Determinants of host specificity in ectomycorrhizal fungi: A focus on host and fungal biogeography

Host phylogenetic relatedness is the most widely accepted factor to explain host-fungus compatibility in ectomycorrhizal (ECM) fungi. The biogeographic similarity between host and fungus has been recently proposed as another important factor. However, as phylogenetically related hosts often have similar biogeography, it remains disputable whether host biogeography is an important determinant of host-fungus compatibility. In the present study, we conducted inoculation tests to evaluate the colonization ability of 13 ECM fungal operational taxonomic units (OTUs) which are putatively associated with Quercus serrata (Fagaceae), to three Japanese (Q. serrata, Castanopsis sieblodii [Fagaceae], and Pinus thunbergii [Pinaceae]) and two Australian species (Eucalyptus globulus and E. camaldulensis [Myrtaceae]). The colonization pattern of the inoculated OTUs could be classified into two categories: ECM fungi that associated only with Fagaceae and those associated with Japanese hosts. Eucalyptus was less able to associate with the inoculated fungi than P. thunbergii. Our results support the notion that the biogeographic similarity between fungi and hosts as well as host phylogeny can explain host-fungus compatibility.