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Snow depth may have a complex influence on carbon cycling in winter. Here we set up a field experiment to investigate how different snow depths (0 cm, 60 cm, 90 cm) influenced carbon dioxide (CO2) in a wetland. The mean ± standard error of CO2 emissions under snow addition treatments (60 cm and 90 cm snow depths) were 0.92 ± 0.16 g·cm−2·s−1 and 0.53 ± 0.16 g·cm−2·s−1, respectively, compared with snow removal treatment (0 cm snow depth), 0.11 ± 0.05 g·cm−2·s−1. In general, snow addition increased CO2 fluxes significantly. As snow depths increased, microbial biomass carbon (MBC) and bacterial diversities increased drastically. More important, the community of bacteria differed under different treatments. Firmicutes, which can resist dehydration and extremely low temperatures, was widely distributed in the snow removal treatment, where it sustained soil biochemical processes. Overall, our study indicates that snow cover counteracts the negative effects on soil microbial activities caused by low temperatures and could play a critical role in winter carbon cycling in wetlands. [ABSTRACT FROM AUTHOR]