Soil properties shape the heterogeneity of denitrification and N₂O emissions across large-scale flooded paddy soils

Flooded paddy soils after rewetting dry soils accompanied by extensive nitrogen fertilizer input are important anthropogenic N2O emitters due to the denitrification process. Owing to multiple complex denitrifying N2O sources, however, the extent to which biotic (fungal or bacterial) and abiotic (chemical) denitrification contribute to total N2O emissions remains largely unquantified. Here we sampled across eight provinces where most of the flooded paddy soils were in China to explore microbial and abiotic denitrification potentials and decipher N2O dynamics. N2O isotopocules and site preference (delta N-15(SP)) analyses found that in most of the sampled paddy soils, fungi-mediated denitrification was the largest N2O contributor (51%-63%); while bacterial and chemical denitrifications contributed 12%-31% and 12%-28% of N2O emissions, respectively. Further, using N-15 labeling, a significant spatial heterogeneity of denitrification performance was observed among these flooded paddy soils. As indicated by variance partitioning and regression analyses, this heterogeneity was mainly determined by soil properties (especially soil organic carbon and total nitrogen) rather than by denitrifying communities. Our findings provide insights into the establishment of predictive models of future N2O emission from global paddy soils considering both the biotic and abiotic contributions.