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

It’s unclear why the C ₄ 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.