Emissions of nitrous oxide from continuous permafrost region in the Daxing'an Mountains, Northeast China

Permafrost ecosystems play an important role in global climate change, and climate warming would result in permafrost thawing and changing microbial mediated N cycles. Emissions of nitrous oxide (N2O) are an important component of N budgets in high-latitude permafrost ecosystems, especially in the context of global climate change. However, few studies have investigated the emissions of N2O from a swamp forest in a permafrost ecosystem. In this paper, we investigated the N2O emissions rates and cumulative budget from continuous permafrost region in the Daxing'an Mountains, northeast China, and identified the key environmental factors affecting N2O emissions from three swamp forests in the growing season. A bootstrapping model estimated that average N2O fluxes during the growing season were 40.76 ± 6.13, 29.56 ± 3.21 and 38.27 ± 8.46 μg m−2 h−1 from three swamp forests consisting of Larix gmelinii - Ledum palustre var. dilatatum (LL), Larix gmelinii - Carex appendiculata (LC) and Betula fruticose - Carex schmidtii (BC), respectively. The types of swamp forests had no statistically significant impact on N2O emissions (P > 0.05). The cumulative N2O emissions were estimated to be 1.07 ± 0.09 (LL), 0.79 ± 0.18 (LC) and 1.05 ± 0.11 kg ha−1 (BC) in the swamp forests, indicating that the permafrost region of the Daxing'an Mountains might be a potential N2O source during the growing season. The N2O emissions were mainly controlled by soil temperature, water table level, pH, ammonium nitrogen, nitrate nitrogen, total organic carbon and the carbon-to-nitrogen ratio. N2O emission showed significant negative correlation with nitrate nitrogen in the three swamp forests; thus, the low nitrate would limit the rate of N2O emissions in the permafrost region. In addition, we found that denitrification could be the potential source of N2O fluxes in the permafrost region of Daxing'an Mountains. Our results indicated that permafrost swamp forests were significant source for N2O emissions, and N2O emissions were controlled by multiple environmental factors.