Species-specific soil communities assemble around plant roots and, in turn, influence plant performance through plant-soil feedback. Negative plant-soil feedback occurs when plants culture soil communities that more negatively affect the fitness of conspecifics than heterospecifics, facilitating coexistence; positive plant-soil feedback occurs when plants culture soil communities that favor conspecifics more than heterospecifics, destabilizing coexistence. Plant-soil feedback can be measured experimentally, and there is strong support showing that variation in the strength of plant-soil feedback is linked to species abundance distributions, plant succession, and the relationship between plant species richness and primary production. However, the factors that determine variation in plant-soil feedback are largely unknown. In two separate experiments, we tested how water availability, a factor related to climate change, influenced plant-soil feedback in grasslands. In the first experiment, we tested how contemporary differences in water availability influenced feedback among plant species native to the Texas coastal prairie in a two-stage pairwise plant-soil feedback experiment. In the second experiment, we leveraged soils and plants from a long-term precipitation manipulation experiment to test whether historical differences in water availability influenced intraspecific plant-soil feedback in switchgrass, a common plant species in Texas grasslands.
In both experiments, we found that increasing precipitation shifted plant-soil feedback to more positive values. Contemporary differences in water availability shifted interspecific plant-soil feedback from neutral in lower water availability treatments to positive in higher water availability treatments, suggesting that plant-soil feedback may contribute to species exclusions in wetter environments. Shifts in intraspecific plant-soil feedback caused by historical differences in water availability were subtler, with increased water availability causing a decrease in the magnitude of negative plant-soil feedback rather than a change in the direction of plant-soil feedback. Interestingly, the effect of historical water availability on plant-soil feedback was not consistent across genotypes, suggesting that past precipitation may lead to plant-soil feedback mediated changes in the relative abundance of switchgrass genotypes. We hope our work motivates more experiments that test how other abiotic factors influence the strength and direction of plant-soil feedback, as understanding how abiotic conditions influence plant-soil feedback may be especially important for predicting plant community change in the face of changing environmental conditions.