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Master of Science (MS) in Biology
The Palouse Prairie of Eastern Washington and Western Idaho, characterized by rolling hills of deep loess soil, is one of the most endangered ecosystems in the world, with more than 99% converted to tilled farmland. To mitigate this loss, Eastern Washington University has begun prairie restoration on a tilled wheat field adjacent to campus, in the northern extent of the Palouse Prairie Ecoregion. However, effective restoration requires understanding reference conditions, and there are relatively few studies of remnant prairie plant communities or soils, particularly in the Northern Palouse. From north to south in the Palouse Prairie Ecoregion, there are gradients in precipitation and temperature that affect plant communities. In addition, the Prairie is intersected by Channeled Scablands, which were formed when the ancient Missoula Floods washed away some of the loess hills, leaving exposed basalt. In deeper soil pockets, Channeled Scablands have plant communities overlapping with Palouse Prairie. In prairies, both the plants and the soil microbiome can play crucial structural roles in supporting the ecosystem. Successful restoration of degraded plant communities may rely on restoration of the original soil microbiome. Therefore, my goal was to identify and survey remnant prairie vascular plant communities in the region surrounding Eastern Washington University to understand how they vary from north to south and differ from Channeled Scabland, and to understand the role that intact prairie soils, with their complement of microbial species, can play in native plant growth. This resulted in a two-part thesis, with Chapter 1 documenting remnant plant communities, and Chapter 2 studying the effect of whole soil inoculation with native prairie soils on plant growth. To document how remnant prairie plant communities near EWU differ from sites in the southern Palouse and from Channeled scablands, I identified over 100 remnants from aerial imagery across Whitman and Spokane Counties, and conducted vegetation surveys at thirteen sites, including both Palouse Prairie and Channeled Scabland locations. Palouse Prairie and Channeled Scabland plant communities, while overlapping, had significant differences as indicated by PERMANOVA analysis. Palouse Prairie remnants had relative more native species, such as Symphoricarpos albus and Balsamorhiza sagittata, as indicators, while Channeled Scablands tended to have more invasive species, including invasive annual grasses such as Bromus tectorum and Poa bulbosa. There were also distinctive differences between northern and southern Palouse sites, with northern sites having more Pinus ponderosa and Geum triflorum while southern sites had more Ventenata dubia and Lomatium dissectum. Unlike when all sites were analyzed, Palouse site community composition was correlated with aspect and solar radiation. To determine the effect of the native prairie soil microbiome on native plant growth, I inoculated native and nonnative grass species with soil from native prairies and the restoration site in a greenhouse experiment. The three inoculum sources were Turnbull National Wildlife Refuge, the EWU restoration site, and Kamiak Butte. Plants were grown in unsterilized background soil collected from the EWU restoration site and sterile or unsterile soil inoculum. In general, inoculum source had no effect on either grass species but sterilization of inoculum resulted in increased growth of the native grass especially in soil collected from the EWU restoration. Invasive grass was unaffected by treatment. Results indicate possible nutrient limitation or altered soil microbiome at the EWU restoration site. Overall, my study results provide a better understanding of reference plant and soil communities for the EWU Prairie restoration site.
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Peterson, Erik E., "Remnant assessment and soil inoculation to inform large-scale prairie restoration at Eastern Washington University" (2021). EWU Masters Thesis Collection. 739.