Identification of the limiting resource within a semi-arid plant association

Our objective was to determine the resource most limiting to plant growth within a semi-arid plant association. We hypothesized that the addition of nitrogen (N) would elicit an increase in biomass more than additions of water, light, phosphorus (P), potassium (K), or sulfur (S). Treatments included the addition of water, N, P, K, or S, or reduction of ambient light on two sites in southwestern Montana within the Festuca idahoensis/Agropyron spicatum plant association. Nitrogen was the only treatment that increased plant community biomass, specifically native grass biomass (about 50% greater than the control). The addition of water decreased above-ground plant community biomass. Our results suggest that N is the primary limiting resource for the dominant functional group within the F. idahoensis/A. spicatum plant association.