Polymer-coated manganese fertilizer and its combination with lime reduces cadmium accumulation in brown rice (Oryza sativa L.)

Controlling exposure to As and Cd from rice via irrigation management

Irrigation management controls biogeochemical cycles in rice production. Under flooded paddy conditions, arsenic becomes plant-available as iron-reducing conditions ensue, while oxic conditions lead to increased plant availability of Cd in acidic soils. Because Cd enters rice through Mn transporters, we hypothesized that irrigation resulting in intermediate redox could simultaneously limit both As and Cd in rice grain due to As retention in soil and Mn competition for Cd uptake. In a 2 year field study, we used 6 irrigation managements that varied in extent and frequency of inundation, and we observed strong effects of irrigation management on porewater chemistry, soil redox potentials, plant As and Cd concentrations, plant nutrient concentrations, and methane emissions. Plant As decreased with drier irrigation management, but in the grain this effect was stronger for organic As than for inorganic As. Grain organic As, but not inorganic As, was strongly and positively correlated with cumulative methane emissions. Conversely, plant Cd increased under more aerobic irrigation management and grain Cd was negatively correlated with porewater Mn. A hazard index approach showed that in the tested soil with low levels of As and Cd (5.4 and 0.072 mg/kg, respectively), irrigation management could not simultaneously decrease grain As and Cd. Many soil properties, such as reducible As, available Cd, soil pH, available S, and soil organic matter should be considered when attempting to optimize irrigation management when the goal is decreasing the risk of As and Cd in rice grain.

NRAMPs and manganese: Magic keys to reduce cadmium toxicity and accumulation in plants

Cadmium (Cd), a toxic heavy metal, poses significant threats to both crop production and human health worldwide. Manganese (Mn), an essential micronutrient, plays a crucial role in plant growth and development. NRAMPs (Natural Resistance-Associated Macrophage Proteins) function as common transporters for both Cd and Mn. Deep understanding of the regulatory mechanisms governing NRAMP-mediated Cd and Mn transport is imperative for developing the crop varieties with high tolerance and low accumulation of Cd. This review reported the advance in studies on the fundamental properties and classification of NRAMPs in plants, and structural characteristics, expression patterns, and diverse functions of NRAMP genes across different plant species. We highlighted the pivotal role of NRAMPs in Cd/Mn uptake and transport in plants as a common transporter. Finally, we also comprehensively discussed over the strategies for reducing Cd uptake and accumulation in plants through using antagonism of Mn over Cd and altering the expression of NRAMP genes.

Physiological and transcriptomic response reveals new insight into manganese tolerance of Celosia argentea Linn

Celosia argentea is a manganese (Mn) hyperaccumulator with high ornamental value and strong stress resistance. It is important to understand the molecular mechanism of tolerance to heavy metals of hyperaccumulators to improve the efficiency of phytoremediation. In this study, the effects of different Mn concentrations (0, 0.8, 3, and 10 mM) on physiological characteristics and molecular changes were determined. Low concentrations of Mn increased the growth of C. argentea, while high concentrations of Mn suppressed its growth, A concentration up to 3 mM did not affect the growth of C. argentea, and the highest transfer factor (TF) was 6.16. Oxidative damage of different Mn level treatments in C. argentea was verified through relative water content, electrolyte leakage, MDA content, H2O2 content and superoxide contents. With an increase in Mn concentration, the contents of chlorophyll a, chlorophyll b, and carotenoids decreased. Our results indicated that low-concentration manganese treatment can reduce the reactive oxygen burst and MDA, soluble sugar and proline, making C. argentea have strong abiotic stress tolerance. The molecular mechanism of C. argentea after 10 mM Mn treatment was analysed through transcriptome analysis, and differentially expressed genes (DEGs) in these pathways were further verified by qRTPCR. Plantpathogen interactions, plant hormone signal transduction, the MAPK signalling pathway and the phenylpropanoid biosynthesis pathway were important in the response to Mn stress, and the heavy metal-associated isoprenylated plant protein, metal transporter Nramp, and zinc transporter play key roles in the strong ability of C. argentea to tolerate heavy metals. These results suggest that C. argentea exhibits strong manganese tolerance and provide new insight into the molecular mechanisms of plant responses to heavy metal stress.

Encapsulated lignin-based slow-release manganese fertilizer with reduced cadmium accumulation in rice (Oryza sativa L.)

