PARENT SESSION
Poster Session 9: Arid Lands and Deserts
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Response of net ecosystem carbon and water exchange to a large winter precipitation pulse in a sotol-grassland at Big Bend National Park, Texas.

Patrick, Lisa^*,1, Robertson, Traesha¹, van Gestel, Natasja¹, Tissue, David¹, ¹ Texas Tech University, Lubbock, TX, USA

ABSTRACT- Changes in the global climate system due to increased levels of carbon dioxide have been linked to an increase in both air and soil temperatures, thereby driving a change in patterns of global air circulation and hydrologic cycling, including regional precipitation regimes. Arid and semi-arid ecosystems are predicted to be particularly sensitive to these future environmental changes since water is the critical limiting factor in these ecosystems. In February 2005, we applied a 19 mm pulse of water to plots dominated by a perennial C3 shrub, Dasylirion leiophyllum, in a sotol- grassland at Big Bend National Park to represent a 25% increase in winter precipitation. Over the past three years, these plots have received additional precipitation in the winter (W) and in both the summer and winter (SW). We evaluated whole-ecosystem and leaf-level CO₂ and water exchange, soil CO₂ efflux, as well as plant and soil water status during the day to understand potential changes in whole-ecosystem carbon and water exchange due to increased precipitation. Prior to the irrigation pulse, all plants had similar rates of mid-day leaf water potential, leaf photosynthetic rate, stomatal conductance, and net ecosystem carbon and water exchange. Twenty-four hours following the experimental application of a pulse, CO₂ efflux, leaf photosynthetic rates, and net ecosystem carbon exchange was greater in both W and SW plots. Future measurements after pulses at different times of the year and of different magnitudes will allow for a more detailed understanding of the regulation of carbon and water fluxes at the ecosystem level in light of increased precipitation.

Key words: desert, photosynthesis, respiration