at 80% of its maximum water retention capacity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Plant physiological analyses\u003c/h2\u003e \u003cp\u003eLeaf gas exchange (photosynthetic rate, transpiration, and stomatal conductance) were evaluated at 45 days of cultivation using a portable gas exchange system (model LI\u0026ndash;6400XT, LI\u0026ndash;COR Bioscences, Lincoln, NE, USA). Measurements were carried out on two leaves of the upper third of the plant. All parameters were measured between 9 am and 11 am, when the plants were physiologically functional. During the measurements, the intensity of the photosynthetic photon flux was maintained at 1800 \u0026micro;mol m\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e (Dourado et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe initial fluorescence (Fo), variable fluorescence (Fv), maximum fluorescence (Fm), and maximum quantum yield index (Fv/Fm) were determined simultaneously, immediately following the gas exchange measurements, using a portable fluorometer (FluorPen, model F100, Photon Systems Instruments). Measurements were carried out on two leaves of the upper third of the plant, which previously had a leaf blade section kept in the dark for 30' (de Souza et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo analyze chlorophyll a and b (Chl a and Chl b) and carotenoid contents, 0.1 g of fresh material from two leaves was extracted with 8 mL of 95% acetone solution for 24 hours at 4\u0026ordm;C in the dark. Subsequently, the extracts were measured in a spectrophotometer at 663.2 nm (Chl a), 646.8 nm (Chl b), and 470 nm (carotenoids); the contents of each pigment were estimated according to Lichtenthaler \u0026amp; Buschmann (2001) and expressed in mg g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e of fresh mass. After these analyses, the plants were collected. The shoots were washed with tap and distilled water, dried at 60\u0026deg;C, and weighed, obtaining the shoots biomass; then, the samples were ground in a knife mill.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Chemical analyses and quality control\u003c/h2\u003e \u003cp\u003eThe concentration of the metals Cd, Pb, and Zn were determined in the extracts of maize shoots after digestion in a microwave system (USEPA 1996) in an acid solution with HNO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at 180\u0026deg;C for 10\u0026rsquo;. Silicon concentration in shoots was obtained according to Elliott \u0026amp; Snyder (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). The heavy metal (Cd, Pb, and Zn) and Si contents in maize shoots were obtained by multiplying the elemental concentrations and the shoots' dry biomass.\u003c/p\u003e \u003cp\u003eBlank samples and plant reference material (SRM 1570a Spinach leaves) with multielement concentrations certified by the National Institute of Standards and Technology (NIST) were analyzed. The element concentrations recovered in the certified sample varied between 90% and 110%. All analyses were carried out in duplicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Statistical analyses\u003c/h2\u003e \u003cp\u003eMean and standard deviation values were computed for all variables subjected to analysis. The normality of the data was assessed using the Shapiro\u0026ndash;Wilk test, and, when necessary, logarithmic or square root transformations were applied to the dataset. Each variable under scrutiny underwent analysis of variance (ANOVA) at a significance level of p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Regression models (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) were then tailored to the dependent variables based on the biochar rates applied to the soil, with the goodness of fit determined by the regression coefficient (r2). Additionally, Pearson's linear correlation analysis (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) was conducted to explore relationships between physiological parameters and the concentrations of Si and metals in the plant shoots. All statistical analyses were executed using STATISTICA (v. 10) and OriginPro 2022b software.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. RESULTS AND DISCUSSION","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Silicon, cadmium, lead, and zinc uptake by maize plants\u003c/h2\u003e \u003cp\u003eThe addition of RSB significantly increased Si accumulation in the plant (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). At the rate of 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, the Si content in the shoots was 98% higher than in control. Yao et al. (\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) observed that the Si concentration in the rice shoots increased, on average, by 105% with the application of 0.3% RSB compared to the control (\u0026ndash;Si). Si concentration in rice straw biochar can vary between 55.0 and 185.0 mg kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e; therefore, RSB can increase the Si bioavailability in the soil and the accumulation of this element in crops (K and S, 2020; Li et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe application of RSB significantly diminished the concentrations of Cd, Pb and Zn in the maize shoots (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA \u0026ndash; \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). Cd accumulation ranged from 0.29 mg pot\u003csup\u003e\u0026ndash;1\u003c/sup\u003e (control) to 0.27(\u0026ndash;7%), 0.25(\u0026ndash;14%), 0.22(\u0026ndash;24%) and 0.19(\u0026ndash;34%) mg pot\u003csup\u003e\u0026ndash;1\u003c/sup\u003e; for Pb, the reduction was from 0.38 mg pot\u003csup\u003e\u0026ndash;1\u003c/sup\u003e (control) to 0.35(\u0026ndash;8%), 0.33(\u0026ndash;13%), 0.28(\u0026ndash;26%) and 0.24(\u0026ndash;37%) mg pot\u003csup\u003e\u0026ndash;1\u003c/sup\u003e; while Zn reduced 3, 6, 12 and 18% in the treatments 5.0, 10.0, 20.0, and 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB, respectively. Other works also reported that applying biochar in soils polluted by metals reduced their concentrations in plants (Ahmad et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Irfan et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Mansoor et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Nie et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Nzediegwu et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). A meta-analysis with 1298 data demonstrated that biochar applied to soils contaminated by metals was able to promote a reduction of 38, 39 and 17% in the concentrations of Cd, Pb and Zn, respectively, in several crops (Chen et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2018\u003c/span\u003e); these results were similar to the 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB rate teste here.