EFFECT OF EXTERNAL SALT CONCENTRATIONS ON WATER RELATIONS IN PLANTS

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Abstract
The difference in osmotic pressures between root xylem and surface depends on the concentration of the external medium. The entire system, soil-plant-atmosphere, should be considered. Under conditions of high transpirtion, the principal resistance to water flow in this system is between plant and atmosphere and unless there are secondary effects, (closure of the stomates) water potential changes at the root surface will only negligibly affect the total water potential dropandwith it the rate of transpiration. However, the total water potential at each place within the plant will be lowered by nearly the same amount as on the root surface. Fluctuations of the osmotic differential between xylem and root surface are compensated by responses in the hydrostatic differential, so, leaf cells, under saline conditions, must take in solutes against a steeper gradient, should turgidity be maintained. Under low transpiration, changes of the root surface water potential significantly affect the rate of water flow. In this case, which leads to guttation or bleeding, the characteristics of salt transport into the xylem also influence the rate of water flow.

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