Predictors of soil fungal biomass and community composition in temperate mountainous forests in Central Europe

Fungi are a highly diverse group of soil organisms greatly contributing to the functioning of forest ecosystems. Consequently, the understanding of factors affecting their productivity and distribution is needed for the understanding of litter and soil ecology. While several drivers of fungal community composition have been identified, it is less clear how their relative importance depends on topsoil habitats and how consistent it is across fungal ecological guilds. Moreover, the predictors of fungal biomass are much less known than those of the community composition. To fill these knowledge gaps, we collected and analyzed a comprehensive dataset from a Central European coniferous forest, covering a broad range of elevations and vegetation types and spanning from managed forests to protected forests with minimal human intervention. Fungal standing biomass and composition (including root, soil and litter habitats) was analyzed in relation to site characteristics, soil and litter chemistry and vegetation (intense botanical surveys and molecular analysis of plant roots). We found that fungal biomass and community composition in soil were vertically stratified in our study area. The nutrient-rich litter contained elevated fungal biomass content and it was dominated by saprotrophic fungi, whereas bulk soil, with less fungal biomass, was dominated by ECM fungi and relatively depleted of saprotrophs. We show that vegetation was a key predictor of fungal community composition across all ecological guilds of fungi and habitats. pH of soil or litter was a significant predictor of fungal community composition in all studied habitats, whereas climatic (altitude) effects were observed for fungal biomass and composition in bulk soil. Finally, P was the most important nutrient in our study, explaining >20% of variance in fungal biomass and affecting fungal community composition across habitats. Our results support the idea that intense atmospheric deposition of N during last decades may have shifted Central European forests from N-limitation to P-limitation. In light of increased global anthropogenic N inputs projected for the next century, our results suggest that fungal productivity might become P-limited rather than N-limited in temperate forests.