Potassium fertiliser enhances the salt-tolerance of common bean (Phaseolus vulgaris L.)

Sodium chloride (NaCl) is the most abundant salt that contributes to soil salinity. The response of plants to excess NaCl is complex, involving changes in their morphology, physiology, and metabolism. Potassium (K) is not only an essential macronutrient for plant growth and productivity, but it is also a primary osmoticum for maintaining the low water potential of plant tissues. A pot experiment was conducted in the wire-house of the National Research Centre, Cairo, Egypt, during the 2010-2011 season, to examine the potential role of K fertiliser in alleviating the deleterious effects of NaCl-salinity on some physiological and biochemical traits of two recombinant inbred lines (RILs) of common bean (Phaseolus vulgaris L.; RIL 147 and RIL 115). The results showed that salinity levels of 25 mM (Si) and 50 mM NaCl (S2) caused significant decreases in the numbers of pods per plant, the fresh weight (FW) and dry weight (DW) of pods per plant, shoot DW per plant, as well as in the level of photosynthetic pigments, compared to plants irrigated with tap water (S0). A dose of 150 mg K2O kg(-1) soil (K2) mitigated these harmful effects of salinity on common bean yield and on the content of photosynthetic pigments. Both salinity levels (S1 and S2) and treatment K2 caused significant increases in proline, free amino acid, and soluble carbohydrate concentrations, as well as peroxidase and polyphenol oxidase activities, relative to the corresponding control plants. In contrast, both RILs show a decrease in their phenolic compound concentrations due to salinity and/or the application of K2 compared to control plants (i.e., treatment S0K1; where K1 =25 mg K2O kg(-1) soil). The K+:Na+ ion ratio decreased significantly as the salinity level increased, and increased significantly under treatment K2. We conclude that treatment K2 mitigated the adverse effects of salinity (NaCl) through the effect of K+ ions enhancing the levels of photosynthetic pigments, anti-oxidant enzyme activities, osmoprotectant concentrations, and the K+:Na ion ratio, all of which were reflected in an improvement in plant performance.