Abstract
Hydrologic alterations of river systems in western North America over the past century have increased soil salinity, contributing to the establishment and spread of an introduced halophytic species, Tamarix ramosissima (Ledeb.). The physiological responses of Tamarix ramosissima to salinity stress are incompletely known. To assess the salinity tolerance of this species, we measured several whole plant and leaf-level physiological responses of Tamarix ramosissima cuttings grown in a controlled environment over three NaCl concentrations (0, 15 and 40 g·l –1 ). Tamarix ramosissima photosynthesis (A2000), stomatal conductance to water (gs), water potential (Ψw), and the maximum quantum yield of photosystem II (Fv/Fm) decreased at 15 and 40 g·l –1 NaCl compared to control treatments. However, after approximately 35 days, Tamarix ramosissima had increased photosynthetic rates, maximum quantum yield of photosystem II, and stomatal conductance to water. These data suggests that physiological functioning of Tamarix ramosissima acclimated to extremely high NaCl concentrations over a relatively short period of time. Additionally, we present preliminary evidence that suggests proline synthesis may be the mechanism by which this species adjusts osmotically to increasing salinity.
Highlights
Many adaptations have been hypothesized as mechanisms facilitating the spread of the invasive, exotic tree species, Tamarix ramosissima Ledeb., along disturbed riparian corridors in western North America
The salt tolerance of Tamarix ramosissima is likely one mechanism by which this species persists and expands its range in western North America compared to native riparian species [29,30,31,32]
Increasing salinity is known to cause physiological stress in most species [19,33,34], but few studies have examined the physiological responses of Tamarix ramosissima to salinity [8,11]
Summary
Many adaptations have been hypothesized as mechanisms facilitating the spread of the invasive, exotic tree species, Tamarix ramosissima Ledeb., along disturbed riparian corridors in western North America. These include high seed production, high growth rates [1], drought tolerance [2], ability to resprout after fire [3] or grazing, and the facultative phreatophytic nature of the species [4]. Plants may synthesize compatible solutes (e.g., proline, glycine betaine) in the cytoplasm to reestablish osmotic balance These low-molecular-mass compounds do not interfere with normal biochemical reactions [20]. Compatible solutes are energetically expensive, requiring as much as 52 ATP per mol for synthesis [21]
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