Salinity Damage to Norfolk Island Pines Caused by Surfactants. I. The Nature of the Problem and Effect of Potassium, Sodium and Chloride Concentration on Uptake by Roots

As part of an investigation into the deterioration of Norfolk Island pine, Araucaria heterophylla (Salisb.) Franco, on the coast of eastern Australia, seedlings were grown in nutrient solutions in which sodium was substituted for potassium over the range 0.1 - 2.1 mM to give six treatments, each with four ratios of sulfate to chloride. Potassium was freely taken up and translocated to the shoots, the levels in the shoots being higher than those in the roots. However, the levels of potassium in both shoots and roots were significantly reduced in solutions in which sulfate predominated over chloride. Uptake and translocation of sodium was restricted, the ratio of sodium (shoots) to sodium (roots) being less than unity. The concentration of chloride in the shoots and roots generally increased with increasing solution chloride concentration but was significantly reduced at the lowest potassium-to-sodium ratio. In a second experiment the ratio of sodium to potassium was kept at 50:1, sodium and chloride in the solutions increasing from 2.5 to 460 mM and potassium from 0.05 to 9.2 mM. At the lower concentrations, uptake and translocation followed similar patterns to those found in the first experiment. However at solution concentrations of 20 mM sodium and above, levels of sodium in the shoots exceeded those of potassium and chloride. At sodium chloride concentrations of 260mM - 460mM, plants showed toxic symptoms with salt encrustations appearing on the stems. Analysis of the saturation extracts of soils taken from beneath affected seaside trees showed that the concentrations of sodium and chloride were not sufficiently high to account for the high levels of these elements found in the shoots of affected trees.