Shifting from competition toward facilitation with abiotic stress is limited for two codominant grass species

Abstract It’s unclear why the C₄ grasses, Andropogon gerardii and Sorghastrum nutans, codominate in the tallgrass prairie despite asymmetric competition and drought tolerance that favors A. gerardii. According to the stress gradient hypothesis (SGH), net interactions between these species may shift from negative (competitive) to positive (facilitative) in harsher conditions. We tested this hypothesis in a greenhouse experiment manipulating community composition and water availability. We found no evidence of such a shift, suggesting limits to the SGH and the existence of other mechanisms driving codominance between these grasses.