| In the present study,the soil was taken from the upstream,mine tailings and downstream areas in the Siding lead-zinc mine in Liuzhou,Guangxi province as the research object.The effects of heavy metal content,soil physical and chemical properties and soil enzyme activity of typical plant rhizosphere / non rhizosphere soil in different seasons on the structure of soil microbial community in mining area were studied.At the same time,the soil heavy metal pollution status in the three regions was evaluated.The main research conclusions were as follows:(1)The highest content of Pb,Zn,Cd,Cu,and Mn elements in the mine tailings,downstream and upstream areas were in the downstream area,followed by the upstream area and the mine tailings area;and the Pi value of the three areas was 0.8~1307.6,and this area was most seriously polluted by Pb,Zn and Cd,reaching the level of heavy pollution;the PN value of Nemerow comprehensive pollution index evaluation was 85.6~1369.8,reaching the level of V heavy pollution.(2)In the three regions of mine tailings,downstream and upstream,the nutrient content and soil enzyme activity in the upstream region were the highest.Among them,the content of K and Na was the highest in the tail mining area,followed by the upstream and downstream areas;The contents of Ca and Mg elements from high to low were downstream area,upstream area and tailings area;The highest contents of total nitrogen,total phosphorus and available phosphorus,ammonium nitrogen,nitrate nitrogen and organic matter were in the upstream area,followed by tailings area and downstream area.The highest activities of soil enzyme was the in the upstream area,followed by the downstream area and mine tailings area;The largest activities of cellulase,dehydrogenase and catalase were in summer,followed by autumn and winter.(3)The soil in the mining area was weakly alkaline,and the seasonal variation had no significant effect on the soil p H value;However,the seasonal variation caused the changes of soil conductivity and available state(B1)of heavy metals in the mining area,and the soil conductivity in summer was the highest,which was 253.5 ?s·cm-1;The B1 form of Pb accounted for the largest proportion in winter(the average proportion was 9.2 %);The largest proportion of B1 forms of Cd and Mn were in winter(the average proportion were 35.1 % and14.4 %),while the largest proportion of B1 forms of Zn and Cu were in autumn(the average proportion were 28.8 % and 15.0 %).The enrichment characteristics of Pteris vittata L.?Miscanthus floridulus and Phragmites australis were obviously different in different seasons.The highest content of Zn enriched in the root of Pteris vittata L.was in summer,reaching2318.8 mg kg-1.In autumn,the transfer coefficient(TF value)of Pb was the highest,which was1.5;In autumn,the content of Zn in the root of Miscanthus floridulus senticosus was the highest,which was 2901.7 mg kg-1.The transfer coefficient(TF value)of Cd reached the maximum in winter,which was 3.36;The highest content of Zn in reed roots was in autumn,which was1426.7 mg kg-1,and the extraction coefficient(PEC value)of Cd was the highest,which was3.65.(4)In different seasons,soil environmental factors caused the changes in soil bacterial community diversity index.In winter,the Shannon index of soil bacteria was most significantly affected by the content of soil Pb(F=4.615,P<0.05),and affected by the content of soil Ca,K,total phosphorus and the ratio of carbon to nitrogen(P< 0.05);In summer,the contents of Cd,Pb and Zn in the soil of the mining area had the most significant effect on Shannon index(F=21.896,P<0.001;F=18.153,P<0.01 and F=7.885,P<0.05),meanwhile affected by the ratio of soil carbon to nitrogen,the contents of K,Ca,Mg,total nitrogen and catalase activity(P<0.05).The environmental factors that significantly affected the Chao1 index in winter and summer(P<0.05)were soil catalase activity and Pb and Cd(F=9.193 and F=6.545,P<0.05).In addition,soil p H,moisture content,total nitrogen,nitrate nitrogen,total phosphorus and Mg content,protease activity,cellulase and alkaline phosphatase activity also significantly affected soil bacterial NMDS1 in winter and summer(P<0.05),but in winter,soil bacterial NMDS1 index was most significantly affected by soil Mn content(F=5.443,P<0.05).