Poster Session # 16: Invasive Species.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Phenologic and physiologic response of native bunchgrasses to Centaurea invasion.

Pankey, J.*,1, Lee, R.1, Black, R.1, 1 Washington State University, Pullman, WA

ABSTRACT- We assessed competition for water between three invasive Centaurea species and two commonly occurring native bunchgrasses in the field. We tested the hypothesis that Centaurea would reduce soil water availability and shorten the active growing season for the co-occurring native grasses. Intraspecific comparisons of predawn leaf water potential, midday leaf water potential, and gas exchange throughout the growing season revealed that native grasses have less access to soil water when growing in the presence of Centaurea. The active growing season duration was quantified for Festuca idahoensis (C3) and Aristida longespica (C4) and the growing season for the grasses was reduced where Centaurea occurred. There was no significant difference however (p= 0.22) in aboveground growth of the grasses in response to Centaurea. Instantaneous measurements of water use efficiency (WUE) varied by day but leaf 13C of Festuca idahoensis growing with Centaurea increased (p< 0.005) by approximately 1‰ over the course of the growing season (-27.6‰ in April compared to -26.5‰ in June) indicating an increase in WUE. In contrast, there was no change in leaf 13C of Festuca idahoensis growing in plots where Centaurea had been experimentally removed (-27.4‰ in April compared to -27.5‰ in June). Increased WUE by the native grasses reduces but does not eliminate the effect of resource competition with Centaurea.

Key words: Festuca, WUE, Centaurea, resource competition