| In recent years, the soil and ecological environment deteriorated due to the unreasonable development and destruction of the mining area which seriously affecting people's normal production and living environment. At present, phytoremediation in heavy metal pollution of soil still has bottleneck, like some cadmium hyperaccumulation plant has little biomass and its growth index are not stable or the photosynthetic growth index and the toxicity mechanism under cadmium stress are not clear enough. This research selected the Boehmeria nivea as material which was the native species in mining area. We measured the enrichment and bioaccumulation characteristics of heavy metals by field investigation, then studied the physiological and ecological adaptability under different cadmium stress by indoor pot experiment, to explore and evaluate the potential and realistic feasibility of Boehmeria nivea in phytoremediation.The results were shown as below:(1)The enrichment and bioaccumulation characteristics of hea vy metals in native Boehmeria nivea growing on mining areas. We selected eight typical sampling sites in Dexing Copper Mine of Jiangxi Province, then collected Boehmeria nivea and soil to investigate the heavy metal contents of Cd, Pb and Cu. The results showed that the soil samples from mining areas were severely polluted by Cu and accompanied slightly polluted by Cd. The contents of Pb in the soils all not reached to the range of soil background values of Jiangxi Province. The average contents of Cd, Pb and Cu in soils of the eight sampling sites were 0.51, 9.36 and 1058.21 mg·kg-1 respectively. In most of the sampling sites, the contents of three heavy metals in the leaves were the lowest and roots the highest which reached to 10~50 times, the contents of the heavy metals in the upper parts were always lower than those of the underground part. The order of the enrichment coefficients and transfer coefficients in B. nivea were Cd> Pb> Cu. The highest enrichment coefficient and transfer coefficient of Cd in B. nivea, were 1.42 and 0.54; the Pb were 0.63 and 0.53; the Cu were 0.08 and 0.37. The average biomass of the B. nivea upper parts in eight sampling sites was 1.41 t·hm-2, and the highest reached to 2.18 t·hm-2. The average bioaccumulation values of Cd, Pb and Cu in the upper parts of B. nivea were 0.2, 1.1 and 24 g·hm-2. Based on the above analysis, we know that ramie had the tolerance of Cu, Cd and we can plant B. nivea in mine area reasonably, which can effectively control heavy metals pollution and provide some certain scientific value for mine restoration.(2)The growth changes and ecological adaptability of the Boehmeria nivea under different cadmium concentration stress by indoor experiment. On the basis of pot experiment methods, we selected Boehmeria nivea as the materials and setted the Cd treatments as 0(control group), 20, 60, 120, 180 and 240 mg·L–1.After two stress time of 21 d and 49 d, we measured all contents of chlorophyll, photosynthetic fluorescence parameters and fluorescence imaging in order to study the relationships among the tolerance to cadmium contamination of B. nivea and its photosynthetic fluorescence characteristics under different cadmium concentration stress. Under the different cadmium concentration stress in the short time of 21 days, the results showed that the values of the most parameters of the B. nivea leaves increased more than those of the control group without any heavy metal stress, and the main parameters which included chlorophyll a, chlorophyll b, the total chlorophyll, and the net photosynthetic rate(Pn), stomatal conductance(Gs),transpiration rate(Tr) and etc., while the values of other parameters included the intercellular CO2 concentration(Ci) and the non-photochemical quenching under stable state(NPQLss) decreased less than those of the control group, and the values of the parameters included the net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Gs) and the maximum quantum yield(QYmax) presented the highest under the stress of the cadmium concentration in the 60 mg·L-1. With the increasing of the stress time, under the different cadmium concentrations stress in the long time of 49 days, the values of chlorophyll a, chlorophyll b, total chlorophyll contents, Pn, Gs, Tr of B. nivea leaves decreased than those of the control group, while the values of Ci increased. And the change trend showed that the values of the QYmax and NPQLsswere lower than those of the control group under the different cadmium concentrations stress except under the cadmium concentration in the 240 mg·L-1, and which values were higher than those of the control group 2.5 %, 75.9 %.(3)Influence on the antioxidant system of Boehmeria nivea under different cadmium concentration stress by indoor experiment. On the basis of pot experiment methods, we also selected Boehmeria nivea as the materials and setted six different groups of Cd treatments as above. After two stress time of 21 d and 49 d, we sdudied the contents of osmoregulation substances, superoxide dismutase(SOD) activities, peroxidase(POD) activities, catalase(CAT) activities, malondialdehyde(MDA) contents in the roots and leaves and root activities in Boehmeria nivea under different cadmium concentration stress in different stress time. The results showed that the contents of osmoregulation substances in roots were significantly higher than those in leaves under high cadmium concentration and the longer stress time of 49 days, which were significantly higher than those of the control group without any heavy metal stress. The highest contents of each osmoregulation substance in roots presented under the cadmium stress of 240 mg·L–1. The contents of osmoregulation substance in roots and leaves were both significantly positive correlated to cadmium concentrations under the stress time of 49 days. The SOD and POD activities in roots were both significantly higher than those in leaves under the two different stress time. And the contents of CAT activities in roots were lower than those in leaves under the stress time of 21 days, but which were higher than those in leaves under the stress time of 49 days. The antioxidant enzyme activities in roots and leaves under the stress time of 21 days were higher than those of 49 days. We also found that the POD activity in roots under the stress time of 49 days were significantly positive correlated to cadmium concentrations, which indicated that the POD activity in roots were dominant in antioxidant enzymes. The changes of MDA contents in roots or leaves were not obvious under the stress of two different cycles, but the fluctuation of the MDA content values in roots or leaves under the stress of 21 days were more obvious than those of 49 days with the increasing of cadmium concentrations, which indicated that plant physiology function appeared a temporary repair in the early stress time. In this study, we also found the root activities under different cadimium stress and different stress time all decreased compared to those of the control group. The study showed that the physiological response mechanism to cadmium in roots or leaves were very different and the response mechanism to cadmium under different stress time also have significant differences, which show that the roots have more stronger resistance. |
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