Permafrost thawing may lead to the release of carbon and nitrogen in high-latitude regions of the Northern Hemisphere, mainly in the form of greenhouse gases. Our research aims to reveal the effects of permafrost thawing on CH4 and N2O emissions from peatlands in Xiaoxing'an Mountains, Northeast China. During four growing seasons (2011-2014), in situ CH4 and N2O emissions were monitored from peatland under permafrost no-thawing, mild-thawing, and severe-thawing conditions in the middle of the Xiaoxing'an Mountains by a static-chamber method. Average CH4 emissions in the severe-thawing site were 55-fold higher than those in the no-thawing site. The seasonal variation of CH4 emission became more aggravated with the intensification of permafrost thawing, in which the emission peaks became larger and the absorption decreased to zero. The increased CH4 emissions were caused by the expansion of the thawing layer and the subsequent increases in soil temperature, water table, and shifts of plant communities. However, N2O emissions did not change with thawing. Permafrost thawing increased CH4 emissions but did not impact N2O emissions in peatlands in the Xiaoxing'an Mountains. Increased CH4 emissions from peatlands in this region may amplify global warming.

Arctic tundra ecosystems are rapidly changing due to the amplified effects of global warming within the northern high latitudes. Warming has the potential to increase the thawing of the permafrost and to change the landscape and its geochemical characteristics, as well as terrestrial biota. It is important to investigate microbial processes and community structures, since soil microorganisms play a significant role in decomposing soil organic carbon in the Arctic tundra. In addition, the feedback from tundra ecosystems to climate change, including the emission of greenhouse gases into the atmosphere, is substantially dependent on the compositional and functional changes in the soil microbiome. This article reviews the current state of knowledge of the soil microbiome and the two most abundant greenhouse gas (CO2 and CH4) emissions, and summarizes permafrost thaw-induced changes in the Arctic tundra. Furthermore, we discuss future directions in microbial ecological research coupled with its link to CO2 and CH4 emissions.

Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an Special Report on Emissions Scenarios (SRES) A2 scenario over the 21st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous versus evergreen plant functional types. Consequently, gains in net ecosystem productivity (NEP) of 29 and 10gCm(-2)yr(-1) were modeled in the tundra and fen after 90years. However, CH4 emissions modeled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations and from indirect effects of increasing sedge growth, which hastened transfer of CH4 through porous roots to the atmosphere. After 90years, landscape CH4 emissions increased from 1.1 to 5.2gCm(-2)yr(-1) while landscape NEP increased from 34 to 46gCm(-2)yr(-1). Positive feedback to radiative forcing from increases in CH4 emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH4 emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.