| Uranium and cadmium are two metals that naturally exist in water and terrestrial environment.However,anthropogenic activities such as uranium mining and smelting and excessive application of phosphate fertilizers will lead to redistribute of uranium and cadmium in the natural environment,increasing the contents of uranium and cadmium in the natural environment that pose a potential threat to the global environment.Both uranium and cadmium are highly toxic heavy metals,and they are highly mobile and threated for human health through the food chains.Therefore,the soil contaminated by uranium and cadmium is urgent to remediate.Microbial-enhanced phytoremediation technology holds the advantages of aesthetically pleasing,environmentally-friendly,small disturbance to the environment and long-lasting effect.Therefore,it can be regarded as a development potential technology for remediating uranium and cadmium contaminated soil.In this study,we investigated the behavior and mechanism of uranium-cadmium tolerant fungi strain Fusarium sp.A-2 to enhancenatural colonizer Macleaya cordata(M.cordata)to remediate the uranium and cadmium combined contaminated soil by pot experiment.Firstly,the fungal were isolated and screened from the roots of M.cordata,and the uranium-and cadmium-resistant of the isolated strains were tested.A strain with the strongest uranium-and cadmium-resistant was screened according to the minimum inhibitory concentration(MIC),and identificated.Secondly,the effects of inoculation of uranium-and cadmium-resistant fungi on the plant growth,photosynthesis,protein synthesis,membrane lipid peroxidation were studied.Thirdly,the changes of functional groups in the plant body were investigated by fourier transform infrared spectroscopy(FTIR)and the changes of speciation of uranium and cadmium in the soil was explored.And then,the effects of uranium and cadmium stress on the subcellular structure of leave of M.cordata and the distribution of uranium and cadmium in its subcellular fraction was analyzed by transmission electron microscopy and energy spectroscopy(TEM-EDS).Finally,the uranium and cadmium of M.cordata were recovered by ashing and leaching.The main results of this study are(1)the strain of A-2 with the strongest uranium-cadmium tolerant is isolated from the roots of M.cordata.The strain belongs to the Fusarium by identifying,its GenBank accession number is MH978624,and it can be named Fusarium sp.A-2,(2)after inoculation with Fusarium sp.A-2,the biomass,chlorophyll a andtotal chlorophyll content,soluble protein in the leaves of M.cordata are increased and the MDA content in the leaves of M.cordata is decreased,(3)FTIR analysis shows that phospholipids and glycogen are produced after inoculation of the strain,which may be one of the mechanisms for mitigating of uranium-cadmium stress and enhancing of bioaccumulation of uranium and cadmium by M.cordata,(4)In the uranium-cadmium compound contaminated soil,the strain increase the proportion of available uranium in the rhizosphere soil,and reduced the proportion of unusable uranium in the soil,which may be one of the mechanism of the strain enhances bioaccumulation of uranium by M.cordata.And then,the strain also increases the proportion of potential available cadmium in the rhizosphere soil,which may be one of the mechanism of the strain enhances bioaccumulation of cadmium by the roots of M.cordata,(5)TEM-EDS analysis shows that uranium and cadmium are mainly bioaccumulated in the cell wall of the leaves,which may be the positive physiological response for the exposure of uranium and cadmium,(6)it is economic and environmental to recover uranium and cadmium from the ash of M.cordata.Leaching test suggests that the leaching rates of uranium in the ash are above 90% of U+A-2 and U+Cd+A-2 groups and the leaching rates of cadmium in the ash are above 80% of Cd+A-2 and U+Cd+A-2 groups in our study.Results can provide a reference for microbial-enhanced phytoremediation of uranium-cadmium compoundcontaminated soil. |
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