Foliar endophytes in a densely planted tree diversity experiment. Endophytes - Kreinitz experiment

Symbiotic foliar fungal endophytes can trigger beneficial effects on host trees, up to alleviating climate-induced stressors. Whether and how the community of foliar endophytes is dependent on the tree neighborhood is still under debate with contradicting results from different tree diversity experiments. Here, we present our finding regarding the effect of the tree neighborhood from the temperate, densely planted and 12-years old Kreinitz tree diversity experiments. We used linear models, redundancy, Procrustes and differential abundance analyses to quantify the effects of the plot-level tree neighborhood on the diversity and composition of foliar fungal endophytes in Fagus sylvatica, Quercus petraea and Picea abies. Against our expectations, we did not find an effect of tree diversity on endophyte diversity. Endophyte composition, however, was driven by the identity of the host species and the functional composition of the tree neighborhood. Fifteen endophytes where overabundant (only present) in tree species mixtures, which might indicate frequent spill-over or positive interactions between foliar endophytes. The independence of di-versity of endophyte from the diversity of tree species might be attributed to the small plot size and the high density of tree individuals. Yet, the mechanistic causes for these cryptic relationships still remain to be uncovered.