Ecophysiological Responses Of Urban Greening Tree Species To Air Pollution In Lanzhou City

With the rapid development of socio-economic and the improvement of the living standards, the air pollution of Lanzhou city is becoming worse and worse. So it becomes the most important factor that disturbs the people's life and restricts the development of the economic. In all kinds of pollutants, SO₂ and dust are becoming the major pollutants of Lanzhou city. Using the urban greening tree species to absorb the air pollutants is a popular method. And the method is developing very rapidly and has become the foreland item. In order to screen out resistant tree species and sensitive monitoring plant species, five kinds of urban greening tree species are tested, and the chlorophyll contents, soluble sugar contents, proline contents are measured. Then the data is analyzed by statistica 6.0 software.The experiment is divided into two parts. The First part is performed in inner house. The main urban greening tree species, for example, Ailanthus altissima, Euonymus japonicus, Populus tomentosa, Sabina chinensis, Cedrus deodara, Sorphora japonica are selected and placed in SO₂ pollution. Then the morphological symptoms change and the physiological indexes are observed. Resistant degree of plant upon sulfur dioxide pollution is estimated. The experiment shows, not only the morphological symptoms, but also the physiological indexes are all changed significantly in the SO₂ fumigation. Though the morphological symptoms change, it shows that Ailanthus altissima, Euonymus japonicus, Populus tomentosa are good SO₂ absorption tree species. Sorphora japonica has a mean sensitivity to SO₂. Sabina chinensis and Cedrus deodara are very sensible to SO₂ pollution, and both of them can be used as the indicators of SO₂ pollution. Though the physiological indexes change, it shows that the proline contents have a significant positive correlation with the SO₂ concentration, but the chlorophyll contents have a significant negative correlation with the SO₂ concentration. The sequence of pollution tolerance ability can be ranked as: Populus tomentosa, Euonymus japonicus, Ailanthus altissima, Sorphora japonica, Sabina chinensis, Cedrus deodara. All the six tree species are divided into three categories: good SO₂ absorption tree species such as Ailanthus altissima, Euonymus japonicus, Populus tomentosa, mean sensitivity to SO₂ pollution such as Sorphora japonica, sensible to SO₂ pollution such as Sabina chinensis and Cedrus deodara. After the dust detetion test, Populus tomentosa and Ailanthus altissima are good dust detention urban greening tree species.The resistance of the urban greening tree species to SO₂ pollution is tested under single SO₂ pollution fumigation, so the result may not be suitable for the natural condition. So the following outside experiment is carried out. Four categories functional areas are screened out, for example, the representative pollution area, traffic hinge pollution area, normal pollution area, cleanness area. In the five sorts of areas, five common urban greening tree species are chosen. And the ingredients of the air are measured. The samples of the urban greening tree species are carried to the lab and are tested.The experiment shows that, the physiological indexes are different from each other, moreover have reached the significant positive or negative correlation. And in the same place, the indexes are also very different. The sequence of pollution tolerance ability can be ranked as: poplar, Buxus microphylla, Ailanthus altissima, Sorphora japonica, Sabina chinensis. The pollution degree of the seven tested sites in Lanzhou can be ranked as: The oil refining plant, the chemical plant, the rubber plant, xiguan station, xizhan station, Lanzhou jiaotong university, xinglongshan mountain. The experiment can offer theories and practices for the air pollution management in Lanzhou city.