Effects of salinity on baldcypress seedlings: Physiological responses and their relation to salinity tolerance

Growth and physiological responses of 15 open-pollinated families of baldcypress (Taxodium distichum var. distichum) subjected to flooding with saline water were evaluated in this study. Ten of the families were from coastal sites in Louisiana and Alabama, USA that have elevated levels of soil-water salinity. The other five families were from inland, freshwater sites in Louisiana. Seedlings from all families tolerated flooding with water of low (2 g l^-1) salinity. Differences in biomass among families became most apparent at the highest salinity levels (6 and 8 g l^-1). Overall, increasing salinity reduced leaf biomass more than root biomass, which in turn was reduced more than stem biomass. A subset of seedlings from the main greenhouse experiment was periodically placed indoors under artificial light, and measurements were made of gas exchange and leaf water potential. Also, tissue concentrations of Cl^-, Na⁺, K⁺, and Ca²⁺ were determined at the end of the greenhouse experiment. Significant intraspecific variation was found for nearly all the physiological parameters evaluated, but only leaf concentrations of Na⁺ and Cl^- were correlated with an index of family-level differences in salt tolerance.