Forest plant cover and mineral type determine the diversity and composition of mineral-colonizing fungal communities

Soil fungi play a fundamental role in the cycling of nutrients and tree nutrition in forests. As mycorrhizal fungi are closely associated with their host trees and provide them essential base cations and phosphorus, we hypothesize that they actively mine soil minerals and transfer their nutritive content to their host. Therefore, mycorrhizal fungi are expected to be important colonizers of soil mineral surfaces relative to other fungal trophic guilds. To test this hypothesis, 50 μm nylon mesh bags were filled with three different mineral types (i.e. calcite, apatite and obsidian) and buried in the same soil colonized by three forest stands (i.e. beech, Corsican pine and coppice with standards). After an in situ incubation period of 29 months in the topsoil, mineral dissolution was detectable in the mesh bags, and the analysis of the fungal communities was therefore undertaken. Minerals presented a lower fungal biomass than the surrounding bulk soil and no difference between the three mineral types tested was observed. The high-throughput sequencing (HTS) approach showed that the fungal communities differed among the three forest stands, but in each case, mineral associated fungal taxa differed significantly from those in the bulk soil. To a lesser extent, fungal communities further varied between the three mineral types. Overall, trophic inference analyses suggested that two groups of plant-associated fungi, namely the ectomycorrhizal and endophytic fungi, were the major fungal mineral colonizers. Saprophytes also appeared significantly enriched on minerals comparatively to the surrounding bulk soil. Together, our data reveal at local scale that the mineral-associated fungal communities are first determined by the forest plant cover and then by the type of mineral.