EFFECTS OF ROOT-ZONE SOLUTES ON EUCALYPTUS-CAMALDULENSIS AND EUCALYPTUS-BICOSTATA SEEDLINGS - RESPONSES TO NA+, MG2+ AND CL-

Specific-ion effects in salt-treated eucalypts were examined with two species known to differ in salt tolerance viz. E. camaldulensis (more tolerant) and E. bicostata (less tolerant). Sand-cultured plants were irrigated with different nutrient solutions designed to impose either osmotic stress (concentrated macronutrients with balanced cations and anions) or specific ion stress from either NaCl or MgCl2, or from nutrient solutions rich in particular ions viz. Na+, Mg2+ and Cl- (balancing counter ions were provided in all cases). Half-strength Hoagland nutrient solution served as control. All treatments were applied at osmotic pressures of approximately 0.52 MPa by appropriate concentrations of each solution. In general, salt-induced growth reductions were greater for E. camaldulensis than for E. bicostata, although E. camaldulensis showed strongest exclusion of Na+, Mg2+ and Cl- from shoots. Application of NaCl and concentrated macronutrients resulted in similar growth reductions. E. bicostata seedlings exposed to high Cl- concentrations in the presence of Mg2+ and concentrated cations suffered significantly more shoot and root reduction than those exposed to other salts. Treatment with solution rich in Cl- resulted in extensive leaf damage, which suggested that Cl- may have exerted a specific effect. No specific Na+ effect was observed for either species, even though shoot Na+ concentrations were considerably higher for E. bicostata than for E. camaldulensis. Root growth was considerably less for plants treated with Mg2+ salts and this effect was associated with low root Ca2+ concentrations. © 1990 Kluwer Academic Publishers.