TAMARIX RAMOSISSIMA PHYSIOLOGY AND GROUNDWATER USE DURING A RECORD DROUGHT

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.