Interactive effects of sodium and potassium on the growth and photosynthesis of spinach and komatsuna

Two cultivars of spinach and one cultivar of komatsuna were sand cultured using a nutrient solution with Na and K in various combinations. The growth (fresh weight of shoot) of spinach cv. Atlas was significantly increased when 1.4 mM KCl of the 7 mM KCl was replaced with 1.4 mM NaCl, although the growth was reduced when more KCl was replaced with NaCl. In another spinach cv. All Right, however, NaCl substituting for 20% of KCl showed no significant effects. In komatsuna, Na used in place of K at any ratio reduced the growth. The growth of spinach cv. Atlas was increased by applying 20 mM NaCl, irrespective of K dose (480 - 2400 mgK(2)O per 1/2000 a Wagner pot). The growth of spinach cv. All Right was also increased by 20 mM NaCl when K was at a deficient level (480 - 960 mg K2O per pot), but was not when K was at an excessive level (1920 - 2400 mg K2O per pot). In komatsuna, 20 mM NaCl reduced the growth. In spinach, Na prevented the decrease of the photosynthetic rate and stomatal conductance caused by K deficiency.