Arsenic contamination threatens rice (Oryza sativa) production, yet the synergistic use of iron plaque (IP) and root-associated biofilms as a rhizosphere barrier to limit arsenic uptake remains unexplored. To address this, we engineered an arsenic-resistant (AR) plant growth-promoting rhizobacterium (AR-PGPR), Bacillus subtilis p43-Taglo1, expressing the speciation-inert arsenic-binding protein TaGlo1. In a contaminated paddy, this strain increased grain yield by 10.7-11.6% and reduced grain arsenic by 28.2-37.4% compared to the wild-type. The engineered strain robustly colonized roots and enhanced the formation of a functional IP-biofilm composite, which sequestered more arsenic. This was driven by a 2.87-fold increase in Fe(II) oxidation and elevated production of extracellular polymeric substances (EPS) (1.4-fold) and siderophores (1.5-fold). Transcriptomic analysis revealed that inoculation upregulated bacterial genes for Fe(II) oxidation, siderophore, and EPS biosynthesis, while in rice roots, it activated phytohormone pathways and downregulated arsenite transporters (OsLsi1 and OsLsi2). We conclude that AR-PGPR can restore beneficial root-microbe interactions under arsenic stress. The IP-biofilm composite acts as an inducible barrier essential for the dual benefits of arsenic exclusion and growth promotion. Our study shows that AR rhizobacteria fortify the IP-biofilm composite to reduce arsenic uptake and promote rice growth, providing a route toward safer rice production in arsenic-affected regions.

In this study, the effects of arbuscular mycorrhizal fungi (Fm), silkworm excrement organic fertilizer (SE), silkworm excrement biochar (BC), and their combinations on the rhizosphere environment of rice and cadmium (Cd) absorption were investigated. The treatment combining BC and Fm was most effective, significantly increasing Cd accumulation in the rice root surface iron oxide gel film (iron plaque) while significantly reducing the Cd content in rice grains. In addition, the treatments combining SE with Fm and BC with Fm promoted Cd fixation in the root surface iron plaque and increased the diversity of rhizosphere microbial communities. The combined treatments mainly reduced the bioavailability of Cd by increasing the soil pH and promoting iron plaque formation. On the microbial level, the relative abundances of dominant bacteria of the genera Bacillus and Clostridium increased under the combined treatments. These microorganisms effectively reduced Cd migration and absorption through pathways such as complexation, precipitation, and transformation. Analysis based on the structural equation model (SEM) confirmed that soil organic matter, pH, and root iron plaque play a core regulatory role in Cd accumulation in rice. The microbial community (especially the bacterial community) promoted the development of root iron plaque and enhanced the stabilization of Cd, thereby limiting its transfer to the grains. In conclusion, the combined application of silkworm excrement biochar and arbuscular mycorrhizal fungi not only improved soil fertility but also effectively reduced the Cd content in the rice grains, showing significant potential for in the remediation of Cd-polluted farmland soil.

Selenium (Se) biofortification in rice addresses dietary Se deficiencies. While Se fertilization is key, the efficiency and molecular mechanisms differ among Se forms (selenate, nano-Se (SeNPs)) and application methods (soil vs. foliar). This study aimed to compare the effects of selenate and biosynthesized SeNPs, applied via soil and foliar methods, on rice growth, Se accumulation, speciation, and the associated transcriptional responses. Rice plants were treated with selenate or biosynthesized SeNPs via soil application or foliar spraying. Biomass, yield, grain Se concentration and speciation were analyzed. Transcriptomic profiling of roots (soil-applied Se) and leaves (foliar-applied Se) was performed, with validation by qPCR and WGCNA. Both application methods enhanced biomass and yield. Foliar spraying was more efficient for grain Se enrichment, increasing Se concentration by 28.13-fold (selenate) and 89.87-fold (SeNPs), versus 7.83–9.87-fold for soil application. Selenomethionine was the predominant Se species in grains. Transcriptomics revealed selenate upregulated sulfate transporter and xylem-related genes in roots, whereas SeNPs enhanced aquaporin and sulfur assimilation gene expression. Foliar SeNPs triggered stomatal and aquaporin-related gene expression. Both forms influenced sulfur/nitrogen metabolism, with SeNPs additionally modulating organic acid and amino acid pathways. WGCNA identified co-expression modules correlated with grain Se content and selenomethionine proportion, enriched in transcription factors (MYB, WRKY, bHLH) and ABC transporters. Foliar application, particularly of SeNPs, is highly effective for Se biofortification in rice, associated with distinct molecular uptake and assimilation pathways. These findings provide insights for optimizing Se fertilization strategies to enhance dietary Se supply.

