|Title||Biogeography of root-associated endophytes. In: Biogeography of Mycorrhizal Symbiosis|
|Year of Publication||2017|
|Authors||Jumpponen, A, Herrera, J, Porras-Alfaro, A, Rudgers, J|
|Number of Pages||195-222|
|Publisher||Springer International Publishing|
|Keywords||Distance decay, Environmental filtering, Helotiales, Pleosporales|
Healthy plant roots usually host heterogeneous communities of root endophytes that are abundant in all plants and ecosystems. Despite their abundance, current understanding of the distribution of these endophytes is superficial at the best. A comprehensive treatise of the distribution of variety of fungi described as root endophytes would most likely prove an exhausting exercise in futility, given the large gaps in current data. As a result, we broadly target the helotialean endophytes that are commonly observed in temperate and boreal, forested ecosystems and the pleosporalean endophytes commonly observed in grassland ecosystems. To explore the sparse data available for the distribution of these root-associated fungal endophytes, we combine references from current literature and a case study to evaluate whether or not the endophyte communities (1) shift over environmental gradients, (2) respond to some specific drivers, or (3) seem limited by dispersal by showing distance-decay responses. The data indicate that communities of endophytic fungi indeed change over large geographical scales. The available data suggest a Helotiales-dominated endophyte guild in forested ecosystems and a Pleosporales-dominated assemblage in grassland ecosystems. Further, large-scale studies and our preliminary analyses of communities across North American grassland ecosystems suggest some shifts corresponding to geographical/environmental gradients. However, specific drivers are difficult to distinguish because abiotic gradients are often correlated, resulting in complex model selection problems. Finally, we observed that our own and published data reach no agreement on distance decay, even though both agree that the distance decay may be of rather minor importance.