Anaerobic Methane Oxidation Sustains Soil Organic Carbon Accumulation

The intensified input of anthropogenic nitrogen (N) fertilizers has accelerated the transformation of active N species (e.g., N2O, NO3- and NO2-) and the coupled methane (CH4) cycling on a global scale, but the impact of N-mediated CH4 metabolism on soil carbon accumulation, which is crucial for agricultural sustainability, remains poorly understood. In this study, we show that more than 60% of the CH4-C were converted to soil organic matter during anaerobic oxidation in two paddy soils with a parent material origin of river and marine sediments. The anaerobic enrichment of C-13 in organic matter and inorganic CO2 indicated that the net C-13 conversion of CH4 could reach up to 120 and 49 nmol g(-1) in two paddy soils, respectively, and these processes were further stimulated significantly by up to 1.8-3.1 fold under denitrifying conditions by reactive N species (N2O, NO3- and NO2-) acting as electron acceptors. Denitrifying methanotrophy is already recognized as the major CH4 sink in marine and freshwater ecosystems, and we now identify this process as a source of soil organic matter in agriculture as well.