The dark side of the Phrag: Exploring the role of dark septate endophytes in salinity tolerance of Phragmites australis

Martina Gonzalez Mateu, Department of Crop and Soil Science, Oregon State University, Corvallis, OR, Andrew H. Baldwin, Department of Environmental Science and Technology, University of Maryland, College Park, MD, Jude E. Maul, USDA-ARS, Sustainable Agriculture Systems Laboratory, Beltsville, MD and Stephanie A. Yarwood, Environmental Science and Technology, University of Maryland, College Park, MD

Background/Question/Methods
The expansion of an invasive lineage of Phragmites australis across the United States is characterized by the establishment of dense monotypic stands, displacement of native species, and alterations of nutrient cycling in invaded areas. Unlike a native American lineage of P. australis that is found in freshwater marshes, the invasive lineage predominantly expanded into oligo to mesohaline areas in the Chesapeake Bay. Although fungal endophytes can improve plant tolerance to abiotic stresses such as salinity, the role of plant-fungal interactions in invasive species ecology and their management implications remain unclear. This study characterized fungal root endophyte communities of native and invasive P. australis, and assessed the role of dark septate endophytes (DSE) in salt tolerance. Illumina sequencing of the ITS region was used to investigate fungal endophyte communities of native and invasive P. australis along a salinity gradient. DSE colonization was further quantified during a growing season and their role in salt tolerance assessed through a laboratory and a greenhouse assay.
Results/Conclusions
Fungal endophyte communities differed between neighboring stands of P. australis (PERMANOVA, p<0.001), and we observed an increase in DSE colonization of invasive P. australis roots across a salinity gradient (r=0.47, p<0.01) in the Choptank River, MD, USA. Furthermore, the laboratory study showed that DSE inoculation increased seedling survival of both native and invasive P. australis exposed to salt-stress. The greenhouse assay allowed further investigation of this effect across three levels of salinity, and we found that DSE inoculation increased plant aboveground biomass (ANCOVA, contrast t15=2.42, p=0.029) but only in mesohaline conditions. These results confirm that DSE can establish a mutualistic relationship with P. australis when subjected to moderate salt-stress. This type of plant-fungal interaction merits further investigation in studies of plant invasion ecology, management and restoration.