Nitrous oxide emission from aerobic soils is controlled by ammonia oxidation processes rather than N application rates

다국어 초록 (Multilingual Abstract)

Nitrous oxide (N2O) emissions from aerobic soil are strongly controlled by the availability of ammonium (NH4 +), a substrate for microbially mediated ammonia oxidation processes, and its concentration can vary substantially depending on the level of nitrogen (N) input. In this study, the effects of N input level on soil inorganic N concentrations and cumulative N2O emissions under aerobic conditions were evaluated by applying ammonium sulfate at rates of 0, 50, 100, 200, and 300 mg N kg-1. To maintain aerobic conditions, soil moisture content was adjusted to field capacity throughout a 51-day incubation at 25°C, and concentrations of inorganic N (NH4 +-N and nitrate, NO3--N), soil pH, and N2O emissions were measured periodically. N2O emissions exhibited a distinct temporal pattern, with an early emission peak shortly after N application, followed by a gradual decline during incubation. Overall, N2O emissions increased with increasing N application rate and showed a proportional increase up to 200 mg N kg-1, with a slope of 0.53 (r2 = 0.99, P < 0.01, n = 4). However, at 300 mg N kg-1, no further increase in cumulative N2O emissions was observed (P > 0.05), which was attributed to excessive N input causing a decline in soil pH to inhibit N mineralization and nitrification. Linear regression analysis revealed a strong positive relationship between net nitrified N (expressed as the increase in NO3--N) and cumulative N2O emissions during the incubation period, with a slope of 0.57 (r2 = 0.98, P < 0.001, n = 5), indicating that N2O production is highly dependent on the extent of ammonia oxidation (nitrification). This study demonstrates that N2O emissions under aerobic soil conditions are quantitatively dependent on the amount of ammonium oxidized to nitrate, and that soil environmental conditions such as acidity regulate N2O emissions primarily by influencing substrate availability (i.e., NH4 +) rather than directly controlling microbial N2O-producing pathways.