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Newman, E.D.; Rowland, J.B.; Hammer, T.G.; Frost, L.A.; Lumibao, C.Y., and Henning, J.A. 2024. Trade-offs in arbuscular mycorrhizal fungal responses to drought and salinity stress in Panicum amarum (United States Gulf Coast). Journal of Coastal Research, 40(1), 51–63. Charlotte (North Carolina), ISSN 0749-0208. Arbuscular mycorrhizal fungi (AMF) are soil and plant root-inhabiting fungi that form symbiotic associations with approximately 95% of terrestrial vascular plants and can aid in survival, growth, and stress tolerance of colonized plants. Coastal dune plants face constant environmental stress from high temperatures, sand burial, low moisture and nutrient retention, and frequent saltwater inundation. Instances of both drought and saltwater inundation stress are predicted to increase as sea levels rise and tropical storm frequency, intensity, and duration increases, with more intense periods of drought between storms. To determine whether native AMF from the United States Gulf Coast improve drought or saltwater inundation tolerance of Panicum amarum, a common Gulf Coast dune grass, a manipulative, crossed-factor greenhouse experiment was conducted by growing P. amarum with and without native AMF under drought or across a gradient of saltwater inundation concentrations: 0.25%, 0.50%, 1.00%, and 1.50%. Under 0.25% salinity, P. amarum grown with native AMF had roughly 47% greater survival, although there were no significant differences in biomass of P. amarum between live and sterile sand treatments. Under drought conditions, plants grown with native AMF had 47% lower survival and three times less biomass than those without native AMF communities. Growth differences between sand treatments were diminished under control conditions, and P. amarum grown with and without native AMF had similar survival and biomass. Despite AMF colonization, P. amarum survival was drastically reduced as salinity concentrations surpassed 0.25%. In conclusion, United States Gulf Coast dune AMF improve salinity inundation tolerance of P. amarum at low salt concentrations; however, the results emphasize the context-dependency of plant responses to AMF colonization. [ABSTRACT FROM AUTHOR]