HR: 1330h
AN: H33B-10    [Abstracts]
TI: Controls on ecosystem respiration in a semi-arid watershed: seasonality and woody plant encroachment
AU: * Cable, J M
EM: cableje@email.arizona.edu
AF: Univeristy of Arizona, 1041 E. Lowell St., BSW 310, Tucson, AZ 85721 United States
AU: Potts, D L
EM: dlpotts@email.arizona.edu
AF: Univeristy of Arizona, 1041 E. Lowell St., BSW 310, Tucson, AZ 85721 United States
AU: Scott, R L
EM: rscott@tucson.ars.ag.gov
AF: Southwest Watershed Research Center, USDA-ARS, 2000 E. Allen Rd., Tucson, AZ 85719 United States
AU: Williams, D G
EM: dgw@uwyo.edu
AF: University of Wyoming, 1000 E. University Ave., Laramie, WY 82071 United States
AU: Goodrich, D C
EM: dgoodrich@tucson.ars.ag.gov
AF: Southwest Watershed Research Center, USDA-ARS, 2000 E. Allen Rd., Tucson, AZ 85719 United States
AU: Huxman, T E
EM: huxman@email.arizona.edu
AF: Univeristy of Arizona, 1041 E. Lowell St., BSW 310, Tucson, AZ 85721 United States
AB: Shifts in desert vegetation composition, such as woody plant encroachment into natural grasslands, may influence ecosystem processes including CO2 and H2O exchange in unknown ways. During the 2003 and 2004 growing seasons we compared CO2 efflux data from a network of three eddy-covariance towers across a woody plant encroachment gradient within a semiarid watershed. We addressed the following question: how does season influence the primary controls of ecosystem respiration as riparian vegetation structure changes? Towers were located in 3 riparian ecosystems along the San Pedro River in southeastern Arizona: grassland, savanna, and woodland. During the monsoon when soil moisture remained high for substantial periods, variation in temperature accounts for much of the short-term shifts in whole ecosystem CO2 loss. However, during the remainder of the year, when persistent drought was punctuated by ephemeral periods of high soil water availability, temperature played a minor role in controlling the respiration response. In these cases, differences in vegetation structure, their access to groundwater and influence over soil carbon and nitrogen characteristics were more important. Thus, how seasonal climate influences the duration of soil water availability in these southwestern ecosystems hierarchically controls additional drivers, such as temperature, in their influence over ecological processes.
DE: 0400 Biogeosciences
DE: 1851 Plant ecology
DE: 1866 Soil moisture
DE: 4805 Biogeochemical cycles (1615)
SC: Hydrology [H]
MN: 2005 Joint Assembly