Salinity tolerance of Kosteletzkya virginica. I. Shoot growth, ion and water relations

Abstract

Abstract. Kosteletzkya virginica (L.) Presl., a dicotyledonous halophyte native to brackish tidal marshes, was grown on nutrient solution containing 0. 85, 170 or 255 mol m‐3 NaCl, and the effects of external salinity on shoot growth and ion content of individual leaves were studied in successive harvests. Growth was stimulated by 85 mol m‐3 NaCl and was progressively reduced at the two higher salinities. Growth suppression at high salinity resulted principally from decreased leaf production and area, not from accelerated leaf death. As is characteristic of halophytic dicots. K. virginica accumulated inorganic ions in its leaves, particularly Na+ and K+. However, the Na+ concentration of individual leaves did not increase with time, but remained constant or even declined, seeming to be well‐coordinated with changes in water content. A striking feature of the ion composition of salinized plants was the development of a dramatic gradient in sodium content, with Na+ partitioned away from the most actively growing leaves. Salt‐treated plants exhibited a strong potassium affinity, with foliar K+ levels higher in salinized plants than unsalinized plants after an initial decrease. These results suggest that selective uptake and transport, foliar compartmentation of Na+ and K+ in opposite directions along the shoot axis, and the regulation of leaf salt loads over time to prevent build‐up of toxic concentrations are whole‐plant features which enable K. virginica to establish favourable K+‐Na+ relations under saline conditions.