Poster: Late and Moved Abstracts

Abs # 1008: Photosynthetic gas exchange in Potentilla gracilis

Presenter:	Berg, Virginia S, bergv@uni.edu
Authors	Nepal, Madhav P (A)   Berg, Virginia S (B)
Affiliations:	(A): Division of Biology, Kansas State University (B): Department of Biology, University of Northern Iowa
Web Site:	http://www.uni.edu/berg

Potentilla gracilis (Rosaceae) grows at an altitude of 3000 m in the alpine meadows of the Rocky Mountains of the U.S., experiencing extremes of photon flux density (PFD), temperature and plant water status (ψ_w) during the growing season. Using a LI-COR 6400, we investigated the photosynthetic gas exchange of this species for a range of PFDs at measurement temperatures from 5 to 25 °C following warm (20 °C) and chilling (4 °C) nights; and at 15 and 20 °C for plants with ψ_w values near -0.4, -1.0 and -1.9 MPa. Assimilation and stomatal conductance increased with measurement temperature; for the same PFD and measurement temperature they were higher following warm nights than following chilling nights. The light saturation point increased at higher measurement temperatures following warm nights, but remained low at all measurement temperatures following chilling nights. At lower measurement temperatures, there was a greater reduction in assimilation at low PFD following high PFD for plants that had experienced a chilling night prior to measurement. Assimilation values declined with lower ψ_w, but even the driest plants (wilted) maintained a positive carbon balance over most PFDs. Potentilla gracilis is constrained by the stressful conditions it regularly experiences in the field, but remains photosynthetically productive over a large range of PFDs, temperatures and water potentials.