Contribution of the nongrowing season to annual N 2 O emissions from the continuous permafrost region in Northeast China

Abstract. Permafrost regions store large amounts of soil organic carbon and nitrogen, which are major sources of greenhouse gas. With climate warming, permafrost regions are thawing, releasing an abundance of greenhouse gases to the atmosphere and contributing to climate warming. Numerous studies have shown the mechanism of nitrous oxide (N2O) emissions from the permafrost region during the growing season. However, little is known about the temporal pattern and drivers of nongrowing season N2O emissions from the permafrost region. In this study, N2O emissions from the permafrost region were investigated from June 2016 to June 2018 using the static opaque chamber method. Our aims were to quantify the seasonal dynamics of nongrowing season N2O emissions and its contribution to the annual budget. The results showed that the N2O emissions ranged from −35.75 to 74.16 μg·m−2·h−1 during the nongrowing season in the permafrost region. The mean N2O emission from the growing season were 1.75–2.86 times greater than that of winter and 1.31–1.53 times greater than that of spring thaw period due to the mean soil temperature of the different specified periods. The nongrowing season N2O emissions ranged from 0.89 to 1.44 kg ha−1, which contributed to 41.96–53.73 % of the annual budget, accounting for almost half of the annual emissions in the permafrost region. The driving factors of N2O emissions were different among during the study period, growing season, and nongrowing season. The N2O emissions from total two-year observation period and nongrowing season were mainly affected by soil temperature, while the N2O emissions from growing season were controlled by soil temperature, water table level, and their interactions. In conclusion, nongrowing season N2O emissions is an important component of annual emissions and cannot be ignored in the permafrost region.