Nitrogen Cycle, N2O Emission, and Its Decomposition Processes in Soil

Nitrous oxide (N2O) is a greenhouse gas of global significance and a fundamental product of nitrogen cycling in soils. This review surveys new and classical research that has uncovered the biological basis for nitrous oxide production as part of nitrification, denitrification, and nitrate respiration. Nitrous oxide evolution from soil is highly spatially and temporally variable, making flux assessment difficult. Multiple biochemical pathways produce nitrous oxide, reflecting the activity of myriad bacteria, archaea, and fungi. The key pathways are nitrification, denitrification, and dissimilatory nitrate reduction to ammonium, which are not mutually exclusive. These different pathways operating in different soil environments at a multitude of spatial scales make environmental control of nitrous oxide evolution problematic. Abiotic formation processes linked to iron reduction in soil occur at relatively high redox potential. New research on nitrous oxide consumption by novel soil groups indicates that its flux from soil is strongly attenuated in certain environments. Suggestions for future research include resolving spatiotemporal sampling scales and better managing soil fertility and structure to mitigate nitrous oxide production and maximize its consumption.