2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 11
Presentation Time: 4:10 PM


NIPPERT, Jesse B.1, BUTLER Jr, James J.2, KLUITENBERG, Gerard J.3, WHITTEMORE, Donald O.2, ARNOLD, Dave4 and WARD, Joy K.5, (1)Division of Biology, Kansas State University, Ackert Hall, Manhattan, KS 66506, (2)Kansas Geological Survey, University of Kansas, 1930 Constant Ave, Lawrence, KS 66047, (3)Department of Agronomy, Kansas State University, Throckmorton Plant Sciences Center, Manhattan, KS 66506, (4)Arnold Ranch, Inc, Rt. 1 Box 256, Ashland, KS 67831, (5)Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Ave, Room 2045, Lawrence, KS 66045, nippert@ksu.edu

Declining groundwater tables and reduced stream flow in the western United States, coupled with increased demand for available water, have focused interest on the water-use dynamics of the invasive riparian shrub Tamarix ramosissima. This species commonly inhabits riparian corridors of the western United States, and alters the structure and function of this ecosystem. As future predictions of climate change include hotter and drier conditions with more variable precipitation, identifying the physiological mechanisms responsible for Tamarix water-use during drought is integral for predicting the future state of riparian ecosystems as well as total change in water availability. We measured Tamarix groundwater use and high leaf gas exchange rates despite water table declines beyond the previous rooting zone during a record drought in southwest Kansas. A significant reduction in diurnal groundwater fluctuations occurred as the water-table dropped below the historic low. Despite continued declines in the water table elevation, the diurnal fluctuations resumed several weeks after initially lost. The most likely explanation is a faster root response relative to water table declines, from advantageous soil water use, high photosynthetic rates, and tolerance of high leaf water stress. The high phenotypic plasticity of belowground growth in Tamarix provides a competitive advantage during periods of extreme water stress, and this adaptation will likely result in continued groundwater use even as groundwater tables decline in a drier future climate.