Lepidopteran pest outbreaks (Chilo suppressalis and Cnaphalocrocis medinalis) in paddy ecosystems and cadmium (Cd) accumulation in brown rice caused by high Cd background values threaten safe rice production. However, research on comprehensive mitigation strategies for these dual challenges is insufficient. In this study, a two-year field experiment was conducted in subtropical areas with high cadmium background values (0.51-0.58 mg kg(-)(1)), and three treatments were used: continuous flooding (FL, 3-5 cm water layer), conventional irrigation (CI, keeping the soil surface moist), and alternating wet and dry (AWD, repeatedly irrigating the soil, allowing the water layer to naturally dry until obvious cracks appeared). The CI and AWD treatments were used as controls. The results revealed that (1) the FL treatment did not reduce the yield of rice (5475-8001 kg ha(-)(1) across two years, with no significant difference from CI) but did significantly decrease the white panicle and leaf curling rates (86.3-97.6 %) induced by C. suppressalis and C. medinalis (p < 0.05). Mechanistically, the FL treatment suppressed 83.6-98.5 % of the egg, larval, and pupal populations of both pests via prolonged soil submersion and increased the stem silicon content (53.0-65.6 %) to increase mechanical resistance. (2) The FL treatment significantly reduced the cadmium content in brown rice to 0.03-0.06 mg kg(-)(1) (p < 0.05), a decrease of 80.6-94.6 %. The mechanisms behind these results include the following: (i) enrichment of Fe/Mn/S-reducing bacteria (e.g., Geobacter, Luteitalea, and Desulfatiglans) promoted the reduction of Fe/Mn/S-related substances and the transformation of cadmium forms from the exchangeable state (EX-Cd decreased 2.64-23.65 %) to the iron-manganese oxide-bound state (OX-Cd increased 5.51-31.67 %) and reduced the availability of cadmium in soil; (ii) the Fe/Mn contents of the root surface iron manganese plaque increased by 16.4-116.7 % compared with that in the AWD treatment, enhancing the barrier effect and reducing the migration coefficient of cadmium from iron manganese plaque to the roots (TF-Cd ([Cd]root/[Cd]plaque) decreased by 26.1-90.3 %. In summary, this study provides a valuable reference for the application of continuous flooding in the field to ensure the quality and safety of rice.

Introduction:Soil co-contamination with cadmium (Cd), lead (Pb), and antimony (Sb) poses significant environmental and health risks, highlighting the need for effective remediation strategies. Sulfate-reducing bacteria (SRB) are promising for bioremediation, but require optimization to improve effectiveness. Methods:Here, we developed SRB@nZVI@BC, a novel composite integrating SRB, nano zero-valent iron-modified biochar (nZVI@BC), and sodium alginate (SA). Its optimal preparation conditions were identified as 2% SA, 2% CaCl2, 30% SRB solution, and 0.1% nZVI@BC based on mass transfer performance, mechanical strength, and sulfate reduction rate. Results:The application of SRB@nZVI@BC increased the proportion of stable forms of Cd, Pb, and Sb in soil and achieved removal efficiencies of 60.22%-63.93% for Cd, 57.13%-59.45% for Pb, and 56.02%-70.37% for Sb in leachate. Compared to alone SRB treatment, SRB@nZVI@BC significantly enhanced SRB activity, promoting sulfur cycling and the generation of S2-, thereby facilitated heavy metal precipitation as insoluble sulfides. SRB@nZVI@BC could improve the adsorption capacity of soil for heavy metals by activating the oxygen-containing functional groups such as C-O-C. Moreover, SRB@nZVI@BC reshaped the soil microbial community by enriching sulfate-reducing genera such as Desulfosporosinus and Desulfitobacterium, driving heavy metal transformation and stabilization. The composite further enhanced soil nutrient availability (N, P, K) and increased enzyme activities, contributing to soil fertility recovery. Discussion:Overall, SRB@nZVI@BC provides an eco-friendly solution for stabilizing multi-metal-contaminated soils and promoting the restoration of barren lands through synergistic adsorption and biomineralization.