As an essential trace element for plant growth and development, manganese plays a crucial role in the uptake of the heavy metal cadmium by rice (Oryza sativa L.). In this study, we developed a novel slow-release manganese fertilizer named Mn@LNS-EL. Initially, lignin nanoparticles were derived from sodium lignosulfonate, and a one-step emulsification strategy was employed to prepare a water-in-oil-in-water (W/O/W) Pickering double emulsions. These double emulsions served as the template for interfacial polymerization of lignin nanoparticles and epichlorohydrin, resulting in the formation of microcapsule wall materials. Subsequently, manganese fertilizer (MnSO4) was successfully encapsulated within the microcapsules. Hydroponic experiments were conducted to investigate the effects of Mn@LNS-EL on rice growth and the cadmium and manganese contents in the roots and shoots of rice under cadmium stress conditions. The results revealed that the treatment with Mn@LNS-EL markedly alleviated the inhibitory effects of cadmium on rice growth, leading to notably lower cadmium levels in the rice roots and shoots compared to the specimens treated without manganese fertilizer. Specifically, there was a reduction of 37.9 % in the root cadmium content and a 17.1 % decrease in the shoot cadmium content. In conclusion, this study presents an innovative approach for the high-value utilization of lignin through effective encapsulation and slow-release mechanisms of trace-element fertilizers while offering a promising strategy for efficiently remediating cadmium pollution in rice.

Cadmium reduced methane emissions by stimulating methane oxidation in paddy soils

Flooded rice paddy fields are a significant source of anthropogenic methane (CH4) emissions. Cadmium (Cd) is one of the most common and toxic contaminants in paddy soils. However, little is known about how the soil microbial communities associated with CH4 emissions respond to the increasing Cd-stress in paddies. In this study, we employed isotopically 13C-labelled CH4, high-throughput sequencing analysis, and gene quantification analysis to reveal the effect and mechanism of Cd on CH4 emissions in paddy soils. Results showed that 4.0 mg kg-1 Cd addition reduced CH4 emissions by 16-99% in the four tested paddy soils, and significantly promoted the transformation of 13CH4 to 13CO2. Quantitative polymerase chain reaction (qPCR) demonstrated that Cd addition increased the abundances of pmoA gene, the ratios of methanogens to methanotrophs (mcrA/pmoA) showed a positive correlation with CH4 emissions (R2 = 0.798, p < 0.01). Furthermore, the composition of the microbial community containing the pmoA gene was barely affected by Cd addition (p > 0.05). This observation was consistent with the findings of a pure incubation experiment where methanotrophs exhibited high tolerance to Cd. We argue that microbial feedback to Cd stress amplifies the contribution of methanotrophs to CH4 oxidation in rice fields through the complex interactions occurring among soil microbes. Our study highlights the overlooked association between Cd and CH4 dynamics, offering a better understanding of the role of rice paddies in global CH4 cycling.

Protective effects of polymer amendment on specific metabolites in soil and cotton leaves under cadmium contamination

Polymer materials have great potential for soil heavy metal contamination remediation, but the metabolic mechanism by which polymer amendments regulate the responses of soil-plant systems to cadmium (Cd) stress is still unclear. To clarify the metabolic mechanism by which a self-developed soluble polymer amendment (PA) remediates Cd contamination in cotton fields, the common and differential metabolites in soil and cotton leaves were analyzed during the critical period of cotton growth (flowering and bolling stage) in a field experiment. The results showed that Cd stress increased Cd concentration in the soil-cotton system, and reduced enzyme activity in soil and cotton leaves. Besides, Cd stress also reduced the abundance of α-linolenic acid in soil and the abundance of 2-Oxoarginine and S-Adenosylmethionine in cotton leaves. These ultimately led to reductions in weight, boll number, yield, and fiber elongation. However, the application of PA to the Cd-contaminated soil significantly reduced the soil exchangeable Cd (Ex-Cd) concentration by 41.43%, and increased the boll number, yield, and fiber strength by 14.17%, 21.04%, and 19.89%, respectively compared with the Cd treatment. The results of metabolomic analysis showed that PA application mainly affected the Nicotinate and nicotinamide metabolism pathway, Lysine degradation pathway, and Arginine and proline metabolism pathway in cotton leaves and soil. Besides, in these metabolic pathways, succinic acid semialdehyde of cotton leaves, saccharopine of soil, and S-Adenosylmethionine of soil and cotton had the most significant response to PA application. Therefore, the application of PA to Cd-contaminated soil can increase soil and cotton leaf enzyme activity and cotton yield (boll number and seed cotton yield) and quality (fiber strength), and maintain soil-plant material balance by regulating the distribution of Cd ions and key metabolites in the soil-cotton system. This study will deepen our understanding of the metabolic mechanism of PA remediating Cd-contaminated cotton fields, and provide a technical reference for the remediation of heavy metal contamination in drip-irrigated cotton fields in arid areas.

