Coupled abiotic-biotic cycling of nitrous oxide in tropical peatlands

Abstract

Atmospheric nitrous oxide (N₂O) is a potent greenhouse gas thought to be mainly derived from microbial metabolism as part of the denitrification pathway. Here we report that in unexplored peat soils of Central and South America, N₂O production can be driven by abiotic reactions (≤98%) highly competitive to their enzymatic counterparts. Extracted soil iron positively correlated with in situ abiotic N₂O production determined by isotopic tracers. Moreover, we found that microbial N₂O reduction accompanied abiotic production, essentially closing a coupled abiotic-biotic N₂O cycle. Anaerobic N₂O consumption occurred ubiquitously (pH 6.4-3.7), with proportions of diverse clade II N₂O reducers increasing with consumption rates. Our findings show that denitrification in tropical peat soils is not a purely biological process but rather a 'mosaic' of abiotic and biotic reduction reactions. We predict that hydrological and temperature fluctuations differentially affect abiotic and biotic drivers and further contribute to the high N₂O flux variation in the region.