The complex landscape of mountainous areas with large ranges in environmental factors provides a multitude of habitats leading to an extensive above and belowground biodiversity. Switzerland is characterized by two mountain ranges, i.e., the Alps and the Jura, that are characterized by large gradients of mean annual temperature, yearly precipitation and soil pH. Using a regular grid with 255 sites (1,010 samples) across Switzerland we assessed soil and geographic drivers of soil bacterial and fungal communities and their associations to plant communities. Bacterial and fungal communities were determined using amplicon sequencing and plant communities were recorded at each site.
In total, 109,693 bacterial and 28,085 fungal amplicon sequence variants (ASVs) were detected, of which about one third and two thirds were assigned to the genus-level for fungi and bacteria respectively, revealing that much of the diversity of soil microorganisms remains unknown and awaits detailed description. Also, we observed 756 plant species. Richness of plant species, bacterial ASVs and fungal ASVs as well as community structures of all three types of organisms differed significantly among biogeographic regions, elevational zones and land-use types. Among the five land-use types, i.e., forest, alpine grassland, meadow, arable land and settlement were 47 alpine grassland sites. They were characterized by the lowest bacterial and fungal ASV richness and the highest plant species richness compared to the other land-use types. Further, 0.8% of the bacterial and 5.7% of the fungal ASVs as well as 25.2% of the plant species were specific to alpine grassland.
Within alpine grassland sites, we found that the community structures of all three types of organisms were significantly associated (r between 0.52 and 0.61) and soil pH was the most important environmental factor for all three communities, explaining 5.5% of the fungal, 10.4% of the plant and 17.6% of the bacterial community structure variation.
In conclusion, alpine grasslands include distinct communities of plants, fungi and bacteria. Further, associations of communities reveal potential interaction probably impacted by soil pH, which was strongest for bacteria followed by plants and fungi.