Prosperity of the commons: Generalist mycorrhizal species dominate a mixed forest and may promote forest diversity by mediating resource sharing among trees

Mechanisms of host–microbe interactions and their direct impact on both parties have been extensively researched, however, much less is known on the effect of these interactions on the ecology of the host-community. Here we investigate tree-fungi mycorrhizal interactions, focusing on mycorrhizal-meditated resource sharing among trees, while examining the dynamics between specialist and generalist fungi and their implications on the forest ecology. Using genetic meta- barcoding, we identified the fungal community colonizing different trees in a mixed forest, and generated an extensive mapping connecting fungal sequences to their tree hosts. The mycorrhizal fungal community diverged between ectomycorrhizal and arbuscular host trees, but, unexpectedly, multiple ectomycorrhizal species colonized roots of non-ectomycorrhizal host trees. We complemented these findings by a novel computational framework, modeling competition between generalist and specialist mycorrhizal fungi, accounting for fungal-mediated resource sharing among neighboring trees. The analysis of the model revealed that generalist mycorrhizal networks may affect the entire tree community, and contribute to the maintenance of forest diversity in the long run. Furthermore, higher initial spatial mixing of trees can promote the evolution of generalist mycorrhizal species. These novel belowground interactions among trees and fungi may significantly impact forest biodiversity. ### Competing Interest Statement The authors have declared no competing interest.