Distinct environmental variables drive the community composition of mycorrhizal and saprotrophic fungi at the alpine treeline ecotone

Soil inhabiting fungi have an important role in ecosystems around the treeline representing both plant symbionts and organic matter decomposers. To identify the drivers of their diversity and community structure, amplicon sequencing of soil fungal DNA was conducted on six elevation transects across the transition from spruce forests to dwarf pine stands in the Krkonoše Mts. (Czech Republic, Central Europe). Between 104 and 269 operational taxonomic units (OTUs) per plot were detected, however, no relation between OTU richness and elevation was found. Importantly, the dominant (representing more than 5% of all sequences per plot) OTUs assigned to ectomycorrhizal taxa decreased with elevation. Whereas the community composition of mycorrhizal fungi followed the elevation gradient and most of the total variability was explained by tree height, communities of saprotrophs were shaped mainly by vegetation, soil cover and soil properties, and differed among the transects.