Fungal communities are an important component of the biological diversity and function of soils in most terrestrial ecosystems.   While molecular tools have opened up the black box of soil microbial communities, most community studies still focus on small-scale processes.    Our research examines macroecological determinants of fungal community structure across a California landscape.  We focus in particular on the role of dispersal in determining species richness and composition.  We do this using a model system of ectomycorrhizal fungi and ‘tree islands’ – patches of host trees in a non-host matrix.   We examine fungal communities on tree islands varying in size, isolation, and age.  In addition, we use experimentally established seedlings and direct estimates of dispersal from spore traps using techniques such as quantitative PCR and 454 pyrosequencing.

Results/Conclusions

Our studies show that macroecological processes are important in determining the species richness and composition of ectomycorrhizal fungi.  We find that richness increases with tree island area and decreases with tree island isolation.   These effects can be quite significant, with our model predicting that the number of ectomycorrhizal species on a tree island will decrease by approximately 50% at distances of 1 km away from forest edge. We also find evidence that differences in dispersal abilities between ectomycorrhizal species can lead to predictable patterns of colonization across the landscape in early successional settings.  However, over time the stochastic effects of dispersal and immigration history appear to become more important.    Understanding the spatial and temporal scales at which we can predict fungal community structure is a critical step in making the link between microbial ecology and large scale ecosystem processes.