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


Effects of summer precipitation on photosynthesis for seedlings of two common Great Basin shrubs.

Gillespie, Ian1, Loik, Michael2, 1 2

ABSTRACT- Anthropogenic induced climate change is expected to cause a 25% increase in summer precipitation in California by 2050. A change in water availability is likely to affect seedling recruitment and establishment. However, this might be complicated by the presence of adult species whose canopies shade and possibly ameliorate harsh conditions. Nurse plants can be important restoration tools because adult plants facilitate seedling recruitment for certain species. We tested the hypotheses that: (1) a 25% increase in summer precipitation would increase photosynthesis of Artemisia tridentata and Purshia tridentata seedlings, and (2) the effects of increased precipitation would ameliorate the stress for transplanted P. tridentata seedlings growing in open microsites, compared to under the canopy of adult nurse plants. We measured water potential , CO2 assimilation, and stress within Photosystem II. There were no significant differences in water potential for watered vs. control seedlings for both A. tridentata and P. tridentata. Water additions increased transpiration nearly 2-fold for A. tridentata, but had no effect on gas exchange for seedlings of P. tridentata. Transplanted P. tridentata seedlings growing in open sites fixed twice as much CO2 compared to transplanted seedlings growing under the canopy of adult shrubs, despite higher temperatures and PFD. Our results suggest that when restoring Great Basin Desert shrublands: (1) photosynthetic increases in response to additional water will be greater for A. tridentata compared to P. tridentata seedlings and (2) open sites between adult shrubs are an important recruitment niche for P. tridentata.

KEY WORDS: Artemisia tridentata, Purshia tridentata, nurse plants, seedlings