| The mining wastelands not only occupied vast land area but also seriously polluted the environment. Therefore, ecological restoration of mine wastelands is an urgent and important research topic. An extensive ecological survey and sampling of soils and plants were conducted in Pingle, Lipu and Bayi Manganese mine wastelands in Guangxi. The soil nutrients and heavy metal concentrations were determined in order to locate the major limiting factors for ecological restoration and revegetation. The main dominant species were used for heavy metal determination to screen the metal-tolerant plants and potential hyperaccumulator. The main research findings were as follows:1. Soil pH ranged from 5.03 to 6.33, indicating an acid nature. EC values were very low. Significant variations existed among the three Mn minelands for macronutrients. Lipu mine soil had the highest TN and TOM. TN and TOM in Pingle and Bayi barely fell into"moderate"class according to China Soil Fertility Standard (NY/T 391-2000). However, when TP were concerned, three minesoils were considered very low in TP which may limit plant growth.2. The total heavy metal concentrations were 850.3~17839.7 mg·kg-1 for Mn, 113.09~289.04 mg·kg-1 for Pb, 87.75~199.64 mg·kg-1 for Zn, 36.19~90.69 mg·kg-1 for Cu, 99.09~464.87 mg·kg-1 for Cr and 4.29~46.50 mg·kg-1 for Cd. The minesoils were characterized by elevated levels of all the studied metals in terms of Guangxi and China soil background concentrations, especially for Mn, Pb and Cd, being 4.93~103.4, 6.0~15.4 and 6.0~15.4 times of their local soil background values respectively. According to China Environmental Quality Standard for Soils (GB 15618-1995 pH<6.5) Pb, Zn and Cu fell within Class II, Cr in Pingle and Lipu soils exceeded the threshold levels of pollution warning and Cd were beyond the Class III. Furthermore, soil Mn level surpassed the upper limit of the moderate range (170~1200 mg·kg-1) which suggested minesoils might be polluted by Mn.3. Pollution index, Geo-accumulation index and the potential ecological risk index were used to assess heavy metal contamination. Pi indicated that minesoils were not polluted by Pb, Zn and Cu, but slightly polluted by Cr and seriously polluted by Cd. All I-geos showed moderate severe to severe contamination for Pb, slight to moderate contamination for Cu and Zn, slight to moderate severe contamination for Cr, extreme contamination for Cd and severe to extreme contamination for Mn. When Ei was concerned, the results showed slight to moderate risk for Pb, slight for Zn, Cu and Cr and severe for Cd. On the whole, the pollution pattern of the studied heavy metals were consistent assessed with the three methods, but variations existed. 4. Fifty three plant species from 49 genera, 27 families were found colonizing in the three minelands, of which 42 species from 23 families were found in Pingle, 47 species from 24 families in Lipu, and 35 species from 21 families in Bayi, respectively. Of the main dominant species Imperata cylindrical, Digitaria sanguinalis (Poaceae), Erigeron acer, Xanthium sibiricum (Asteraceae), Hedyotis auricularia (Rubiaceae) and Dicranopteris linearis (Osmundoceae) can be used as good pioneer species. Ficus tikoua, a tailings creeper, was a good stabilizer of Mn tailing dams. Schima superba contained 9975.6mg?kg-1 Mn in leaf, very close to the suggested Mn hyperaccumulator threshold. Moreover, its biological accumulating coefficient and biological transfer coefficient for Mn were 0.96 and 13.5, showing this woody plant could be a prospective Mn hyperaccumulator. Phytolacca acinosa and S. superba were proved to have good Mn accumulation and transfer ability, and they could be ideal species in phytoremediation of Mn-contaminated soil.5. S. superba seedlings were cultivated under different Mn treatment levels in room condition to study its uptake and accumulation capacity. Under the sand culture conditions, S. superba grew normally and did not show any symptoms of Mn toxicity with Mn supply below 60 mmol·L-1. When the external Mn was above 80 mmol·L-1 for 45 days, necrotic patches appeared on adult leaves and gradually enlarged. At 150 mmol·L-1 and 200 mmol·L-1 Mn there were obvious symptoms of Mn toxicity at day 60 of treatment. The total biomass decreased with the increasing external Mn levels. Mn concentrations and contents per plant in leaves and stems first increased and then decreased reaching the maximum at 150mol·L-1. When Mn supply was over 40 mmol·L-1 (7.91 g·L-1), the Mn levels in the leaves and stems were all beyond 10000 mg·kg-1, the accepted Mn hyperaccumulation threshold.6. Ecological restoration techniques were proposed according to the above results, the actual landform, climatic condition and vegetation in Guangxi. The basic restoration measures comprises land leveling for open-pits, guest soil cover for tailing dams, substrate amelioration and revegetation for areas topsoil retained. Vegetation collocation pattern includes: P. massoniana, S. superba + I. cylindrical, E. acer, D. sanguinalis, H. auricularia, D. linearis in Pingle mineland; O. fragrans, P. pubescens + P. acinosa, H. auricularia, E. acer, X. sibiricum in Lipu mineland; E. tereticornis, E.s robusta + D. linearis, P. acinosa in Bayi mineland. Bayi mineland can also be used as building areas and recreation sites. The criteria of restoration success should be clearly established to evaluate restoration efforts, and ecosystem attributes, such as diversity, vegetation structure and ecological processes can be employed for evaluation.
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