Physiological aspects of vetiver grass for rehabilitation in abandoned metalliferous mine wastes
Introduction
The heavy metals contamination of the environment by soil erosion in agricultural lands, urban wastes and by-products of rural, industrial and mining industries attracts world-wide concern, especially in developing countries (Tordoff et al., 2000; Mejáre and Bülow, 2001). In China, there are many abandoned metalliferous mine wastelands and the areas become larger and larger (Young, 1988). Economically there is an urgency to decontaminate or re-vegetate the mine wastelands in order to improve environment. Although there are many methods used to treat them, most of them are either expensive or impossible to carry out, as the volume of contaminated material is very large, such as the coal mine tailings (Salomons et al., 1995). Therefore, a more economical and practical approach is urgently needed at present, especially for the developing countries.
Vegetative methods are thought to be the most practical and economical method for rehabilitation of the mine wastelands (Flathman and Lanza, 1998). However, re-vegetation of these sites is often difficult and slow due to the hostile growing conditions, which include toxic levels of heavy metals. Therefore, selection or screening of plant species which are tolerant to toxic levels of heavy metals has attracted much attention in the treatment of the abandoned mine wastelands (Chaney et al., 1997; Salt et al., 1998). There are a wealthy of evidence to show that vetiver grass is highly tolerant to the hostile soil conditions and widely used as a natural, effective, and low-cost alternative mean to vegetate the heavy metal-contaminated lands (Truomg, 1996).
The aim of this paper is to investigate the physiological responses of vetiver grass to heavy metals. The experiments were carried out in greenhouse, where vetiver plants were grown in different proportions of lead/zinc (Pb/Zn) tailings collected from the abandoned mine near Guangdong province, China. The results showed that vetiver plants grown well in suitable proportions of tailings-contained soil medium, and there exited dose- and time-effects of the responses of vetiver plants to Pb/Zn-tailings, and when being grew in the high proportion of tailings-contained soil and/or for a extended period of treatment, the growth of vetiver plants was significantly influenced. The growth of vetiver plants when grew in high tailing-contained soil could be greatly improved if nitrogen fertilizer is applied.
Section snippets
Plant materials and treatments
Vetiver plants (Vetiveria zizanioides L.) were provided by Zhongshan University, Guangzhou and pre-cultivated in the John Innes No. 2 soil compost for about 30 days when the vetiver grasses grown well. One hundred and fifty uniform-sized plants (30 plants per treatment) were selected and five treatments were designed (30 plants for each treatment). Plants were transplanted into the plastic pots (18 cm in diameter, 25 cm in height; one plant per pot) containing different proportions of Pb/Zn
Results
Pb/Zn mine tailing contains high levels of heavy metals, especially Pb and Zn (Table 1), which are toxic to plants or inhibitory to plant growth. Experiment was conducted with different proportions of tailings to determine the tolerance of vetiver grass to high levels of heavy metals. Vetiver plants were transplanted into pots containing different proportions of tailings, and physiological parameters were measured. Fig. 1 showed the effects of different proportions of tailings on the tillering
Discussion
The areas of heavy metal-polluted soils increased significantly throughout the world during past several decades, as the results of industry development, mining activity, irrigation of waste water, etc. (Smith et al., 1996; Herawati et al., 2000; Tordoff et al., 2000), which has become a global problem because of its deterious influences not only on plant growth (yield and quality) and environmental quality, but also on the health of human beings. Therefore, much effort has been made to
Acknowledgments
This project is supported by the National Programme on Key Basic Study and Development (G1999011700).
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