Ecological Response of the Australian Native Species Acacia harpophylla and Atriplex nummularia to Soil Salinity : Effects on Water Content, Leaf Area, and Transpiration Rate
The water relations of the legume Acacia harpophylla (brigalow) and of the chenopod Atriplex nummularia (old man saltbush) in response to salinity are described, and also the response of At. Nummularia to associated water stress. Both species tolerated salinities up to and beyond sea water concentration under high insolation stress: viz. 10-400 m-equiv. sodium chloride per litre for At. nummularia and 8-588 m-equiv.11, of the chlorides of sodium, potassium, calcium, and magnesium in factorial combination, for Ac. harpophylla. Development was not checked up to 400 m-equiv. chloride per litre in At. nummularia but was in Ac. Harpophylla, as shown by differences in leaf area and leaf number. Both species benefited by the conservation of their water supply under high salinity, the water content of their tissues being higher, especially that of the laminae, and transpiration per unit of leaf area being reduced in both species. Reduced symptoms of wilting and more rapid recovery from wilting than in controls accom- panied high salinity in At. Nummularia. The water content of wilted plants, and the proportion of whole plant water in their laminae, increased with salinity. Potassium increased tissue hydration more than sodium did in Ac. harpophylla. Salinity benefits water relations in these species, especially under drought stress; this adaptation is a distinct ecological advantage.