SALT TOLERANCE IN SPOROBOLUS-VIRGINICUS - THE IMPORTANCE OF ION RELATIONS AND SALT SECRETION

The role of ion relations and salt secretion in salt tolerance in the halophytic, C-4 grass, Sporobolus virginicus (L.) KUNTH, Was investiga ted. Plants were subjected to 0.2, 20, 40, 60 and 80% sea water for 12 weeks. There was no significant growth stimulation with increase in s alinity from 0.2 to 20% sea water, while further increases to 80% sea water significantly reduced total biomass accumulation and growth of r oots and shoots. The predominant ions secreted by salt glands were Na and Cl- with smaller amounts of K+, Ca2+ and Mg2+. Increase in substr ate salinity from 0.2 to 20% sea water significantly increased secreti on of Na+ and Cl-, but had no effect on tissue concentrations of these ions. Further increases in substrate salinity from 20 to 80% sea wate r had no effect on secretion of Na+ and Cl- but increased tissue conce ntrations of these ions. High rates of Na+ secretion and greater reten tion of K+ at high salinities resulted in stable Na+/K+ ratios in all treatments. Concentrations of proline in roots and shoots increased si gnificantly with salinity increase. In all treatments, leaf water pote ntials were lower than media water potentials. Salt secretion was effe ctive in maintaining salt balance at low to moderate salinities and in effective at high salinities.