CHANGES IN THE RESISTANCE TO WATER MOVEMENT THROUGH THE SOIL/PLANT PATHWAY IN SALINIZED SUNFLOWER (HELIANTHUS ANNUUS L. GIGANTEUS).

Abstract

The water potential gradient through the plant and the resistance to the viscous flow of water are two properties that may be affected by salinity stress within a plant. In this study, sunflowers in sand culture were irrigated with various concentrations of NaCl up to 75 mM. The concentration of NaCl was gradually raised to avoid osmotic shock and the Ca2+ concentration was maintained at 4.0 mM. Non-destructive techniques such as stem-flow gauges, psychrometers, porometry and weighing were used to determine changes in the resistance to flow and the pattern of water movement. Estimates of water potential were obtained for the rooting medium, the xylem at the shoot-root junction, and the upper leaves. From measurements of transpiration values, resistance to water flow across the roots, and between roots and leaves could be calculated. At 5 and 6 days of salinization, there were increases in the resistance to water flow across roots at the 75 mM salt level. This was accompanied by an increase in stomatal resistance to water vapor. These results suggest that moderate increases in salt level markedly affect the water relations of sunflower.