Document: PET-3-33-9

Effects of a nitrogen and competition gradient on the growth of an exotic invasive annual and a slow-growing native perennial.

LOWE, P.N.*, W.K.LAUENROTH and I.C.BURKE

Colorado State University, Fort Collins, Colorado 80523 USA ¹

Abstract:
Exotic plant invasions are a serious concern for land managers and conservationists. Exotic plant invasions may be exacerbated by alterations in the global nitrogen cycle, so it is important to compare the effects of nitrogen availability on the growth and competitive abilities of both exotic and native plant species. This study was conducted to determine the effects of increasing and decreasing nitrogen availability on the growth and competitive ability of two grass species with contrasting life histories, Bromus tectorum, an exotic, and Bouteloua gracilis, a native. We investigated the effects of nitrogen availability and competition on aboveground biomass, belowground biomass, height, and % nitrogen tissue concentrations by growing the two species in the greenhouse under five levels of nitrogen and five levels of competition. Both species had a significant response to increasing nitrogen availability, with Bromus having a much stronger response than Bouteloua. The exotic weed species was able to exploit excess nitrogen enrichment, but the native species was not able to expand its growth past a certain level when the excess nitrogen was available. Competition significantly affected both species. Bromus was negatively impacted only by intraspecific competition, while Bouteloua was strongly negatively affected by interspecific competition from Bromus. Reducing available nitrogen suppressed the growth of both species, but did not give the native species a competitive advantage over the exotic species. Our results suggest that the success of efforts which attempt to suppress the spread of exotic weeds by reducing nitrogen availability may depend on the species of weed present.

Keywords: nitrogen, exotic species, Bromus tectorum, Bouteloua gracilis, competition

This abstract is being presented at: 9:15 AM in session:
Oral Session #61: Plant Responses to Nutrients.