Plant-microbe interactions are key determinants of plant health in a variety of ecosystems; however, our understanding of what controls endophyte diversity and composition in plants is still in its infancy. Both abiotic environmental factors as well as host plant species can influence microbiomes. Furthermore, invasive plants might associate with diverse and distinct fungal communities that may promote expansion and spread. Here we explore the impact of environmental factors (salinity) and plant host on plant-microbe interactions in Louisiana coastal marshes, where plant species are often distributed across salinity gradients. We predict that plants will have more microbial symbionts in sites with higher salinity, indicating an adaptive response to salinity stress or increased pathogen invasion. We also expect invasive Phragmites australis to have distinct fungal communities and associate with a higher diversity of microbes compared to native plants, which may aid in invasive spread. Individuals of P. australis and 4 native species were collected from fresh, brackish, and salt marsh sites. Root samples were surface sterilized and plated on 2% MEA agar. Fungal endophytes were grown, isolated, and categorized by morphotype. Simpson’s diversity indices were calculated and community relationships were assessed using ordination methods (non-metric multidimensional scaling and PERMANOVA).
Results/Conclusions
For the plant species that were present at all three sites, we cultured a total of 32 fungal morphotypes from invasive Phragmites australis, 42 from Spartina patens, and 27 from Spartina alterniflora. For the plant species that were found at only one site, 16 (Juncus roemarianus) and 2 (Sagittaria lanceolata) morphotypes were cultured. We found that microbial diversity within host plants was highest in the brackish site (0.6087), followed by the high salinity site (0.5458), and lowest in the freshwater site (0.333). We also found that site had a nearly significant effect on endophyte composition but that host plant species did not affect community composition. These results suggest that salinity is an important driver of microbial communities. It has been shown that a greater diversity of fungal root endophytes can help alleviate plant stress. Therefore, plants growing in freshwater environments may not need as many endophytic associations. Interestingly, the invasive species did not differ much from native plants in its endophyte diversity or species composition, suggesting that other factors are likely responsible for its invasiveness. However, 22 of the morphotypes were unique to Phragmites australis, and future research will assess functions of these taxa.