THE EFFECT OF SALT SPECIES AND COtKENTRATION ON PHOTOSYNTHESIS AND GROWTH

Osmotic adjustment (lin), stomatal res istance (r ), net photosynthes is s (P N) and three growth parameters (fresh weight-FW; dry weight-DW and length-L) were measured in pea plants grown in different concentrations (85-390 mosmol) of either NaCl, KC1, Na 2 S0 4 or K 2 S0 4 . Complete osmotic adjustment was not attained in any of the treatments, and lin decreased with increasing external sal inity, indicating a possible reduction in turgor. FW and L of the plants decreased accordingly. Stomatal resistance in plants grown in NaCl rose with increasing sal­ inity and in parallel a decrease in DWand in P N was observed. Stomatal resistance generally rose with increasing concentrations of potassium salts, but at a KCl concentration of 'V 100 mosmol rs was lower and PN was double than that of the controls. However, the dry weight of these plants was lower than of plants exposed to K 2 S0 4 . The latter had the highest dry weight of the four treatments which was even higher than that of the controls. At 'V 100 mosmol K2S04 , PN was not affected although rs increased 'V 40% above that of the controls, indicating increased capacity of the photosynthetic mechanism. High levels of potassium seem to benefit photosynthesis in Alaska peas exposed to sal inity. The osmotic component does not appear to be the main factor affecting PW ' The nature of the specific ions appear to be of greater importance, although the mechanism of their effect is as yet unclear.