Long-term effects of N deposition on N2O emission in an alpine grassland of Central Asia

Nitrogen (N) deposition is considered to be an important source of atmospheric N2O emission. Although N deposition simulated experiments have been conducted in grassland, forest and arctic tundra, the effect of long-term N deposition on N2O emission is not well understood in alpine grassland. To assess the response, a 9-yr N addition experiment was conducted in an alpine grassland of the Tianshan Mountains of Central Asia, to characterize the relationship between N2O emission and N application rate. An N addition rate of 10 kg N ha(-1) yr(-1) had no significant effect on N2O, while increases in N2O emission were clearly observed with N deposition of up to 30 kg N ha(-1) yr(-1) with a low emission factor (EF). The average N2O emission factor was 0.19% (range: 0.03%-0.42%), lower than the current IPCC default value of 1%. Nitrogen application significantly increased soil accumulated N2O emission throughout the growing season from 2013 to 2017, showing an increasing tendency in N2O emission with time. Depending on the amount and duration of N application, the interannual variability was 48.55%, 27.56%, 15.12% and 10.16% at the control (no N addition), 10, 30, 90 kg N ha(-1) yr(-1) plots, respectively. These would help to refine the accuracy of N2O mitigation protocols with insignificant N2O promotion under double present N deposition scenarios in alpine grassland.