Tavernier, Austyn2024-06-252024-06-252024-06https://hdl.handle.net/1794/2958216 pagesClimate change is predicted to alter interannual precipitation patterns and increase drought severity and frequency. Although plant ecologists are actively investigating the impacts of climate change, we still lack robust and generalizable predictions of future plant community dynamics in light of novel precipitation regimes. One of the most pressing obstacles for making these predictions is understanding how the many species in these communities, as well as the interactions between them, respond to drought. Among the more important biotic players in structuring herbaceous plant communities are arbuscular mycorrhizal fungi (AMF) which have been shown to contribute to plant responses to drought at both an individual and community level. However, the mechanisms of drought-dependent mycorrhizal effects on plant competition have yet to be empirically assessed. To explore how AMF may modify the effect of drought on plant competitive dynamics, we conducted a greenhouse competition experiment within a two-by-two factorial manipulation of soil moisture and AMF presence. We used the data from this experiment to parameterize population dynamic models for each species (Clarkia amoena, Collinsia grandiflora, and Plectritis congesta) within each treatment combination. We used posterior distributions of our parameter estimates to explore how mycorrhizae and drought singularly and interactively influenced species vital rates, interaction coefficients, and the niche and fitness differences underlying pairwise species coexistence. We found that intrinsic growth rates of species generally decreased with drought and increased with AMF inoculation. The effects of drought and AMF were highly variable between species pairs. Overall, we found evidence of a three-way interaction between drought, mycorrhizae, and species pair on niche and fitness differences and the probability of coexistence. Most species pairs exhibited the highest probability of coexistence when both inoculated with AMF and exposed to drought conditions. The results of this study suggest that drought and AMF singularly and/or interactively influence the demographic parameters and interaction coefficients underlying plant community dynamics. Differences in coexistence probability between our treatments may implicate AMF as a key factor in whether species are able to coexist during projected increases in drought frequency. Thus, AMF could prove to be a potentially useful tool for managing plant community resilience to climate change. However, variable species responses to both drought and mycorrhizae suggest that under these conditions competitive outcomes might be affected by the strength of species-specific mycorrhizal mutualisms. Future studies on the interactive effects of mycorrhizae and droughts on plant competition should focus on identifying axes for plant species variation which may underlie the complex, species-specific interactions between mycorrhizal mutualisms and water availability.en-USCreative Commons BY-NC-ND 4.0-USUO theses and dissertations are provided for research and educational purposes and may be under copyright by the author or the author’s heirs. Please contact us <mailto:scholars@uoregon.edu> with any questions or comments. In your email, please be sure to include the URL and title of the specific items of your inquiry.coexistencearbuscular mycorrhizal fungimodern coexistence theorydroughtniche differencesfitness inequalitiesmutualismsplant competitionThesis / Dissertation