Contribution of the nongrowing season to annual NO emissions from the permafrost wetland in Northeast China.

Permafrost regions store large amounts of soil organic carbon and nitrogen, which are major sources of greenhouse gas. With climate warming, permafrost is thawing and releasing an abundance of greenhouse gases into the atmosphere and contributing to climate warming. Numerous studies have shown the mechanism of nitrous oxide (NO) emissions from the permafrost region during the growing season. However, little is known about the temporal pattern and drivers of nongrowing season NO emissions from the permafrost region. In this study, NO emissions from the permafrost region were investigated from June 2016 to June 2018 using the static opaque chamber method. We aimed to quantify the seasonal dynamics of nongrowing season NO emissions and their contribution to the annual budget. The results showed that the NO emissions ranged from - 35.75 to 74.16 μg m h with 0.89 to 1.44 kg ha being released into the atmosphere during the nongrowing season in the permafrost region. The permafrost wetland types had no significant influence on the nongrowing season NO emissions due to the nitrate content. The cumulative NO emissions during the nongrowing season 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 NO emissions were different among the nongrowing season, growing season, and entire period. The NO emissions from the nongrowing season and total 2-year observation period were mainly affected by soil temperature, which could explain 3.01-9.54% and 6.07-14.48% of the temporal variation in NO emissions, respectively. In contrast, the NO emissions from the growing season were controlled by soil temperature, water table level, pH, NH-N, NO-N, total nitrogen, total organic carbon, and C/N ratio, which could explain 14.51-45.72% of the temporal variation of NO emissions. Nongrowing season NO emissions are an essential component of annual emissions and cannot be ignored in the permafrost region.