High overlap in the richness and composition of ectomycorrhizal fungal communities associated with Corylus shrubs and co-occurring Quercus and Pinus trees

Despite being present in many North American forest understories, the ectomycorrhizal (ECM) fungal communities associated with Corylus shrubs have received no prior study. To address this knowledge gap, we characterized the ECM fungal communities on roots of Corylus shrubs as well as co-occurring Quercus and Pinus trees in Minnesota, USA. ECM-colonized root tips from pairs of Corylus shrubs and four ECM tree species, Quercus macrocarpa, Quercus ellipsoidalis, Pinus strobus, and Pinus resinosa, growing in close proximity (<1 m), were sampled at the Cedar Creek Ecosystem Science Reserve. ECM fungal communities were assessed using high-throughput sequencing of the ITS2 region. ECM fungal operational taxonomic unit (OTU) richness was equivalent among the two Quercus species and their associated Corylus shrubs, but significantly higher on P. strobus–associated Corylus shrubs compared with P. strobus, P. resinosa, and P. resinosa–associated Corylus shrubs. ECM fungal community composition on Corylus shrubs largely mirrored that on each of the Quercus and Pinus species, although the two Pinus communities were significantly different from each other. Further, the same ECM fungal OTUs were commonly encountered on paired Corylus–tree host samples, suggesting a high potential for co-colonization by the same fungal individuals. Collectively, these results support the growing consensus that woody understory plants often associate with similar ECM fungal communities as co-occurring tree hosts regardless of phylogenetic relatedness.