Salt excretion in alien and native Tamarix species in South Africa and the effects of salt on the Tamarix Leafhopper (Opsius stactogalus
Phytoremediation using Tamarix on contaminated mine sites in South Africa has been common practice for over a century. The use of exotic Tamarix species for phytoremediation has resulted in the spread of Tamarix as an alien invasive. In this study, the ability of different Tamarix species to take up and excrete salt has been investigated. The study included one indigenous species (Tamarix usneoides), two exotic species (Tamarix ramosissima and Tamarix chinensis) and two hybrids (T. chinensis x T. ramosissima and T. chinensis x T. usneoides). In addition, the effects of salt on the herbivory of the Tamarix Leafhopper (Opsius stactogalus) on the selected Tamarix species was investigated. A pot experiment with the aforementioned Tamarix species was conducted with each species exposed to salt at a concentration of 3% (w/w) (180mM) for a 3 week period. Subsequently, the salt treated plants were exposed to O. stactogalus to investigate the effects of salt on the herbivory of the insects for a further three week period. Phase 1 of the experiment involved the salt treatment and Phase 2 involved the insect treatment, where ten replicates were used for T. usneoides, T. ramosissima and T. usneoides x T. chinensis and five replicates were used for T. chinensis and T. ramosissima x T. chinensis in both phases of the experiment for the treatments and the controls. The experiment took place in an open air area exposed to natural light and sheltered from wind and rain at ambient temperature and humidly ranging from 22.1°C to 42.9°C (average 32.5°C) and from 21% to 97% (average of 59%), respectively. The specific aims of this work were to investigate whether the indigenous Tamarix species excretes more salt than the exotic species and the hybrids and to investigate the effects of salt on the herbivory of O. stactogalus on the selected Tamarix species. Measurements of chlorophyll content, plant vigour, stomatal conductance, chlorophyll fluorescence, water pressure and electroconductivity were used to evaluate the potential of salt excretion by each of the Tamarix plants and their effects on the plants as well as the herbivory of O. stactogalus. The experimental data suggest that the exotic species, T. chinensis, excreted significantly more salt than the other Tamarix taxa (including the indigenous T. usneoides) and that salt had no significant effect on the herbivory of O. stactogalus or the plant vigour of the selected Tamarix taxa. These findings suggest that the exotic species (T. chinensis) may be the most effective species for salt extraction from soils, but that the indigenous species excretes the same amount of salt as T. ramosissima and the hybrids (T. chinensis x T. ramosissima and T. chinensis x T. usneoides). Although T. usneoides excretes less salt than T. chinensis, other traits, such as superior plant growth under saline conditions may give mining companies an incentive to plant the native T. usneoides rather than the exotic invasive species.
A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science. School of Animal, Plant and Environmental Sciences, Johannesburg, May 2018.
Allem, Stawm (2018) Salt excretion in alien and native Tamarix species in South Africa and the effects of salt on the Tamarix Leafhopper (Opsius stactogalus, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/25846>