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 ameliorated by calcium (Ca). The mechanisms of Ca amelioration of Na stress in plants have received much more attention than has the effect of the anion of the Ca salt. Our objective was to determine the relative effects of the chloride (Cl-) and sulfate (SO4(2-)) anions on Ca amelioration of Na stress. We exposed Phaseolus vulgaris L., cv. Contender seedlings 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 calcium sulfate (CaSO4) or calcium chloride (CaCl2). Plants in each styrofoam pot were irrigated with 300 mL of salt solution (leaching fraction = 0.25) every fourth day for four weeks. Increasing Na concentration decreased shoot dry weight, number and weight of pods, and number of nodules. The photo- synthesis rate was affected by all levels and types of Na salts. Calcium sulfate treatments ameliorated Na-induced salinity in snapbeans more than did comparable CaCl2 treatments. The thermodynamic activity of Ca, Na, and Cl was linearly related to the tissue content of each ion.