Increased N2O emissions from aerobic soil with warming is mainly attributable to increased mineralization of organic nitrogen: An incubation study

Nitrous oxide (N 2 O) can be produced via microbial oxidation of ammonia (nitrification) in the aerobic soil.Warming, a factor influencing microbial activity, can increase the rates of ammonia oxidation and N 2 O emissions.However, the amount of ammonia, a substrate of nitrification process, is a critical factor in determining the cumulative N 2 O emissions from agricultural fields receiving nitrogen (N) fertilizer.To investigate the effects of increasing temperature on temporal variation and cumulative amount of N 2 O emissions in aerobic soil, we conducted an incubation experiment with soil treated with ammonium sulfate at 15 and 25C.To maintain soil aeration, the soil water content during the incubation period was adjusted to the field capacity, and the concentrations of inorganic soil N (NH 4 + -N and NO 3 --N) and N 2 O emissions were periodically measured.During the incubation period, the sum of inorganic soil N increased due to the mineralization of organic N. The net increase in NO 3 -concentration, a product of ammonia oxidation, was 6% higher at 25C than at 15C, reflecting the increase in nitrification process following the increased mineralization of organic N. Nitrous oxide was mainly emitted during periods when sufficient NH 4 + was present in soil, reflecting that ammonia oxidation was the main process of N 2 O production.Accumulated N 2 O emissions were 10% higher at 25C than at 15C, but the difference was statistically insignificant (P > 0.05).Despite the small and insignificant difference in accumulated N 2 O emissions between 15 and 25C, 60% of the difference is attributable to the increase in the nitrification reaction.The results of this study suggest that N 2 O emissions may increase due to increased temperature in soil fertilized with N, but this increase is mainly attributable to increased mineralization of organic N and subsequent increased nitrification.