Global climate change is altering snow depth in winter, which could significantly affect soil respiration and microbial communities. However, belowground responses are still uncertain as they depend on the thermal effects on soils, the acclimation of soil microbial communities and ecosystem type. Here, we conducted a snow manipulation experiment including 50% removal of snowpack (mean snow depth after treatment was 3.1 +/- 0.7 cm), ambient snow (mean snow depth was 6.3 +/- 0.7 cm), and 50% increase of snowpack (mean snow depth after treatment was 9.6 +/- 1.5 cm) to explore the effects of altered snow depth on winter soil respiration and microbial communities in a mid-latitude plantation forest with continental climate with dry winters. Winter soil CO2 effluxes varied from 0.09 to 0.84 mu mol m(-2)S(-1) with a mean of 0.32 +/- 0.07 mu mol m(-2)s(-1). The cumulative soil CO2 effluxes from 11 December 2014 to 21 March 2015 were 27.3 +/- 1.1, 26.5 +/- 2.1, and 29.5 +/- 1.3 g Cm-2 under reduced, ambient and added snowpack, which corresponded to 5.7 +/- 0.2%, 5.5 +/- 0.3%, and 5.8 +/- 0.1% of the annual soil CO2 effluxes, respectively. Our one-year observation results suggested that although snow reduction decreased soil temperature, microbial biomass carbon (MBC) and soil respiration did not change, suggesting microbial adaptation to cold conditions between - 4 degrees C and -1 degrees C. In contrast, snow addition increased soil temperature, MBC, and soil respiration. Microbial community structure (F/B, ratio of fungi to bacteria) was also changed and soil enzymatic (beta-glucosidase) activities increased under snow addition. However, these effects were short-lived and disappeared when soil temperature did not differ between the addition and control plots at the 14th day after treatment. These results indicated that the responses of soil microbial communities and respiratory activities to changing soil temperature were rapid and the response of soil respiration to snow addition was transient. Consequently, altered snow depth did not affect cumulative soil CO2 effluxes. Our study suggests that wintertime soil respiration rates are generally low and snow manipulation has minor effects on soil CO2 efflux, soil temperature (the determinant driver of wintertime soil CO2 efflux) and soil microbial biomass at our site.

Warming of the arctic landscape results in permafrost thaw, which causes ground subsidence or thermokarst. Thermokarst formation on hillslopes leads to the formation of thermal erosion features that dramatically alter soil properties and likely affect soil carbon emissions, but such features have received little study in this regard. In order to assess the magnitude and persistence of altered emissions, we use a space-for-time substitution (thaw slump chronosequence) to quantify and compare peak growing season soil carbon dioxide (CO2) fluxes from undisturbed tundra, active, and stabilized thermal erosion features over two seasons. Measurements of soil temperature and moisture, soil organic matter, and bulk density are used to evaluate the factors controlling soil CO2 emissions from each of the three chronosequence stages. Soil CO2 efflux from the active slump is consistently less than half that observed in the undisturbed tundra or stabilized slump (1.8 versus 5.2 g CO2-C m(-2) d(-1) in 2011; 0.9 versus 3.2 g CO2-C m(-2) d(-1) in 2012), despite soil temperatures on the floor of the active slump that are 10-15 degrees C warmer than the tundra and stabilized slump. Environmental factors such as soil temperature and moisture do not exert a strong control on CO2 efflux, rather, local soil physical and chemical properties such as soil organic matter and bulk density, are strongly and inversely related among these chronosequence stages (r(2) = 0.97), and explain similar to 50% of the variation in soil CO2 efflux. Thus, despite profound soil warming and rapid exposure of buried carbon in the active slump, the low organic matter content, lack of stable vegetation, and large increases in the bulk densities in the uppermost portion of active slump soils (up to similar to 2.2 g(-1) cm(-3)) appear to limit CO2 efflux from the active slump. Future studies should assess seasonal fluxes across these features and determine whether soil CO2 fluxes from active features with high organic content are similarly low.

Soil CO2 efflux from an ecosystem responds to the active layer thawing depth (H) significantly. A Li-8100 system was used to monitor the CO2 exchange from a wet meadow ecosystem during a freeze-thaw cycle of the active layer in a permafrost region on the Qinghai-Tibet Plateau. An exponential regression equation () has been established on the basis of observed soil CO2 efflux versus the thawed soil thickness. Using this equation, the total soil CO2 efflux during an annual freeze-thaw cycle has been calculated to be approximately 8.18 x 10(10) mg C. The results suggest that freeze-thaw cycles in the active layer play an important role in soil CO2 emissions and that thawed soil thickness is the major factor controlling CO2 fluxes from the wet meadow ecosystem in permafrost regions on the Qinghai-Tibet Plateau. It can be concluded that with active layer thickening due to permafrost degradation, massive amounts of soil carbon would be emitted as greenhouse gases, and the permafrost region would become a carbon source with a positive feedback effect on climate warming. Hence, more attention should be paid to the influences of the active layer changes on soil carbon emission from these permafrost regions.