Effects of high manganese-cultivated seedlings on cadmium uptake by various rice (Oryza sativa L.) genotypes

Cadmium (Cd) contamination in paddy soil threatens rice growth and food safety, enriching manganese (Mn) in rice seedlings is expected to reduce Cd uptake by rice. The effects of 250 μM Mn-treated seedlings on reducing Cd uptake of four rice genotypes (WYJ21, ZJY1578, HHZ, and HLYSM) planted in 0.61 mg kg-1 Cd-contaminated soil, were studied through the hydroponic and pot experiments. The results showed that the ZJY1578 seedling had the highest Mn level (459 μg plant-1), followed by WYJ21 (309 μg plant-1), and less Mn accumulated in the other genotypes. The relative expression of OsNramp5 (natural resistance-associated macrophage protein) was reduced by 42.7 % in ZJY1578 but increased by 23.3 % in HLYSM. The expressions of OsIRT1 (iron-regulated transporter-like protein) were reduced by 24.0-56.0 % in the four genotypes, with the highest reduction in ZJY1578. Consequently, a greater reduction of Cd occurred in ZJY1578 than that in the other genotypes, i.e., the root and shoot Cd at the tillering were reduced by 27.8 % and 48.5 %, respectively. At the mature stage, total Cd amount and distribution in the shoot and brown rice were also greatly reduced in ZJY1578, but the inhibitory effects were weakened compared to the tillering stage. This study found various responses of Cd uptake and transporters to Mn-treated seedlings among rice genotypes, thus resulting in various Cd reductions. In the future, the microscopic transport processes of Cd within rice should be explored to deeply explain the genotypic variation.

Can simultaneous immobilization of arsenic and cadmium in paddy soils be achieved by liming?

Liming acidic paddy soils to near-neutral pH is the most cost-effective strategy to minimize cadmium (Cd) accumulation by rice. However, the liming-induced effect on arsenic (As) (im)mobilization remains controversial and is called upon for further investigation, particularly for the safe utilization of paddy soils co-contaminated with As and Cd. Here, we explored As and Cd dissolution along pH gradients in flooded paddy soils and extracted key factors accounting for their release discrepancy with liming. The minimum As and Cd dissolution occurred concurrently at pH 6.5-7.0 in an acidic paddy soil (LY). In contrast, As release was minimized at pH < 6 in the other two acidic soils (CZ and XX), while the minimum Cd release still appeared at pH 6.5-7.0. Such a discrepancy was determined largely by the relative availability of Fe under overwhelming competition from dissolved organic carbon (DOC). A mole ratio of porewater Fe/DOC at pH 6.5-7.0 is suggested as a key indicator of whether co-immobilization of As and Cd can occur in flooded paddy soils with liming. In general, a high mole ratio of porewater Fe/DOC (≥ 0.23 in LY) at pH 6.5-7.0 can endow co-immobilization of As and Cd, regardless of Fe supplement, whereas such a case is not in the other two soils with lower Fe/DOC mole ratios (0.01-0.03 in CZ and XX). Taking the example of LY, the introduction of ferrihydrite promoted the transformation of metastable As and Cd fractions to more stable ones in the soil during 35 days of flooded incubation, thus meeting a class I soil for safe rice production. This study demonstrates that the porewater Fe/DOC mole ratio can indicate a liming-induced effect on co-(im)mobilization of As and Cd in typical acidic paddy soils, providing new insights into the applicability of liming practice for the paddy soils.

