Water and Nutrient Competition Between Salsola Kali and Two Native Grass Species (Agropyron Smithii and Bouteloua Gracilis)

A greenhouse experiment was conducted to determine the effect of watering regime on competition between the introduced annual Salsola kali var. tenuifolia and the native perennial grasses Agropyron smithii and Bouteloua gracilis. The treatments consisted of pots and had mixed cultures of Salsola with either one of the grass species, and pure cultures of all three species, under wet and dry soil moistures conditions. Plants were analyzed for leaf resistance (r 1 ), N, P, K, Ca, and Mg concentrations, and aboveground biomass. Both grass species had lower biomass and higher r 1 when growing in mixed culture with Salsola than in pure culture in the dry regime, but there were no significant differences in the wet regime. The presence of Salsola did not change nutrient concentrations of the grass species in the dry regime. All three species had higher concentrations of P in the wet than in the dry regime in mixed and pure cultures, and Salsola also had higher Ca and Mg content in the wet regime. Multivariate discriminant analysis of r 1 , nutrients, and biomass showed that the response to competition by Salsola and Agropyron was more pronounced in the dry than in the wet regime. These results support the hypothesis that competition is more intense when a resource, such as water, is more limiting. The response of Salsola was changed by the grasses even though it was the superior competitor in terms of biomass. Bouteloua had increased P and K when growing with Salsola in the wet regime, so discriminant analysis showed a response to the present of Salsola in both watering regimes. Because r 1 of the grasses was higher when Salsola was present, competition for moisture may be an important mechanism bu which Salsola colonizes Bouteloua—Agropyron grassland during drought.