INFLUENCE OF WATER AND SALT STRESS ON WATER RELATIONSHIPS AND CARBON DIOXIDE EXCHANGE OF TOP AND ROOTS IN BEANS

Abstract

SUMMARYWhen low‐salt plants, grown in nutrient solution, were exposed to osmotic potentials in the root medium (πs)* of minus 2.7 and minus 4.7 bar due to the addition of KNO3, osmotic adjustment occurred. The leaf osmotic potential (π1,) decreased, leaf turgor potential (Ψp) and leaf water content (W) were maintained, no wilting took place, stomatal conductance (g) was partially regained and net photosynthesis was only moderately depressed.When low‐salt plants were exposed to πs of minus 2.7 and minus 4.7 bar due to the addition of PEG 1500, no adjustment to water stress was observed. Ψp decreased, the leaves became dehydrated and a high percentage wilted. Stomatal conductance, net photosynthesis, top dark respiration and root respiration were depressed. NO3‐uptake ceased completely at minus 4.7 bar.When low‐salt plants were exposed to πs of minus 4.7 bar, due to both PEG (minus 2 bar) and KNO3 (minus 2 bar), osmotic adjustment took place; π1 decreased, Ψp, W, g, net photosynthesis, top dark respiration and root respiration recovered to some extent, but the proportion of wilted leaves was high.When medium‐ and high‐salt plants, osmotically adjusted to πs of minus 2.7 and minus 4.7 bar due to KNO3 were exposed to water stress due to PEG (minus 2 and minus 4 bar), (Ψp and W were maintained, none or few leaves wilted and g was depressed less than in low‐salt plants. These responses are attributed to influence of pre‐osmotic adjustment on turgor maintenance and hydration of the plant.It is concluded that osmotic adjustment by inorganic solute uptake, before or during exposure to water and salt stress, can reduce the severe effects of low water potentials in the root medium.