Potential of granular complexes of lime and montmorillonite for stabilizing soil cadmium and the underlying mechanisms

Cadmium (Cd) contaminated soils were widely remediated by alkaline materials in powder, while the effects of granular materials are still unknown. This study was conducted to prepare granular materials based on hydrated lime and montmorillonite with ratios of 1:1, 1:2, and 1:3 (LM1, LM2, and LM3); their effects and mechanisms on stabilizing Cd in hydroponic, pot, and field conditions were further explored. The results showed that powdery materials caused intense pH elevations within 30-60 min and dissolved-Cd reductions within 8-100 min. However, granular materials significantly delayed these effects; the highest solution pH and lowest dissolved-Cd occurred after 250 min. The LM1 granules induced a much higher reduction of dissolved-Cd (99.8%) than that in the LM2 (53.6%) and LM3 granules (14.3%) due to the generation of more cadmium carbonate precipitates. Additionally, the soil pH gradually decreased after an intense elevation induced by powdery materials, but the LM1 granules maintained the soil pH at approximately 7.0, resulting in a lower level of CaCl₂-extractable Cd (0.03 mg kg^-1) than the LM1 powder (0.22 mg kg^-1) after 30 d of cultivation. Similar to lime powder, a small spatial variation (Std. of 3.45) of DGT (diffusive gradient in thin films) extractable Cd in soil profile was observed in the LM1 granules, revealing a homogeneous stabilization effect induced by the LM1 granules. Accordingly, the LM1 granules induced a higher reduction in brown rice Cd (50.9%) than that in the LM1 powders (35.1%). Thus, the granular material of hydrated lime and montmorillonite (1:1) h the potential to replace lime powder in the remediation of Cd-contaminated field.

Soil applied silicon and manganese combined with foliar application of 5-aminolevulinic acid mediate photosynthetic recovery in Cd-stressed Salvia miltiorrhiza by regulating Cd-transporter genes

Salvia miltiorrhiza is an important medicinal plant that experiences significant growth and biomass losses when cultivated on cadmium (Cd) contaminated soils. High Cd accumulation in plant tissues also increases the risk of metal entry into the food chain. In this study, we proposed that Cd accumulation in S. miltiorrhiza can be restricted through plant growth regulators and nutrient management. Therefore, S. miltiorrhiza seedlings were transplanted into mixed nutrient soil for two weeks, then treated with 30 mg kg^-1 CdCl₂, 200 mg kg^-1 Na₂SiO₃·9H₂O, and 100 mg kg^-1 MnSO₄, and simultaneously sprayed with 10 mg L^-1 ALA on the leaves one week later. This study showed that elevated Cd accumulation significantly reduced plant growth and biomass. This growth inhibition damaged photosynthetic machinery and impaired carbon assimilation. In contrast, 5-aminolevulinic acid (ALA) significantly promoted the biomass of S. miltiorrhiza, and the dry weight of plants treated with ALA combined with manganese (Mn)/silicon (Si) increased by 42% and 55% as compared with Cd+Mn and Cd+Si treatments. Exogenously applied ALA and Si/Mn significantly activated antioxidant enzymes and promoted the growth recovery of S. miltiorrhiza. Further, exogenous ALA also reduced the Cd concentration in S. miltiorrhiza, especially when combined with Si. Compared with the Cd+Si treatment, the Cd+Si+ALA treatment reduced the Cd concentration in roots and leaves by 59% and 60%, respectively. Gene expression analysis suggested that ALA and Si significantly up-regulated genes associated with Cd transport. Other genes related to heavy metal tolerance mechanisms are also regulated to cope with heavy metal stress. These results indicated that the combined action of ALA and Si/Mn could reduce Cd-toxicity by increasing chlorophyll content and changing oxidative stress and can also affect Cd accumulation by regulating gene expression.

Zn alleviated salt toxicity in Solanum lycopersicum L. seedlings by reducing Na+ transfer, improving gas exchange, defense system and Zn contents

