HR: 16:50h
AN: B34A-03    [Abstracts]
TI: Ecohydrological Consequences of Shifts in Grass-to-Woody Plant Dominance in Water Limited Ecosystems
AU: * Huxman, T E
EM: huxman@email.arizona.edu
AF: University of Arizona, Ecology and Evolutionary Biology 1041 E. Lowell St., Tucson, AZ 85721-0088, United States
AU: Scott, R L
EM: rscott@tucson.ars.ag.gov
AF: USDA-ARS Southwest Watershed Research Center, 2000 EAST ALLEN ROAD, Tucson, AZ 85719, United States
AU: Barron-Gafford, G
EM: gregbg@email.arizona.edu
AF: University of Arizona, Ecology and Evolutionary Biology 1041 E. Lowell St., Tucson, AZ 85721-0088, United States
AU: Jenerette, G D
EM: gdj@email.arizona.edu
AF: University of Arizona, Ecology and Evolutionary Biology 1041 E. Lowell St., Tucson, AZ 85721-0088, United States
AB: An increase in the representation of woody plants in historic grasslands has been a wide-spread recent phenomena in the drylands of North America. The consequences of this vegetation change for ecosystem services are uncertain and likely related to how soil-plant interactions are influenced by precipitation. Here we compare ecosystem water and carbon dioxide fluxes, determined over four years by eddy covariance, for a grassland, a grassland-shrubland mosaic, and a fully developed woodland to evaluate the relationship between land surface cover and biosphere-atmosphere exchange. Since our system is located in a riparian system, it interacts with vegetation type to accentuate differences in soil water availability and helps us to disentangle with how different carbon cycling components are coupled to the hydrologic cycle. Compared to our grassland, our grassland-shrubland mosaic often uses a similar amount of water throughout a growing season (equivalent values of evapotranspiration), whereas it accumulated a similar amount of carbon from the atmosphere as our fully developed mesquite forest (resulting higher ecosystem water-use efficiency). This pattern depends on seasonal precipitation, where changes in the size-class distribution of rainfall events and season total differentially influence ecosystem respiration and photosynthesis, depending upon woody-plant abundance and woody-plant age. Interestingly the differences in vegetation type also change the relationship between soil carbon cycling and precipitation, where microsites with high resource availability become hot-spots of activity that are important in regulating ecosystem carbon balance. A careful understanding of the complexities of both the plant and soil compartment to vegetation change is important to predicting the consequences of vegetation change on biosphere-atmosphere material and energy exchange.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly