Boreal forests represent the world’s largest terrestrial biome and provide ecosystem services of global importance. Highly imperilled by climate change, these forests host Earth’s greatest phylogenetic diversity of endophytes, a hyperdiverse group of symbionts that are defined by their occurrence within living, symptomless plant and lichen tissues. Endophytes shape the ecological and evolutionary trajectories of plants and are therefore key to the function and resilience of terrestrial ecosystems. A critical step in linking the ecological functions of endophytes with those of their hosts is to understand the distributions of these symbionts at the global scale; however, turnover in host taxa with geography and climate can confound insights into endophyte biogeography. As a result, global drivers of endophyte diversity and distributions are not known. Here, we leverage sampling from phylogenetically diverse boreal plants and lichens across North America and Eurasia to show that host filtering in distinctive environments, rather than turnover with geographical or environmental distance, is the main determinant of the community composition and diversity of endophytes. We reveal the distinctiveness of boreal endophytes relative to soil fungi worldwide and endophytes from diverse temperate biomes, highlighting a high degree of global endemism. Overall, the distributions of endophytes are directly linked to the availability of compatible hosts, highlighting the role of biotic interactions in shaping fungal communities across large spatial scales, and the threat that climate change poses to biological diversity and function in the imperilled boreal realm.
Bibliographical noteFunding Information:
We thank S. Irwin, L. Taylor, J. Stenlid, R. Andronova, A. Knorre, A. Dutbyeva, M. Zhurbenko, K. Arendt, E. Lefèvre, B. Ball, V. Wong, R. Oono, T. Gleason, J. Gonzales III, J. Riddle and K.-H. Chen for field and laboratory assistance; G. Hestmark, B. Hodkinson, S. LaGreca, J. Lendemer, B. McCune, L. Myllys, S. Stenroos and C. Truong for lichen identifications; B. Hurwitz, R. Steidl and G. Burleigh for helpful discussions; K. Youens-Clark and T. O’Connor for computational assistance; staff at the University of Arizona Genetics Core and D. New and A. Gerritsen at the University of Idaho IBEST Genomics Core for technical assistance; and M. Miller for deploying tools and databases used in T-BAS on CIPRES. This study was funded by the US National Science Foundation (NSF) Dimensions of Biodiversity program (A.E.A., DEB-1045766; I.C., DEB-1046167; G.M., DEB-1045608; F.L., DEB-1046065) and the Huron Mountain Wildlife Foundation (A.E.A.). N.B.Z. was supported by the Gordon and Betty Moore Foundation through grant number GBMF 2550.03 to the Life Sciences Research Foundation. The CIPRES RESTful API is supported by the National Institutes of Health (NIH; 5 R01 GM1264635), NSF (DBI-1759844) and an award (TG-DEB090011) of computer time and development support from the XSEDE project (also sponsored by NSF). Data collection that was performed by the IBEST Genomics Resources Core at the University of Idaho was supported in part by NIH (COBRE grant P30GM103324).