| Woody plants host diverse communities of associated organisms, including woodinhabiting
fungi. In this group, host effects on species richness and interaction network structure
are not well understood, especially not at large geographical scales.
We investigated ecological, historical and evolutionary determinants of fungal species richness
and network modularity, that is, subcommunity structure, across woody hosts in Denmark,
using a citizen science data set comprising > 80 000 records of > 1000 fungal species on
91 genera of woody plants.
Fungal species richness was positively related to host size, wood pH, and the number of
species in the host genus, with limited influence of host frequency and host history, that is,
time since host establishment in the area. Modularity patterns were unaffected by host history,
but largely reflected host phylogeny. Notably, fungal communities differed substantially
between angiosperm and gymnosperm hosts.
Host traits and evolutionary history appear to be more important than host frequency and
recent history in structuring interactions between hosts and wood-inhabiting fungi. High
wood acidity appears to act as a stress factor reducing fungal species richness, while large host
size, providing increased niche diversity, enhances it. In some fungal groups that are known
to interact with live host cells in the establishment phase, host selectivity is common, causing
a modular community structure.|