Host tree organ is the primary driver of endophytic fungal community structure in a hemiboreal forest.

Despite numerous studies on plant endophytes, little is known about fungal communities associated with different aboveground tissues of living trees. We used high-throughput sequencing to compare the diversity and community structure of fungi inhabiting leaves, branches and trunks of Alnus incana and Corylus avellana growing at three hemiboreal forest sites. Our analysis revealed that tree organs are the main determinants of the structure of fungal communities, whereas the effects of host species and locality remained secondary and negligible, respectively. The structure of fungal communities in trunks was the most distinct compared to that in leaves and branches. The foliar fungal communities were more similar within than between individual trees, implying that certain fungi may grow through parts of the tree crown. The weak effect of locality compared to host organs and species identity suggests that the structural variation of fungal communities in the aboveground parts of trees depends mainly on deterministic factors rather than dispersal limitation. © FEMS 2019.