Enhancing experimentally the structural heterogeneity of forests increase soil fungal diversity but functional lifestyles in contrasting ways

Fungal communities in soils are highly diverse both in species and functions forming a major backbone of forest ecosystems. Recent observational high-throughput-sequencing studies have shown that fungal diversity is correlated with resource availability and climate across different spatial scales. However, the underlying mechanisms remain poorly understood. Across Germany, we experimentally manipulated 11 typically homogeneous, broadleaf production forests to increase their between-patch-heterogeneity (ESBC) and compared them with a control forest. In specific, we enhanced light availability via canopy openness and deadwood resources in the ESBC treatments. Fungal communities were determined by metabarcoding at 234 patches and analysed using a novel meta-analytical approach for pairwise comparisons of taxonomic and phylogenetic diversity along Hill numbers. We hypothesized that γ-diversity is primarily driven by β-diversity increasing with canopy mediated microclimate variability and secondarily by α-diversity increasing with resource availability. Furthermore, we expected an increase in γ-diversity by unique phylogenetic lineages supporting the insurance hypothesis . Our results showed a significant increase in γ-diversity in ESBC forests, first by α- and second by β-diversity, both of which were influenced mainly by microclimate and not resource availability. The increase of phylogenetic diversity with ESBC was weak indicating functional similarity of species. Analysis of symbiotic, saprotrophic and parasitic fungal assemblages revealed contrasting effects of resource availability and microclimate across the scales. As in the UN Decade of Ecosystem Restoration many forest managers aim to increase the heterogeneity of forests and are simultaneously face rising tree mortality, our study provides first robust empirical evidence for the varying effects of forest gaps and deadwood on fungal diversity across α-, β-, γ-scales for this major kingdom.