Cadmium (Cd) contamination in paddy soils poses a persistent threat to rice production and food safety. Three amendment treatments (nFe, BC, and nFe+BC) were applied in a Cd-contaminated paddy soil system to evaluate their effects on rhizosphere processes, thereby influencing Cd uptake and tissue partitioning in rice. A greenhouse pot experiment was conducted with four treatments (CK, nFe, BC, and nFe+BC). Rice growth and Cd concentrations in plant tissues were measured, along with Fe, Mn, and Cd contents in root iron plaque. Soil properties were also analyzed, including pH, DTPA-extractable Cd, Cd fractionation (F1–F4), and enzyme activities. Bacterial communities were characterized using 16S rRNA gene sequencing. Network analysis, correlation analysis, Mantel tests, and structural equation modeling (SEM) were integrated to link environmental variables, microbial characteristics, and Cd dynamics, and to explore potential regulatory mechanisms. Relative to CK, the nFe+BC treatment showed the strongest mitigation effect, significantly reducing grain Cd concentrations and DTPA-extractable Cd (p < 0.05). Cadmium shifted from labile to more stable fractions, indicating reduced bioavailability. These changes were accompanied by enhanced root iron plaque formation and rhizosphere microbial community reassembly, as reflected by increased network modularity. Structural equation modeling (SEM) further revealed that iron plaque Fe (IFe) was positively associated with microbial diversity but negatively associated with DTPA-Cd (p < 0.05), whereas DTPA-Cd showed the strongest positive association with grain Cd. Together, these results suggest an indirect linkage among plaque Fe, microbial diversity, and bioavailable Cd. The co-application of nFe and BC synergistically improved the rhizosphere environment by enhancing root iron plaque formation and increasing microbial diversity and soil enzyme activities, thereby reducing Cd bioavailability and limiting Cd accumulation in rice grains. These findings provide evidence supporting the combined use of iron-based nanomaterials and bacterial cellulose as a practical strategy for improving rice safety in Cd-contaminated paddy fields.

Bioremediation represents a sustainable, environmentally friendly, and economical approach to mitigating heavy metal contamination in soils. This study investigated the synergistic effects and mechanisms of Trichoderma harzianum DAA8 and Trichoderma asperellum LDA4 strains inoculation in king grass (KG) and Sedum alfredii (S. alfredii) for phytoremediation of Cd-Cr co-contaminated farmland soils. The inoculation of DAA8+LDA4 effectively enhanced plant biomass by 15.37-23.28 % in king KG and 10.91-23.75 % in S. alfredii, while increasing Cd/Cr extraction by 25.54-37.20/14.19-17.30 % in KG and 15.42-22.45/8.86-9.92 % in S. alfredii under low-high pollution level compared to uninoculated plants. The maximum removal efficiency was 32.56 % for Cd in S. alfredii and 22.56 % for Cr in KG inoculated with DAA8+LDA4. Root secretions of jasmonic acid, palmitic acid, oleic acid, and isobavachalcone were closely correlated with Cd-Cr phytoextraction under low and high pollution levels. DAA8+LDA4 colonization induced favorable rhizosphere conditions by reducing soil pH (1.57-2.12 and 2.17-2.25 units), increasing soil organic matter (2.92-4.64 and 1.03-2.48 %), enhancing electrical conductivity (17.26-22.91 and 8.20-16.09 %), and improving cation exchange capacity (22.91-23.12 and 20.72-21.71 %) under low-high pollution levels in inoculated KG and S. alfredii respectively, as compared uninoculated KG and S. alfredii. The inoculation also improved soil enzyme activities and significantly increased the relative abundance of rhizosphere fungal (KG; Ascomycota; 3-6 %, and S. alfredii; 3-7 %) and bacterial (KG; Actinobacteriota; 2-7 %, and S. alfredii; 7-11 %) communities as compared to unlocated KG and S. alfredii. Nitrogen fixation and nitrification were more prominent in the KG rhizosphere with DAA8+LDA4 inoculation compared to S. alfredii under both pollution levels. The findings demonstrate that phytoremediation efficiency of KG and S. alfredii was improved by T. harzianum DAA8 and T. asperellum LDA4 through regulation of plant growth, root exudation, and microbial functioning in Cd/Cr-polluted soils. The findings of the present work highlight the potential of Trichoderma inoculation as a sustainable, effective strategy to promote phytoremediation, providing an effective solution to the remediation of HM-polluted lands and reduction of the environmental cost of cadmium and chromium pollution.

