Ectomycorrhizal fungal diversity may be influenced by arbuscular mycorrhizal trees in mixed temperate forests

Mycorrhizal fungi are critical plant mutualists that influence nutrient cycling, yet we have an incomplete understanding of factors driving their diversity and function. While it's presumed that diverse host plant communities support diverse mycorrhizal fungal communities, abiotic factors and non-host plants may also be important. We investigated whether ectomycorrhizal fungal (ECMF) communities in soils and roots varied among plots differing in tree and soil properties in three mixed ectomycorrhizal (ECM)-arbuscular mycorrhizal (AM) forests in NY, USA. We used mixed-effects models and multivariate tests to investigate ECMF taxonomic and functional responses to (1) ECM tree dominance, (2) taxonomic and phylogenetic diversity of ECM and AM trees, and (3) soil properties. ECMF taxonomic diversity was most strongly related to ECM tree dominance and the diversity of AM - but not ECM - trees. ECMF functional diversity was mostly related to soil factors and to a lesser extent tree communities. In most cases, soil nitrogen negatively influenced ECMF diversity. Collectively, our results suggest non-host (i.e., AM) tree diversity is associated with increased ECMF diversity, potentially by modifying soil conditions and resource availability. As such, mixed plots dominated by trees associating with different mycorrhizal types may be hotspots for ECMF diversity, with consequences for ecosystem functioning.