In situ 15 N‐N 2 O site preference and O 2 concentration dynamics disclose the complexity of N 2 O production processes in agricultural soil

Abstract

Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N 2 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 2 O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N 2 O fluxes in an arable soil, combined with in situ high‐frequency measurements of soil matrix oxygen (O 2 ) and N 2 O concentrations, in situ 15 N labeling, and N 2 O 15 N site preference (SP). The in situ O 2 concentration and further microcosm visualized spatiotemporal distribution of O 2 both suggested that O 2 dynamics were the proximal determining factor to matrix N 2 O concentration and fluxes due to quick O 2 depletion after N fertilization. Further SP analysis and in situ 15 N labeling experiment revealed that the main source for N 2 O emissions was bacterial denitrification during the hot‐wet summer with lower soil O 2 concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold‐dry winter with higher soil O 2 concentration. The robust positive correlation between O 2 concentration and SP values underpinned that the O 2 dynamics were the key factor to differentiate the composite processes of N 2 O production in in situ structured soil. Our findings deciphered the complexity of N 2 O production processes in real field conditions, and suggest that O 2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N 2 O production processes in undisturbed structure soils. Our results help to develop targeted N 2 O mitigation measures and to improve process models for constraining global N 2 O budget.

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