Salinity Damage to Norfolk Island Pines Caused by Surfactants. III. Evidence for Stomatal Penetration as the Pathway of Salt Entry to Leaves

Abstract

The paper describes the effect of varied surfactant concentrations on penetration of NaCl into leaves of Norfolk Island Pine, Araucaria heterophylla (Salisb.) Franco. It confirms that the damage observed along the sea-coast in Sydney is similar to that produced by high NaCl levels in the foliage. The effect of surfactant in increasing NaCl uptake from sea-water spray is related to the reduction in surface tension and to the advancing contact angle of the spray on the leaf surface. It is suggested that sea-spray enters A. heterophylla needles through the stomata, and that the cuticle is particularly resistant to NaCI, compared with other plant species. Similar penetration and damage was found with sprays of CaCl₂, MgCl₂ and KCl showing that the damage was not due specifically to NaCI.