Responses of nitrous oxide fluxes to autumn freeze-thaw cycles in permafrost peatlands of the Da Xing'an Mountains, Northeast China.

Climate warming has intensified changes of permafrost freeze-thaw process and postponed the starting period of soil freezing, which significantly affected the processes of NO production and emission from the soils. However, responses of soil NO fluxes to freeze-thaw cycles (FTC) during autumn freezing period in permafrost peatlands in field remain unclear. Therefore, the static chamber-GC techniques were used to explore the effects of autumn FTC on NO fluxes in the three permafrost peatlands [Calamagrostis angustifolia peatland (CA), Larix gmelini-Sphagnum swamp (LS), and Eriophorum vaginatum peatland (EV)] in Da Xing'an Mountains, Northeast China, from September to November 2019. The response peaks of NO fluxes to autumn FTC in CA (29.22 ± 14.90 μg m h) and EV (19.70 ± 7.26 μg m h) occurred in the autumn FTC prophase, whereas LS (11.33 ± 0.90 μg m h) appeared in the autumn FTC metaphase. CA (394.90 μg m) and EV (497.82 μg m) acted as a NO source, and LS (- 1321.43 μg m) was a NO sink. The effects of autumn FTC on NO fluxes were significantly different (p < 0.001) in the three permafrost peatlands. NO emissions during autumn FTC were mainly driven by soil NH-N, DOC content and soil NO-N content. The results implied that autumn FTC could stimulate soil NO emissions in permafrost peatlands and confirmed the important contribution of NO emissions during autumn FTC to annual nitrogen budget. This study could improve the accuracy of regional estimates of annual nitrogen budget.