| In recent years, with the rapid development of economic and society in the western of China, industrialization and urbanization became faster and faster. At the mean time, the industrial and living waster caused serious pollution on the environment, especially heavy metals pollution. The lead pollution has become the most common environmental problem. The anthropogenic Pb mining, refine, burning of Pb gasoline, industrial "three wastes" lead to sharp increase in soil Pb content. Pb seriously affects plant growth and development. The plant accumulated Pb can enter the human body through the food chain, affecting the human hematopoietic system, digestive system and nervous system, and thus a serious threat to human health. Therefore, the ecological restoration of soil pollution has become the most urgent environmental issues. In various methods used by the human, the phytoremediation has a low cost, good effect and no secondary pollution. Woody plants have deep roots, larger leaves, large biomass and long growth cycle characteristics compared with herbaceous. So woody plants can clean up Pb pollution for deeper soils, accumulate a larger amount of Pb, have long-term effects.To character the growth and Pb enrichment properties of Toona ciliata under Pb polluted soils, the growth characteristics, the various organs of nutrient uptake and allocation, photosynthetic, the Pb content and enrichment of various organs of one-year-old T. ciliata seedlings were investigated under different Pb treatments in acid purple soil, alkaline purple soil and alluvial soil in western Sichuan. We also analyze the tolerance and transfer efficiency of T. ciliata to Pb pollution and provide a scientific basis for soil repair by native woody plants on the Pb contaminated. The results showed:Pb significantly affected the growth characteristics of T. ciliata. Low concentrations of Pb increased leaf length and leaf area, while high concentrations of Pb significantly inhibited leaf length and leaf area. Leaf chlorosis and wrinkle is not obvious under low Pb treatment, Leaf chlorosis and wrinkle increased under high Pb treatment. Low concentrations promoted the stem of T. ciliata longitudinal growth while high concentrations inhibited the stem longitudinal growth. Low concentration promoted the stem lateral growth while high concentration of Pb inhibited stem lateral growth. Pb stress obviously changed the root/shoot ratio of the samplings and increased leaf litters. The total biomass was decreased significantly (P<0.01) with the increase of Pb stress.With the increased Pb stress, average C, P content in vivo of T. ciliata showed a downward trend, while the average N content showed an arising trend. Under the influence of Pb stress, C, N, and P concentration and C, N, P storage of organs changed significantly. C, N, P distribution among the body of T. ciliata was affected. With increasing Pb stress, the C storag of belowground part was more affected than aboveground part. The proportion of belowground C storage was reduced while the proportion of aboveground C storage gradually increased under increasing Pb pressure. With the increasing Pb stress, the N content of leaves was greatly inhibited while the average N content of the coarse roots, stems, and body was obvious increased. Low concentrations of Pb promoted P absorption, and high concentrations of Pb inhibited P absorption.The total content of chlorophyll was significantly negatively correlated with Pb concentration. Net photosynthetic rate first increased and then decreased with the increase of Pb stress. Stomata conduction, transpiration rate and intercellar CO2increased with the Pb stress as well as net photosynthetic rate. In low light intensity within each processing, Pn showed rapid upward trend as the PAR increases. In high light intensity, Pn as the PAR increases showing a slight upward trend, and gradually in a stable state.Pb treatments significantly affected Pb accumulation of T. ciliata samplings. With the increased Pb concentration in treatments, average Pb content and cumulative quantity of organs and body increased. Organs and body average Pb content and cumulative quantity were significantly positively correlated with Pb concentration in treatments. The Pb absorptive and accumulation capacity of different organs were different, fine root has the highest Pb content in the six organs, followed by coarse root.The Pb of aerial parts were low and there were no obvious differences between them.The Pb tolerance indices of T. ciliate samplings were from0.67to1.06, depending on Pb stress and soil substrates. The tolerance index decreased with the increase of Pb stress. The enrichment and transfer efficiencies were lower than0.3and was rapidly decreased with the increasing Pb stress. T. ciliata was tolerant to Pb pressure and the tolerance was gradually decreased with increasing Pb stress.T. ciliate showed good growth characteristics in three soil types, especially in alkaline purple soils. The absorptive capacity of Pb were different under different soil. Chlorophyll a, chlorophyll b content and average C, N, P content were different under different Pb stress. |
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