The importance of K+ in Ameliorating the Negative Effects of Salt Stress on the Growth of Pepper Plants

An experiment was conduced to study the response of pepper plants under saline conditions (30 mM NaCl) on growth, cation uptake, and water and ion relations. The physiological role of K under the saline conditions was studied. Pepper plants were cultivated with five different nutrient solutions that included four K+ treatments (0.2, 2.0, 7.0 and 14.0 mM K+) with 30 mM NaCl and an additional treatment with 7 mM K+ without salt. Plants were grown in hydroponics in a controlled-environment greenhouse and the experiment was carried out until the start of the fruiting phase. Salinity reduced reproductive organs dry weight and shoot dry weight but not root dry weight. Salinity did not affect water relations at dawn but affected ion relations in leaf sap and decreased relative water content at midday. The concentration in leaf sap of Cl- and the organic solutes fructose, glucose and myo-inositol increased in salt-stressed plants. In addition, salinity produced nutrient unbalance in both leaf and root by increasing the Cl-/NO3- ratio. On the other hand, increasing K+ concentration in the nutrient solution increased salt tolerance as indicated by the increases in shoot and root dry weights. This effect was mainly due to the fact that plants under high K+ concentrations are able to keep adequate water and ion relations with a high K/Na ratio while plants under low K+ decreased the osmotic potential and showed dehydration leaf signs. Leaf sap oxalic acid concentration increased in parallel to leaf sap K+ concentration and leaf sap fructose and glucose decreased with the increase of the K+ level in the nutrient solution.