When plants experience stress, they become more susceptible to disease, but endophytes -- fungi that live within plant leaves -- may ameliorate some of these negative effects. Thus, determining the effects of sea-level rise and storms on endophytic communities may be important in understanding plant community dynamics in coastal systems in the context of global climate change. Using mesocosms in which we manipulated flooding, salinity, and sediment load, we asked whether coastal processes simulating storm surges affect community structure of endophytic communities in two focal wetland plants (Taxodium distichum and Sagittaria lancifolia). Twenty weeks after the onset of treatments, we surface-sterilized mature leaves produced under mesocosm conditions and incubated small tissue fragments on 2% malt extract agar to isolate fungal endophytes. Data from the nuclear ribosomal internal transcribed spacer and large subunit (ca. 1000bp) were used to estimate species boundaries. We calculated diversity using Fisher's alpha for each individual plant. We used diversity as the metric in an ANOVA to determine whether there were significant differences in fungal diversity among treatments. We also used nonmetric multidimensional scaling to determine whether communities differed between plant hosts and among treatments.
Results/Conclusions
Overall, in fresh water, flood stress was associated with lower diversity when sediment was added. Conversely, in high salt conditions, diversity was decreased when sediment was not added to the mesocosms. Fungal diversity in S. lancifolia exceeded that in T. distichum, overall. Sediment addition was the only factor that affected community structure in T. distichum. In general, Sagittaria lancifolia community structure was unaffected by sediment. When conditions were favorable for the host, however, rare fungal species were present at the expense of common, cosmopolitan species. One common species that inhabited most of the leaf tissues sampled in both hosts was never found in individual plants exposed to highly favorable treatments. Instead, rare fungi occupied these tissues. In addition, these rare fungi were never found in both hosts, suggesting that highly favorable conditions for the plant host select for host specific endophytic fungi. Therefore, endophyte community response to sea level rise and storms may depend on the host they inhabit.
