PARENT SESSION
Tuesday, August 8, 5:00-6:30 pm
Poster Session 11 - Plant physiological ecology
Exhibit Hall, Ballroom Level, Cook Convention Center
Potential changes in photosynthetic performance of two Mojave Deserts shrubs in response to elevated CO2.
Ebbets, Allison*,1, Barker, David1, Ebbert, Volker2, Rosenstiel, Todd2, Adams, William2, Tissue, David3, Smith, Stan1, 1 University of Nevada, Las Vegas, Las Vegas, NV2 University of Colorado, Boulder, CO3 Texas Tech University, Lubbock, TX
ABSTRACT- A major predicted effect of elevated CO2 on plant ecophysiology is an overall increase in water-use efficiency (WUE; CO2 fixed per unit water loss) due to an increase in internal CO2 concentration, allowing stomata to partially close while supporting potentially enhanced levels of photosynthesis. Additionally, factors conferring drought tolerance may be enhanced during growth in elevated CO2 due to increases in osmolyte production (particularly sugars) coupled with increases in WUE. In the Mojave Desert, the two dominant perennial shrub species, Larrea tritentata and Ambrosia dumosa, were studied under elevated (55 Pa) and ambient (38 Pa) CO2 concentrations at the Nevada Desert FACE (Free-air CO2 Enrichment) Facility, and evaluated for differences in photosynthetic performance. The hypothesis that growth in elevated CO2 enhances photosynthesis during drought was tested by measuring photosynthetic gas exchange, chlorophyll fluorescence, and pigment, sugar, amino acid, and protein contents as seasonal water stress increased. Net photosynthesis (at respective growth CO2 concentrations) was consistently higher at elevated CO2. Photosynthetic capacity, carboxylation capacity and electron transport rate were also higher at elevated CO2 during the onset of seasonal water stress, in contrast to most other studies. However, analyses of sugar, pigment, and rubisco contents did not indicate a clear biochemical basis for this apparent photosynthetic up-regulation at elevated CO2. Our results indicate that stomatal control, and not biochemical adjustments in the mesophyll, leads to increased photosynthetic performance during seasonal water stress at elevated CO2.
Key words: elevated co2, desert ecophysiology, photosynthesis and water stress