Document: MIC-3-34-21

Chlorophyll fluorescence for Mojave Desert plants exposed to elevated CO₂ in wet and dry years.

LOIK, M.E.* ¹, T.E.HUXMAN ², D.C.HOUSMAN ³ and S.D.SMITH ³

University of California, Santa Cruz, CA 95064 ¹
University of Colorado, Boulder, CO 80309 ²
University of Nevada, Las Vegas, NV 89154 ³

Abstract:
Little is known about the potential effects of anthropogenic elevated CO₂ on the efficiency of PSII, especially for desert plants exposed to combined conditions of intense PFD, high temperatures, and drought. Elevated CO₂ may alter PSII performance by enhancing the sink for excitation, or by altering the degree of photoprotection. We examined the chlorophyll fluorescence responses of plants exposed to a FACE manipulation in the Mojave Desert to test the hypotheses that (1) elevated CO₂ increases the efficiency and photoprotection of PSII, and (2) interannual differences in precipitation alter the responses of PSII to elevated carbon dioxide. Plants were exposed in situ to ambient (360 mol mol^-1) or elevated (550 mol mol^-1) CO₂; water relations and PAM chlorophyll fluorescence were measured throughout 1998 and 1999. Water potential varied in a species-specific manner from about -2.0 MPa in 1998 to below -6.0 MPa in 1999. F_V/F_M for Larrea tridentata was higher in both years for plants under elevated CO₂, whereas the opposite pattern occurred for Krameria erecta. Downregulation of PSII quantum yield was less for plants in ambient vs. elevated CO₂ plots. Non-photochemical quenching was affected by CO₂ treatment at certain times. The results are consistent with other studies that show that species-specificity will be important for physiological performance of desert species in a future climate. At certain times when water potential is suitable for stomatal opening, elevated CO₂ may alter PSII quantum yield and energy dissipation for Mojave Desert plants.

Keywords: El Nino, La Nina, water potential, F_V/F_M, non-photochemical quenching, Photosystem II

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.