Temporal in situ dynamics of N₂O reductase activity as affected by nitrogen fertilization and implications for the N₂O/(N₂O + N₂) product ratio and N₂O mitigation

Abstract

In vitro, high nitrate (NO₃⁻ ) concentrations significantly inhibit N₂O reductase activity. However, little information is available on the in situ temporal effects of excessive N fertilization on soil N₂O reductase activity and the regulation of the N₂O/(N₂ + N₂O) product ratio in agricultural soil. This study examined the monthly in situ dynamics of NO₃⁻ concentration, N₂O reductase activity, and N₂O/(N₂ + N₂O) product ratio for 2 years in loamy soil that had received either continuous N fertilizer at 400 kg N ha⁻¹ year⁻¹ for 15 years (N400) or no N fertilizers (CK). N₂O reductase activity was significantly lower under the N400 treatment than under the CK and correlated negatively with soil NO₃⁻ concentration. The decrease in N₂O reductase activity resulted in the N₂O/(N₂ + N₂O) product ratio increasing. These results demonstrate that excessive N fertilization has the potential to increase N₂O emissions by reducing N₂O reductase activity in soils. These results highlight the need for N₂O mitigation options to embrace the reduction of soil NO₃⁻ concentrations.