Cadmium (Cd) contamination in rice poses severe global health risks. Nanotechnology provides an efficient method for addressing a wide range of environmental issues. The potential applications and underlying mechanisms of biosynthesized selenium nanoparticles (BioSeNPs) in mitigating Cd accumulation in rice grains and reducing health risks from rice consumption remain largely unexplored. In this study, Bacillus megaterium LZCY-1, isolated from selenium-rich soil, was used to synthesize novel BioSeNPs, which was foliar-sprayed onto rice in Cd-contaminated soil. It was found that BioSeNPs treatments significantly increased rice biomass while reducing grain Cd concentration. Transcriptomic analysis revealed that differentially expressed genes in rice leaves were enriched in pathways such as glutathione metabolism and flavonoid biosynthesis. Furthermore, NRAMP1 was downregulated while HIPP16, ABCB1, ABCC1, and transcription factor WRKY were upregulated. These findings indicate that BioSeNPs enhance rice resistance to Cd stress by synergistically regulating cell wall biosynthesis and Cd transporters, reducing grain Cd accumulation. In vitro experiments confirmed BioSeNPs decreased Cd bioaccessibility and intake risk, while increasing mineral nutrients (Zn, Fe) and protein content but reducing phytic acid. Collectively, these compositional changes suppress Cd bioaccessibility during digestion. This work provides a promising nano-enabled strategy for producing safe, nutritious rice in contaminated soils.

Mesona chinensis Benth, a member of the Lamiaceae family, is an important dual-purpose economic crop in China, serving as a key ingredient in the traditional delicacy "Shaoxiancao" and the herbal tea "Wong Lo Kat.". This study explored the differential expression of key bioactive compounds in two Mesona chinensis Benth populations using broad-target metabolomics. The Taiwan (TW) population exhibited higher levels of polysaccharide components, including glucose, xylose, and galacturonic acid. In contrast, the Fujian (FJ) population showed elevated abundances of flavonoids (quercetin, kaempferol, and astragalin) and phenolic acids (caffeic acid and melitric acid A). The volatile metabolites exhibited distinct differed characteristics between the two populations, with the FJ population showing a higher concentration of monoterpenes, while alkanes predominated in the TW population. Integrative metabolomic and transcriptomic analyses revealed that the TW population had higher levels of polysaccharide precursors, such as sucrose and UDP-glucose, and increased expression of SUS, UXS1, and GALE genes. Conversely, the FJ population had higher levels of phenylalanine and (-)-Jasmonoyl-L-isoleucine, potentially linked to their response to intense light. Additionally, transcription factors bHLH (Unigene9935), M-type MADS (Unigene18343), AP2 (Unigene22135) and NF-YA (Unigene13012) were likely influencing terpenes, polysaccharide, flavonoid, and phenolic acid metabolism in Mesona chinensis Benth. This study integrates metabolomic and transcriptomic analyses to explore differences in bioactive compound accumulation and gene expression between two Mesona chinensis Benth populations, offering insights for raw material selection and implications for trait improvement and genetic research.

