Many studies have shown that high nitrogen availability encourages the community dominance of exotic, weedy species.Other researchers have attempted to reduce existing exotic species infestations by reducing soil nitrogen availability. We tested the hypothesis that exotic weeds and native species differ in their response to nitrogen availability, predicting that the exotics would have a much more positive response than the natives at high nitrogen levels but that natives would better tolerate low nitrogen levels. To test this hypothesis, we conducted a greenhouse experiment investigating the aboveground biomass, belowground biomass, height, and aboveground tissue nitrogen concentration response of 2 North American native plant species, blue grama (Bouteloua gracilis H.B.K. Lag.) and western wheatgrass (Pascopyrum smithii (Rybd.) A. Love), and 4 exotic species, cheatgrass (Bromus tectorum L.), leafy spurge (Euphorbia esula L.), Canada thistle (Cirsium arvense L.), and Russian knapweed (Centaurea rej ens L.), to 5 levels of nitrogen availability, 0 g N/m2,1 g N/m , 4 g N/m2, 7g N/m2, and 10 g N/m2. We grew single individuals of each species from seed in 3 liter pots in the greenhouse for 75 days. The exotics and natives did differ in their response to nitrogen availability, but not in the predicted manner. The exotics did not have a more positive response to nitrogen availability than the native species, and the species with the poorest response was an exotic. There were no differences between the exotic and native species at any level of nitrogen availability in root:shoot ratios, total biomass, or percent leaf tissue nitrogen, but the native species as a group gained more height than the exotics at every level of nitrogen availability. Our data do not show a generalizable relationship between exotic or native plant groups and growth response to nitrogen.Key Words: nutrient response, Bromus tectorum, Cirsium arvense, Centaurea repens, Euphorbia esula, greenhouse ResumenMuchos estudios han demostrado que la alta disponibilidad de nitrogeno promueve el dominio de la comunidad por especies de plantas exoticas y malezas. Otros investigadores han intentado reducir la infestacion de especies exoticas reduciendo la disponibilidad de nitrogeno del suelo. Probamos la hipotesis de que las malezas exoticas y las especies nativas difieren en su respuesta a la disponibilidad de nitrogeno, prediciendo que las exoticas tendrian una respuesta mucho mas positiva que las nativas a los altos niveles de nitrogeno, pero que las nativas tolerarian mejor los bajos niveles de nitrogeno. Para probar esta hipotesis se condujo un experimento en invernadero investigando la respuesta de la biomasa aerea y subterranea, la altura de planta y la concentracion de nitrogeno en los tejidos aereos de dos especies nativas de Norte America "Blue grama" (Bouteloua gracilis H.B.K. Lag.) y "Western wheatgrass" (Pascopyrum smithii (Rybd.) A. Love) y cuatro especies exoticas "Cheatgrass" (Bromus tectorum L.), "Leafy spurge" (Euphorbia esula L.), "...

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