Atmospheric H2O2 deposition matters: Overlooked abiotic CH4 emission from paddy soils

Methane (CH4) emissions in rice paddies is a major driver of global warming, traditionally attributed to microbial methanogenesis under anaerobic conditions. However, the potential for abiotic mechanisms to contribute to CH4 emissions has been largely overlooked, creating a critical gap in our understanding of the global methane budget. In this study, we identified an abiotic CH4 generation pathway driven by atmospheric hydrogen peroxide (H2O2) through Fenton-like reactions in paddy soils. Microcosm experiments with sterilized soils from ten major rice-growing regions in China showed that the addition of environmentally relevant concentration of H2O2, a common secondary air pollutant, induced a 10.1-209% increase in hydroxyl radical (•OH) production, which in turn enhanced abiotic methane production by 3.34-37.9%. Mechanistic investigations revealed that •OH radicals convert methylated organic sulfur compounds into methyl radicals, initiating CH4 formation. Furthermore, we estimated that this H2O2-driven abiotic pathway could contribute an additional 86.0-128 Gg of annual CH4 emissions from major Chinese rice paddies during 2010-2019, with projected contributions of 97.2 and 98.5 Gg in 2030 and 2050, respectively. These findings provide insights into the interconnections between atmospheric H2O2 deposition and terrestrial methane fluxes, emphasizing the potential of atmospheric H2O2 in driving abiotic methane production.