THE PINE CANYON WATERSHED PROGRAM: IMPACTS OF CHANGES IN TIMING AND MAGNITUDE OF PRECIPITATION ON PLANT PHYSIOLOGY AND GROWTH

The Hadley Climate Model indicates that winter and summer precipitation will likely increase by 25% at Big Bend National Park. Water availability in arid ecosystem is often the crucial limiting factor for plant recruitment and growth, nutrient dynamics, and net ecosystem productivity. However, there are plant species differences in response to water availability that are dependent upon photosynthetic pathway, plant morphology, and root architecture. Many desert C3 species respond most strongly to winter precipitation, whereas C4 grasses respond to summer precipitation. Plants that use CAM, such as Opuntia, can respond to both summer and winter precipitation events. To address these issues of climate change on plant species in a desert landscape and differential responses depending upon photosynthetic pathway of the plant, a study has been developed within the Sotol-Grassland in Pine Canyon as part of the larger Pine Canyon Watershed Program. The study will evaluate the impacts of altered amounts and timing of precipitation on three dominant plant species within the Sotol-Grasslands: Sotol, Side-Oats Grama, and Brownspine Prickly Pear. We have established 36 plots covering 4 ha, with each plot containing one of the selected plants species. Experimental manipulations include: 1) no water addition, 2) summer water addition, 3) winter water addition, and 4) winter and summer water addition. Within each plot we will measure, leaf gas exchange, leaf chemistry, plant biomass and reproductive output, carbon flux and water flux, and nutrient and microbial dynamics These data will allow us to integrate both plant and soil responses.