DOM-Driven Methane Cycling and Arsenic Mobilization in Paddy Soils

Soil texture strongly regulates redox-driven interactions among dissolved organic matter (DOM), methanogenesis, and arsenic (As) mobilization in paddy soils, but the molecular and microbial controls remain unclear. We integrated porewater geochemistry, 3D-EEM fluorescence, FT-ICR-MS molecular analysis, 16S rRNA sequencing, and metagenomic functional profiling to compare coarse loam and fine silt soils from the Jianghan Plain. Loam soils showed stronger reducing conditions, faster DOM decomposition, selective loss of aromatic and nitrogen-rich unsaturated compounds, higher CH4 production, and elevated porewater As, consistent with enhanced Fe(III) reduction and As release. Microbial and genomic data indicated enrichment of methanogens, anaerobic methane-oxidizing archaea (Candidatus Methanoperedens), and Fe/As-reducing bacteria, together with higher abundances of methane-cycling (mcrA, fwd) and arsenic-transforming genes (arrA, arsM), supporting a coupled methane cycling-arsenic reduction network. These results demonstrate that soil texture governs DOM reactivity and microbially mediated Fe-As redox processes, providing mechanistic insight into methane-driven arsenic mobilization and groundwater As risk in rice agroecosystems.