Salt Tolerance in the Succulent, Coastal Halophyte,Sarcocornia natalensis

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Abstract
The effects of 0, 50, 100, 200, 300, 400 and 500 mol m−3 NaCl on growth and ion accumulation in the succulent, coastal halophyte Sarcocornia natalensis (Bunge ex Ung.-Sternb.) A. J. Scott were investigated. Increase in salinity from 0 to 300 mol m−3 NaCl stimulated production of fresh, dry, and organic dry mass, increased succulence and shifted resource allocation from roots to shoots. Growth was optimal at 300 mol m−3 and decreased with further increase in salinity. Water contributed to a large proportion of the increase in fresh mass. Inorganic ions, especially Na+ and Cl− contributed substantially to the dry mass. At 300 mol m−3 NaCl inorganic ions contributed to 37% of total dry mass and NaCl concentration in the shoots was 482 mol m−3. Expressed sap osmotic potentials decreased from −2.10 to −3.95 MPa as salinity increased from 0 to 300 mol m−3 NaCl. Massive accumulation of inorganic ions, especially Na+ and Cl−, accounted for 86% of the osmotic adjustment at 300 mol m−3 NaCl. Salinity treatments decreased the concentrations of K+ in shoots. Plant Na+ :K+ ratios increased steadily with salinity and reached a maximum of 16.6 at 400 mol m∽3 NaCl. It is suggested that the exceptional salt tolerance of S. natalensis is achieved by massive inorganic ion accumulation which provides sufficient solutes for osmoregulation, increased water flux and turgor-induced growth.