In the Southwestern United States, flooding regimes of fluvial systems have been altered drastically over the past century. Damming and diversions for water use have decreased the rate in which periodic overbank flooding occurs which contributes to highly saline riparian ecosystems. Increased salinity is changing the structure and function of this ecosystem, and may contribute to the invasion of the tree species, Tamarix ramosissima. Tamarix species are facultative phreatophytes that are also salt-tolerant (halophytes). The halophytic nature of Tamarix may contribute to its establishment and prevalence; however, little is known about the primary physiological mechanisms associated with the salt-tolerance in this species. We are investigating the physiological responses of Tamarix to increased salinity. This species appears to maintain constant gas exchange rates and water uptake even when stressed in extremely high saline environments. This response allows the species to maintain growth across a wide range of conditions.

Jacob and Jesse have initiated a field and growth chamber experiment to study the effects of salinity on Tamarix physiology. Plots were established at Ashland, KS and the Cedar Bluff Reservoir near Ellis, KS that span a salinity gradient that ranges from very excessive to low exchangeable sodium (%). We are measuring transpiration, conductance, and photosynthetic rate to assess changes in leaf-level physiology. Plant stress is characterized by changes in Fv/Fm as well as changes in water potential. We are also measuring changes in leaf δ¹³C to assess changes in integrated water use efficiency across the salinity gradient. At each of these sites we have collected cuttings and planted them in 8”*8” pots in potting soil. Pots are watered every week with 400 mL of water and 100 mL of a nutrient solution. Using a Conviron growth chamber, cuttings are grown on a 12 hour photoperiod with 65% average relative humidity at an average temperature of 25°C. After new stems have formed, salinity treatments (0, 15, & 40 g-L^-1) were implemented. We conduct the same meausrments as in the field experiment to assess Tamarix responses to increasing salinity.