Tamarix efficiency in salt excretion and physiological tolerance to salt-induced stress in South Africa

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.

On the salty side of life: molecular, physiological and anatomical adaptation and acclimation of trees to extreme habitats

Saline and sodic soils that cannot be used for agriculture occur worldwide. Cultivating stress-tolerant trees to obtain biomass from salinized areas has been suggested. Various tree species of economic importance for fruit, fibre and timber production exhibit high salinity tolerance. Little is known about the mechanisms enabling tree crops to cope with high salinity for extended periods. Here, the molecular, physiological and anatomical adjustments underlying salt tolerance in glycophytic and halophytic model tree species, such as Populus euphratica in terrestrial habitats, and mangrove species along coastlines are reviewed. Key mechanisms that have been identified as mediating salt tolerance are discussed at scales from the genetic to the morphological level, including leaf succulence and structural adjustments of wood anatomy. The genetic and transcriptomic bases for physiological salt acclimation are salt sensing and signalling networks that activate target genes; the target genes keep reactive oxygen species under control, maintain the ion balance and restore water status. Evolutionary adaptation includes gene duplication in these pathways. Strategies for and limitations to tree improvement, particularly transgenic approaches for increasing salt tolerance by transforming trees with single and multiple candidate genes, are discussed.