Soil secondary salinization is a serious menace that has significant influence on the sustainability of agriculture and threatens food security around the world. Zinc (Zn) as an essential plant nutrient associated with many physio-biochemical processes in plants and improve resistance against various abiotic stresses. The role of Zn in acclimation of Solanum lycopersicum L. challenged with salt stress is miserly understood. A hydroponic study was performed with two tomato varieties (Riogrande and Sungold) exposed to the salinity stress (0 mM and 160 mM NaCl) under two Zn concentrations (15 μM and 30 μM ZnSO₄). The results revealed that salt stress exerted strongly negative impacts on root and shoot length, fresh and dry biomass, plant water relations, membrane stability, chlorophyll contents, Na⁺/K⁺ ratio along with inferior gas exchange attributes and activities of antioxidant enzymes. Moreover, Riogrande was found to be more resistant to salinity stress than Sungold. However, Zn supply significantly alleviated the hazardous effects of salinity by altering compatible solutes accumulation, photosynthetic activity, water relation, soluble sugar contents and providing antioxidant defense against salt stress. The salinity + Zn2 treatment more obviously enhanced RWC (19.0%), MSI (30.8%), SPAD value (17.8%), and activities of SOD (31.7%), POD (28.5%), APX (64.5%) and CAT (23.3%) in Riogrande than Sungold, compared with the corresponding salinity treatment alone. In addition, salinity + Zn2 treatment significantly (P > 0.05) ameliorated salinity stress due to the depreciation in Na⁺/K⁺ ratio by 63.3% and 40.8%, Na⁺ ion relocation from root to shoot by 10.4% and 6.4%, and thereby significantly reduced Na⁺ ion accumulation by 47.4% and 16.3% in the leaves of Riogrande and Sungold respectively, compared to the salinity treatment alone. Therefore, it was obvious that 30 μM Zn concentration was more effective to induce resistance against salinity stress than 15 μM Zn concentration. Conclusively, it can be reported that exogenous Zn application helps tomato plant to combat adverse saline conditions by modulating photosynthetic and antioxidant capacity along with reduced Na⁺ uptake at the root surface of tomato plant.

Effects of Cd uptake, translocation and redistribution in different hybrid rice varieties on grain Cd concentration

In order to identify the key transport process that determines the Cd concentration in brown rice, this study used 21 hybrid rice varieties as experimental materials and conducted field experiments in Qiyang (cadmium-contaminated site) and Yongding (low-cadmium site). Cd concentrations in 8 organs were measured, and bioconcentration factors and transfer factor were further calculated. The results showed that the Cd concentrations of the organs related to the xylem transport were as follows: root > node > stem > leaf sheath > leaf. In the phloem, the Cd concentrations were as follows: rachis > brown rice > rice husk. And the results of the correlation analysis found that Cd concentration between brown rice and root showed a significant positive correlation in Cd-contaminated site, but no significant correlation in low-cadmium site. Meanwhile, at both experimental sites, the Cd concentration of brown rice showed the most significant correlation with the phloem transfer factor from leaf and leaf sheath to brown rice. Principal Component Analysis (PCA) and stepwise regression analysis likewise found that Cd concentration in leaf and leaf sheath and their phloem transport of Cd to brown rice were significantly and positively correlated with Cd concentration in brown rice. The above results showed that the transport of leaf and leaf sheath to brown rice was a key process, and played a more important role in the accumulation of cadmium in brown rice than in root.

Sustainability assessment and carbon budget of chemical stabilization based multi-objective remediation of Cd contaminated paddy field

The feasibility of chemical stabilization-based strategy for extensive field application is under debate due to lacking a proper framework for its sustainability assessment during its life cycle. Herein, a comprehensive framework consisting of crop production, soil quality, and carbon footprint was constructed for assessing agricultural land remediation based on a two-year paddy field trial. Results show that between the two representative agents, biochar scenario substantially benefits for environmental, social, and agricultural sustainability, because of its more positive impacts on human health and ecosystem, public acceptance, soil reproductive, and rice yield. A notably higher sustainability score of 80.7 for biochar scenario than that of 47.0 for lime is found, in spite of the economical sustainability of lime. The net ecosystem carbon budget of the biochar scenario exhibits an unprecedentedly positive value of 17.8 t CO₂-eq ha^-1, which can finely contribute to a positive carbon budget during remediation. Our finding demonstrates that biochar strategy enables a multi-objective achievement of soil quality - crop production - carbon budget during agricultural land remediation. This study provides new insights into sustainability assessment for restoring agricultural land for safe crop production and synergizing with carbon neutral plan.

Liming and tillering application of manganese alleviates iron manganese plaque reduction and cadmium accumulation in rice (Oryza sativa L.)

