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The aims of current study are to asses the levels of heavy metals (Cr, Cu, Ni, Fe, Zn, Co, Pb, and Cd) in sediments of lakes in Yangtze wetland and discuss the relationships between the sources and human activities. A total of 54 samples covering seven lakes along the Yangtze route in Anqing were selected. The concentrations of metals in lake sediments were (mg-kg⁻¹): Cr, 4.08~12.58; Cu, 22.40~74.36; Ni, 29.89~142.17; Fe, 22899.20~50956.40; Zn, 102.31~242.04; Co, 8.35~26.89; Pb, 23.38~88.77; and Cd, 0.29~2.95. The situation of Xizi Lake was the most serious among the seven lakes investigated. Geoaccumulation index (Igeo) analysis showed that overall risk of heavy metals in sediments was approximately in the order: Cd > Pb = Zn = Cu = Ni > Fe > Co = Cr. The results of principal component analysis (PCA) suggested the main sources of Cd, Cu, Zn, Ni, and Pb on PC 1 were fuel combustion, metal smelting, industrial manufacturing, and other human activities, while Fe on PC 2 originated fromrock weathering and other geochemical processes.
As most gramineous plants, guinea grass (Panicum maximum) comprise cellulosic biomass, which may be used as a feedstock for bioenergy. In order to develop such potential energy plants on copper-polluted lands, the hydroponic experiments with Cu, Paclobutrazol (PP333, a kind of antigibberellin) and plant growth-promoting bacterial endophyte (PGPB) treatments were carried out in a greenhouse. The seedlings of two cultivars of guinea grass, GG1 (P. maximum var. Natsukomaki) and GG2 (P. maximum var. Natsukaze) in 3 weeks old were treated, respectively, with different Cu treatments [0(CK), 100, 200, 300, 400, 500 µM l⁻¹ Cu] for estimating Cu toxicity. The results showed that elevated Cu restrained plant growth and reduced biomass. According to the EC50 value [the Cu concentration when the relative gain in fresh weight ratio was 50% of control] of two tested cultivars, the concentration of Cu for further experiments was decided as 300 µM l⁻¹. Both pretreatments of PP333 (200, 400, 600 mg l⁻¹) and PGPB (Pantoea sp.) significantly alleviated the negative affect caused by stress of 300 µM l⁻¹ Cu. The pretreatment of 400 mg l⁻¹ PP333 promoted both two cultivars in biomass, compared to 300 µM l⁻¹ Cu treat. The inoculation of Pantoea sp. Jp3-3 increased shoot dry weight, compared to Cu treat. The results suggested that the main reason for both PP333 and Pantoea sp. Jp3-3 enhanced Cu tolerance in guinea grass was that their pretreatments significantly decreased Cu absorption and accumulation under excessive Cu stress. The present study has provided a new insight into the exploitation of energy plant in heavy metal polluted condition by the way of plant growth regulation for increasing heavy metal tolerance.
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