The Effects On The Microbial Community Structure And Diversity In The Soil That Polluted By Lead And Zinc Mine Tailing Under Ligustrum Lucidum

Hunan province is one of the top five mineral resources of lead and zinc in China.The rich mineral resources lead to frequent mining activities.Among them,the unreasonable waste disposal method brings serious soil heavy metal pollution,which threatens the stability of the ecosystem and the health of surrounding organisms.Therefore,the treatment and remediation of soil heavy metal pollution are urgent.In this study,we choose the 2-year-old Ligustrum lucidum as the experiment material,and four gradients of lead-zinc slag mixed soil were set up(CK:100%soil;L1:10%slag+ 90%soil;L2:25%slag+75%soil;L3:50%slag+50%soil).We simulated the environment that the Ligustrum lucidum that lived in field had been polluted by lead and zinc mine tailings.We studied the relationship among the lead-zinc mine tailing,soil physicochemical property and Ligustrum lucidum,and we also explored the effects of lead-zin mine tailing on soil microbial community construction and diversity and found the indicator microbial community in lead-zinc mine tailing soils.The main results are as follows:(1)Pb,Zn,Cu and Cd are the four main heavy metals in lead-zinc mine tailingpolluted soil.With the increase of soil Pb-Zn slag mass ratio,the contents of soil organic carbon during the phytoremediation of Ligustrum lucidum,total phosphorus and pH increased significantly,all of which showed as L3>L2>L1>CK,and the difference was significant(p<0.05).The total nitrogen content decreased significantly,showing a trend of CK>L1>L2>L3,and the difference was significant(p<0.05).In addition,with the increase of soil lead and zinc slag mass ratio,soil C:N ratio showed an increasing trend.CK,L1,L2 and L3 were 12.5,20.9,33.2 and 91.1,respectively.The ratio of C:P and N:P showed a decreasing trend,and the ratio of C:P was 58.6,53.1,48.0 and 53.2,respectively.The N:P ratios were 4.7,2.5,1.4 and 0.6,respectively.(2)With the increase of the proportion of Pb and Zn slag in the soil during thephytoremediation of Ligustrum lucidum,the plant height,ground diameter,relative growth rate and root biomass of Ligustrum lucidum showed the trend as L3<L2<L1<CK,and the differences were significant(p<0.05).The results showed that the lead-zinc slag inhibited the growth of Ligustrum lucidum,and the higher the proportion of lead-zinc slag,the higher the negative effects on it.In each treatment group,the plant height of Ligustrum lucidum at the end of the experiment was significantly higher than that at the beginning of the experiment,indicating that Ligustrum lucidum could still grow even in the contaminated soil with the content of lead-zinc slag up to 50%,and privet had a certain tolerance to lead-zinc slag.(3)With the increase of the proportion of Pb and Zn slag in the soil during the phytoremediation of Ligustrum lucidum,the diversity of the microbial community structure in the soil showed a decreasing trend.Specifically,the richness and evenness of the bacterial community in the soil decreased,and the Shannon index showed as L3<L2<L1<CK.Simpson index is L3>L2>L1>CK;The index of Chao 1 was L3<L2<L1<CK,and the difference was significant(p<0.05).The diversity of soil microbial community structure showed that with the increase of Pb-Zn slag mass ratio,the soil microbial community structure of the control group and the three treatment groups differed.There was a significant difference between CK and L1,and the difference in community composition between L2 and L3 was smaller than that between CK and L1.The analysis of soil microbial community structure diversity showed that Pb and Zn slag had significant influence on soil microorganism and inhibited the diversity of soil microbial community structure to some extent.(4)With the increase of the proportion the lead-zinc slag contaminated soil,the total type of bacterial community did not change significantly,while the bacterial community structure changed.The bacteria(phylum level)in the top ten of the total communities in the samples were Proteobacteria(35.9-47.1%),Acidobacteria(6.3-22.1%),Bacteroidetes(3.8-16.0%),Actinobacteria(4.6-10.7%),Firmicutes(0.4-17.1%),Gemmatimonadetes(4.0-8.6%)and Chloroflexi(2.4-10).2%),Patescibactria(1.4-3.9%),Cyanobcteria(0.6-5.0%)and Verrucomicrobia(1.5-2.6%).The major bacteria(phyla level)at the phyla classification level are Proteobacteria,Acidobacteria and Bacteroidetes,whose relative abundance amounts to 46.0-85.2%of the entire microbial community.(5)RDA analysis and Mentel-carlo test shows that in lead-zinc slag contaminated soil,heavy metals(Pb,Zn,Cu,Cd)and soil physical and chemical properties(organic carbon,total nitrogen,total phosphorus,PH,water content)both have an impact on the bacterial community structure,especially Pb,Zn and soil organic carbon content significantly affect the bacterial community changes.(6)With the increase of lead-zinc slag mass ratio during the phytoremediation of Ligustrum lucidum,specific indicator species appeared in each group.Acidobacteria(phylum to genus level)and Gemmatimonadetes(phylum to genus level)were mainly enriched in the soil of CK group,Actinobacteria(phylum to class level)and Cyanobcteria(phylum to order level)were mainly enriched in the soil of L1 group,and Betaproteobacteriales(MND1 at order to family level)were mainly enriched in the soil of L2 group.Gammaproteobacteria(order to family level Acidiferrobacterales,Sulfurifustis and Hydrogenophilaceae)mainly in the L3 group concentration in the soil.At the same time,it can be found that there are more unique populations in CK group,while there are the least unique populations in L3 group.In these populations,Acidobacteria and Gammaproteobacteria(phylum)are closely related to the nutrient state of the soil(C,N,P).Above all,lead and zinc slag significantly inhibitory effect on the growth of Ligustrum lucidum,lead and zinc slag reduces the diversity of soil microbial community structure and performance in a significant reduction in the uniformity of the soil microbial community and diversity,at the same time with the increase of lead and zinc slag quality proportion,soil microbial community structure has changed,the change significantly associated with soil physical and chemical properties.In highly contaminated soil,Proteobacteria(phylum level)increased significantly.This phyla may have a strong tolerance to high concentration of lead and zinc slag,and its principle can be further studied.