IntroductionSugarcane (Saccharum spp.) is an economically important crop cultivated primarily for sugar and bioethanol production. In southern China, sugarcane grown in acidic soils often exhibits severe leaf chlorosis owing to excessive soil manganese (Mn) levels. However, the mechanisms by which Mn toxicity disrupts soil nitrogen (N) cycling, particularly the roles of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in regulating nitrification and N availability in sugarcane, remain unexplored.MethodsTo address this gap, we conducted laboratory soil incubation experiments and greenhouse pot trials using four treatments consisting of combinations of two N levels (N1:0.14 g·kg-1; N2:0.28 g·kg-1) and two Mn levels (−Mn: 0 mg·kg-1; +Mn: 328 mg·kg-1, simulated using anhydrous Mn sulfate), along with a blank control (CK). Key measurements included rhizosphere soil physicochemical properties, AOB/AOA community structure, nitrification potential, and sugarcane N uptake efficiency.ResultsResults showed that Mn toxicity significantly reduced soil pH and nitrification potential by 75.9–78.0% compared to non-Mn treatments, and AOB amoA gene abundance by 44.9–46.5%, while altering AOB/AOA community composition. Redundancy analysis (RDA) identified soil organic carbon, total nitrogen, and ammonium nitrogen as the primary drivers of AOB community shifts, whereas exchangeable Mn, ammonium nitrogen, and pH dominated AOA community changes. Correlation analysis confirmed that nitrification potential and AOB amoA abundance were strongly positively linked to sugarcane N accumulation and uptake efficiency, which decreased by 47.3–53.4% under Mn toxicity due to reduced nitrate availability.DiscussionThese findings indicate that Mn toxicity impairs sugarcane N utilization by disrupting ammonia-oxidizing microbial communities and suppressing nitrification, thereby providing insights for optimizing N management strategies in Mn-contaminated acidic soils.

Selenium (Se) is an essential trace element for human, but its low availability in soils results in its inadequacy in edible crops, thereby limiting its human intake. However, the role of the plant growth-promoting bacteria in soil Se availability and the pathways involved in biofortification in edible plants remain poorly understood. In this study, a Se-tolerant, plant growth-promoting bacterium, Bacillus amyloliquefaciens strain G02, which activates Se was isolated from the soils in Se-rich fields in Guangxi, China. We employed soil microcosm and potted experiments, along with metabolomics and 16S rRNA sequencing, to investigate how strain G02 incubation promotes elemental Se (0) solubilization, soil Se activation, and Se enrichment in lettuce. The strain G02 exhibited high phosphate solubilization (87.36 mg/L), IAA production (8.35 mg/L), as well as siderophore and ACC deaminase activities. Strain G02 is capable of dissolved Se(0) and Se minerals, increased pH, and secreted metabolites enhancing Se solubility. Soil microcosm experiments showed that the incubation of strain G02 increased available Se forms [soluble selenium (SOL-Se) and exchangeable selenium (EXC-Se)] in soil. Moreover, potted experiments revealed that the incubation of strain G02 increased biomass, Se concentration in lettuce, soil enzyme activities, beneficial microbial abundance and the native bacterial taxa. The strain G02 enhances soil Se availability through metabolites secretion, Se solubilization, and rhizosphere microbial regulation, improving ability of lettuce to absorb and transport Se. This study provides novel insights into the microbially mediated Se biofortification.

IntroductionSugarcane (Saccharum spp.) is a crucial crop for sugar and bioethanol production. However, sugarcane grown in the acidic soils of southern China often suffers from severe leaf chlorosis due to excessive soil manganese (Mn). This study investigates the effects of Mn toxicity on the physicochemical properties and microbial communities in sugarcane rhizosphere soil, as well as its impact on sugarcane growth and nitrogen uptake and utilization.MethodsSoil samples were collected from sugarcane fields with varying levels of Mn toxicity. Physicochemical properties of the rhizosphere soil were analyzed, including soil pH, available nitrogen, and microbial community composition. The impact of Mn toxicity on sugarcane growth was assessed through measurements of plant biomass, leaf chlorosis, and nitrogen uptake efficiency.ResultsMn toxicity significantly lowered soil pH and altered the soil microbial community structure. Bacterial genera such as Nocardioides and Sinomonas, which are involved in ureolysis, cellulolysis, and Mn oxidation, were promoted. In contrast, genera like Nitrospirota, associated with nitrogen fixation, were inhibited. This disruption hindered the conversion of soil ammonium nitrogen to nitrate nitrogen, reducing soil available nitrogen. Consequently, sugarcane growth and development were suppressed, and nitrogen uptake was limited.DiscussionThe findings highlight the detrimental effects of Mn toxicity on sugarcane cultivation in high-Mn areas. The altered microbial community composition and reduced soil nitrogen availability directly impact sugarcane growth. These results underscore the importance of applying appropriate fertilizers to mitigate Mn toxicity and improve soil fertility in such regions. Future research should focus on developing strategies to enhance soil nitrogen cycling and promote beneficial microbial communities to support sustainable sugarcane production.

