The Effects Of Heavy Metals Pollution On Soil Microbial Diversity

Zinc-lead mine resources are very rich in the southwest of china, although mineral resources have made tremendous contributions to the development of economy in our country. However, a large number of soil damage or degradation because of heavy metals pollution caused soil ecosystem damage seriously. The heavy metals pollution has now become one of the most serious environmental problems.This research studied the numbers, activities and diversity of soil microorganisms near a lead-zinc mine which located in Fuquan town, Baoxing country, Ya'an, Sichuan Province under field situation. This research focused on effects of soil microbial diversity by combined heavy metals contamination, which was supposed to support the ecological remediation of contaminated by heavy metals. The conclusions are as follow:(1) Zn, Pb, Cd content of zinc-lead mine in the soil was significantly higher than that of non-mining, and the order of the metal content:Zn> Pb> Cd. Significantly positive correlation was achieved between the available heavy metals contents and the total heavy metal contents.(2) We can find that there were significantly inhibited between heavy metals and soil microbial biomass C. The degrees of influence about heavy metals pollution on several soil enzymes were different. Negative correlated was founded between the available heavy metals contents and soil microbial biomass, phosphatase activity and urease activity. But there was significant or maximum significant relationship between catalase activity and the available heavy metals contents.(3) Heavy metals pollution has a greater impact on the number of soil microbes in Lead-Zinc district. With the intensification of heavy metal pollution levels, the total number of soil microorganisms declined. Correlation analysis showed there was a maximum significant negative correlation between the number of bacteria and heavy metal content (P<0.01), and significant negative correlation for the number of fungi, actinomycetes (P<0.05).(4) The cultured actinomycetes were analyzed by 16S rDNA PCR-RFLP with three kinds of restriction endonucleases including Haeâ…¢, Hinfl and Taqâ… . Thirty-two genotypes were identified. BOXAIR-PCR and 16S-PCR-RFLP clustering analysis showed that the strains isolated from soil sample with the high content of heavy metal clustered together, and the heavy metal content affect the distribution of actinomycetes. The dominant strains were mainly Streptomyces at the lead-zinc mine in Haiyuan country.(5) PCR-DGGE pattern profiles showed that diversity of bacteria, actinomycetia, fungi were quite different among the five soil samples with gradient of the content of heavy metal. Bands of fungi were the most, bacteria followed, while the bands of actinomycetes least. Diversity index had the same trend in band numbers, which showed the type of fungi was the most complicated.Available lead and bacteria diversity index reached significant negative correlation, and maximum significantly negative correlation were achieved between bacteria diversity index and available zinc content. There were a negative trend between the contents of available cadmium, lead, zinc and the diversity index of actinomyces, fungi, but did not reach negatively significant level.The community similarity of bacteria, actinomycetes and fungi analyses showed the microbial community structure associated with the content of heavy metals:The DGGE pattern profiles of 5th soil sample was clustered into a separate group, while the No.1 tailings stacking area and No.4 transport clustered into one class, while the No.2 factory district and 3 Spoil field clustered into one class. From the cluster analysis we found that No.1 and No.4, clustered together with high concentration of heavy metals, while a low level of heavy metals in control samples clustered into a separate category.Recovery sequence of DGGE bands showed the distributions of microbial were different among soil samples with different content of heavy metals. The dominant bacterial group was beta proteobacterium; The dominant actinomycetes group were Pseudonocardia, Frankia; The dominant fungi group was Ascomycetes.From this research, we can conclude that PCR-DGGE could better reveal the effect of heavy metal pollution on microbial diversity in lead-zinc mine, could evaluate on soil conditions in macroscope. However, the sequences recovered from the DGGE bands could not certain the taxonomic position.