Changes in the resistance to water movement through the soil/plant pathway in salinized sunflower (Helianthus 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 (Helianthus giganteus) grown in sand culture were irrigated with various concentrations of NaCl up to 150 mM. The concentration of NaCl was gradually raised to avoid osmotic shock and 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. By 5 and 6 days of salinization, there were increases in the resistance to water flow across roots at the 75 mM and higher salt levels. 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. The ability of calcium to ameliorate the effect of salinity stress on sunflowers was also investigated in this study. Findings show that at salt concentrations of 50, 100, and 150 mM, and elevated calcium concentrations of 10 mM, salinity stress was reduced in all parameters studied.