Poster Session #31: Climate Change.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall


Photosynthetic responses to increased summer precipitation for two Great Basin Desert shrubs.

Loik, Michael 1, 1

ABSTRACT- Current GCMs predict a 25% increase in precipitation by 2050 for California due to anthropogenic climate forcing. For the desert ecosystems of eastern California, predicted precipitation changes are highly uncertain, but an increase in summer monsoon activity is considered likely. Although increased precipitation could be beneficial for survival and productivity of desert plants, not all species utilize summer rain. I tested the hypothesis that increased summer precipitation will enhance photosynthesis for the widespread dominant Great Basin Desert shrubs Artemisia tridentata and Purshia tridentata. I added supplemental water over the range of 0 to 200% of average precipitation to account for uncertainty in GCM predictions. I measured water relations, photosynthesis and stress within PSII. Results show that water potential increased dramatically between 0 and 25% additional water. However, photosynthesis was not significantly affected by the experimental 25% increase in precipitation. For plants treated with 200% of average precipitation, assimilation increased by 6-fold for A. tridentata and by 8-fold for P. tridentata. Based on transpiration, WUE increased 11-fold for A. tridentata, but only 2-fold for P. tridentata. There were no significant changes in stress within PSII as indicated by chlorophyll a fluorescence. Future patterns of photosynthesis in response to increased summer rainfall will be species-specific and will depend importantly on the magnitude of actual precipitation changes.

KEY WORDS: water relations, Artemisia tridentata, Purshia tridentata, monsoon