The predictive power of ecological niche modeling for global arbuscular mycorrhizal fungal biogeography

The distributions of arbuscular mycorrhizal (AM) fungal communities are driven by climate, soil nutrients, and plant community composition. However, these distributions are estimated at the community level and AM fungal taxa will respond to selection pressure of global change at the species level. Thus, ecological niche models of individual AM fungal taxa may be an informative approach to predict AM fungal composition and function under future climates at the global scale. Here we present the first attempt to model AM fungal distributions with ecological niche models for the widespread AM fungal taxon Rhizophagus irregularis (formerly Glomus intraradices). We show that despite varying the definition of the operational taxonomic unit (OTU) for R. irregularis, the predicted distributions of this species complex are consistently affected by a positive association with soil moisture. The spatial extent of ecological niche models affected the predicted distribution of R. irregularis, with climatic drivers and resources affecting its distribution more strongly in the northern and southern hemispheres, respectively. Given that AM fungi are not dispersal limited and coexist at the landscape scale relevant for ecological niche model predictions, this widely distributed fungal clade provides a robust case study to apply hypothesis-driven distributional models to predict the biogeography of microorganisms.