The application time and soil pH are key to manganese (Mn) bioavailability, which may influence Mn effects on cadmium (Cd) accumulation in rice. Accordingly, this study investigated the effects of Mn application at different stages, alone or with basal liming, on Cd accumulation in rice through pot and field experiments. The results showed that basal Mn application maximally elevated soil dissolved Mn, and increasing Mn accumulation in rice by 140%-367% compared to the control. Additionally, basal or tillering applications had better effects on enhancing iron manganese plaque (IMP) and inhibiting CaCl₂-extractable Cd than later applications. Therefore, basal and tillering Mn reduced brown rice Cd by 24.6% and 18.9% compared to the control, respectively. Liming reduced CaCl₂-extractable Cd by 83.3% compared to the control but inhibited soil dissolved Mn (25.8%-76.6%) and IMP (28.9%-29.7%), resulting in only a 41.7% reduction in brown rice Cd. Liming combined with tillering Mn maximally reduced brown rice Cd by 67.4%, structural equation modeling revealed CaCl₂-extractable Cd and manganese plaque played the greatest positive and negative roles, respectively. Therefore, basal liming and tillering application of Mn is most effective at reducing rice Cd through inhibition of Cd bioavailability and alleviation of IMP reduction.

Remediation effect of mercapto-palygorskite combined with manganese sulfate on cadmium contaminated alkaline soil and cadmium accumulation in pak choi (Brassica chinensis L.)

Cadmium pollution in alkaline soil in some areas of northern China seriously threatens agricultural production and human health, but there are few materials and methods to remediate cadmium pollution in alkaline soil. Therefore, it is necessary to further study the economic and adaptive remediation and regulation techniques of cadmium pollution in alkaline soil. In the study, a pot experiment was conducted to study the effects of MP and MnSO₄ combined treatment on the immobilization effect of cadmium contaminated alkaline soils. The results showed that LM and HM treatments in different periods had little effect on the content of extractable Cd fraction in soil without MP treatment, but the EXC-Cd content in the soil with Mn(15) was lower than that in the soil with Mn(29). The EXC-Cd content under MP+ LM and MP + HM treatments reduced by 3%-7% and 7%-9%, respectively. The OX-Cd content increased by 13%-16% after MP + Mn treatment. The content of DTPA-Cd decreased by 17.9%-28.6% under MP + Mn treatment except for MP + HM(15). Under the treatment of MP, LM(29), HM, MP + LM and MP + HM, the content of Cd in shoots of pak choi were decreased by 27.2%, 13.1%, 19.8%-27.9%, 28.5%-54.2% and 34.2%-41.1%, respectively. Compared with CK, the TF_Cd values in HM(15), LM(29), HM(29), MP + LM(29) and MP + HM(29) treatments were reduced to 35.7%, 41.1%, 35.7%, 42.9% and 37.5%, respectively, while no statistical difference was observed in other treatments. There was no significant difference in BCF_Cd between MP(15) and LM(15), but the BCF_Cd was significantly decreased. For MP + MnSO₄ treatment group, the content of Mn oxides in soil was negatively correlated with the content of EXC-Cd (P < 0.05) and positively correlated with the content of OX-Cd (P < 0.05).

Evaluation of manganese application after soil stabilization to effectively reduce cadmium in rice

In order to produce safe rice from cadmium (Cd) contaminated soils, a special pot experiment in the field was proposed to facilitate the study of multiple remediation measures. In the field experiments, four treatments were selected for the first half of the year: rice without soil treatment (R); rice with zeolite stabilization (RZ); oilseed rape phytoremediation (OR); and inter-cropping Sedum alfredii and maize phytoremediation (IC). As the early rice with zeolite stabilization still contained elevated Cd, manganese (Mn) fertilizer was added in the late rice with a special pot experiment in the field. Results showed that, in the first crops, the grains of maize and oilseed rape contained Cd below the food standard limit, while Cd in rice grain exceeded the limit of 0.2 mg/kg. The RZ treatment did not reduce Cd in rice but decreased significantly Mn in rice straw. In the late rice, Mn fertilizer additionally reduced Cd in rice grain to 0.12 mg/kg in combination with the RZ treatment. Mn accumulation in rice straw was enhanced by Mn fertilizer. These results indicate that the pot experiment in the field provides a useful tool to further evaluate effective treatment combinations to reduce Cd in rice.

