INTERACTIVE EFFECTS OF SODIUM-CHLORIDE, SODIUM-SULFATE, CALCIUM-SULFATE, AND CALCIUM-CHLORIDE ON SNAPBEAN GROWTH, PHOTOSYNTHESIS, AND ION UPTAKE

Excessive sodium (Na) accumulation in soil, which can be a problem for production agriculture in arid and semiarid regions, may be ameliorat ed by calcium (Ca). The mechanisms of Ca amelioration of Na stress in plants have received much more attention than has the effect of the an ion of the Ca salt. Our objective was to determine the relative effect s of the chloride (Cl-) and sulfate (SO4(2-)) anions on Ca amelioratio n of Na stress. We exposed Phaseolus vulgaris L., cv. Contender seedli ngs growing in 1-L styrofoam pots under greenhouse conditions to sodum chloride (NaCl) or sodium sulfate (Na2SO4) at concentrations of 0, 15 , 30, 45, and 60 mmol/L combined with either 15 and 30 mmol/L of calci um sulfate (CaSO4) or calcium chloride (CaCl2). Plants in each styrofo am pot were irrigated with 300 mL of salt solution (leaching fraction = 0.25) every fourth day for four weeks. Increasing Na concentration d ecreased shoot dry weight, number and weight of pods, and number of no dules. The photo- synthesis rate was affected by all levels and types of Na salts. Calcium sulfate treatments ameliorated Na-induced salinit y in snapbeans more than did comparable CaCl2 treatments. The thermody namic activity of Ca, Na, and Cl was linearly related to the tissue co ntent of each ion.