In situ N-N O site preference and O concentration dynamics disclose the complexity of N O production processes in agricultural soil.

Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in situ studies to elucidate the key factors controlling soil N O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N O fluxes in an arable soil, combined with in situ high-frequency measurements of soil matrix oxygen (O ) and N O concentrations, in situ N labeling, and N O N site preference (SP). The in situ O concentration and further microcosm visualized spatiotemporal distribution of O both suggested that O dynamics were the proximal determining factor to matrix N O concentration and fluxes due to quick O depletion after N fertilization. Further SP analysis and in situ N labeling experiment revealed that the main source for N O emissions was bacterial denitrification during the hot-wet summer with lower soil O concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold-dry winter with higher soil O concentration. The robust positive correlation between O concentration and SP values underpinned that the O dynamics were the key factor to differentiate the composite processes of N O production in in situ structured soil. Our findings deciphered the complexity of N O production processes in real field conditions, and suggest that O dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N O production processes in undisturbed structure soils. Our results help to develop targeted N O mitigation measures and to improve process models for constraining global N O budget.