| With the rapid development of rare earth mining,a large number of damaged and polluted abandoned lands come into being which have caused serious environmental problems including heavy metal pollution and land desolation and soil drought.The objective of this study is to provide a scientific and technological support and find an effective way to repair the mined rare earth mine land.During the phytoremediation,Paspalum conjugatum with fast growth and high biomass was used as the pioneer plant and the rhizosphere microbe diversity in different repair stages was observed.Relationship about plant-soil-microbe was analyzed.Through hydroponics and pot cultivation,the mechanism of heavy metal resistance and drought tolerance of P.conjugatum were studied.At the same time,field experiment and site observation were carried out to verify its effects of on the restoration of the exploited rare earth mine land.According to this study,P.conjugatum was expected to be used as the pioneer plant for phytoremediation in the exploited rare earth mine land for ecological restoration.The results are as follows:(1)Through the analysis of rhizosphere microbe diversity of P.massoniana and Pinus massoniana in the mined land in different repair stages,it could be concluded that the bacteria content and flora diversity in 5 soil samples were characterized by M2(from P.massoniana in 2 year repaired land)> L2(from P.conjugatum in 2 year repaired land)> L1(from P.conjugatum in 1 year repaired land)> M1(from P.massoniana in 1 year repaired land)> CK(from the soil in the unrepaired land).The experimental results showed that the soil microbe diversity of the restored land was significantly higher than original mined land,indicated that P.conjugatum and P.massoniana had obvious effects on the soil restoration.(2)By 16 S rDNA high-throughput sequencing,the top 10 microbe phylums in the above 5 soil samples were Proteobacteria,Chloroflexi,Firmicutes,Actinobacteria,Acidobacteria,Bacteroidetes,Cyanobacteria,Saccharibacteria,Verrucomicrobia and Planctomycetes,according to their abundance,Proteobacteria was with the highest abundance as the predominant microbe.(3)Through hydroponic experiment,Cd and Pb content of P.conjugatum from the roots,stems and leaves was different,their accumulation from large to small was:root > stem > leaf.The transfer coefficients of Cd and Pb of P.conjugatum was higher than 1,and the total content of Cd was 98.33 mg/kg,on the verge of the critical value of the super-accumulated plant on Cd(100 mg/kg).The total content of Pb was 137mg/kg,lower than the critical value of the the super-accumulated plant on Pb(1000mg/kg).It was shown that P.conjugatum was resistant to Cd and Pb with a strong Cd accumulation,and strongly tolerant to Pb.(4)Three crops,Daucus carota,Solanum tuberosum and Brassica chinensis could grow at the repaired land normally.The contents of Cd,Pb,Cu and Zn in the harvest were significantly reduced compared with that in the soil.The four kinds of heavy metal in the harvest were not more than the maximum value of the national safety standards,which meant that P.conjugatum could be used to repair the soil contaminated by heavy metals.(5)Through pot cultivation,it was concluded that P.conjugatum could keep its normal morphology under drought stress to some extent,Determination of some physiological indexes about water physiology(WSD,RWC),osmotic regulation substances(Pro content),MDA content and enzyme(SOD,POD,CAT)activity suggested that P.conjugatum was certainly resistant to drought. |
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