Flooding of paddy fields during the rice growing season enhances arsenic (As) mobilization and greenhouse gas (e.g., methane) emissions. In this study, an adsorbent for dissolved organic matter (DOM), namely, activated carbon (AC), was applied to an arsenic-contaminated paddy soil. The capacity for simultaneously alleviating soil carbon emissions and As accumulation in rice grains was explored. Soil microcosm incubations and 2-year pot experimental results indicated that AC amendment significantly decreased porewater DOM, Fe(III) reduction/Fe²⁺ release, and As release. More importantly, soil carbon dioxide and methane emissions were mitigated in anoxic microcosm incubations. Porewater DOM of pot experiments mainly consisted of humic-like fluorophores with a molecular structure of lignins and tannins, which could mediate microbial reduction of Fe(III) (oxyhydr)oxides. Soil microcosm incubation experiments cospiking with a carbon source and AC further consolidated that DOM electron shuttling and microbial carbon source functions were crucial for soil Fe(III) reduction, thus driving paddy soil As release and carbon emission. Additionally, the application of AC alleviated rice grain dimethylarsenate accumulation over 2 years. Our results highlight the importance of microbial extracellular electron transfer in driving paddy soil anaerobic respiration and decreasing porewater DOM in simultaneously remediating As contamination and mitigating methane emission in paddy fields.

中文翻译：

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活性炭的应用通过减少孔隙水溶解有机物来同时减轻稻田土壤砷的动员和碳排放

水稻生长季节稻田的洪水会增加砷 (As) 的迁移和温室气体（例如甲烷）的排放。在这项研究中，将溶解有机物（DOM）的吸附剂，即活性炭（AC）应用于受砷污染的水稻土。探索同时缓解土壤碳排放和稻米砷积累的能力。土壤微观世界培养和2年盆栽实验结果表明，AC改良剂显着降低了孔隙水DOM、Fe(III)还原/Fe ²⁺释放和As释放。更重要的是，在缺氧微环境孵化中，土壤二氧化碳和甲烷的排放量得到了减少。盆栽实验的孔隙水 DOM 主要由具有木质素和单宁分子结构的类腐殖质荧光团组成，可以介导 Fe(III)（羟基）氧化物的微生物还原。碳源和活性炭共掺的土壤微观世界孵化实验进一步证实了DOM电子穿梭和微生物碳源功能对于土壤Fe(III)还原至关重要，从而驱动了稻田土壤As的释放和碳排放。此外，两年多来，AC的施用减轻了稻米二甲基砷酸盐的积累。我们的研究结果强调了微生物细胞外电子转移在驱动稻田土壤厌氧呼吸和降低孔隙水 DOM 方面的重要性，同时修复稻田砷污染和减少甲烷排放。