\u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe lower Cd, Pb, and Zn concentrations in maize is likely related to reduced bioavailability in the soil amended with biochar. De Lima Veloso et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) found that applying 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB, in the same soil used in this experiment, promoted a reduction of 34, 32 and 33% in the bioavailability of Cd, Pb, and Zn assessed by DTPA, respectively. The immobilization of metals in the soil by biochar can take place through direct mechanisms (e.g., adsorption, ion exchange, complexation, and precipitation reactions) and indirect (increases in pH, organic matter, electrical conductivity, and cation exchange capacity) that will inhibit the absorption of metals by plants (Cao et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Ding et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Lu et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Qiu et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Other works with RSB at the same pyrolysis temperature reported more significant adsorption of metals compared to biochar produced at different temperatures (Ding et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAnother determining factor for reducing heavy metals in maize may be the higher Si uptake due to RSB addition. Linear and negative relationships were observed between the accumulations of Si and heavy metals in shoots (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD \u0026ndash; \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF). With the addition of 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB, the accumulation of 100 \u0026micro;g Si in maize promoted a reduction of 39, 39, and 22% in the Cd, Pb, and Zn accumulations in the crop, respectively. Other studies have observed that Si nutrition reduced the uptake of heavy metals in plants (Bhat et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Debona et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; El-Saadony et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Etesami and Jeong, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Imtiaz et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Pereira et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Silva et al., \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Vacul\u0026iacute;k et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSilicon induces internal mechanisms in the plant that can reduce the absorption and transport of metals from roots to shoots. These effects may occur due to (i) a physical barrier of amorphous silica in the apoplast (biosilicification), hindering the influx of metals into the symplast and/or transpiration flow (Guerriero et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), (ii) reduced cell wall porosity in roots, decreasing the metal loading into the xylem and its translocation towards shoots (Keller et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), (iii) the decrease in the transport of metals via the apoplast due to adsorption reactions in the cell wall (Ye et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and (iv) (co)precipitation of heavy metals with Si in the roots (Adrees et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; da Cunha and do Nascimento, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Ma et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Leaf photochemical traits, pigment profile and gas exchange\u003c/h2\u003e \u003cp\u003ePlants treated with RSB showed a better physiological status due to reduced metal accumulation and possibly lower oxidative stress. In the 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB treatment, photosynthetic rate, transpiration, and stomatal conductance increased by 68, 67, and 55% compared to the control (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA \u0026ndash; \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). Regarding photosynthetic pigments, Chla contents rose from 0.69 to 1.22 mg g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e (+\u0026thinsp;77%); for Chlb, the increase was from 0.49 to 0.77 mg g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e (+\u0026thinsp;57%); for total carotenoids, there was an increase from 0.71 to 1.01 mg g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e (+\u0026thinsp;42%) when the results between control (no Si) and 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e were compared (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD \u0026ndash; \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF). Studies have confirmed that the addition of biochar in soils polluted by heavy metals can have a positive effect on the content of photosynthetic pigments and, consequently, on the photosynthetic capacity of plants (Garc\u0026iacute;a et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Haider et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e; Kamran et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Zhen et al., \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eRen et al. (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) found improvements in gas exchange parameters and a significant increase in the photosynthetic pigments in tobacco grown in soil contaminated with 20.0 mg kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e of Cd and treated with 1.0% peanut shell biochar. The authors reported that in biochar-treated plants, Chla, Chlb, and carotenoid contents were 9.9, 12.6, and 10.3% higher than in the treatment without adding biochar, respectively. There was also an increase of 11% in the photosynthetic rate and stomatal conductance in the treatment with biochar. The authors suggested that biochar can mitigate the Cd phytotoxic effects by protecting the chloroplast structure in leaves and increasing the levels of photosynthetic pigments.\u003c/p\u003e \u003cp\u003eChlorophyll fluorescence is a physiological parameter that reflects photoinhibition (Kalaji et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Various works found significant inhibition in the photosystem II (PSII) (e.g., decrease in maximum quantum yield values - Fv/Fm) in metal-stressed plants (Chu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Hou et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Paunov et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Rajput et al., \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In this study, initial, variable and maximum fluorescence in corn leaves decreased by 23, 15 and 22% at the rate of 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA \u0026ndash; \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC); on the other hand, Fv/Fm varied from 0.69 (control) to 0.71 (+\u0026thinsp;3%), 0.73 (+\u0026thinsp;6%), 0.76 (+\u0026thinsp;10%) and 0.80 (+\u0026thinsp;16%) at doses of 5.0; 10.0; 20.0 and 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e RSB, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). This behavior is similar to that reported by Rajput et al. (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), where the maximum quantum yield of barley leaves increased from 0.68 to 0.71 (+\u0026thinsp;4%) by applying 2.5% biochar in soil polluted by heavy metals. The reduction in fluorescence intensity (Fo, Fv, and Fm) and the increase in maximum quantum yield in plants treated with RSB indicate a lower energy expenditure in electron transport in photosystem II and, therefore, greater photosynthetic activity (Zhang et al., \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). It can be observed that there is maximum efficiency in the conversion of luminous energy into chemical energy in PSII when the Fv/Fm ratio results in values close to 0.8. In this state, PSII is absorbing enough light for energy transfer to occur to produce energy compounds, essential for the synthesis of carbohydrates (Bjorkman and Demmig, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Martins et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe Si supply to maize in treatments with RSB contributed to the alleviation of physiological stress. Significant correlations were obtained between Si and parameters related to photosynthesis (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Previous studies confirmed the impacts of Si on chlorophyll biosynthesis and photosynthetic mechanisms of species such as cucumber (Feng et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), maize (Mihaličov\u0026aacute; Malčovsk\u0026aacute; et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), wheat (Hussain et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), rice (Song et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), barley (Shen et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and cotton (Bharwana, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) exposed to heavy metals. According to Rastogi et al. (\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), Si can inhibit the abiotic stress caused by heavy metals through improved photosynthesis by (i) protecting the photosynthetic structure, (ii) increasing water use efficiency, (iii) improving electron transport, (iv) preventing the photosynthetic machinery from reactive oxygen species (ROS) damages, and (v) regulating genes and interaction with physiological processes, such as nutrient uptake and production of phytohormones that influence photosynthetic activity.\u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e)\u003c/p\u003e \u003c/div\u003e"},{"header":"4. CONCLUSION","content":"\u003cp\u003eApplying rice straw biochar (RSB) in the soil polluted by Cd, Pb, and Zn efficiently reduced metal stress to maize plants. The 30.0 Mg ha\u003csup\u003e\u0026ndash;1\u003c/sup\u003e rate supplied Si to the plants and significantly reduced the metal accumulation in the maize shoots. Furthermore, RSB promoted improvements in the photosynthetic apparatus, including greater gas exchange efficiency, production of photosynthetic pigments, and optimization of the use of free electron energy in photosystem II (PSII). Applying RSB associated with maize cultivation can phytoattenuate Cd, Pb, and Zn contamination since RSB increases the biomass and maize tolerance to metal stress. This phytotechnology can be applied in areas where resources available for remediation are scarce, enabling an income for the stakeholder while reducing environmental and human health risks.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDisclosure statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo potential conflict of interest was reported by the author(s).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStudy conception and design: C.W.A.N., V.L.V; data collection: V.L.V., F.B.V.S., T.S.P.; analysis and interpretation of results: C.W.A.N., V.L.V; F.B.V.S., E.R.S., P.R.M.A.; draft manuscript preparation: C.W.A.N., V.L.V; F.B.V.S., E.R.S., P.R.M.A., T.S.P.; manuscript revision and approval: C.W.A.N., V.L.V; F.B.V.S., E.R.S., P.R.M.A., T.S.P. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author, C.W.A.N., upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have approved the manuscript and consent to publish it in Environmental Monitoring and Assessment.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAdrees M, Ali S, Rizwan M, Zia-ur-Rehman M, Ibrahim M, Abbas F, Farid M, Qayyum MF, Irshad MK (2015) Mechanisms of silicon-mediated alleviation of heavy metal toxicity in plants: A review. Ecotoxicol Environ Saf 119:186\u0026ndash;197. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2015.05.011\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2015.05.011\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhmad M, Usman ARA, Al-Faraj AS, Ahmad, Mahtab, Sallam A, Al-Wabel MI (2018) Phosphorus-loaded biochar changes soil heavy metals availability and uptake potential of maize (Zea mays L.) plants. Chemosphere 194:327\u0026ndash;339. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2017.11.156\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2017.11.156\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBharwana S (2013) Alleviation of Lead Toxicity by Silicon is Related to Elevated Photosynthesis, Antioxidant Enzymes Suppressed Lead Uptake and Oxidative Stress in Cotton. J Bioremediat Biodegrad 04:10\u0026ndash;4172. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.4172/2155-6199.1000187\u003c/span\u003e\u003cspan address=\"10.4172/2155-6199.1000187\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBhat JA, Shivaraj SM, Singh P, Navadagi DB, Tripathi DK, Dash PK, Solanke AU, Sonah H, Deshmukh R (2019) Role of Silicon in Mitigation of Heavy Metal Stresses in Crop Plants. Plants 8:71. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/plants8030071\u003c/span\u003e\u003cspan address=\"10.3390/plants8030071\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBjorkman O, Demmig B (1987) Photon yield of O2 evolution and chlorophyll fluorescence characteristics at 77 K among vascular plants of diverse origins. Planta 170:489\u0026ndash;504. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/BF00402983\u003c/span\u003e\u003cspan address=\"10.1007/BF00402983\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBurges A, Alkorta I, Epelde L, Garbisu C (2018) From phytoremediation of soil contaminants to phytomanagement of ecosystem services in metal contaminated sites. Int J Phytorem 20:384\u0026ndash;397. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/15226514.2017.1365340\u003c/span\u003e\u003cspan address=\"10.1080/15226514.2017.1365340\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCao X, Ma L, Gao B, Harris W (2009) Dairy-Manure Derived Biochar Effectively Sorbs Lead and Atrazine. Environ Sci Technol 43:3285\u0026ndash;3291. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/es803092k\u003c/span\u003e\u003cspan address=\"10.1021/es803092k\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen D, Liu X, Bian R, Cheng K, Zhang X, Zheng J, Joseph S, Crowley D, Pan G, Li L (2018) Effects of biochar on availability and plant uptake of heavy metals \u0026ndash; A meta-analysis. J Environ Manage 222:76\u0026ndash;85. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2018.05.004\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2018.05.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChew J, Joseph S, Chen G, Zhang Y, Zhu L, Liu M, Taherymoosavi S, Munroe P, Mitchell DRG, Pan G, Li L, Bian R, Fan X (2022) Biochar-based fertiliser enhances nutrient uptake and transport in rice seedlings. Sci Total Environ 826:154174. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2022.154174\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2022.154174\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChu J, Zhu F, Chen X, Liang H, Wang R, Wang X, Huang X (2018) Effects of cadmium on photosynthesis of Schima superba young plant detected by chlorophyll fluorescence. Environ Sci Pollut Res 25:10679\u0026ndash;10687. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-018-1294-x\u003c/span\u003e\u003cspan address=\"10.1007/s11356-018-1294-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCui L, Pan G, Li L, Bian R, Liu X, Yan J, Quan G, Ding C, Chen T, Liu, Yang L, Yuming, Yin C, Wei C, Yang Y, Hussain Q (2016) Continuous immobilization of cadmium and lead in biochar amended contaminated paddy soil: A five-year field experiment. Ecol Eng 93:1\u0026ndash;8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoleng.2016.05.007\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoleng.2016.05.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCundy AB, Bardos RP, Puschenreiter M, Mench M, Bert V, Friesl-Hanl W, M\u0026uuml;ller I, Li XN, Weyens N, Witters N, Vangronsveld J (2016) Brownfields to green fields: Realising wider benefits from practical contaminant phytomanagement strategies. J Environ Manage 184:67\u0026ndash;77. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2016.03.028\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2016.03.028\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eda Cunha KPV, do Nascimento CWA (2009) Silicon Effects on Metal Tolerance and Structural Changes in Maize (Zea mays L.) Grown on a Cadmium and Zinc Enriched Soil. Water Air Soil Pollut 197:323\u0026ndash;330. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11270-008-9814-9\u003c/span\u003e\u003cspan address=\"10.1007/s11270-008-9814-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eda Silva WR, da Silva FBV, Ara\u0026uacute;jo PRM, do Nascimento CWA (2017) Assessing human health risks and strategies for phytoremediation in soils contaminated with As, Cd, Pb, and Zn by slag disposal. Ecotoxicol Environ Saf 144:522\u0026ndash;530. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2017.06.068\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2017.06.068\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede Lima A, Bernardez LRP, L.A (2011) Characterization of the lead smelter slag in Santo Amaro, Bahia, Brazil. J Hazard Mater 189:692\u0026ndash;699. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2011.02.091\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2011.02.091\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede Lima Veloso V, da Silva FBV, dos Santos NM, do Nascimento CWA (2022) Phytoattenuation of Cd, Pb, and Zn in a Slag-contaminated Soil Amended with Rice Straw Biochar and Grown with Energy Maize. Environ Manage 69:196\u0026ndash;212. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00267-021-01530-6\u003c/span\u003e\u003cspan address=\"10.1007/s00267-021-01530-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede Souza AAB, do Nascimento CWA, de Souza ER (2021) Mineral composition, chlorophyll fluorescence and zinc biofortification in Vigna unguiculata fertilized with bulk and nanoparticulate zinc oxides. Acta Physiol Plant 43:159. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11738-021-03333-y\u003c/span\u003e\u003cspan address=\"10.1007/s11738-021-03333-y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDebona D, Rodrigues FA, Datnoff LE (2017) Silicon\u0026rsquo;s Role in Abiotic and Biotic Plant Stresses. Annu Rev Phytopathol 55:85\u0026ndash;107. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1146/annurev-phyto-080516-035312\u003c/span\u003e\u003cspan address=\"10.1146/annurev-phyto-080516-035312\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDezhban A, Shirvany A, Attarod P, Delshad M, Matinizadeh M, Khoshnevis M (2015) Cadmium and lead effects on chlorophyll fluorescence, chlorophyll pigments and proline of Robinia pseudoacacia. J Res 26:323\u0026ndash;329. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11676-015-0045-9\u003c/span\u003e\u003cspan address=\"10.1007/s11676-015-0045-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDing W, Dong X, Ime IM, Gao B, Ma LQ (2014) Pyrolytic temperatures impact lead sorption mechanisms by bagasse biochars. Chemosphere 105:68\u0026ndash;74. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2013.12.042\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2013.12.042\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDourado PRM, de Souza ER, Santos MA, dos, Lins CMT, Monteiro DR, Paulino MKSS, Schaffer B (2022) Stomatal Regulation and Osmotic Adjustment in Sorghum in Response to Salinity. Agriculture 12:658. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/agriculture12050658\u003c/span\u003e\u003cspan address=\"10.3390/agriculture12050658\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDuarte B, Pires V, Carreiras J, de Carvalho RC, Ferreira R, Pereira MFC, Maur\u0026iacute;cio AM, Martins-Dias S, Ca\u0026ccedil;ador I (2023) Cistus ladanifer metal uptake and physiological performance in biochar amended mine soils. South Afr J Bot 153:246\u0026ndash;257. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.sajb.2023.01.002\u003c/span\u003e\u003cspan address=\"10.1016/j.sajb.2023.01.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Saadony MT, Desoky E-SM, Saad AM, Eid RSM, Selem E, Elrys AS (2021) Biological silicon nanoparticles improve Phaseolus vulgaris L. yield and minimize its contaminant contents on a heavy metals-contaminated saline soil. J Environ Sci 106:1\u0026ndash;14. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jes.2021.01.012\u003c/span\u003e\u003cspan address=\"10.1016/j.jes.2021.01.012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eElliott CL, Snyder GH (1991) Autoclave-induced digestion for the colorimetric determination of silicon in rice straw. J Agric Food Chem 39:1118\u0026ndash;1119. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/jf00006a024\u003c/span\u003e\u003cspan address=\"10.1021/jf00006a024\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEtesami H, Jeong BR (2018) Silicon (Si): Review and future prospects on the action mechanisms in alleviating biotic and abiotic stresses in plants. Ecotoxicol Environ Saf 147:881\u0026ndash;896. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2017.09.063\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2017.09.063\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFeng J, Shi Q, Wang X, Wei M, Yang F, Xu H (2010) Silicon supplementation ameliorated the inhibition of photosynthesis and nitrate metabolism by cadmium (Cd) toxicity in Cucumis sativus L. Sci Hortic (Amsterdam) 123:521\u0026ndash;530. