| The culture experiment,pot experiment and investigations of mining area were conducted to study ecological effect and mechanism of heavy metal cadmium(Cd),zinc(Zn),copper(Cu)and lead(Pb)on soil microbes and enzymes.This study.conveys some useful information for soil remediation,environmental quality evaluation and building early warning system in heavy metal contaminated soils.The main results are as follows:1.The basic physical and chemical properties of soils significantly decreased in the mining area because of heavy metal contamination.The soil pH,and available nitrogen(N),phosphorus(P) and potassium(K)decreased markedly with decreasing of the distance from the mining site. Significantly different activities of soil enzymes were found in different sections of the mining area.The activities of soil enzymes increased with increasing of the distance from the mining site.The inhibition of heavy metals on soil enzymes was in the order of dehydrogenase> acid phosphatase> urease> catalase> saccharase.The heavy metals inhibited soil microbial activities,and the number of soil microbes,the soil microbial biomass carbon(C)and nitrogen (N)remarkable decreased with increasing of the distance from the mining site,but the C:N ratio of the soil microbial biomass increased.The bacteria and actinomycosis in soil markedly decreased while the fungus was relatively stable.2.Under constant temperature(25℃)culture,the activities of urease and invertase in soil increased at Cd≤10 mg kg-1and the activities of urease,invertase,dehydrogenase and catalase in soil were enhanced at Pb≤200 mg kg-1.The activities of soil enzymes decreased with increasing of heavy metal level at Zn and Cu treatments and at Cd and Pb treatments which levels were more than 10 mg kg-1(Cd)and 200 mg kg-1(Pb)..Significant decline of soil enzymes was found at high heavy metal level.3.Different effects of heavy metals on different soil microbes were observed under constant temperature(25℃)culture.The activities of soil bacteria,fungus and microbial biomass C and N increased at low heavy metal level,but remarkable decline was found at high heavy metal level.The toxicity of heavy metals on soil microbes was in the order of Cd>Cu and Zn>Pb.4.The effect of combined pollution of cadmium,zinc,copper and lead on soil enzymes and microbes was greater than the individual heavy metal.The influence of combined pollution was not a simple superposition,including coordination and the counteraction.The coordination was found among Cd,Zn and Cu,and the counteraction was observed between Pb and.Cd,Pb and Zn,and Pb and Cu.5.Except for urease,the activities of soil enzymes and microbes decreased first,and then increased with increasing of time under heavy metal pollution at constant temperature(25℃) culture.The lowest activities of soil enzymes were observed at 20th day.The activity of urease decreased with increasing of time in Cd and Cu contaminated soil.The number of soil microbes,and the soil microbial biomass C and N also decreased first and then increased with increasing of cultural time.The high inhibition of heavy metals on soil microbe number,and the soil microbial biomass C and N were found at 20th day.6.In pot experiment,a stimulation on.growth of rape(Brassica napus L.)was observed in Pb (<100mg/kg),but high inhibition on rape biomass was found in other heavy metals.The shoot biomass decreased by 56.3%,67.3%,56.7%.and 62.7%,and root biomass decreased by 38.2%, 42.2%,38.2%and 40.2%at high heavy metal level compared to the control.The greater decline of rape biomass was observed in combined pollution of Cd,Pb,Zn and Cu.The concentration of Cd and Pb was higher in shoot than in roots,but concentration of Cu and Zn was lower in shoot than in roots.The similar changes of soil enzymes and microbes were found in culture experiment and pot experiment.However,the activities of soil enzymes and indictors of soil microbes were higher in pot experiment than in culture experiment due to plant growth.
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