PARENT SESSION
Oral Session #66: Invasions: Plants. Mechanisms, patterns, controls. Presiding: R. Mack.
Thursday, August 9, 2001. 1:00 PM to 4:45 PM. Hall of Ideas E.
Nutrient competition in a diffuse knapweed (Centaurea diffusa) -invaded prairie.
LEJEUNE, KATHERINE1,2, SEASTEDT, TIMOTHY1, SUDING, KATHARINE1, 1 2
ABSTRACT- Five species of knapweed (Centaurea) have invaded millions of hectares of western North American grasslands. We suspect that Centaurea species invade by exploiting region-wide increases in N availability. Centaurea species then may maintain dominance by preventing the resources from returning to levels that favor the native species and by competing successfully for the new limiting resource. Evidence from ongoing fertilization studies in C. diffusa-invaded mixed-grass prairies in Colorado suggests that P limitation or a co-limitation of P and water best explain the current dominance patterns. In 1999, neither C. diffusa adult biomass nor non-C. diffusa plant biomass responded significantly to added N. However, C. diffusa responded strongly to added P. Results from the same site in 2000 were similar. At a second site fertilized only in 2000, N and P co-limited C. diffusa biomass, while P alone limited seed head production. A comparison of nutrient concentrations in soils dominated by C. diffusa and Buchloe dactyloides, a native C4 grass, showed that total C, N, and P and labile P concentrations are significantly greater under B. dactyloides than under C. diffusa. Nitrate concentrations are significantly greater under C. diffusa. Centaurea diffusa may retard soil succession by reducing C and N storage in soil and maintaining high rates of nutrient cycling. Our ongoing research will address the temporal variation in N-transformation rates that we expect occur under this C3 forb.
KEY WORDS: Centaurea diffusa, Invasive species, Nutrient cycling, Nutrient competition