Sensitivity of soil respiration and microbial communities to altered snowfall

Winter respiration is a quantitatively important, yet variable flux of carbon dioxide (CO2) from soils to the atmosphere. Variability in winter soil respiration may be influenced by the effects of snowfall on microbial communities and their metabolic activities. In this study, we evaluated the importance of snowpack depth on soil respiration and microbial communities in a temperate deciduous forest. Snow removal created relatively dry, frequently frozen, and carbon substrate-poor soils, while snow additions led to wetter, warmer, and relatively carbon substrate-rich soils. Using time-series multiple regression, we observed enhanced sensitivity of respiration to moisture under ambient snow and snow removal; however, this effect was accompanied by a temporal lag suggesting that microorganisms had a delayed response to increases in free-water during soil thawing events. Conversely, soil respiration was only sensitive to temperature in the snow addition treatment when soil temperatures were consistently above 0 !C. The snow-induced respiration dynamics were accompanied by shifts in the structure of wintertime fungal and bacterial communities. We detected an impact of altered snowpack on bacterial richness during the growing season, but our manipulation did not have legacy effects on other features of the soil microbial community at spring thaw. Our results suggest that microbial communities may be “reset” during seasonal transitions from winter to spring, and that soil microorganisms are likely adapted to annual fluctuations in snowpack depth. As snowpack becomes more variable in mid-latitude systems due to climate change, our findings suggest that soil moisture and temperature will co-regulate wintertime respiration through a non-linear relationship surrounding soil freezeethaw cycles, with snow-mediated changes in microbial community structure likely influencing wintertime respiration dynamics. ! 2012 Elsevier Ltd. All rights reserved.