Small and transient response of winter soil respiration and microbial communities to altered snow depth in a mid-temperate forest

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 µmol m−2 s−1 with a mean of 0.32 ± 0.07 µmol 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 C m−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 °C and −1 °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 (β-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.