Soil microbial communities follow distinct seasonal cycles which result in drastic changes in processes involving soil nutrient availability. The biomass of fungi has been reported to be highest during winter, but is fungal growth really occurring in frozen soil? And what is the effect of plant cover on biomass formation and on the composition of fungal communities? To answer these questions, we monitored microbial biomass N, ergosterol, and the amount of fungal hyphae during summer and winter in vegetated and unvegetated soils of an alpine primary successional habitat. The winter fungal communities were identified by rDNA ITS clone libraries. Winter soil temperatures ranged between -0.6°C and -0.1°C in snow-covered soil. We found distinct seasonal patterns for all biomass parameters, with highest biomass concentrations during winter in snow-covered soil. The presence of plant cover had a significant positive effect on the amount of biomass in the soil, but the type of plant cover (plant species) was not a significant factor. A mean hyphal ingrowth of 5.6 m g(-1) soil was detected in snow-covered soil during winter, thus clearly proving fungal growth during winter in snow-covered soil. Winter fungal communities had a typical species composition: saprobial fungi were dominating, among them many basidiomycete yeasts. Plant cover had no influence on the composition of winter fungal communities.

Our main aim was to understand whether the use of pooled DNA extracts bias the results of investigations in soil fungal communities in an alpine habitat. To avoid bias by DNA extraction methods, we used a commercial DNA extraction kit and consecutively pooled 1-4 DNA extracts from 0.25 g soil, each, before cloning. We expected to detect abundant species in all approaches, and the same diversity in clone libraries from pooled extracts. Soil fungal communities of primary successional sites mainly consist of rare species. Irrespective of pooling, no significant differences of species richness or diversity were detected between clone libraries.