Effect of nano-silicon on the regulation of ascorbate-glutathione contents, antioxidant defense system and growth of copper stressed wheat (Triticum aestivum L.) seedlings

Copper (Cu²⁺) toxicity can inhibit plant growth and development. It has been shown that silicon (Si) can relieve Cu²⁺ stress. However, it is unclear how Si-nanoparticles (SiNPs) relieve Cu²⁺ stress in wheat seedlings. Therefore, the current study was conducted by setting up four treatments: CK, SiNP: (2.5 mM), Cu²⁺: (500 µM), and SiNP+Cu²⁺: (2.5 mM SiNP+500 µM Cu²⁺) to explore whether SiNPs can alleviate Cu²⁺ toxicity in wheat seedlings. The results showed that Cu²⁺ stress hampered root and shoot growth and accumulated high Cu²⁺ concentrations in roots (45.35 mg/kg) and shoots (25.70 mg/kg) of wheat as compared to control treatment. Moreover, Cu²⁺ treatment inhibited photosynthetic traits and chlorophyll contents as well as disturbed the antioxidant defense system by accumulating malondialdehyde (MDA) and hydrogen peroxidase (H₂O₂) contents. However, SiNPs treatment increased root length and shoot height by 15.1% and 22%, respectively, under Cu²⁺ toxicity. Moreover, SiNPs application decreased MDA and H₂O₂ contents by 31.25% and 19.25%, respectively. SiNPs increased non-enzymatic compounds such as ascorbic acid-glutathione (AsA-GSH) and enhanced superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbic peroxidase (APX) activities by 77.5%, 141.7%, 68%, and 80%, respectively. Furthermore, SiNPs decreased Cu²⁺ concentrations in shoots by 26.2%, as compared to Cu²⁺ treatment alone. The results concluded that SiNPs could alleviate Cu²⁺ stress in wheat seedlings. The present investigation may help to increase wheat production in Cu²⁺ contaminated soils.

New directions for agricultural wastes valorization as hydrogel biocomposite fertilizers

The tremendous amount of waste is an environmental and social problem worldwide. The agri-food sector is the largest producer of waste and requires the extensive use of fertilizers, which entails the need to look for innovative solutions in waste management. Properly recycled bio-waste can be reused as fertilizer. Polymer capsules with immobilized waste biomass can be applied as carriers for fertilizer nutrients. The amount of components exerts a certain influence on the effectiveness of copper ions binding. The most important physicochemical properties of biocomposites, such as swelling, SEM (Scanning Electron Microscopy) and FTIR (Fourier Transform Infrared Spectroscopy) were investigated. FTIR analyzes revealed that carboxyl and hydroxyl groups play a key role in Cu²⁺ ion binding. Morphology analysis showed that ion binding leads to homogenization of the composite surface, while coating the structure makes it more regular and cohesive. The sorption kinetics and the determination of the process's equilibrium parameters (Q_max = 29.4 ± 0.493 mg g^-1) play an important role. The study of Cu²⁺ ion release in different media showed that the chitosan layer slowed down the diffusion of cations by about 50% in NaNO₃ (1% m/m) solution. Preliminary studies of the applicability of the capsules in germination tests demonstrate that the biocomposites have no phytotoxic effects on the test plant. The chitosan coating slows the release of Cu²⁺ ions by about 20% compared to uncoated capsules. New fertilizer formulations containing chitosan-encapsulated hydrogel with biomass-immobilized micronutrients can be applied for precision agriculture to minimize the loss of fertilizer nutrients to the environment. These fertilizers could be used to cultivate houseplants and greenhouse crops.

Boron application mitigates Cd toxicity in leaves of rice by subcellular distribution, cell wall adsorption and antioxidant system

Cadmium (Cd) is a hazardous heavy metal and some of its negative effects include inhibition of rice growth, while also accumulates in the rice grains. Boron (B) has been implicated in mitigating Cd toxicity. Nevertheless, a few studies have been performed up to now to evaluate whether B could encourage Cd tolerance in rice by regulating Cd adsorption on cell walls (CW) in leaves of rice. The current experiment used different concentrations of B (0, 20, and 30 µM) along with 50 µM Cd to rice seedlings. The results indicate that single treatment of Cd significantly inhibited root and shoot growth and caused leaf chlorosis. However, B application at 20, and 30 µM reduced Cd concentrations in the roots by 66% and 77%, and in shoots by 72% and 83%, respectively, and increased plant development. Boron supply at 30 µM increased Cd in leaf CW fraction by 79% and decreased Cd by 64% in the organelle fraction. Moreover, B addition regulated the antioxidant system and decreased malonaldehyde contents (45%) in rice leaves. The present study demonstrates that B reduces Cd translocation and facilitates Cd adsorption on CW and regulates an efficient antioxidant system in rice leaves.