Hurricane effects on cryptic fungi in wetland plants

Background/Question/Methods

Ecologically important plants that maintain the hydrologic features and stability of deltaic systems are strongly affected by disturbance events such as hurricanes. Direct effects of hurricanes on plant communities are increasingly well documented, but indirect effects due to impacts on foliar fungal symbionts have rarely been evaluated. Recent work has shown that wetland plants along the US Gulf Coast harbor diverse endophytic fungi, many of which influence plant physiology and persistence. In this study we examined the short-term effects of a simulated hurricane on fungal endophyte communities within six wetland plants species in different habitat types. Specifically, we asked what are the effects of hurricane-mediated events (flooding, sedimentation, increased salinity, changes in nutrient content) on fungal endophyte diversity and composition in wetland plants? In a four-year mesocosm study we simulated a hurricane by flooding mature plants, altering soil deposition and salinity, and exposing plants to hurricane-force winds for six hours. Endophytic fungi were isolated in culture from mature leaves that emerged after hurricane treatment. We extracted total genomic DNA and amplified and sequenced a ca. 1000 basepair region of the nuclear ribosomal repeat (internal transcribed spacers and 5.8S and 28S gene) to determine endophyte diversity and composition.

Results/Conclusions

A total of 486 fungal isolates representing 25 species was obtained from 113 plants, including representatives of all focal species and habitat types. The simulated hurricane did not influence endophyte diversity in any species or habitat type, except within Sagittaria lancifolia, which had significantly greater diversity in controls than in plants subjected to hurricane conditions. Endophytic community composition in Taxodium distichum differed significantly after hurricane treatment vs. controls, and were strongly influenced by microhabitat conditions. Among mesocosm vessels not subjected to the hurricane, one habitat type – mesic soil, intermediate salinity, and fertilized without sediment addition -- contained endophyte communities that differed from all other habitat types. After the simulated hurricane, three of the five habitat types differed significantly from each other. Microhabitat-specific and thus differential responses to hurricane-driven disturbances may produce a mosaic of fungal endophyte diversity among coastal wetland plants in Gulf Coast systems.  As microhabitats change due to human activity and as hurricanes become more frequent or intense, fungal communities in wetland plants may be altered profoundly, with major implications for the ecology of deltaic systems.