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The co-contamination of arsenic (As) and cadmium (Cd) in rice fields presents a global imperative for resolution. However, understanding the complex microbially driven geochemical processes and network connectivity crucial for As and Cd bioavailability under the frequent redox transitions in rice fields remains limited. Here, we conducted a series of microcosm experiments, using flooding and drainage, alongside fertilization treatments to emulate different redox environment in paddy soils. Soil As significantly reduced in drained conditions following applications of biochar or calcium-magnesium-phosphate (CMP) fertilizers by 26.3 % and 31.2 %, respectively, with concurrent decreases in Cd levels. Utilizing geochemical models, we identified the primary redox cycles dynamically altering during flooding (Fe and S cycles) and drainage (Fe, Mn, and N cycles). PLS-SEM elucidated 76 % and 61 % of the variation in Cd and As through Mn and N cycles. Functional genes implicated in multi-element cycles were analyzed, revealing a significantly higher abundance of assimilatory N reduction genes (nasA, nirA/B, narB) in drained soil, whereas an increase in ammonia-oxidizing genes (amoA/B) and a decrease in nitrate reduction to ammonium genes were observed after CMP fertilizer application. Biochar application led to significant enrichment of the substrate-binding protein of the Mn transport gene (mntC). Moreover, Fe transport genes were enriched after biochar or CMP application compared to drained soils. Among 40 high-quality metagenome-assembled genomes (MAGs), microbial predictors associated with low Cd and As contents across different treatments were examined. Bradyrhizobacea harbored abundant Mn and Fe III transport genes, while Nitrososphaeraceae carried nitrification-related genes. Two MAGs affiliated with Caulobacteraceae, carrying diverse Fe transport genes, were enriched in biochar-applied soils. Therefore, applying CMP fertilizer or biochar in aerobic rice fields can synergistically reduce the bioavailability of Cd and As by specifically enhancing the circulation of essential elements., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Arsenic (As) and cadmium (Cd) accumulation in rice grains is a global food safety issue, and various methods and materials have been used to remove or reduce As and Cd in agricultural soils and rice grains. Despite the availability of synthesized materials capable of simultaneous As and Cd reduction from soil and rice grains, the contributions, efficiency, and main ingredients of the materials for As and Cd immobilization remain unclear. The present study first summarized the biogeochemistry of As and Cd in paddy soils and their transfer in the soil-food-human continuum. We also reviewed a series of reported inorganic and organic materials for simultaneous immobilization of As and Cd in paddy soils, and their reduction efficiency of As and Cd bioavailability were listed and compared. Based on the abovementioned materials, the study conducted a meta-analysis of 38 articles with 2565 observations to quantify the impacts of materials on simultaneous As and Cd reduction from soil and rice grains. Meta-analysis results showed that combining organic and inorganic amendments corresponded to effect sizes of -62.3% and -67.8% on As and Cd accumulation in rice grains, while the effect sizes on As and Cd reduction in paddy soils were -44.2% and -46.2%, respectively. Application of Fe based materials significantly (P < 0.05) reduced As (-54.2%) and Cd (-74.9%), accounting for the highest immobilization efficiency of As and Cd in rice grain among all the reviewed materials, outweighing S, Mn, P, Si, and Ca based materials. Moreover, precipitation, surface complexation, ion exchange, and electrostatic attraction mechanisms were involved in the co-immobilization tactics. The present study underlines the application of combined organic and inorganic amendments in simultaneous As and Cd immobilization. It also highlighted that employing Fe-incorporated biochar material may be a potential strategy for co-mitigating As and Cd pollution in paddy soils and accumulation in rice grains., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Trivalent arsenicals such as arsenite (As III ) and methylarsenite (MAs III ) are thought to be ubiquitous in flooded paddy soils and have higher toxicity than pentavalent forms. Fungi are widely prevalent in the rice rhizosphere, and the latter is considered a hotspot for As uptake. However, few studies have focused on alleviating As toxicity in paddy soils using fungi. In this study, we investigated the mechanism by which the protein TaGlo1, derived from the As-resistant fungal strain Trichoderma asperellum SM-12F1, mitigates As III and MAs III toxicity in paddy soils. Taglo1 gene expression in Escherichia coli BL21 conferred strong resistance to As III and MAs III , while purified TaGlo1 showed a high affinity for As III and MAs III . Three cysteine residues (Cys13, Cys18, and Cys71) play crucial roles in binding with As III , while only two (Cys13 and Cys18) play crucial roles for MAs III binding. TaGlo1 had a stronger binding strength for MAs III than As III . Importantly, up to 90.2% of the homologous TaGlo1 proteins originate from fungi by GenBank searching. In the rhizospheres of 14 Chinese paddy soils, Taglo1 was widely distributed and its gene abundance increased with porewater As. This study highlights the potential of fungi to mitigate As toxicity and availability in the soil-rice continuum and suggests future microbial strategies for bioremediation.