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scienta.2009.10.013\u003c/span\u003e\u003cspan address=\"10.1016/j.scienta.2009.10.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarc\u0026iacute;a AC, Tavares OCH, de Oliveira DF (2020) Biochar as agricultural alternative to protect the rice plant growth in fragile sandy soil contaminated with cadmium. Biocatal Agric Biotechnol 29:101829. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.bcab.2020.101829\u003c/span\u003e\u003cspan address=\"10.1016/j.bcab.2020.101829\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuerriero G, Hausman J-F, Legay S (2016) Silicon and the Plant Extracellular Matrix. Front. Plant Sci 7:463. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fpls.2016.00463\u003c/span\u003e\u003cspan address=\"10.3389/fpls.2016.00463\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaider FU, Farooq M, Naveed M, Cheema SA, Ain Nul, Salim MA, Liqun C, Mustafa A (2022a) Influence of biochar and microorganism co-application on stabilization of cadmium (Cd) and improved maize growth in Cd-contaminated soil. Front Plant Sci 13:983830. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fpls.2022.983830\u003c/span\u003e\u003cspan address=\"10.3389/fpls.2022.983830\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaider FU, Wang X, Farooq M, Hussain S, Cheema SA, Ain Nul, Virk AL, Ejaz M, Janyshova U, Liqun C (2022b) Biochar application for the remediation of trace metals in contaminated soils: Implications for stress tolerance and crop production. Ecotoxicol Environ Saf 230:113165. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2022.113165\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2022.113165\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHou X, Han H, Cai L, Liu A, Ma X, Zhou C, Wang G, Meng F (2018) Pb stress effects on leaf chlorophyll fluorescence, antioxidative enzyme activities, and organic acid contents of Pogonatherum crinitum seedlings. Flora 240:82\u0026ndash;88. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.flora.2018.01.006\u003c/span\u003e\u003cspan address=\"10.1016/j.flora.2018.01.006\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang S, Tan L, Zhu H, Sheng GD (2021) Root damages induced by extended phytotoxic effects of cadmium pre-exposure against subsequent lindane uptake in rice seedlings. Environ Exp Bot 189:104553. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envexpbot.2021.104553\u003c/span\u003e\u003cspan address=\"10.1016/j.envexpbot.2021.104553\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHussain I, Ashraf MA, Rasheed R, Asghar A, Sajid MA, Iqbal M (2015) Exogenous application of silicon at the boot stage decreases accumulation of cadmium in wheat (Triticum aestivum L.) grains. Brazilian J Bot 38:223\u0026ndash;234. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s40415-014-0126-6\u003c/span\u003e\u003cspan address=\"10.1007/s40415-014-0126-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eImtiaz M, Rizwan MS, Mushtaq MA, Ashraf M, Shahzad SM, Yousaf B, Saeed DA, Rizwan M, Nawaz MA, Mehmood S, Tu S (2016) Silicon occurrence, uptake, transport and mechanisms of heavy metals, minerals and salinity enhanced tolerance in plants with future prospects: A review. J Environ Manage 183:521\u0026ndash;529. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2016.09.009\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2016.09.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIrfan M, Mudassir M, Khan MJ, Dawar KM, Muhammad D, Mian IA, Ali W, Fahad S, Saud S, Hayat Z, Nawaz T, Khan SA, Alam S, Ali B, Banout J, Ahmed S, Mubeen S, Danish S, Datta R, Elgorban AM, Dewil R (2021) Heavy metals immobilization and improvement in maize (Zea mays L.) growth amended with biochar and compost. Sci Rep 11:18416. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41598-021-97525-8\u003c/span\u003e\u003cspan address=\"10.1038/s41598-021-97525-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIzydorczyk G, Mikula K, Skrzypczak D, Moustakas K, Witek-Krowiak A, Chojnacka K (2021) Potential environmental pollution from copper metallurgy and methods of management. Environ Res 197:111050. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envres.2021.111050\u003c/span\u003e\u003cspan address=\"10.1016/j.envres.2021.111050\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiang J, Xu R, Jiang T, Li Z (2012) Immobilization of Cu(II), Pb(II) and Cd(II) by the addition of rice straw derived biochar to a simulated polluted Ultisol. J Hazard Mater 229\u0026ndash;230. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2012.05.086\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2012.05.086\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eK A, S, J.S (2020) Production and characterization of vermicompost and biochar from rice straw. J Pharmacogn Phytochem 9:1556\u0026ndash;1562. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.22271/phyto.2020.v9.i5v.12557\u003c/span\u003e\u003cspan address=\"10.22271/phyto.2020.v9.i5v.12557\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKabata-Pendias A (2010) Trace Elements in Soils and Plants, 4th ed, Trace Elements in Soils and Plants, Fourth Edition. CRC Press, Boca Raton. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1201/b10158\u003c/span\u003e\u003cspan address=\"10.1201/b10158\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKalaji HM, Bąba W, Gediga K, Goltsev V, Samborska IA, Cetner MD, Dimitrova S, Piszcz U, Bielecki K, Karmowska K, Dankov K, Kompała-Bąba A (2018) Chlorophyll fluorescence as a tool for nutrient status identification in rapeseed plants. Photosynth Res 136:329\u0026ndash;343. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11120-017-0467-7\u003c/span\u003e\u003cspan address=\"10.1007/s11120-017-0467-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKamran M, Malik Z, Parveen A, Huang L, Riaz M, Bashir S, Mustafa A, Abbasi GH, Xue B, Ali U (2020) Ameliorative Effects of Biochar on Rapeseed (Brassica napus L.) Growth and Heavy Metal Immobilization in Soil Irrigated with Untreated Wastewater. J Plant Growth Regul 39:266\u0026ndash;281. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00344-019-09980-3\u003c/span\u003e\u003cspan address=\"10.1007/s00344-019-09980-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKeller C, Rizwan M, Davidian J-C, Pokrovsky OS, Bovet N, Chaurand P, Meunier J-D (2015) Effect of silicon on wheat seedlings (Triticum turgidum L.) grown in hydroponics and exposed to 0 to 30 \u0026micro;M Cu. Planta 241:847\u0026ndash;860. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00425-014-2220-1\u003c/span\u003e\u003cspan address=\"10.1007/s00425-014-2220-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKr\u0026oacute;l A, Mizerna K, Bożym M (2020) An assessment of pH-dependent release and mobility of heavy metals from metallurgical slag. J Hazard Mater 384:121502. