Screening Of Plants For Revegetation In Bayan Obo Mining Area

Bayan Obo mining area is the largest light rare earth mining area in the world.The surface vegetation has been destroyed continuously with the massive exploitation of mineral resources.Therefore,it is particularly important to carry out vegetation restoration in mining areas.However,the process of natural vegetation restoration in the mining area is slow.On the basis of fully considering the immediate and long-term effects of vegetation restoration,we need to take artificial measures to combine trees,shrubs,grass and vines to speed up the process of vegetation restoration in the mining area.A field investigation method was used to identify the plant species in the sample area,from which plant species with decent growth and dominance in abundance and frequentness were selected.Plants and their corresponding rhizosphere and non-rhizosphere soils were collected to determine heavy metal and rare earth concentrations and to analyze the enrichment characteristics of plants for heavy metals and rare earth elements.In order to screen out more plant species suitable for vegetation restoration in Bayan Obo mining area,the analytic hierarchy process was used to establish a calculation model to screen out more excellent vegetation restoration species based on the consideration of vegetation adaptability,soil improvement,ecological service function,plant growth cycle and economy.At the same time,the plant species selected by analytic hierarchy process were further subjected to single factor and multi factor simulated stress experiments of drought,nutrients and rare earth elements,so as to study the response mechanism of different plants to environmental stress.Through the comprehensive evaluation of stress resistance,the pioneer species suitable for vegetation restoration in Bayan Obo mining area were selected.The main conclusions of this study are as follows:(1)A total of 52 plant species belonging to 21 families and 46 genera were collected in the mining area,and 11 dominant herbaceous plants were selected.The average content of heavy metals and total rare earth in the rhizosphere and non-rhizosphere soil of dominant plants in the mining area was higher than the background values of soil in Inner Mongolia,and the soil was combined polluted by heavy metals and rare earth in different degrees.Different parts of the plants had different absorbing capacities for heavy metals and rare earth elements,and the average content of heavy metals and rare earth elements in the underground parts was higher than those in the aboveground parts except Cu.The highest values of a variety of heavy metals in plants were higher than the normal range,but they did not reach the standard of hyperaccumulator.The bioaccumulation and translocation factors of Salsola collina for Cu and Hg,Artemisia argyi for Cu,Saussurea japonica for Cu and most rare earth elements,and Inula salsoloides for La,Ce,Pr,Nd,Sm,Eu and Gd were all greater than 1,which indicated that they belonged to accumulator plants with the potential to remediation of contaminated soil.Heavy metals and rare earth elements absorbed by Taraxacum mongolicum,Peganum harmala,Artemisia capillaris,Juncus effusus and Lespedeza bicolor were mainly accumulated in the roots,but were less in the above-ground parts.The root bioaccumulation factors were greater than 1,and the translocation factors were less than 1.They belonged to the root compartment plants,which could be used for plant immobilization of contaminated soil.The bioaccumulation factors of all heavy metals and 11 rare earth elements of Mulgedium tataricum and the aboveground and underground parts of Suaeda glauca were less than 1,so they belonged to excluders plants and could be used as pioneer plants for vegetation restoration in mining area.(2)Eight plants were selected as ecological restoration vegetation species in the mine area of Bayan Obo by using analytic hierarchy process.The arbors were Amorpha fruticosa Linn.and Ulmus pumila L.Shrubs were Lespedeza bicolor Turcz.and Caragana microphylla Lam.The herbs were Medicago sativa L.and Artemisia argyi.The vines were Parthenocissus quinquefolia and Campsis grandiflora.(3)Through environmental stress experiments,different stress conditions were set up to analyze the resistance of different plants under stresses.Principal component analysis was carried out on the stress resistance of 8 plants.Finally,the selected arbor was Ulmus pumila L.Shrub was Caragana microphylla Lam.The herb was Medicago sativa L.The vine was Campsis grandiflora.