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Climate change models envision ail increase in summer precipitation in eastern California and adjacent arid regions by 2050, due to anthropogenic activities. Changes in the frequency, intensity and spatial patterns of rainfall pulses are likely to influence seedling recruitment and establishment, and ultimately community composition and dynamics. The effects of altered water availability might be complicated by the effect of adult plants on resources and conditions, potentially altering seedling recruitment success and affecting community succession. We tested the hypotheses that: (1) an experimental pulse representing a 25% increase in summer precipitation would increase photosynthesis for Artemisia tridentata and Purshia tridentata seedlings, and (2) for P. tridentata, experimentally applied rainfall pulses lead to greater effects on photosynthesis for seedlings planted in open microsites compared to seedlings planted under the canopy of adult A. tridentata nurse plants. We tested these hypotheses based on measurements of plant water potential, CO2 assimilation, and stress within Photosystem 11 (PSII). Water potential was higher (but not significantly) for seedlings 3 days following watering that simulated future summer monsoon rainfall pulses for both A. tridentata and P. tridentata. Water pulse treatment increased the quantum efficiency of PSI] for A. tridentata, but not for P. tridentata. Water pulses increased transpiration nearly twofold for seedlings of A. tridentata, but had no effect on gas exchange for P. tridentata. Transplanted P. tridentata seedlings growing in open microsites fixed twice as much CO2 compared to transplanted seedlings growing under the canopy of adult A. tridentata shrubs, despite higher temperatures and photosynthetic photon flux density in the open. However, neither location nor water pulse treatment affected chlorophyll a fluorescence from PSII. Our results suggest that for precipitation pulses in Great Basin Desert shrublands: (1) photosynthetic increases in response to additional summertime rainfall pulses 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. (C) 2004 Elsevier Ltd. All rights reserved.