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2019.121502\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2019.121502\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi Z, Song Z, Singh BP, Wang H (2019) The impact of crop residue biochars on silicon and nutrient cycles in croplands. Sci Total Environ 659:673\u0026ndash;680. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2018.12.381\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2018.12.381\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi Z, Yuan Y, Xiang L, Su Q, Liu Z, Wu W, Huang Y, Tu S (2022) Silicon-Rich Biochar Detoxify Multiple Heavy Metals in Wheat by Regulating Oxidative Stress and Subcellular Distribution of Heavy Metal. Sustainability 14:16417. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/su142416417\u003c/span\u003e\u003cspan address=\"10.3390/su142416417\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLichtenthaler HK, Buschmann C (2005) Chlorophylls. Handbook of Food Analytical Chemistry. John Wiley \u0026amp; Sons, Inc., Hoboken, NJ, USA, pp 153\u0026ndash;199. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/0471709085.ch21\u003c/span\u003e\u003cspan address=\"10.1002/0471709085.ch21\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLu H, Zhang W, Yang Y, Huang X, Wang S, Qiu R (2012) Relative distribution of Pb2\u0026thinsp;+\u0026thinsp;sorption mechanisms by sludge-derived biochar. Water Res 46:854\u0026ndash;862. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.watres.2011.11.058\u003c/span\u003e\u003cspan address=\"10.1016/j.watres.2011.11.058\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLu K, Yang X, Shen J, Robinson B, Huang H, Liu D, Bolan N, Pei J, Wang H (2014) Effect of bamboo and rice straw biochars on the bioavailability of Cd, Cu, Pb and Zn to Sedum plumbizincicola. Agric Ecosyst Environ 191:124\u0026ndash;132. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.agee.2014.04.010\u003c/span\u003e\u003cspan address=\"10.1016/j.agee.2014.04.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMa J, Cai H, He C, Zhang W, Wang L (2015) A hemicellulose-bound form of silicon inhibits cadmium ion uptake in rice (Oryza sativa) cells. New Phytol 206:1063\u0026ndash;1074. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/nph.13276\u003c/span\u003e\u003cspan address=\"10.1111/nph.13276\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMansoor S, Kour N, Manhas S, Zahid S, Wani OA, Sharma V, Wijaya L, Alyemeni MN, Alsahli AA, El-Serehy HA, Paray BA, Ahmad P (2021) Biochar as a tool for effective management of drought and heavy metal toxicity. Chemosphere 271:129458. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2020.129458\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2020.129458\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartins JB, Santos J\u0026uacute;nior JA, Leal LY, de Paulino C, de Souza MKSS, Gheyi ER, H.R (2020) Fluorescence emission and photochemical yield of parsley under saline waters of different cationic nature. Sci Hortic (Amsterdam) 273:109574. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scienta.2020.109574\u003c/span\u003e\u003cspan address=\"10.1016/j.scienta.2020.109574\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeng J, Tao M, Wang L, Liu X, Xu J (2018) Changes in heavy metal bioavailability and speciation from a Pb-Zn mining soil amended with biochars from co-pyrolysis of rice straw and swine manure. Sci Total Environ 633:300\u0026ndash;307. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2018.03.199\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2018.03.199\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMihaličov\u0026aacute; Malčovsk\u0026aacute; S, Dučaiov\u0026aacute; Z, Maslaň\u0026aacute;kov\u0026aacute; I, Bačkor M (2014) Effect of Silicon on Growth, Photosynthesis, Oxidative Status and Phenolic Compounds of Maize (Zea mays L.) Grown in Cadmium Excess. Water, Air, Soil Pollut. 225, 2056. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11270-014-2056-0\u003c/span\u003e\u003cspan address=\"10.1007/s11270-014-2056-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoradi L, Ehsanzadeh P (2015) Effects of Cd on photosynthesis and growth of safflower (Carthamus tinctorius L.) genotypes. Photosynthetica 53:506\u0026ndash;518. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11099-015-0150-1\u003c/span\u003e\u003cspan address=\"10.1007/s11099-015-0150-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMurakami M, Ae N (2009) Potential for phytoextraction of copper, lead, and zinc by rice (Oryza sativa L.), soybean (Glycine max [L.] Merr.), and maize (Zea mays L). J Hazard Mater 162:1185\u0026ndash;1192. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2008.06.003\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2008.06.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNie C, Yang X, Niazi NK, Xu X, Wen Y, Rinklebe J, Ok YS, Xu S, Wang H (2018) Impact of sugarcane bagasse-derived biochar on heavy metal availability and microbial activity: A field study. Chemosphere 200:274\u0026ndash;282. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2018.02.134\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2018.02.134\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNiemeyer JC, Moreira-Santos M, Ribeiro R, Rutgers M, Nogueira MA, da Silva EM, Sousa JP (2015) Ecological Risk Assessment of a Metal-Contaminated Area in the Tropics. Tier II: Detailed Assessment. PLoS ONE 10:e0141772. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1371/journal.pone.0141772\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0141772\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNzediegwu C, Prasher S, Elsayed E, Dhiman J, Mawof A, Patel R (2019) Effect of biochar on heavy metal accumulation in potatoes from wastewater irrigation. J Environ Manage 232:153\u0026ndash;164. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2018.11.013\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2018.11.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePaunov M, Koleva L, Vassilev A, Vangronsveld J, Goltsev V (2018) Effects of Different Metals on Photosynthesis: Cadmium and Zinc Affect Chlorophyll Fluorescence in Durum Wheat. Int J Mol Sci 19:787. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/ijms19030787\u003c/span\u003e\u003cspan address=\"10.3390/ijms19030787\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeng X, Shi G, Liu G, Xu J, Tian Y, Zhang Y, Feng Y, Russell AG (2017) Source apportionment and heavy metal health risk (HMHR) quantification from sources in a southern city in China, using an ME2-HMHR model. Environ Pollut 221:335\u0026ndash;342. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envpol.2016.11.083\u003c/span\u003e\u003cspan address=\"10.1016/j.envpol.2016.11.083\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePereira TS, Pereira Tha\u0026iacute;s, Soares, Souza CLF, de Lima C, Batista EJA, Lobato BL (2018) A.K. da S. Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants. Physiol. Mol. Biol. Plants 24, 99\u0026ndash;114. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12298-017-0494-z\u003c/span\u003e\u003cspan address=\"10.1007/s12298-017-0494-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeršić V, Đerđ T, Varga M, Hackenberger BK (2019) Real-time CO2 uptake/emission measurements as a tool for early indication of toxicity in Lemna-tests. Aquat Toxicol 206:154\u0026ndash;163. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.aquatox.2018.11.013\u003c/span\u003e\u003cspan address=\"10.1016/j.aquatox.2018.11.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiu B, Tao X, Wang H, Li W, Ding X, Chu H (2021) Biochar as a low-cost adsorbent for aqueous heavy metal removal: A review. J Anal Appl Pyrol 155:105081. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jaap.2021.105081\u003c/span\u003e\u003cspan address=\"10.1016/j.jaap.2021.105081\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRajput VD, Gorovtsov AV, Fedorenko GM, Minkina TM, Fedorenko AG, Lysenko VS, Sushkova SS, Mandzhieva SS, Elinson MA (2021) The influence of application of biochar and metal-tolerant bacteria in polluted soil on morpho-physiological and anatomical parameters of spring barley. Environ Geochem Health 43:1477\u0026ndash;1489. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10653-019-00505-1\u003c/span\u003e\u003cspan address=\"10.1007/s10653-019-00505-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRastogi A, Yadav S, Hussain S, Kataria S, Hajihashemi S, Kumari P, Yang X, Brestic M (2021) Does silicon really matter for the photosynthetic machinery in plants\u0026hellip; Plant Physiol. Biochem 169:40\u0026ndash;48. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.plaphy.2021.11.004\u003c/span\u003e\u003cspan address=\"10.1016/j.plaphy.2021.11.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRen T, Chen N, Mahari W, Xu WA, Feng C, Ji H, Yin X, Chen Q, Zhu P, Liu S, Liu H, Li G, Lam L, S.S (2021) Biochar for cadmium pollution mitigation and stress resistance in tobacco growth. Environ Res 192:110273. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envres.2020.110273\u003c/span\u003e\u003cspan address=\"10.1016/j.envres.2020.110273\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRusinowski S, Krzyżak J, Sitko K, Kalaji HM, Jensen E, Pogrzeba M (2019) Cultivation of C4 perennial energy grasses on heavy metal contaminated arable land: Impact on soil, biomass, and photosynthetic traits. Environ Pollut 250:300\u0026ndash;311. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envpol.2019.04.048\u003c/span\u003e\u003cspan address=\"10.1016/j.envpol.2019.04.048\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003edos Santos NM, Accioly AM, de Nascimento A, do CWA, Silva IR, Santos JAG (2015) Bioavailability of lead using chemical extractants in soil treated with humic acids and activated carbon. Rev CI\u0026Ecirc;NCIA AGRON\u0026Ocirc;MICA 46:663\u0026ndash;668. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5935/1806-6690.20150052\u003c/span\u003e\u003cspan address=\"10.5935/1806-6690.20150052\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShen X, Xiao X, Dong Z, Chen Y (2014) Silicon effects on antioxidative enzymes and lipid peroxidation in leaves and roots of peanut under aluminum stress. Acta Physiol Plant 36:3063\u0026ndash;3069. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11738-014-1676-8\u003c/span\u003e\u003cspan address=\"10.1007/s11738-014-1676-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSilva Gonzaga MI, Oliveira da Silva PS, Carlos de Jesus Santos J, Junior GdeO, L.F (2019) Biochar increases plant water use efficiency and biomass production while reducing Cu concentration in Brassica juncea L. in a Cu-contaminated soil. Ecotoxicol Environ Saf 183:109557. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2019.109557\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2019.109557\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSilva JR, Veloso VdeL, Silva FBV, da, Nascimento CWA (2021) do Cadmium, silicon and nutrient accumulation by maize plants grown on a contaminated soil amended with a diatomaceous Earth fertilizer. Ci\u0026ecirc;ncia Rural 51. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1590/0103-8478cr20190804\u003c/span\u003e\u003cspan address=\"10.1590/0103-8478cr20190804\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSilvany Neto AM, Carvalho FM, Tavares TM, Guimaraes GC, Amorim CJB, Peres MFT, Lopes RS, Rocha CM, Ra\u0026ntilde;a MC (1996) Lead poisoning among children of Santo Amaro, Bahia, Brazil in 1980, 1985, and 1992. Bull. Pan Am. Heal. Organ. (PAHO); 30 (1), mar. 1996\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh B, Camps-Arbestain M, Lehmann J (2017) Biochar: a guide to analytical methods. Csiro Publishing\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh R, Kumar V, Tewari RK, Pratap SG, Singh PK (2023) Hazardous waste leachates induced changes in plant water relation, photosynthetic pigments, heavy metal accumulation and yield of mustard (Brassica juncea L.) plant. J Hazard Mater Adv 10:100306. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.hazadv.2023.100306\u003c/span\u003e\u003cspan address=\"10.1016/j.hazadv.2023.100306\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong A, Li P, Fan F, Li Z, Liang Y (2014) The Effect of Silicon on Photosynthesis and Expression of Its Relevant Genes in Rice (Oryza sativa L.) under High-Zinc Stress. PLoS ONE 9:e113782. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1371/journal.pone.0113782\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0113782\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUSEPA (United States Environmental Protection Agency) (1996) Method 3050B: Acid Digestion of Sediments, Sludges, and Soils. Z. F\u0026uuml;r Anal. Chem\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUSEPA E (2007) Method 3051: Microwave assisted acid digestion of sediments, sludges, soils, and oils. Test Methods Eval Solid Waste 1\u0026ndash;30\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVacul\u0026iacute;k M, Lukačov\u0026aacute; Z, Bokor B, Martinka M, Tripathi DK, Lux A (2020) Alleviation mechanisms of metal(loid) stress in plants by silicon: a review. J Exp Bot 71:6744\u0026ndash;6757. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/jxb/eraa288\u003c/span\u003e\u003cspan address=\"10.1093/jxb/eraa288\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang J, Wang L, Wang Y, Tsang DCW, Yang X, Beiyuan J, Yin M, Xiao T, Jiang Y, Lin W, Zhou Y, Liu J, Wang, Liang, Zhao M (2021) Emerging risks of toxic metal(loid)s in soil-vegetables influenced by steel-making activities and isotopic source apportionment. Environ Int 146:106207. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envint.2020.106207\u003c/span\u003e\u003cspan address=\"10.1016/j.envint.2020.106207\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang M, Wang JJ, Tafti ND, Hollier CA, Myers G, Wang X (2019) Effect of alkali-enhanced biochar on silicon uptake and suppression of gray leaf spot development in perennial ryegrass. Crop Prot 119:9\u0026ndash;16. