| Eucalyptus grandis, an important fast-growing fertility tree species, was widely planted in Sichuan province. In order to understand the growth adaptability of E. grandis under Pb stress and the effect of Pb stress on physiological characteristics, distribution of nutrition elements and Pb accumulation in E. grandis seeddling planted in three types of soil (alkaline purple soil, acid purple soil and alluvial soil). A controlled pot-experiment cultivated with one-year old eucalypt seedling was arranged with treatments of four Pb concentrations (CK:Omg·kg-1; T1:200mg·kg-1; T2:450mg·kg-1; T3:2000mg·kg-1). The results were as followed:1) Within the range of Pb concentration in our experiments, the leaf length, leaf area, plant height and ground diameter of eucalypt seedlings all increased first and then decreased in three types of soil, with the increase of Pb concentration. They went through the maximum at T1and decreased to the minimum at T3. All those characters were significantly different from those of contrast group (P<0.05). The biomass of each organ and total biomass showed a similar trend. It indicated that low levels of Pb stress promoted the growth of eucalypt seedlings in a certain degree, while it was severely inhibited under the high levels of Pb stress. The biomass of belowground part and root shoot ratio increased with the increase of Pb concentration, which indicated that eucalypt can develop some degree of tolerance under Pb stress.2) Under the four levels of Pb and in the three types of soil, the C, N, P content of the aboveground part of eucalypt were higher than the belowground part, and they were also higher in the fresh leaves than those in litters. The C, N, P content in most organs of eucalypt were not significantly changed by the increase of Pb levels, except C content in fresh leaves in the alluvial soil and the acid purple soil, which significantly increased under higher Pb levels. The P content of each organ in the alluvial soil was significantly higher than those in acid purple soil, possibly owning to fact that P was the limit element in the tested soil. Certain concentration of Pb had significant effects on the P content of eucalypt seedlings. With the increasing of Pb levels, the P content of each organ showed a significant decreased tendency in the alkaline purple soil, but they increased first and then decreased significantly in the alluvial soil and the acid purple soil.3) The Pb content of aboveground part of eucalypt was far less than that of belowground part in the three soil types under different Pb levels. As the activity of Pb was higher in the acid purple soil, the Pb content of aboveground part and belowground part in the acid purple soil were higher than in other two soils. The Pb content of all organs of eucalypt in the three soil types showed a significant increase with the increasing of Pb concentration, and the bioaccumulation coefficient of eucalypt showed a similar tendency, but the transfer coefficient was decreased as the Pb concentration increased. Although the bioaccumulation coefficient of eucalypt was greater than1, the Pb content of aboveground part was less than1000mg/kg5and the transfer coefficient is less than1. Eucalypt, therefore, can only be an enrichment plant, rather than a super enrichment plant. The eucalypt seedlings grown in the acid purple soil had higher bioaccumulation coefficient and tolerance index than those in other soil types, and this result suggested that eucalypt had a better repair effect in the Pb polluted acid soil. |
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