Movin\u27 on Up: Mycorrhizal Mutualisms and Assisted Migration of Coastal Plant Species

Coastal marshes are among the first ecosystems to be altered by climate change. With increasing sea-level rise, assisted migration may be necessary to establish founder populations in more favorable upslope habitats. Mycorrhizal mutualisms could play a key role in determining success of these moving populations. If the assemblages of fungal spores are well mixed across the coastal transition gradient, then landward-retreating plant species can form associations with the same fungal species in the new habitat. The objectives of this study were: (1) to identify potential mycorrhizal relationships by determining if assemblages of spores exhibit zonation mirroring that of coastal plant communities and (2) to test whether or not abundance and composition of mycorrhizae in roots of a dominant marsh species (Juncus roemerianus) differ with simulated assisted migration into upslope soils. Soil samples and seeds for trap plants were collected from the coastal coenocline at Grand Bay National Estuarine Research Reserve in coastal Mississippi, USA. A total of 1607 unique operational taxonomic units (OTUs) was found across the entire gradient and was classified into five genera: Rhizophagus, Glomus, Funneliformis, Diversispora and Scutellospora. The soil samples had an average of 196.25 OTUs per sample, while the root samples were less diverse with an average of 29.04 OTUs per sample. DNA analysis of soil samples show that Glomeromycete propagules exhibit zonation on the seaward-most end of the gradient (salt marsh), but AMF composition becomes increasingly mixed with increasing elevation in brackish marsh, fresh marsh and pine woodlands zones. Salt marsh showed isolation in its species composition, sharing only two OTUs with the other three zones. Only one OTU (Rhizophagus sp.) was present across all four vegetation zones. Species richness and abundance of mycorrhizal spores in the soil samples increased along the elevation gradient; they were highest in the pine woodlands (dry end) and lowest in the salt marsh (wet end). OTU richness and abundance significantly increased in the roots of J. roemerianus trap plants when transplanted to soils upslope of its naturally dominant zone (brackish marsh). These results indicate that, apart from the salt marsh, plant-mycorrhizae relationships can persist after upslope migration of coastal plant species. New, as well as old, fungal associations may aid in the survival of the host plant in the new habitat