Ectomycorrhizal fungal richness declines towards the host species' range edge.
Plant range boundaries are generally considered to reflect abiotic conditions; however, a rise in negative or decline in positive species interactions at range margins may contribute to these stable boundaries. While evidence suggests that pollinator mutualisms may decline near range boundaries, little is known about other important plant mutualisms, including microbial root symbionts. Here, we used molecular methods to characterize root-associated fungal communities in populations of two related temperate tree species from across the species' range in the eastern United States. We found that ectomycorrhizal fungal richness on plant roots declined with distance from the centre of the host species range. These patterns were not evident in nonmycorrhizal fungal communities on roots nor in fungal communities in bulk soil. Climatic and soil chemical variables could not explain these biogeographic patterns, although these abiotic gradients affected other components of the bulk soil and rhizosphere fungal community. Depauperate ectomycorrhizal fungal communities may represent an underappreciated challenge to marginal tree populations, especially as rapid climate change pushes these populations outside their current climate niche.
['Lankau|Richard A|RA|', 'Keymer|Daniel P|DP|']
D029401:Betulaceae D044822:Biodiversity D016014:Linear Models D038821:Mycorrhizae D018517:Plant Roots D058441:Rhizosphere D012988:Soil Microbiology D013559:Symbiosis D014197:Trees D014481:United States
species range Carpinus caroliniana Ostrya virginiana biogeography ectomycorrhizae range limit