Restoration Effect After Different Treatment Years On The Wasteland Of Heap-leaching Mine Area Of The Rare Earth Mining In Changting

The conducted research on the vegetation restoration technology of Changting rare earth waste mine in the early stage and selected the optimal vegetation allocation model suitable for the waste land of Changting rare earth mine abandoned areas,and applied it in this area,achieving a better ecological recovery effect.However,in the process of popularization and application of vegetation restoration technology,we have found that vegetation in rare earth mine abandoned areas has shown signs of variety degradation,poor growth,and even some vegetation has disappeared over time,which has affected the long-term restoration of vegetation ecology in abandoned areas.The paper adopts the method of spatial sequence instead of time successional sequence,the vegetation allocation model of" Liquidambar formosana + Schima superba + Lespedeza tomentosa + Paspalum wettsteinii " was selected in the heap leaching abandoned area of Changting rare earth mine selected in the early period,and the fixed sample plots for different years of treatment were set up.In 2016(this time 2007,2010,2013’ s sample plots were 9 years of governance,6 years of governance and 3 years of governance)and 2017(2007,2010,2013’ s sample plots were 10 years of governance,7 years of governance and 4 years of governance),the method of standard sample plots survey was used to investigate the vegetation and soil in fixed sample plots of different plant remediation years in Changting rare earth mine heap leaching abandoned area,and to investigate the vegetation types,quantity,coverage and growth conditions in different treatment years,and measured the SPAD value and chlorophyll fluorescence and other physiological indicators of the plants(Liquidambar formosana,Schima superba,Lespedeza tomentosa,Paspalum wettsteinii)that appeared in different treatment years,as well as the soil physicochemical properties and microorganisms.Compare the vegetation communities,plant physiological indicators,soil physicochemical characteristics and microbial diversity of rare earth mine leaching abandoned area in different years of governance,and determining whether there are degradation problems in the restoration process of this area,and the degree and impact factors of degradation.Provide basis for the long-term maintenance of rare earth mine heap leaching abandoned area treatment effect.The main research results are as follows:(1)With the increase of the treatment years,the plants coverage,Simpson,Shannon-Wiener,Louie,McIntosh and the chlorophyll fluorescence parameters and SPAD values of Liquidambar formosana,Schima superba,Lespedeza tomentosa,and Paspalum wettsteinii of Changting rare earth mine heap leaching abandoned area also show the law of increasing first and then decreasing.The governance show an increasing trend in the first 4 years.But when the treatment period was more than 4 years,with the treatment years increasing,the coverage and quantity of plants have been significantly reduced,and the important values,SPAD values,and chlorophyll fluorescence parameters of the plants have gradually decreased,and the plant communities have been degraded a certain degree.(2)With the increase of the number of treatment years,physical properties such as soil moisture content,capillary water holding capacity,and maximum and minimum water holding capacity of Changting rare earth mine heap leaching abandoned area are expressed as the law of increasing first and then decreasing,and the soil bulk density is shown as the law of decreasing first and then increasing.(3)With the increase of the treatment years,the soil chemical properties of Changting rare earth mine heap leaching abandoned area also show the law of increasing first and then decreasing.In the first four treatment years,the nitrogen,phosphorus,potassium,carbon and organic matter of the soil increase gradually.But more than 4 years later,with the increase of treatment time,all of them decreased.The content of heavy metals in soil decreased with the increase of treatment time.The fertility decreased,soil pH value decreased with the increase of treatment time,acidification problem occuring.(4)Species richness and evenness of soil microbial groups decreased with treatment years increasing.At the gate level,the top 5 bacterial gates were:Euryarchaeota,Planctomycetes,Phylum firmicutes,Abnormalcocci portal,Chlamydiae.Simpson diversity index,Shannon-Wiener diversity index,species relative abundance,and community similarity showed a downward trend.The number of fungi decreased.Vegetation restoration had a certain role in promoting soil microbial diversity,but it also had the problem of decreasing with the increase of treatment years,which is the same as the physicochemical properties changing law of soil.(5)A comprehensive evaluation of the soil fertility of rare earth mine heap leaching abandoned area in different treatment years showed that the soil fertility index of governance show an increasing trend in the first 4 years,the soil fertility index reached the highest level(0.545)at four years.The soil fertility index reached the lowest level(0.387)after ten years of treatment.Soil fertility index of different control years was lower than that of unexploited control area.Synthesize soil physical and chemical properties and species diversity of vegetation,using gray correlation analysis method to comprehensively evaluate the ecological restoration effect of the rare earth mine heap leaching abandoned area for different treatment years.The results showed that the physical and chemical properties of the soil were gradually improved in the first four treatment years,but after that,the ecological restoration effect showed a downward trend.