Warming promotes soil CO2 and CH4 emissions but decreasing moisture inhibits CH4 emissions in the permafrost peatland of the Great Xing'an Mountains.

Permafrost peatlands, as large soil carbon pools, are sensitive to global warming. However, the effects of temperature, moisture, and their interactions on carbon emissions in the permafrost peatlands remain unclear, when considering the availability of soil matrixes. The permafrost peatland (0-50 cm soil) in the Great Xing'an Mountains was selected to explore the deficiency. The cumulative carbon dioxide (CO2) and methane (CH4) emissions from soil were measured under different temperatures (5 °C, 10 °C, and 15 °C) and moisture content (130%, 100%, and 70%) treatments by the indoor incubation. The results showed that the soil carbon and nitrogen matrix determined soil carbon emissions. Warming affected the availability of soil carbon and nitrogen substrates, thus stimulating microbial activity and increasing soil carbon emissions. With soil temperature increasing by 10 °C, soil CO2 and CH4 emission rates increased by 5.1-9.4 and 3.8-6.4 times respectively. Warming promoted soil carbon emissions, and the decrease of moisture content promoted CO2 emissions but inhibited CH4 emissions in the permafrost peatland. Soil moisture and the carbon and nitrogen matrix determined the intensity of CO2 and CH4 emissions. The results were important to assess soil carbon emissions from permafrost peatlands under the impact of future climate warming and to formulate carbon emission reduction policies.

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 N2O production and emission from the soils. However, responses of soil N2O fluxes to freeze-thaw cycles (FTCS) 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 FTCS on N2O 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 N2O fluxes to autumn FTCS in CA (29.22 ± 14.90 µg m-2 h-1) and EV (19.70 ± 7.26 µg m-2 h-1) occurred in the autumn FTCS prophase, whereas LS (11.33 ± 0.90 µg m-2 h-1) appeared in the autumn FTCS metaphase. CA (394.90 µg m-2) and EV (497.82 µg m-2) acted as a N2O source, and LS (- 1321.43 µg m-2) was a N2O sink. The effects of autumn FTCS on N2O fluxes were significantly different (p < 0.001) in the three permafrost peatlands. N2O emissions during autumn FTCS were mainly driven by soil NH4+-N0-50 cm, DOC30-40 cm and 40-50 cm content and soil NO3--N0-50 cm content. The results implied that autumn FTCS could stimulate soil N2O emissions in permafrost peatlands and confirmed the important contribution of N2O emissions during autumn FTCS to annual nitrogen budget. This study could improve the accuracy of regional estimates of annual nitrogen budget.