PARENT SESSION
Oral Session # 45: Plant Ecology III: Plant - Water Relations I.
Presiding: R Giuliani
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Differences in water use and photosynthetic gas exchange in Centaurea maculosa and competitors.

Hill, Judson^*,1, Germino, Matthew¹, Wraith, Jon², Olson, Bret³, ¹ Idaho State University, Pocatello, ID² Montana State University, Bozeman, MT³ Montana State University, Bozeman, MT

ABSTRACT- Whether interspecific, ecophysiological differences in water uptake and water use influence community invasibility is not well known for semiarid rangelands of the Western US. Previous research showed that water contents were lower in soils of SW Montana grassland communities containing spotted knapweed (Centaurea maculosa; CEMA) one of the most problematic invasive species of the northwestern region. The purpose of this research was to determine if interspecific differences in water status and photosynthetic gas exchange exist between CEMA and several co-occurring, established species: Pseudoregneria spicata (PSSP), Agropyron smithii, and Bromus inermis (BRIN). Microclimate, plant water potential (), and photosynthesis were measured for naturally occurring plants, and for plants grown under varying soil water availabilities in a greenhouse. No differences in photosynthesis or water use efficiency (WUE) were detected between CEMA and natives in the greenhouse during 4 days of progressive drying. However, photosynthesis of CEMA was 40-60% greater than BRIN and PSSP in the field, but it had lower WUE, which agreed with previous estimates based on carbon isotopes. CEMA also maintained 85% greater than BRIN during early and mid summer, and moreover had persistent photosynthesis in August and September when nearly all other grasses and forbs had become dormant. These ecophysiological differences may reflect greater soil water extraction in CEMA, possibly through dual use of shallow roots and taproots, which could contribute to its competitiveness under water-limited conditions.

Key words: water relations, Centaurea maculosa, WUE