DISSERTATION RESEARCH: The role of plant-soil interactions in woody shrub expansion in the White Mountains of California

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Plant and animal distributions are changing rapidly as a result of environmental and land use change. Because species respond to these changes in different ways, the composition of ecological communities is also changing. One important result is the movement or "encroachment" of woody species of shrubs and trees into grasslands around the world. Because woody plant species have very different characteristics than non-woody plants, their encroachment can have dramatic effects. For example, encroaching plants may affect microbial organisms living in the soil, such as bacteria and fungi. These soil organisms are very important for nutrient cycling and soil health because they break down decaying plant and animal material and fertilize the soil in ways that affect plant growth. Therefore, changes in the species of microbial organisms, or how they function, could in turn affect other plants in the area. This research studies how a woody species, a sagebrush shrub, that is moving uphill in the White Mountains of California, affects composition and function of soil microbial communities and the plant species they associate with. This work will be helpful in improving land management strategies in areas experiencing woody plant encroachment. It will enable training of graduate and undergraduate students and outreach to a museum and local conservation groups.This project will build upon previous work demonstrating that in the White Mountains, sagebrush has been expanding its range into alpine grasslands over the last 50 years. The project will integrate field and greenhouse experiments, modern molecular and enzymatic tools for characterizing soil communities, and plant demographic modeling to: 1) assess effects of sagebrush on soil fungal community structure and extracellular enzyme production, and 2) determine how these belowground changes feed back to affect the performance of other native alpine plants. The primary hypothesis is that native range-expanding species may affect soil microbial communities in ways that have critical feedbacks on the fitness of the existing plant community, including altering nutrient cycling and the relative frequency of pathogens vs. mutualists. This research will result in a more complete understanding of the above- and belowground impacts of alpine shrub expansion. Results will provide valuable information on the long-term status of alpine plant species under future environmental and landscape change, and the underlying mechanisms that link soil microbial communities and plant performance.