COMBINATION EFFECT OF NACL SALINITY, NITROGEN FORM AND CALCIUM-CONCENTRATION ON THE GROWTH, IONIC CONTENT AND GASEOUS EXCHANGE PROPERTIES OF TRITICUM-AESTIVUM L CV GAMTOOS

The effects of NaCl salinity have been investigated with respect to the growth response, ionic content and gas exchange characteristics of wheat plants (Triticum aestivum L. cv. Gamtoos) raised on nitrate or ammonium nutrition at different Ca2+ concentrations in the nutrient medium. Salinity up to 100 mm reduced the biomass production, moisture content and water use efficiency of both NO3- and NH4+-supplied wheat but the biomass production of NO3--supplied wheat was reduced to a far greater degree than that of NH4+-supplied wheat. There was no clear trend in the photosynthetic response of these plants to moderate salinity stress (50 mM NaCl). The stomatal conductances and transpiration rates of NH4+-supplied wheat were between 20 and 40 % lower than those of NO3--supplied wheat, depending on the degree of salinity stress; at higher salinity (70-100 mM NaCl) the moisture content of NH4+-supplied plants was c. 10% higher than that of NO3--supplied salinized plants. An increase in Ca2+ concentration from 0.5 to 5.0 mm resulted in an increase in biomass production, moisture content, shoot: root ratio, K+ content and a decrease in Na+ content of 50 mm NaCl-stressed, NO3--supplied plants. Supplemental Ca2+ had no effect on the biomass production, shoot: root ratio or moisture content of 50 mm NaCl-stress, NH4+-supplied plants relative to the controls.