CAREER: Microbial regulation of plant coexistence and invasive dominance: changes with environmental stress

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Thousands of microorganisms (e.g., fungi, bacteria) live in soil, in and around plant roots. We know that these microbes impact plant health in both positive and negative ways – some microbes help plants take up nutrients, others cause disease. Environmental change can shift plant-microbe interactions in ways that may have negative consequences for plant diversity and exacerbate species invasions. Wetlands are globally important for carbon sequestration (removal of CO2 from the atmosphere), protecting coastal cities from hurricanes, and as nursery habitat for fisheries. A severe threat to wetlands is saltwater intrusion, where saline water moves inland due to sea level rise. The biota in these systems may not be adapted to prolonged, high salinity levels and so this project will investigate how saltwater intrusion affects plant-microbe interactions with consequences for plant coexistence and invasion of Gulf Coast marshes. Competitive interactions among plants also influence coexistence and invasion and will likely shift with elevated salinity, and so the research will compare the relative importance of competitive vs. microbial interactions in driving plant community responses to saltwater intrusion. Data collection and analysis will be integrated with a high school summer course, an undergraduate service-learning course, a graduate statistics course, and this project will provide training opportunities for graduate and undergraduate researchers. A deeper understanding of how plant-microbe interactions, plant diversity, and the growth of invasive species will be affected by changing environmental conditions is important for managing our natural resources and making predictions of future change. The proposed research will elucidate how plant-microbe interactions influence biodiversity and invasion under conditions of environmental change. It utilizes and extends the Plant-Soil Feedback (PSF) research framework which has become enormously effective for studying plant-microbial interactions and their effect on plant community coexistence and invasion outcomes. The project studies the ubiquitous wetland invader Common Reed (Phragmites australis) as its model invasive species. First, the proposed research will test how salinity affects plant-fungal and plant-bacterial interactions and feedbacks in coastal marshes using a field survey and feedback experiment combined with next generation amplicon sequencing. Second, the proposed work will apply modern coexistence theory to the PSF framework to partition how salinity alters competitive and microbially-mediated coexistence mechanisms. Third, the proposed work will extend PSF theory in a novel way by explicitly modeling microbial taxa in a three-year, outdoor, mesocosm experiment using linked plant-microbial population models to assess the timescales over which specific plant-microbe interactions play out to influence community structure and invasion. New modeling techniques will be developed to pinpoint the particular microbes that are causing plant community change, a difficult task due to the incredible biodiversity of microorganisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.