NDINGA MUNIANIA, Cedric2024-01-052024-01-052023-09https://hdl.handle.net/11299/259618University of Minnesota Ph.D. dissertation. September 2023. Major: Plant and Microbial Biology. Advisor: Georgiana May. 1 computer file (PDF); ix, 147 pages.Plants harbor tremendously diverse microbial symbiont communities (“the microbiome”) that affect the host fitness and response to environmental changes. Despite their importance, less attention has been given to the response of microbial symbionts to environmental difference, the understanding of which is crucial if we are to use these important organisms for plant conservation and restoration under future stressful conditions. Because microbial symbionts deal with environments at two different scales: the environment inside the host plant and the wider environments outside of the host, understanding the response of these organisms to changing environments requires understanding of the interplay of biotic and abiotic factors on communities. Hence, focusing on dominant members of the plant microbiomes, the fungal endophytes, the main goal of this research was to investigate how the ecological context affect microbial symbiont community structure and assembly. To do that, first, I investigated patterns of carbon resource use and growth of fungal endophytes associated with the prairie grass, Andropogon gerardii, to better understand the processes generating and maintaining functional diversity in this key group of plant symbionts. I found that fungal endophyte communities are comprised of phylogenetically distinct assemblages of slow- and fast-growing fungi that differ in their use and growth on differing carbon substrates. Importantly result revealed that traits characterizing fungi in these assemblages originate from both ancient diversification and ongoing evolutionary processes. Then, to understand how differing deterministic and stochastic processes may contribute to the assembly the fungal symbionts, and the variation of these processes across site environments, spatial scale and time, I sampled roots of the widespread prairie grass, little bluestem (Schizachyrium scoparium) across a 700 km gradient of mean annual precipitation (MAP) and over a span of two years. I used Illumina sequencing of the fungal barcode rDNA (ITS2) to characterize the diversity and composition of fungal communities and employed a community phylogenetic framework to infer the relative contributions of deterministic and stochastic assembly processes. I found that spatial distance and MAP differences among sites significantly affect fungal diversity and community composition. Despite these difference in composition, results revealed that deterministic and stochastic processes exhibit comparable contributions to community assembly across site environments, and that the importance of stochastic processes increases relative to deterministic processes at smaller spatial scales. Interestingly, comparing among years, I found that the composition of fungal communities of historically drier sites tends to shift with interannual differences in weather whereas that of communities in historically wetter environments remain stable, suggesting an importance of past weather on symbiont communities’ response to environmental changes. Lastly, I compared the root and foliar endophytes communities of little bluestem with those of the cultivated crop, corn (Zea mays), to gain insight into the impacts of agriculture on microbial symbiont community diversity and composition. Using Illumina sequencing (ITS2), I characterized root and foliar communities from the two hosts at five locations across a gradient in MAP spanning over 450 km. Results showed that across each sampled location, the composition and diversity of endophyte communities differ between little bluestem and corn, but the magnitude and direction of differences depend on the tissue sampled (roots or leaves) and the site. Collectively these three studies demonstrate that diversity and composition of microbial symbiont communities reflect outcomes of both historical and contemporary process and environmental conditions. Importantly, this study suggests that the composition and diversity of fungal communities will likely shift in response to anthropogenic climate change, but the magnitude and direction of these shifts will depend on the interplay between many biotic and abiotic factors.encommunity assemblycommunity phylogeneticsecological contextfunctional diversityfungal endophytesHost and land useThesis or Dissertation