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The residues from the extraction of lead/zinc (Pb/Zn) ores of most Pb/Zn mines are permanently stored in tailings ponds, which require revegetation to reduce their environmental impact. This can only be done if the main constraints on plant establishment are evaluated. This can readily be done by field and greenhouse studies.To test this, the properties of different tailings from Lechang Pb/Zn mine located at the north of Guangdong Province in southern China have been studied. Physical and chemical properties including concentrations of metals (Pb, Zn, Cd and Cu) in the tailings and soils collected from different sites have been measured. The results showed that tailings contain low nitrogen (0.016-0.075%), low-organic matter (0.58-1.78%), high salt (3.55-13.85 dS/m), and high total and diethylene-tetramine-pentaacetic acid (DTPA)-extractable metal concentrations (total: 1019-1642 lg g À1 Pb, 3078-6773 lg g À1 Zn, 8-23 lg g À1 Cd, and 85-192 lg g À1 Cu; DTPA-extractable: 59-178 lg g À1 Pb, 21-200 lg g À1 Zn, 0.30-1.5 lg g À1 Cd, and 4.3-12 lg g À1 Cu). Aqueous extracts of tailings/soils (10%, 20% and 30%, w/v) from different sites were prepared for testing their effects on seed germination and root elongation of a vegetable crop Brassica chinensis and a grass species Cynodon dactylon. It was found that root elongation provided a better evaluation of toxicity than seed germination. The ranking of toxicity using root elongation was: high-sulfur tailings > tailing dam > sparsely vegetated tailings > densely vegetated tailings > mountain soil for both plants. This order was consistent with DTPA-extractable Pb contents in the tailings and soils. B. chinensis seedlings were then grown in the mixtures of different proportions of tailings and farm soil for 4 weeks, and the results (dry weights of seedlings) were in line with the root elongation test. All these demonstrated that heavy metal toxicity, especially available Pb, low content of nutrient, and poor physical structure were major constraints on plant establishment and colonization on the Pb/Zn mine tailings. Ó

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Cultivation-independent molecular approaches were used to investigate the phylogenetic composition of Archaea and the relative abundance of phylogenetically defined groups of methanogens in the leachate of a closed municipal solid waste landfill. Cloning and phylogenetic analysis of archaeal 16S rRNA gene sequences (16S rDNA) revealed that the landfill leachate harbored a diverse Archaea community, with sequence types distributed within the two archaeal kingdoms of the Euryarchaeota and the Crenarchaeota. Of the 80 clones examined, 51 were phylogenetically associated with well-defined methanogen lineages covering two major methanogenic phenotypes; 20 were related to Thermoplasma and were grouped with some novel archaeal rRNA gene sequences recently recovered from various anaerobic habitats; finally, five belonged to Crenarchaeota and were not closely related to any hitherto cultivated species. Most of the methanogen-like clones were affiliated with the hydrogenotrophic Methanomicrobiales and the methylotrophic and acetoclastic Methanosarcinales. Quantitative oligonucleotide hybridization experiments showed that methanogens in the leachate accounted for only a very small fraction of the total community (approximately 2%) and that Methanomicrobiales and Methanosarcinales constituted the majority of the total methanogenic population.

Mine tailings can have a specific assemblage of plant species due to their unique physicochemical properties, and this process can be important in developing ecological theory and restoration practice. Physicochemical properties and natural colonization of plants on five lead/zinc (Pb/ Zn) mine tailings in southern China were investigated. The tailings studied included Fankou and Lechang in Guangdong Province, and Huangshaping, Shuikoushan, and Taolin in Hunan Province. Physicochemical properties of the tailings varied greatly both among and within tailings ponds, but in general, all contained high concentrations of heavy metals (Pb, Zn, Cu, and Cd) and low concentrations of N, P, and organic matter. Toxic levels of heavy metals and deficiency of major nutrients appeared to be the major constraints for colonization of plants on these Pb/Zn tailings and were reflected in the metal concentration of the plant tissues. The natural colonization of plants on these tailings was limited, with only some small patches distributed mainly on the edge of tailing ponds and even fewer patches on the center of the ponds. In total 54 plant species belonging to 51 genera and 24 families were recorded on the five tailings ponds, of which the 13 species belonging to Gramineae were major components of the tailings' flora. Species establishing on the tailings at the initial colonization phase greatly depended on their seeddispersal capacity. Further establishment and growth were then dependent on at least one of the three ecological strategies: (1) microsite (avoidance) strategy: plant establishment on tailings depended on dispersing onto microsites of relatively favorable edaphic conditions; (2) tolerance strategy: plant establishment was a result of evolving metal-tolerant ecotypes or constitutional metal tolerance; and (3) rhizome strategy: plant establishment on tailings depended on clonal growth by rhizomatous extension.

Abstract:The lead (Pb)/zinc (Zn) tailings contained high concentrations of heavy metals (total Pb, Zn, Cu and Cd concentrations 4164, 4377, 35 and 32 mg kg -1 , respectively), and low contents of major nutrient elements (N, P, and K) and organic matter. A field trial was conducted to compare growth performance, metal accumulation of Vetiver (Vetiveria zizanioides) and two legume species (Sesbania rostrata and Sesbania sesban) grown on the tailings amended with domestic refuse and/or fertilizer. It was revealed that domestic refuse alone and the combination of domestic refuse and artificial fertilizer significantly improved the survival rates and growth of V. zizanioides and two Sesbania species, especially the combination. However, artificial fertilizer alone did not improve both the survival rate and growth performance of the plants grown on tailings. Roots of these species accumulated similar levels of heavy metals, but the shoots of two Sesbania species accumulated higher (3-4 folds) concentrations of Pb, Zn, Cu and Cd than shoots of V. zizanioides. Most of the heavy metals in V. zizanioides were accumulated in roots, and the translocation of metals from roots to shoots was restricted. Intercropping of V. zizanioides and S. rostrata did not show any beneficial effect on individual plant species, in terms of height, biomass, survival rate, and metal accumulation, possibly due to the rather short experimental period of 5 months. Key words: growth performance, intercropping, Pb/Zn mine, Sesbania rostrata, Sesbania sesban, tailings amendment, Vetiveria zizanioides Email contact: Wensheng Shu TRODUCTIONExploitation of mineral resource has resulted in the destruction of vast amounts of land. This has caused very serious environmental problems, which have received much attention from most countries in the world, including China. Revegetation of metalliferous mine tailings is necessary for long-term stability of the land surface. A good vegetation cover is beneficial in the restoration of contaminated land and results in enhanced amenity values as well as prevention of surface soil erosion (Baker et al., 1994). However, adverse factors such as acidity, nutrient deficiencies, toxic heavy metal ions, and poor physical structure, and their interactions of most mine tailings inhibit plant establishment and growth on the tailings (Pichtel and Salt, 1998). The toxicity of heavy metals and deficiency of major nutrients are often the limiting factors for plant establishment on mine tailings, therefore, the success of reclamation schemes should overcome the two major problems (Bradshaw, 1987).In general, amendments such as applications of organic materials (such as sewage sludge, domestic refuse) or inorganic fertilizer are necessary for establishment of plants on mine tailings. For long-terms remediation, metal tolerant species are commonly used for revegetation of mine tailings