Selection And Valuation Of City Landscape Plants Tolerant To Heavy Metal Contamination In Beijing

The potential ecological hazard was used to evaluate the ecological hazards of heavy metals in different functional zones. Specificity of heavy metals pollution in index urban soil of Beijing city was studied. Physicochemical properties including soil texture,soil organic matter and pH which influence the absorbability and the accumulation of soil heavy metal were analyzed. Growth and the capacity of resistance of 28 kind plants were also studied to provide theoretical basis for the selection of landscape plants resistant to heavy-metal in Beijing.Urban soils of Beijing lost the natural characteristics,showed a trend of increasing soil pH and coarse particle contents,decreasing soil organic matter. The pollution by heavy metals Pb, Zn and Cu in the urban soil widely existed. The potential ecological risk of different functional zones appeared in the order of industrial areas>shopping areas>urban park>transportation areas>culture and education areas>residence areas,The urban soil was of the slightly ecological hazard in Beijing city. The main pollution source came from the industry production and transportations.After the plant was polluted by heavy metal, their roots system were often hurted firstly, and growth retardation, missing the green and dry spots of leaves, permeability increased of cell membranes and other characteristics appeared. Moreover, between danger degree and soil heavy metal pollution degree were a positive correlation. Because the underground part of plants were difficult to observe in actual production, biomass, dry spot and discoloration of leaves were selected as the preliminary evaluation index of heavy metal pollution tolerance. If the plant has the symptom of chlorosis and the blocked growth, then plant leaves would be taken to observe its penetrable changes of cell membrane to determine the suffering injury and the soil heavy metal pollution degree of the plant.Integrated clustering analysis showed that: The Ginkgo L., the Salix matsudana Koidz., the Populus tomentosa Carr., and the Amorpha fruticosa L. had strong absorption and accumulation ability to copper, zinc and nickel, they could grow well under the environment of the heavy metal pollution ,and could be widely used in the green land of the city. Plants had certain ability to absorb and accumulate heavy metal like copper, zinc, plumbum and chromium from soil, but the capability differ from different tree species. Salix babylonica L., Koelreuteria Laxm., Metasequoia glyptostrobides Hu et Cheng, Prunus persica L., Ginkgo biloba., Prunus serrulata, Acer mono Maxim., Sabina chinensis (L.) Ant., Sabina procumbens, Lonicera maackii (Rupr.)Maxim., Buxus microphylla Sieb.et Zucc., Rosa chinensis L., Cercis chinensis Bunge and Platanus acerifolia could adsorb and accumulate all kinds of heavy metal element, but the ability was not very strong. They could be widely used to landscape configuration. Moreover, the five tree species: Prunus persica L., Ginkgo biloba Linn., Cercis chinensis Bunge, Prunus serrulata (Lindl.)G.Don ex London, Sabina chinensis (L.). were quite sensitive to the polluted environment, so they may be taken as the environmental pollution instruction tree species, monitoring heavy metal contamination of the soil; Sophora japonica L., Pinus bungeana Zicc.Ex Endl., Pinus tabulaeformis Carr., Amygdalus triloba Lindl., f.atropurpurea(Jacq.)Rehd. and Euonymus japonica Thunb. can strongest absorb Chromium and plumbum from soil, simultaneously also had certain absorption accumulation ability to the nickel. Tree species that grown in the contaminated environments by heavy metal elements, could often be observed their suffering injury degree from the tree condition, the tree withered phenomenon, leaf shape and leaf size. Torsythia suspense and Cedrus deodara were strongest to the nickel in absorption accumulation ability, and the treetop had the withered phenomenon obviously in the contaminated environments. The plants that grown in soils polluted by heavy metal could change their own living-type to adapt the environment, and they had strongly tolerance ability than the homogeneous plants under clean environment. Meanwhile, they resisted the adverse effects by developing the activity of POD, SOD, CAT, and other activities.