Water Use and Xylem Cavitation Resistance in two Invasive Tamarix Species in Mojave Desert Riparian Ecosystems
Authors:Linda Block, Mark DeGuzman, Alexandria Pivovaroff
Mentor:Louis Santiago, Associate Professor of Physiological Ecology, UC Riverside
We are studying the resistance to xylem cavitation and water use of two invasive species of Tamarix to better understand their ecology, specifically the conditions under which drought-induced mortality will occur in established stands. Since their introduction over two hundred years ago, several Tamarix species have naturalized or become invasive in the Southwestern U.S. where they have extensively invaded riparian ecosystems. Once established, these plants have been shown to drastically alter both the biology and hydrology of these systems by lowering the water table and causing salinization of topsoil. We characterized the water use and resistance to xylem cavitation of two widespread Tamarix species, T. aphylla and T. ramossissima through physiological measurements. Samples from both species were collected from a riparian ecosystem on land protected by the Bureau of Land Management near the border of the Sonoran and Mojave Deserts. We measured the hydraulic conductivity of excised stems to generate xylem vulnerability curves (P50; 50% loss of conductivity). Pre-dawn and mid-day stem (Ψstem) and leaf water potentials (Ψleaf) were measured, as well as wood density, maximum net photosynthetic rate (Amax), stomatal conductance (gs), and transpiration (E). Based on our results neither species measured was very resistant to cavitation, with a P50 value of only -0.49 MPa for T. ramossissima and -0.98 MPa for T. aphylla. The midday Ψstem for T. ramossissima and T. aphylla were significantly lower than the P50 of either species, at -1.25 and -1.91 MPa respectively. These data correspond to a 74% and 83% loss of conductivity (PLC) for T. aphylla and T. ramossissima, respectively. Based on our water potential data, these species are experiencing significant losses in their hydraulic conductivity on a daily basis and may experience significant mortality following a drought.