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cropro.2019.01.013\u003c/span\u003e\u003cspan address=\"10.1016/j.cropro.2019.01.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang Y, Duan X, Wang L (2020) Spatial distribution and source analysis of heavy metals in soils influenced by industrial enterprise distribution: Case study in Jiangsu Province. Sci Total Environ 710:134953. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2019.134953\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2019.134953\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWRB-FAO IWG (2015) IUSS Working Group WRB. 2015. World Reference Base for Soil Resources 2014, update 2015 International soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports N\u003csup\u003eo\u003c/sup\u003e. 106\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYadav M, George N, Dwibedi V (2023) Emergence of toxic trace elements in plant environment: Insights into potential of silica nanoparticles for mitigation of metal toxicity in plants. Environ Pollut 333:122112. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envpol.2023.122112\u003c/span\u003e\u003cspan address=\"10.1016/j.envpol.2023.122112\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao D, Wu J, Gao H, Wu D, Wei Z (2022) Changes in soil silicon forms and availability as affected by rice straw and its biochar. Eur J Soil Sci 73:e13316. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/ejss.13316\u003c/span\u003e\u003cspan address=\"10.1111/ejss.13316\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYe J, Yan C, Liu J, Lu H, Liu T, Song Z (2012) Effects of silicon on the distribution of cadmium compartmentation in root tips of Kandelia obovata (S., L.) Yong. Environ Pollut 162:369\u0026ndash;373. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envpol.2011.12.002\u003c/span\u003e\u003cspan address=\"10.1016/j.envpol.2011.12.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang H, Xu Z, Guo K, Huo Y, He G, Sun H, Guan Y, Xu N, Yang W, Sun G (2020) Toxic effects of heavy metal Cd and Zn on chlorophyll, carotenoid metabolism and photosynthetic function in tobacco leaves revealed by physiological and proteomics analysis. Ecotoxicol Environ Saf 202:110856. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2020.110856\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2020.110856\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang R-H, Xie, Yanlan, Zhou G, Li Z, Ye A, Huang X, Xie, Yanfeng, Shi L, Cao X, Zhang J, Lin C (2022) The effects of short-term, long-term, and reapplication of biochar on the remediation of heavy metal-contaminated soil. Ecotoxicol Environ Saf 248:114316. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2022.114316\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2022.114316\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang S, Yao H, Lu Y, Shan D, Yu X (2018) Reclaimed Water Irrigation Effect on Agricultural Soil and Maize (Zea mays L.) in Northern China. CLEAN - Soil Air Water 46:1800037. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/clen.201800037\u003c/span\u003e\u003cspan address=\"10.1002/clen.201800037\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhen K, Zhu Q, Zhai S, Gao Y, Cao H, Tang X, Wang C, Li J, Tian L, Sun H (2022) PPCPs and heavy metals from hydrothermal sewage sludge-derived biochar: migration in wheat and physiological response. Environ Sci Pollut Res 29:83234\u0026ndash;83246. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-022-21432-2\u003c/span\u003e\u003cspan address=\"10.1007/s11356-022-21432-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu S, Ma X, Guo R, Ai S, Liu B, Zhang W, Zhang Y (2016) A field study on heavy metals phytoattenuation potential of monocropping and intercropping of maize and/or legumes in weakly alkaline soils. Int J Phytorem 18:1014\u0026ndash;1021. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/15226514.2016.1183570\u003c/span\u003e\u003cspan address=\"10.1080/15226514.2016.1183570\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eŻurek G, Rybka K, Pogrzeba M, Krzyżak J, Prokopiuk K (2014) Chlorophyll a Fluorescence in Evaluation of the Effect of Heavy Metal Soil Contamination on Perennial Grasses. PLoS ONE 9:e91475. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1371/journal.pone.0091475\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0091475\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":"potentially toxic element, soil remediation, photosynthesis, abiotic stress, gas exchange","lastPublishedDoi":"10.21203/rs.3.rs-4252712/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4252712/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSoils polluted by heavy metals soils pose a high risk to human health and must be remediated. Applying biochar to such soils can reduce metal bioavailability and phytotoxicity, improving phytoremediation techniques. This work aimed to assess the effects of rice straw biochar (RSB) on mitigating metal stress and accumulation of Si, Cd, Pb, and Zn in maize plants grown in soil contaminated by metallurgy slag. The soil in pots was amended with RSB rates equivalent to 0.0, 5.0, 10.0, 20.0, and 30.0 t ha\u003csup\u003e-1\u003c/sup\u003e and grown with maize for 45 days. Chlorophyll fluorescence, photosynthetic pigment contents, and gas exchange parameters were evaluated as metal toxicity indicators. The RSB rates significantly increased Si uptake while reducing Cd, Pb, and Zn accumulation in maize shoots. The addition of 30.0 t ha\u003csup\u003e-1\u003c/sup\u003e RSB promoted 18, 34, and 37% reductions for Zn, Cd, and Pb in the plants. Photosynthetic rate, transpiration, and stomatal conductance increased by 68%, 67%, and 55%, while chlorophyll a, b, and carotenoid contents increased by 77%, 57%, and 42%, correspondingly. Chlorophyll fluorescence measurements showed a linear and positive relationship between photosystem II energy consumption efficiency (Fv/Fm) and RSB rates. Applying RSB associated with maize cultivation can assist in the phytoattenuation of Cd, Pb, and Zn contamination in soils since RSB increases biomass and the plant's tolerance to metal stress.\u003c/p\u003e","manuscriptTitle":"Rice straw biochar mitigates metal stress in maize and assists in the phytoattenuation of a slag-contaminated soil","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-16 10:37:54","doi":"10.21203/rs.3.rs-4252712/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":"4e20e930-2964-42a7-ba89-ad8dfb47735b","owner":[],"postedDate":"April 16th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-04-21T10:42:07+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-16 10:37:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4252712","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4252712","identity":"rs-4252712","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}