DISSERTATION RESEARCH: Mechanisms of microbe-mediated plant species coexistence across spatial and temporal scales

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Interactions between plants and their unseen microbial associates are ubiquitous in nature, yet their role in driving the diversity and coexistence of plants is not well understood. One way microbes could enhance plant coexistence is through negative plant-soil feedbacks: Plants often accumulate species-specific pathogens in their roots and soils. As a plant species increases in number, so do their pathogens, which limits unrestricted growth and can be a mechanism to allow coexistence of many plant species. This mechanism has been tested in the greenhouse, but we have little knowledge of its importance in nature. This research aims to investigate plant-soil feedbacks and its consequences for competition and coexistence between plant species by first testing it in the greenhouse, and then examining it in a field experiment. New projects that focus on culturing and sequencing the fungal associates of plants in the field and greenhouse experiments will answer questions such as: Which microbes are most important in plant-soil feedbacks? What are their effects on plant hosts? Are these effects dependent on climate? The results of these investigations will shed light on the drivers of coexistence in two foundational arid-land grasses, and will be shared with land managers to improve stewardship. This research will also provide research opportunities for undergraduate students, as well as increase public understanding of arid-land ecosystems via summer camp experiences for school children and outreach.Substantial theory and mechanistic models predict that plant-microbe interactions contribute to species coexistence, and greenhouse experiments show considerable evidence of microbe-driven plant-soil feedback (PSF). However, field tests of the role of PSF in long term vegetation dynamics are critical to determining the relative importance of PSF compared to other mechanisms of coexistence, such as spatial abiotic niche variation, operating in nature. Dissertation work fills that gap by linking the strengths of PSF (measured in field experiments) to decades-long variation in the stability of coexistence. Proposed improvements will resolve questions that have arisen from dissertation work by characterizing the belowground mechanisms of PSF using next-generation sequencing methods and targeted greenhouse inoculation of fungal cultures. Results will advance knowledge by increasing the ability to scale plant-microbe interactions from the greenhouse to the field, resolving the degree to which fungal community composition explains vegetation dynamics over spatial and temporal scales, and determining the ecological roles of a poorly understood group of fungi (dark septate endophytes), which has the potential to revolutionize current paradigms on how plants respond to abiotic stress.