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Biology of Dryland Plants

Williams, David [1].

The use of stable isotopes to investigate dynamics of dryland communities and ecosystems.

Understanding impacts of precipitation variability across multiple spatial and temporal scales represents one of the greatest challenges in dryland ecology. Integrated plant and ecosystem responses to precipitation can be evaluated from stable isotope measurements. Isotope measurements provide fingerprints of physiological responses to precipitation (past and present) and are useful for evaluating the relative activities and dynamics of different ecosystem components in complex landscapes. Isotopic studies conducted in southeastern Arizona reveal considerable landscape-level variation in response to precipitation inputs. The δ13C value of soluble leaf carbohydrates integrates short-term changes in stomatal "openness" in response to single precipitation events. The δ13C values of soluble carbohydrates extracted from leaves of adult mesquite plants in the Sonoran Desert reveal site-specific photosynthetic responses to large and small precipitation inputs. Many plants in drylands record these photosynthetic responses over time in the isotope composition of wood and other residual tissues. The δ13C value of tree-rings in desert riparian cottonwood reveals site-specific responses to interannual variation in moisture availability. The δ13C values of cellulose in rings laid down over multiple years in this obligate phreatophyte were correlated with interannual variation in stream flow of the entire reach, but only at a drier, intermittently flowing section of the river. Finally, isotope measurements of the CO2 exchanged at the ecosystem scale quantifies relative changes in respiration from soil organic matter decomposition and that from autotrophic activity. SOM decomposition dominates the respiration flux during wetting events in floodplain mesquite woodland, often causing this system to be a net source of CO2 to the atmosphere during the rainy, summer monsoon period. These and other isotopic studies highlight the very heterogeneous responses of dryland communities and ecosystems to the principal environmental driver, precipitation, and show how such measurements can be used to integrate responses in time and space.


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1 - University of Wyoming, Renewable Resources and Botany, Dept 3354, 1000 E University Ave., Laramie, Wyoming, 82071, USA

Keywords:
stable isotopes
ecosystem dynamics
precipitation variability.

Presentation Type: Symposium or Colloquium Presentation
Session: 41-8
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 10:45 AM
Abstract ID:202


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