Osmotic adjustment, water relations and gas exchange in pepper plants grown under NaCl or KCl

Pepper plants (Capsicum annuum L. cv. Orlando) were used to compare the effects of NaCl and KCl on osmotic adjustment, water relations, and gas exchange. Thus, two different saline treatments, 60 mM NaCl and 60 mM KCl, were applied and different measurement times (1, 2, 3 and 10 days) were assayed in order to determine the effect of the treatment duration on the parameters studied. Reductions in root hydraulic conductance, stomatal conductance and net assimilation of CO2 were observed after NaCl and KCl addition. Mineral composition of leaf sap was also determined and it was observed that Cl- and NO3 were the main anions used by pepper plants to achieve the osmotic adjustment. Also, salinity induced a decrease in the concentrations of Ca2+ and Mg2+ in leaves. Osmotic regulation by organic solutes was also determined, by analysis of the contents of sugars and amino acids. It appeared that sucrose was the main carbohydrate accumulated by the plants in order to maintain turgor. However. the decree of osmotic adjustment observed indicated that changes in leaf turgor occurred after either saline treatment, for all application times, suggesting that pepper plants could not adjust their water relations sufficiently. Thus, Na+ and K+ exerted a toxic effect on pepper plants mainly by affecting the plant water relations, although the effect of Na+ on water relations parameters was more significant than that of K+. (C) 2004, Elsevier B.V. All rights reserved.