BOOK OF ABSTRACTS 91 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Tuesday, 25 August 2026 / Hall B+C Environment, Agriculture, and Forestry SL41 Arsenic Reduces Methane Emissions from Paddy Soils: Insights from Continental Investigation and Laboratory Incubations Ouyuan Jiang1, Siyu Zhang2, Xianjin Tang3 1 Institute of Soil and Water Resources and Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China, ouyuan@zju.edu.cn 2 School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China 3 Institute of Soil and Water Resources and Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China Arsenic (As) contamination and methane (CH4) emissions co-occur in rice paddies. However, how As impacts CH4 production, oxidation, and emission dynamics is unknown. Here, we investigated the abundances and activities of CH4-cycling microbes from 132 paddy soils with different As concentrations across continental China using metagenomics and the reverse transcription polymerase chain reaction. Our results revealed that As was a crucial factor affecting the abundance and distribution patterns of the mcrA gene, which is responsible for CH4 production and anaerobic CH4 oxidation. Laboratory incubation experiments showed that adding 30 mg kg–1 arsenate increased 13CO2 production by 10-fold, ultimately decreasing CH4 emissions by 68.5%. The inhibition of CH4 emissions by As was induced through three aspects: (1) the toxicity of As decreased the abundance and activity of the methanogens; (2) the adaptability and response of methanotrophs to As is beneficial for CH4 oxidation under As stress; and (3) the more robust arsenate reduction would anaerobically consume more CH4 in paddies. Additionally, significant positive correlations were observed between arsC and pmoA gene abundance in both the observational study and incubation experiment. These findings enhance our understanding of the mechanisms underlying the interactions between As and CH4 cycling in soils. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (grant numbers 42122048, 42107135, and 41991332).
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