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Source: Xia et al., Proc. 3rd Int. Vetiver Conf., Guangzhou, China, 532.

adequately supplied with nitrogen and phosphorus fertilizers, excellent growth was obtained on sites with pH ranging from 2.7 to 3.6, high in sulphate (0.37 to 0.85%), total sulfur (1.31 to 3.75%), and low in plant nutrients. Liming was not needed on sites with higher pH (3.5), but the addition of 20 t ha-1 of agricultural lime significantly improved vetiver growth on sites with pH of 2.7.

21.6 REHABILITATION OF MINE TAILINGS IN SOUTH AFRICA AND CHINA

Rehabilitation trials conducted by De Beers on slime dams at several sites have found that vetiver possess the necessary attributes for self-sustainable growth on kimberlite spoils. Vetiver grew vigorously on the alkaline kimberlite and contained runoff, arrested erosion, and created an ideal microhabitat for the establishment of indigenous grass species [123]. Vetiver has also been used successfully in the rehabilitation diamond mines at Premier and Koffiefonteine and slime dams at the Anglo-American platinum mine at Rastenburg, and the Velkom, President Brand gold mine (Tantum, pers. com.). In China, vetiver produced biomass more than twice that of Paspalum notatum, Cynodondactylon, and Imperata cylindrica in the rehabilitation of the Lechang Pb and Zn mine; tailings there contain very high levels of heavy metals (Pb at 3231 mg kg-1, Zn at 3418 mg kg-1, Cu at 174 mg kg-1, and Cd at 22 mg Kg-1) [124].

Vetiver grass has also been successfully used to rehabilitate coal mine tailings that were saline and highly sodic, with high levels of soluble sulfur, magnesium, and calcium and extremely low nitrogen and phosphorus levels [125]. Bentonite tailings are extremely erodible because they are highly sodic (with exchangeable sodium percentage (ESP) values ranging from 35 to 48%), high in sulphate, and extremely low in plant nutrients. Vetiver established readily on these tailings and effectively controlled erosion, conserved moisture, and improved seedbed conditions for the establishment of indigenous species. Residue of bauxite processing known as red mud is highly caustic, with pH levels as high as 12. Vetiver established successfully on the red mud when its pH was raised to 9.0.

Vetiver has been used very successfully for this purpose in Australia to contain leachate runoff from landfills. For this application, high-density planting is required at strategic locations such as the toes of major slopes of highly contaminated areas.

The vetiver system is proven technology; its effectiveness as an environmental protection tool has been demonstrated around the world. It is a very cost-effective, environmentally friendly, and practical phytoremedial tool for the control and attenuation of heavy metal pollution when appropriately applied.

Jarvis and Leung [126] observed Chamaecytisus palmensis plants growing in hydroponic culture exposed to Pb(NO3)2, with and without the addition of the chelating agents H-EDTA and EDTA, for 1 week. The unchelated lead accumulated predominantly in root tissue; lead chelated with H-EDTA or EDTA was taken up principally by the shoots. With transmission electron microscopy, ultrastructural observations were carried out on ultrathin sections derived from lead-treated C. palmensis tissues. Unchelated lead was found in cell walls, bacteroids and mitochondria in root nodule tissue, and in middle lamellae and intercellular spaces in root tissues. In roots, chelated lead was found in mitochondria, and in shoot tissues it was found in chloroplasts, pit membranes, and plasmodesmata.

21.7 EXPRESSION OF STRESS PROTEINS BY THE MEMBERS OF POACEAE

The relationship between some plant hormones and heavy metal stress in Oryza sativa; trace element stress and expressionof signalling/metabolic pathways in some Poaceae are detailed in Tables 21.3 and 21.4 respectively.

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