Salt Tolerance in the HalophyteSuaeda maritimaL. Dum.: Evaluation of the Effect of Salinity upon Growth

Abstract

The effects of the concentrations and species of ions in the external medium upon the growth of Suaeda maritima, a coastal halophyte, have been investigated. Plants grown in highly saline conditions (340 mol m−3 NaCl) had larger fresh and dry weights than plants grown in a standard culture medium (13 mol m−3). However, differing contributions of water and inorganic ions meant that these increases in fresh and dry weights greatly exaggerated the increase in growth, i.e. organic dry matter production. Enhanced growth in high salt concentrations was evident only after prolonged exposure and was attributable to increased cell size. Growth increased smoothly with increasing mineral concentration in the external medium and was maximal at 170 mol m−3 added NaCl, although 90% maximal growth was obtained at only one tenth of this concentration. Ion-specific growth enhancement was not apparent at low concentrations of NaCl. Growth at high concentrations (340 mol m−3) was maximal in NaCl and the effects of other salts ranged between this and toxicity in KC1. It is suggested (1) that the description of growth stimulation in halophytes by salt is somewhat arbitrary, (2) that increased organic growth with increasing salt concentration results from the relationship between turgor pressure and extension growth, and (3) that tolerance to extreme salinities is a separate phenomenon from the growth response.