Background/Question/Methods Plants can alter the soil environment in which they grow, this altered soil environment can in turn impact subsequent plant growth and population dynamics. These plant-soil interactions can drive plant and microbial diversity and function in ecosystems across the globe. This change in function can be in response to changing abiotic factors, including water availability. Variation in the strength and direction of intraspecific plant-soil feedbacks in response to variable water availability remains to be examined in great detail. We explored the variation in direction and strength of plant-soil feedbacks using three ecotypes of Polemonium viscosum sampled from three sites along an elevational gradient. We used live soil microbial communities from these sites and subjected the plants to three watering regimes, in a fully factorial experimental design. These plants were grown in the greenhouse to determine the magnitude of plant-soil feedbacks. We measured effects on biomass production, nutrient content, and physiological responses. Results/Conclusions In this species, ecotype did not impact the variation in response to the soil microbes as much as water-availability or soil microbial inoculum. The plants inoculated with soil microbial communities, displayed increased tolerance to reduced water availability, specifically those inoculated with soil from our Slope 2 site. Surprisingly, we see evidence for positive plant-soil feedbacks in Polemonium viscosum when inoculated with soil microbial communities based on site. The direction and strength of these feedbacks is altered depending on the amount of water available to the plants. Our results support that microbial inoculum and environmental factors have significant effects on plant growth and function, and that the covariate of ecotype in locally-adapted field populations may be overpowered in the greenhouse by other factors. Water availability can have profound effects on plant-soil feedbacks and may alter soil functioning, soil microbial community composition, and plant community composition in a changing climate.
