PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Plant responses to variation in timing and magnitude of precipitation in Big Bend National Park.

Robertson, Traesha^*,1, Walker, Erin¹, Zak, John¹, Tissue, David¹, ¹ Texas Tech University, Lubbock, TX

ABSTRACT- Water availability is the primary limiting factor for plant growth, soil nutrient dynamics, and ecosystem productivity in arid ecosystems. Plant species have different responses to water availability that are dependent on photosynthetic pathway, plant morphology, and root architecture. We tested effects of predicted future changes in precipitation patterns and water availability by altering the precipitation received by the dominant plant species of the sotol-grassland community: sotol (Dasylirion leiophyllum; C3), sideoats grama (Bouteloua curtipendula; C4) and brownspine prickly pear (Opuntia phaeacantha; CAM). The first experiment investigated how a 25% increase in summer and winter precipitation affected plant photosynthetic performance, growth and species competition. A second experiment used rainout shelters to exclude natural rainfall and then we added rainfall pulses of different amounts and frequency to the plots. Plants received rainfall as small but frequent pulses, pulses of moderate size and frequency, or large but infrequent pulses to determine how a shift in pulse timing and magnitude might affect plant photosynthetic performance. In the first year of study, following the summer watering of 2002 and the winter watering of 2003, we found that the 25% increase in water availability significantly increased the photosynthetic performance of grama (C4) during the summer and sotol (C3) during the winter. However, the growth response (i.e. changes in leaf area, leaf volume, and biomass) was not altered for any species in either season. In the rainout shelter experiment, small, frequent summer rain pulses increased photosynthesis in grama, while larger, less frequent pulses in both the summer and winter increased photosynthesis in sotol. Therefore, differences in pulse size and frequency may differentially affect photosynthesis in these desert species. It remains to be determined whether differences in carbon assimilation will change long-term plant growth.

Key words: Chihuahuan Desert, photosynthesis, Rain pulse, growth