Management practices shape soil fungal diversity and functional traits in Swiss forests

Forests have been exploited for resources for centuries, which has caused disturbances, altered community structure, and reduced diversity at different scales. Strict forest reserves, where no forest management is practiced, have been implemented to promote biodiversity, by allowing old trees with microhabitats and high deadwood amounts. However, the effectiveness of forest reserves on soil microbial diversity and functional traits is little known at a national scale in Swiss forests. Here, we compared the diversity of soil prokaryotes, fungi and micro-eukaryotes in unmanaged forest reserves with managed forests across nine locations within Switzerland. Although forest management did not exert a dominant, overarching effect on microbial community structure when all locations were pooled (likely due to strong inter-site environmental variation), it became a significant structuring factor when analyzed at the individual forest location scale. Fungal community structure was more controlled by forest management than the prokaryotic and micro-eukaryotic ones. Fungal functional trait analysis revealed lower relative abundances of saprotrophs and higher abundances of symbiotrophs (mycorrhiza) in unmanaged compared to managed forests across all locations, suggesting an improved mutualism between tree roots and mycorrhiza in natural reserves. Local environmental conditions, such as soil pH, organic C, N, deadwood volume, MAT and MAP, and forest type (coniferous vs deciduous) also significantly structured microbial communities. Although our study highlights a clear influence of forest management on soil biodiversity, it failed to identify reliable indicator taxa in relation to forest-management practices, due to environmental variation and shifts within the microbial community assembly.