Leaf-level physiological responses of Tamarix ramosissima to increasing salinity

Over the past century, the invasive halophytic shrub Tamarix ramosissima Ledeb. has increased in abundance and distribution in riparian ecosystems of western North America. These increases coincide with anthropogenic modification of river systems, which decrease the rate of periodic overbank flooding, leading to an increase in soil salinity. Increased soil salinity negatively impacts the physiology of native riparian tree species, but the impact of increased soil salinity on T. ramosissima physiology is incompletely known. To measure the impacts of soil salinity on T. ramosissima, we measured leaf-level responses across a broad range of surface-soil salinity concentrations at two sites in western Kansas. Photosynthesis at 2000 μmol m−2 s−1 (A2000), stomatal conductance to water (gs), intercellular CO2 concentration (Ci), and leaf δ13C showed little change over surface-soil salinities from 0.5 to 17.65 mmhos/cm. The small variation in leaf-level physiological responses suggests robust functioning of T. ramosissima across a broad range of surface-soil salinities. Leaf-level physiology and δ13C responses were assessed by canopy position, but responses were not significantly different. These results are among the first to show broad acclimation and robust physiological functioning for many leaf-level processes measured on mature trees grown across a wide surface-soil salinity gradient in the field.

► We show physiological responses of Tamarix ramosissima to a salinity gradient under field conditions.
► Tamarix ramosissima shows robust physiological responses across a range of salinities (low to high).
► A canopy*salinity interaction was not seen for the physiological responses measured.