| Nowdays,the heavy metal pollution of soil is more and more serious,and the heavy metal pollution in soil incidents happen frequently,which seriously threaten the quality of agricultural products and human health.Therefore,the treatment of heavy metal pollution is necessary and imninent.The traditional methods of soil heavy metal pollution,such as physical method,ehemieal method,are expensive and with secondary pollution that limit their application,However,the treatment of heavy metals pollution in soil,plants and microorganisms which has low cost,get attention.This experiment succeeded in isolating a microorganisms from the heavy metal pollution soil Enterobacter sp.;and study in Enterobacter sp.and cadmium hyperaccumulator asiatica(Centella asiatica L.),to explore the effects of environmental factors(initial heavy metal concentration,temperature,pH)on the cadmium adsorption rate and cadmium adsorption mechanism of Enterobacter sp.On this basis,the experiment applied Enterobacter sp on remediation of cadmium contaminated soil,to explore the effect of Enterobacter sp on the biomass,cadmium contents and absorption of mining and non mining asiatica(Centella asiatica L.).And explore the effects of on the rhizosphere pH and available of cadmium.The main results are as follows:1.By gradient dilution plate methods,successfully isolated a Cd-tolerant bacteria strain from the Hezhou mine soil.On the basis of the morphological,physiological and 16S rRNA sequence analysis,the stain was recognized as a species of the genus Enterobacter sp..2 The bacteria could grow normally in the solid culture medium containing 40 mmol/L of Cd2+.The strains was able to grow normally in the liquid culture medium 0.25-0.5 mmol/L of Cd2+,but in more than 1 mmol/L the growth of the strains was inhibition by different degrees in the liquid culture medium.The logarithmic phase to stable period was also prolonged significantly.In addition,the optimum temperature for the growth of the bacteria was 30,and the optimum pH was 7.3 The stain was studied the environmental factors(initial Cd concentration,temperature,pH)on the adsorption of Cd,and the response surface method was optimized.In the single factor experiment,the best adsorption condition of the bacteria is:initial cadmium concentration 4-8 mmol/L,temperature 30-35?,pH 7-8.The result of response surface method showed that the optimal adsorption condition were 5 mmol/L of the initial cadmium concentration,30? of the temperature,and pH 8.4.The correlation coefficients R2 of the Freundlich model and Langmuir model were 0.9795,0.9669.It showed that Freundlich model is more suitable for describing the adsorption process,which indicated that the adsorption process of Enterobacter had physical adsorption and chemical adsorption.So it is a multi molecular layer adsorption process.The initial cadmium concentration in the 2,4 and 8 mmol/L conditions,the correlation coefficient R2 of first-order kinetics of Enterobacter on Cd adsorption were 0.8842,0.9444,0.9348 and the second-order kinetics respectively were 0.9985,0.999 and 0.9979.It showed that the second order kinetics was more suitable to describe the adsorption of cadmium process,which showed that the adsorption processis is dominated by chemical adsorption.5.By SEM-EDS and FTIR observing the micro changes of cell surface of Enterobacter and the functional groups in the adsorption process.It showed that,after the adsorption of cadmium,cells morphology changed long and thick to short and thin,length by 0.731-1.11?m variable for 0.881-1.14?m,width by 0.340-0.384?m for 0.320-0.364 ?m and a large number of white floe around the cell.By EDS analysis the floe was cadmium substances.And the Na content was significantly decreased,which showed that the ion exchange was carried out.Finally,the functional groups on the surface of the stains,such as-OH,-NH2,P=0 and PO43-,M-O(O-M-O),were involved in the absorption process.6 Effects of Enterobacter on the biomass of asiatica.The treatment of Enterobacter improved the plant height and weight of mine asiatica in upstream area,mining area,downstream area mines,and plant high of tailing mine area,but the weight of mine asiatica in tailing mine areas was redued.The treatment of Enterobacter improved the height and weight of non nine asiatica in upstream area,milling area and downstream areas,included the plant height of asiatica in tailing mine area.The impact of the plant weight of non mlne asiatica in tailing mine area is not obvious.Effects of Enterobacter on the cadmium eontent of asiatica(Centella asiatica L.)in roots,stems,and leaves.The treatment of Enterobacter promoted the cadmium content in root of mine asiatica in upstream area,and also promoted the Cd content in roots,stems,leaves of mining area,downstream area,but the impact on the cadmium content in stems and leaves were not obvious,decreased the Cd content in roots,stems in tailings.The treatment of Enterobacter,promoted the Cd content in roots,stems of non mine asiatica in downstream area,tailing area,and had little effect on upstream area and mining area.Effeets of on the cadmium absorption in roots,stems and leaves.of asiatica.The treatment of Enterobactery significantly increased the root Cd uptake of mine asiatica in upstream area,and improved the Cd uptake in toors,stens,leaveas,of mine asiatica in mining area and tailing area,but the effect on stems and leaves was not significant in upstream area.The treatment of Enterobacter significantly increased the root,stems and leaves Cd uptake of non mine asiatica in upstream area,downstream area and tailing area,and also the treatment on mining area were not obvious.9 The treatment of Enterobacter decreased significantly the pH of mine asiatica rhizosphere soil in upstream area,downstream area,and mining area.The effects of C0.5 on pH of rhizosphere soil was the most obvious.The treatment of Enterobacter had little effect on pH of rhizosphere soil in tne non mining asiatica.The pH of rhizosphere soil in tne non mining asiatica in mining area had varied degrees of decline,pH of rhizosphere soil increased significantly in tailing area.10.The treatment of Enterobacter had an significant impact on the availability of cadmium of mining asiatica in upstream area,mining area,but the tailings and downstream areas were not significantly affected.The treatment of Enterobacter had an significant impact on the bio availability of cadmium of non mining asiatica in upstream area,mining area and downstream area,but the tailing area impact is not obvious. |
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