Effect of Salinity on Growth and on Mineral and Organic Constituents of the Halophyte Disphyma australe (Soland.) J.M. Black

Abstract

The growth of the succulent halophyte Disphyma australe was stimulated by increments of salinity to a level of 200 mol m^-3 NaCl. This was due to increases in leaf number per plant and in leaf water and total inorganic content, but not in leaf organic content. At high (500 mol m^-3) salinity, leaf growth per plant was c. 30% less than the optimum and was attributable to decreases in leaf number per plant. Individual leaf fresh weight, water content and total inorganic content increased throughout the salinity range. At 500 mol m^-3 NaCl, the inorganic component was 55 % of total leaf dry matter.

Leaf sap osmotic potential decreased from - 0.84 to - 2.24 MPa as salinity increased, and the uptake of Na⁺ and Cl^- accounted for > 90 % of this osmotic adjustment. Leaf proline content also increased, from 0.7 to 8.3 mol m^-3 (tissue water basis), over the salinity range of 0-500 mol m^-3 NaCl, but was insufficient to account for osmotic equilibrium between cytoplasm and vacuole if it was assumed that all the proline was confined to a cytoplasmic relative volume of 5%. In the absence of external salinity, K⁺, NO₃^- and soluble sugars were the predominant contributors to osmotic potential of leaf cell sap.