The effects of high salinity (NaCl) and supplementary phosphorus and potassium on physiology and nutrition development of spinach
An outdoor pot experiment was carried out in sand culture to investigate the response of spinach (Spinacia oleracea ) cv. “Matador” grown at high salinity to supplementary phosphorus and potassium. Plants were tested during a period from germination to vegetative growth stage. Treatments initiated for seedling and more matured vegetative growth stages were (1) complete nutrient solution alone (C), (2) C+supplementary 5mM KH2PO4 supplied via leaves (C+FoKP), (3) C+60 mM NaCl (C+S) and (4) C+S+supplementary 5 mM KH2PO4 supplied via leaves (C+S+FoKP). Seedling growth, vegetative growth, relative water content (RWC) chlorophyll concentration and water use of spinach were reduced significantly by high salinity. The C+S+FoKP treatment resulted in increases in fresh weight, RWC, water use and chlorophyll concentrations. Membrane permeability was impaired in the plants grown at high salinity. Foliar application of 5mM KH2PO4 solution maintained membrane permeability by decreasing electrolyte leakage from leaves of plants grown at high salinity. High (60 mmol.L–1) NaCl in nutrient solution resulted in plants with very leaky root systems as measured by high K efflux; this leakiness was ameliorated by foliar application of 5 mM KH2PO4. Cumulative potassium release from intact roots was higher in plants at high salinity. These data clearly show that NaCl status affects root membrane integrity.Sodium (Na) concentration in plant tissues increased for both species, especially in lettuce, in the elevated NaCl level. High salinity lowered the concentrations of P and K in leaves, but supplementary potassium (K) and phosphorus (P) enhanced concentrations of these two elements in the leaves. The results suggest that supplementary P and K can reduce the adverse effects of high salinity on plant growth and physiological development.