Effect of sodium chloride salinity on the water balance of Atriplex halimus

Sodium chloride was found to improve the water balance of A. halimus plants under conditions of high evaporative demand. This improvement was expressed by higher values of turgor pressure and percentage saturation value in plants grown in salinized culture solutions (Knop solution to which sodium chloride was added to give final osmotic potentials of from -3 to -10 bars) as compared with plants grown in the control (Knop) solutions. However, only in leaves of plants grown in saline culture solutions whose osmotic potential did not exceed -5 bars was a constant water potential gradient maintained between the culture solution and the leaf. Furthermore the hydraulic conductivity of the root system appeared to have been impaired by salinity. The improved water balance of plants which were exposed to salinity could be ascribed to a reduction of transpiration. This was due to some extent to an increase of stomatal resistance but also to a highly significant increase of mesophyll resistance to water loss (r_m).Photosynthesis was not affected by r_m. The ecological implications of the presence of the _m factor to the measured transpiration/photosynthesis ratio are discussed.