Selenium (Se) is an essential micronutrient for humans, and crop Se biofortification presents a global health strategy to ensure safe dietary Se intake. However, low Se bioavailability in paddy soils limits Se uptake by rice (Oryza sativa L.), hindering agronomic Se biofortification. Although microorganisms play a pivotal role in mediating Se transformation within soil biogeochemical cycles, the underlying mechanisms remain to be fully elucidated. In this study, a Se-tolerant bacterium, Bacillus sp. S01, was isolated from high-Se soil and demonstrated the ability to convert Se(0) into bioavailable Se species. Integrated metabolomic and genomic analyses putative Se(0)-solubilizing genes in strain S01, including sulfur assimilation-related genes (gene1757, gene2869, and gene1971). Heterologous expression confirmed that gene1757, gene2869, and gene1971 enhanced Se(0) dissolution in Escherichia coli. Soil microcosm and pot experiments revealed that inoculation with strain S01 increased soluble and exchangeable Se fractions while reducing residual Se content. Additionally, it significantly improved soil pH, enzyme activities (sucrase, acid phosphatase, catalase, urease), and reshaped the rhizosphere microbial community, with Bacillus, Fonticella, and Lutispora identified as key taxa driving Se activation and bioavailability. These changes collectively enhanced rice biomass, yield, and enhanced grain Se content by 91 %. In summary, strain S01 likely transform Se(0) into bioavailable forms via sulfur metabolism pathways while improving Se bioavailability through modulation of soil properties and rhizosphere microbiota. These findings advance our understanding of microbial Se cycling and highlight the potential of Se-solubilizing bacteria in sustainable Se biofortification.

In regions rich in selenium (Se), the coexistence of Se and cadmium (Cd) in paddy soil presents risks to the safety of rice (Oryza sativa L.) products. In this study, the Cd-tolerant Se-solubilizing bacterial strain Bacillus cereus LB2 was shown to solubilize mineral Se and adsorb Cd, potentially mediated by its extracellular metabolites derived from tryptophan and purine metabolic pathways. Pot experiments revealed that the inoculation of strain LB2 promoted rice growth in Se-Cd-rich soil. Compared with the control, inoculation with strain LB2 increased the grain Se content by 20-23 %, whereas the Cd content decreased by 18.33-36.6 %. The reassembly of the rhizosphere microbiome is an important mechanism for promoting Se enrichment and reducing Cd in rice. Stronger iron (Fe) respiration and sulfate respiration in the rhizosphere bacterial community promoted the transformation of oxides, increased the availability of Se by 13-36 %, and decreased the availability of Cd by 3-17.69 %. In addition, the abundance of purine metabolites was strongly correlated with bacterial abundance, which may be the key driving force through which strain LB2 can recruit functional microorganisms. This study provides a new perspective for the safe use of Se-Cd-rich soil.

