Intraspecific plant-soil feedbacks alter root traits in a perennial grass

Drought is a common stressor faced by plants and their associated microbiomes. Projected climate data point toward an increase in the severity and frequency of extreme precipitation events, such as droughts. Previous research has shown that long-term exposure to drought can shape plants' genomes, resulting in genetic variation for drought tolerance. We hypothesized that these genetic changes also affect patterns of microbial colonization in the rhizosphere, potentially feeding back to influence plant drought responses. Here, we tested 33 soils conditioned by 33 genotypes of Tripsacum dactyloides (eastern gamagrass) that originated from native populations across a precipitation gradient in the southern plains of the United States. We used these 33 soils as inocula for a fully factorial experiment to test the responses of conspecific plants to the differentially conditioned soils under drought or well-watered conditions. Variation in aboveground traits such as shoot length, weight, and root-to-shoot ratios was primarily explained by watering treatment. However, many belowground traits, such as root anatomical and architectural traits, were more likely to be affected by the genotype of the conditioning plant. Of the traits we measured, only aerenchyma area was affected by the interaction between current watering treatment and genotype of the conditioning plant. Ultimately, both the current watering treatment and conditioning plant genotype altered plant physiological traits and the associated microbiome. The differential intraspecies plant-soil feedback dynamics driven by plant local adaptation will be key to understanding future plants’ responses to rapidly shifting climates, in both restoration projects and agricultural systems.