Effects on Casuarina and Allocasuarina Species of Increasing Sodium Chloride Concentrations in Solution Culture

Abstract

Ten species of Casuarina and Allocasuarina were exposed to increasing levels of NaCl (max 550 mM) in solution culture over a period of 5 months. Na⁺ and Cl^- ion concentrations increased in the tissues of all species as the salinity increased and K⁺ was selectively accumulated. Those species which ultimately survived to the highest salinities tested had lower concentrations of Na⁺ and Cl^- in both shoot and roots and lower Na⁺/K⁺ ratios than the more sensitive species at low external salinities. Osmotic adjustment of the Casuarina species was principally accounted for by Na⁺ and Cl^- in the shoots. Turgor pressure was not lost until the plants were close to death, so that inhibition of height growth by NaCl was probably due to the high cellular ion concentrations. Plants were more sensitive to osmotic shock than to a gradual increase in salinity.