Winter–spring transition induces changes in nutrients and microbial biomass in mid-alpine forest soils

•Soil microbial biomass was more abundant under snow.•A higher predominance of fungi characterised the snow-covered winter months.•The decline in microbial biomass during snowmelt was related to resource availability.•We observed a rapid turnover in bacterial biomass during spring snowmelt.•Microbial biomass and nutrient dynamics were independent of vegetation cover.

Active microbial biomass beneath seasonal snowpacks may influence biogeochemical processes in mountain soils. Here we show that soil microbial biomass in temperate forest ecosystems reaches its annual peak under snow, and declines rapidly as snow melts in the spring. This decline was associated with changes in temperature regime and resource availability. However, in contrast to alpine ecosystems at higher elevations, fungal/bacterial ratios, evaluated by amino sugar analysis, were lower in snow-covered winter soils and increased during snowmelt. We associated this shift to a faster decline in bacterial with respect to fungal biomass during snowmelt.