Spatio-temporal dynamics of endophyte diversity in the canopy of European ash (Fraxinus excelsior)

Leaf-inhabiting endophytic fungi of Fraxinus excelsior growing in a floodplain forest were isolated during 2008 to investigate vertical community structure, species richness and seasonal variation. The analysis of 848 fungal endophytes from 213 leaves resulted in 50 different species. In the understorey, infection density and species richness were higher than in the crowns of mature trees throughout the whole vegetation period. Within tree crowns, sun-exposed leaves of the top canopy exhibited the lowest infection rates. Most species were rare or absent in spring and in the light crowns and frequent in autumn and the understorey. However, some species, especially the two most frequent, Alternaria infectoria and A. alternata, deviated from these patterns. Young leaves were nearly free of endophytes. Apparently, the subsequent infection and establishment of fungi strongly depend on microclimatic parameters and leaf characters, which create highly variable spatial and temporal colonisation patterns within an individual tree.