(5)In different seasons,soil properties caused changes in soil bacterial community.The dominant phyla in the soil bacteria in the mining area in winter and summer were Proteobacteria,Chloroflexi,Actinobacteriota and Acidobacteriota,with a total proportion of 70%.Among them,Proteobacteria and Chloroflexi were the most dominant bacteria in winter and summer,with an average proportion of 22.08 % and 27.25 % respectively;In winter,the contents of Mg,Ca and moisture content of soil had the most significant effect on the composition of soil bacterial community(P<0.05),and the total amount of explanation for the composition and distribution of bacterial community was 50.6 %;The environmental factors that significantly affected the composition of soil bacterial community in summer were the contents of soil Ca,Pb,total nitrogen and Pb residue,the activities of cellulase,alkaline phosphatase,protease and urease(P<0.05).The total amount of explanation for the composition and distribution of bacterial community reached 89.6 %,of which the amount of explanation for the content of Pb and Pb residues was 13.4 %.(6)In winter,the Shannon index of soil fungi was affected not only by the heavy metals Mn and Zn,but also by the physical and chemical properties of soil,but almost not by the activity of soil enzymes.The effect of Mn reached a very significant level(F= 19.752,P<0.001),and the effect of Zn on Shannon index F reached 4.520,which was a significant level(P<0.05).In summer,in addition to the p H,moisture content and soil organic matter,it was also affected by the activities of soil sucrase,protease,dehydrogenase,cellulase and alkaline phosphatase.In winter,Chao1 index was greatly affected by the changes of content of soil heavy metals Mn,Zn,Cu and other metals,and its F values were 13.586,6.885 and 6.390 respectively.Among them,the influence of Mn reached a very significant level(P<0.01),Zn and Cu was a significant level(P<0.05).In addition,it was also significantly affected by the content of soil K,Ca,Mg and organic matter and urease activity(P<0.05);In summer,the environmental factors that significantly affected the Chao1 index were the content of K,Na,p H,moisture content,organic matter and the activities of protease,dehydrogenase,cellulase and alkaline phosphatase(P<0.05).In winter,the effect of soil Mn content on NMDS1 index was very significant(F=12.512,P<0.01),and the contents of soil p H,organic matter,Mn,Mg,water content,total nitrogen and nitrate nitrogen and the activities of soil cellulase,alkaline phosphatase,dehydrogenase and protease were significant(P<0.05);The environmental factors that significantly affected the NMDS1 index(P<0.05)in summer were soil nitrate nitrogen,ammonium nitrogen,K,electrical conductivity,available phosphorus,Na,p H,water content and organic matter content,as well as the activities of soil sucrase,urease,dehydrogenase,cellulase,protease and alkaline phosphatase.(7)In winter,Ascomycota and Fungi were the dominant fungi in the soil in the mining area,which accounted for more than 80 % of the total.In summer,Ascomycota,Basidiomycota,Rozelomycota,Fungi and Mortierellomycota were the dominant fungi in the soil of the mining area,accounting for more than 98 %,it could be seen that the dominant phyla of soil fungi was more abundant in summer.Among them,Ascomycota was the dominant phylum accounting for the largest proportion of soil fungi in winter,with an average proportion of 69.18 %;Ascomycota was the most dominant phylum of soil fungi in summer,accounting for an average of 40.68 %.In winter,the composition of soil fungal community was significantly affected by the content of soil nitrate nitrogen and Mg(P< 0.05),which explained 50.3 % of the distribution of fungal community composition;The environmental factors that had a significant impact on the composition of soil fungal community in summer(P< 0.05)were the content of soil p H,K,Pb reducible state and Pb residue state,as well as the activitie of soil protease and dehydrogenase with a total explaination of 75.4 %,of which the explaination of the content of Pb reducible state and Pb residue state were 38.8%.(8)In conclusion,the contamination of Pb,Zn,Cd,Cu and Mn in the soil of mining area significantly affected soil microorganisms(including bacteria and fungi)(P<0.05).Other environmental factors that were significantly correlated with soil microorganisms were soil K,Na,Ca,Mg,soil organic matter,total nitrogen,nitrate nitrogen,total phosphorus content,soil p H and water content(P<0.05).In addition,seven soil enzymes were significantly correlated with bacterial community composition and diversity(P<0.05).Including sucrase,dehydrogenase,hydrooxidase,protease,cellulase,alkaline phosphatase and urease. |
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