Sources of nitrous oxide and the fate of mineral nitrogen in subarctic permafrost peat soils

[摘要] Nitrous oxide (N 2 O) emissions from permafrost-affected terrestrialecosystems have received little attention, largely because they have beenthought to be negligible. Recent studies, however, have shown that there arehabitats in the subarctic tundra emitting N 2 O at high rates, such as barepeat (BP) surfaces on permafrost peatlands. Nevertheless, the processes behind N 2 Oproduction in these high-emission habitats are poorly understood.In this study, we established an in situ 15 N-labeling experiment with twomain objectives: (1) to partition the microbial sources of N 2 O emitted from BP surfaces on permafrost peatlands and (2) to study the fate ofammonium and nitrate in these soils and in adjacent vegetated peat (VP) surfaces showing low N 2 O emissions. Our results confirm the hypothesis thatdenitrification is mostly responsible for the high N 2 O emissions fromBP. During the study period, denitrification contributed ∼  79 % of the total N 2 O emissions from BP, whereas the contribution fromammonia oxidation was less (about 19 %). Both gross N mineralization andgross nitrification rates were higher in BP than in VP, with high C / N ratios and a low water content likely limiting N transformationprocesses and, consequently, N 2 O production in the latter soil type. Our results show thatmultiple factors contribute to high N 2 O production in BP surfaceson permafrost peatlands, with the most important factors being the absence of plants, anintermediate to high water content and a low C / N ratio, which all affectthe mineral-N availability for soil microbes, including those producingN 2 O. The process understanding produced here is important for thedevelopment of process models that can be used to evaluate futurepermafrost–N feedbacks to the climate system.

[学科分类] 大气科学