Cadmium (Cd) pollution in water and soil seriously threatens human health. Biochar and nanomaterials have high potential for solving the cadmium pollution problem due to their abundant pores and high specific surface area. Here, the preparation of the composite material SiO2NPs@BC (SBC) using SiO2 NPs (SN) and silkworm excrement biochar (BC) is described, along with its application in the remediation of cadmium-contaminated water and soil. Characterization experiments (SEM EDS, BET, FTIR, XRD, and XPS) demonstrated that SiO2NPs@BC has a high specific surface area (46.5767m2/g), a well-developed pore structure (0.608375cm3/g), and abundant surface functional groups (Si–C, Si–O, Si–O–Si), providing active sites for the adsorption of Cd. Batch adsorption experiments in water showed that the adsorption capacity of SBC is higher than that of biochar (BC) and SN, with a maximum Langmuir adsorption capacity of 141.99 mg/g. After five adsorption cycles, the removal rate of SBC was 73.04

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

Rice (Oryza sativa L.) consumption represents a major route of human exposure to cadmium (Cd) and arsenic (As), especially in Asia. This study investigated the effects of adding MnSO4 (0, 200, 400, and 800 mg kg-1-1) on the formation of soil Fe/Mn oxides and Cd and As uptake in rice. The application of MnSO4 reduced soil pH, increased Eh, increased the contents of Fe/Mn oxides in the soil, and decreased the total Fe and Mn2+ contents in the porewater. It also led to lower contents of available Cd and As, higher levels of Cd and As bound to Fe/Mn oxides, and higher abundances of Thiobacillus and Syntrophobacter. Furthermore, Mn application increased the Fe and Mn contents in the root Fe/Mn plaque and decreased the grain Cd and As contents. Therefore, Mn appli-cation may modify the microbial community and porewater composition in soil, resulting in higher levels of Fe/ Mn oxides in soil and Fe/Mn plaque at the root surface and in a lower accumulation of Cd and As in rice grains. Thus, Mn application can be a promising strategy for Cd and As stabilization in soils.

Rice (Oryza sativa L.) consumption represents a major route for the exposure to cadmium (Cd) and arsenic (As). Compared with un-amendment soil, silkworm excrement (SE) amendment at a rate of 0.20 % (m/m) reduced the rice grains Cd and As concentrations by 15.99 % and 8.70 %, respectively, with the following mechanisms: 1) increasing the soil pH, electrical conductivity, and organic matter content (for Cd); 2) regarding the total soil bacteria (16S rRNA), SE-0.2 increased the abundances of Chloroflexi and decreased the abundances of Firmicutes, Bacillus, and Clostridium_sensu_stricto_1. Regarding the microorganisms involved in As methylation (arsM) in soil, SE-0.2 increased the abundances of Actinobacteria_d__bacteria, Firmicutes, Chloroflexi, and Rubriviva (for Cd and As); 3) promoting the formation of the iron plaque (for Cd and As). Collectively, SE can remediate Cd- and As-polluted soil and prevent the migration of Cd and As, thus ultimately resulting in decreased Cd and As in rice grains. This provides a new way to improve the utilization rate of agricultural waste resources and ensure the safe production of food.

Cadmium (Cd) is one of the heavy metals that contaminate rice cultivation, and reducing Cd contamination in rice through agronomic measures is a hot research topic. In this study, foliar sprays of gibberellins (GA) and brassinolide (BR) were applied to rice under Cd stress in hydroponic and pot experiments. After foliar spraying of GR and BR, the biomass of rice plants grown in either hydroponics or soil culture was significantly higher or even exceeded that in the absence of Cd stress. In addition, photosynthetic parameters (maximum fluorescence values), root length and root surface area, and CAT, SOD and POD activities were significantly improved. The MDA content decreased in the shoots, suggesting that the application of GR and BA may have enhanced photosynthesis and antioxidant function to alleviate Cd stress. Furthermore, the BR and GA treatments decreased the Cd content of rice roots, shoots and grains as well as the Cd transfer coefficient. Cd chemical morphology analysis of rice roots and shoots showed that the proportion of soluble Cd (Ethanol-Cd and Water-Cd) decreased, whereas the proportion of NaCl-Cd increased. Analysis of the subcellular distribution of Cd in rice roots and above ground showed that the proportion of Cd in the cell wall increased after foliar spraying of GA and BR. The results indicate that after foliar application of GA and BR, more of the Cd in rice was transformed into immobile forms and was fixed in the cell wall, thus reducing the amount in the seeds. In summary, foliar sprays of GA and BR can reduce the toxic effects of Cd on rice plants and reduce the Cd content in rice grains, with GA being more effective.