Competition between Schizachyrium scoparium and Buchloe dactyloides: The role of soil nutrients

A greenhouse experiment was conducted to evaluate the competitive abilities of Schizachyrium scoparium (little bluestem) and Buchloe dactyloides (buffalo grass) in low and high nutrient soil. These species have overlapping ranges and co-occur in semi-arid North American grasslands. Both species showed increases of approximately 2 g plant −1 in aboveground dry mass when soil nutrients were added. Aboveground dry mass of S. scoparium was slightly higher in mixture than in monoculture in low nutrient soil; however, in high nutrient soil, aboveground dry mass in mixture was significantly less than in monoculture. Buchloe dactyloides aboveground dry mass was the same in mixture and monoculture in low nutrient soil; in high nutrient soil, aboveground dry mass was significantly higher in mixture than monoculture. The competitive abilities of these species in shallow soils are dependent upon soil resource levels. At low soil resources, competitive intensity is not great and the two species appear to be equal competitors. At high soil resources, competitive intensity is greater and B. dactyloides reduced the growth of S. scoparium in mixtures. Differences in competitive abilities suggest that during the establishment phase, B. dactyloides would dominate in shallow-high nutrient soils and that coexistence would occur in low nutrient soils.