Rodent dispersal of fungal spores promotes seedling establishment away from mycorrhizal networks on Quercus garryana

Abstract

With global warming and the possible decline of conifers, more habitat may be available to oaks, particularly at higher elevations and more northerly latitudes. Whether oaks expand into new habitats will depend on their ability to disperse and establish at the margins of existing woodlands. Because oaks have a symbiotic relationship with ectomycorrhizal fungi, range expansion requires dispersal of both symbionts: the acorns and the mycorrhizal inoculum. Little is known of this dual dispersal. Here we assess the availability of ectomycorrhizal inoculum as a function of the distance from mature oaks. We examined soil cores for ectomycorrhizal roots and rodent fecal pellets for fungal spores along transects away from mature trees of Quercus garryana Dougl. ex Hook., and planted acorns as bioprobes. We identified spores by microscopy, and mycorrhizas by DNA sequences of the ITS region. Mycorrhizas were present in soil cores 5 m from parent trees, but not beyond. Spores of hypogeous fungi were found in rodent fecal pellets at distances up to 35 m from mature trees. Hypogeous fungi formed ectomycorrhizas with first-year seedlings within the root zone of mature trees and with second-year seedlings beyond the root zone. These data indicate that for seedlings near mature trees, the source of fungal inoculum was the mycorrhizal network of mature trees, and for seedlings beyond that, rodents dispersed the inoculum. We conclude that rodent dispersal of fungal spores promotes seedling establishment away from mycorrhizal networks in Q. garryana.