The effects of changing water availability on the photosynthetic response of plants in the sotol-grasslands of Big Bend National Park, Texas

Date

2003-08

Journal Title

Journal ISSN

Volume Title

Publisher

Texas Tech University

Abstract

The Hadley Climate Model 11 predicts that Big Bend National Park will receive a 25% increase in both summer and winter rainfall over the next 100 years and that seasonal rainfall patterns will shift from frequent, small storm events to fewer, large storm events. The physiological responses of sotol {Dasylirion leiophyllum) and sideoats grama (Bouteloua curtipendula) to future predicted rainfall patterns were examined over the summer of 2002 through the winter of 2003 in the sotol-grasslands of the Pine Canyon Watershed in Big Bend National Park. Stomatal conductance and photosynthesis were measured for plants that received a 25% increase in seasonal precipitation in either the summer, winter, both the summer and winter, or that received no increase in seasonal rainfall. Stomatal conductance and photosynthesis were also measured for plants that received small, frequent rainfall pulses, rainfall pulses of moderate size and frequency, and large, infrequent rainfall pulses. The 25% increase in seasonal rainfall had no effect on stomatal conductance and photosynthesis for either D. leiophyllum or B. curtipendula, but manipulating rainfall pulses size and frequency did affect the physiological response of the two species. The increase in stomatal conductance and photosynthesis for D. leiophyllum when it received larger, less frequent rainfall pulses, and the favorable response of 5. curtipendula to rainfall pulses of moderate size and frequency suggests that the response of both species is dependent on their rooting habit. Because of its shallow roots, B. curtipendula relied on numerous small pulses to maintain soil water availability in the upper-most soil layers, whereas D. leiophyllum required larger pulses that percolate into its deeper root zone. These results suggest that both species will have a favorable response to the future rainfall patterns predicted by the Hadley Climate Model II.

Description

Keywords

Groundwater -- Rio Grande Valley, Rio Grande watershed, Rainfall frequencies -- Mathematical models, Big Bend National Park (Tex.), Growth (Plants), Desert ecology, Photosynthesis

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