Septate endophyte colonization and host responses of grasses and forbs native to a tallgrass prairie
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Native tallgrass prairies support distinct dark septate endophyte (DSE) communities exemplified by Periconia macrospinosa and Microdochium sp. that were recently identified as common root symbionts in this system. Since these DSE fungi were repeatedly isolated from grasses and forbs, we aimed to test their abilities to colonize different hosts. One Microdochium and three Periconia strains were screened for colonization and growth responses using five native grasses and six forbs in an in vitro system. Previously published data for an additional grass (Andropogon gerardii) were included and reanalyzed. Presence of indicative inter- and intracellular structures (melanized hyphae, microsclerotia, and chlamydospores) demonstrated that all plant species were colonized by the DSE isolates albeit to varying degrees. Microscopic observations suggested that, compared to forbs, grasses were colonized to a greater degree in vitro. Host biomass responses varied among the host species. In broad comparisons, more grass species than forbs tended to respond positively to colonization, whereas more forb species tended to be non-responsive. Based on the suspected differences in the levels of colonization, we predicted that tallgrass prairie grasses would support greater DSE colonization than forbs in the field. A survey of field-collected roots from 15 native species supported this hypothesis. Our study supports the “broad host range” of DSE fungi, although the differences in the rates of colonization in the laboratory and in the field suggest a greater compatibility between grasses and DSE fungi. Furthermore, host responses to DSE range from mutualism to parasitism, suggesting a genotype-level interplay between the fungi and their hosts that determines the outcome of this symbiosis.
KeywordsDark septate endophytes (DSE) Mycorrhizal dependency Mutualism–parasitism continuum
This work was supported in part by NSF DEB-0344838 (to AJ). Konza Prairie Biological Research Station maintained the field sites and was supported by National Science Foundation Long Term Ecological Research (LTER) program. Chad Fox completed the microscopic analyses as a part of Konza Prairie LTER “Research Experiences for Undergraduates” program. Richard Wynia at the United States Department of Agriculture Natural Resources Conservation service provided some of the native seeds for the described studies. Authors thank Justin Trowbridge for assistance in acquiring the field-collected materials.
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