Background/Question/Methods Developments of dams, stream diversions, and groundwater pumping have altered stream flow regimes in riparian ecosystems of western North America.  These alterations have decreased periodic overbank flooding which has led to salinization and lowered water table height in riparian ecosystems.  These factors have subsequently contributed to the decline of native mesic tree species.  As hydrologic processes have changed over the past century, the exotic, invasive plant species Tamarix ramosissima has increased in range, abundance and cover in riparian ecosystems.  Understanding how changes in riparian salinization impact Tamarix physiology may facilitate predictions of Tamarix responses in the future.  In this study, we investigated the response of Tamarix leaf-level and whole-plant physiology to increasing salinity using both field and controlled environment studies.  To measure the impacts of soil salinity on Tamarix physiology in the field, we measured leaf-level responses across a broad range of salinity concentrations at two sites in western Kansas.

Results/Conclusions Light saturated photosynthesis (A_sat), stomatal conductance to water (g_s), intracellular [CO₂] (C_i), leaf δ¹³C, and leaf water potential (Ψ_w) were relatively constant over a range of soil salinities (0.5 to 17.65 mmhos/cm).  Leaf-level responses were also assessed by canopy position (bottom, middle, or top of tree), but a salinity*position response was not significant (p > 0.05) for leaf-level physiological responses and δ¹³C.  To increase the range of soil salinities (0, 22, 54 mmhos/cm), Tamarix cuttings from both field sites were grown in a controlled environment.  Tamarix leaf-level physiology was consistently lower at the highest salinity (54 mmhos/cm).  Results from this study also suggest that acclimation to high salinity occurs quickly over time as reflected by leaf-level physiology and dark-adapted chlorophyll fluorescence (F_v/F_m).  This data illustrates the robust physiological functioning of Tamarix in response to increasing salinity. Our results suggest that the physiological tolerance of Tamarix to a range of soil salinities is one mechanism facilitating range expansion and persistence in riparian ecosystems.