This study, investigated the salt excretion efficiency and the level of the physiological response to salt-induced stresses between the native and exotic Tamarix species as well as their hybrids (Tamarix chinensis × Tamarix ramosissima and Tamarix chinensis × Tamarix usneoides). Ten potted plants from each of the five taxa were exposed to salt at a concentration of 3% (w/w) (180 mM) for 3 weeks. Measurements of electro-conductivity (EC), physiological parameters such as stomatal conductance, chlorophyll fluorescence, and water pressure and plant growth were taken from salt-treated and control plants. The EC in the exotic T. chinensis significantly increased by >30% compared with all other Tamarix taxa, suggesting that it is the most effective taxon for phytoremediation. Although there was no significant difference in plant growth between T. chinensis and T. usneoides, they both showed a significantly greater plant growth than the other taxa. However, the plant physiological parameters indicated that T. usneoides was less stressed by the salt exposure than the T. chinensis and the others. Thus, considering the T. usneoides greater tolerance to salt-induced and/water stresses and the strict environmental regulations of planting exotic Tamarix, the native Tamarix remains the preferred plant of choice for phytoremediation in South Africa.
Keywords: Excretion; Tamarix; genotypes; heavy metals; phytoremediation; salt glands.