| According to the investigation of previous researchers,Cd,Pb and Cr contamination are the main types of heavy metal contamination in heavy metal contaminated areas.Studies have shown that heavy metal contamination exists in tea leaves from some tea plantations.Some researchers also tested the soil of more than 100 tea gardens and found that some of them were contaminated with Pb.In soil ecosystems,microorganisms have several essential functions.The effect of Pb contamination on soil microorganisms in tea gardens must be determined.This study determined the content of soil Pb in different forms through the European Community Bureau of Reference extraction procedure.The effect of Pb on microbial activity was indicated by measuring microbial biomass,soil respiration and enzyme activity.The effect of Pb on culturable microorganisms was studied using Biolog Eco Plate detection technology,and the plate culture method.The community structure,species diversity,and functional abundance of soil bacteria and fungi were examined through Illumina Nova Seq high-throughput sequencing.As the Pb contamination slowly entered the soil environment with low dose,two modes of Pb contamination(multiple-time contamination and one-time contamination)and three gradients of Pb concentration(low concentration,medium concentration and high concentration)were used.The main conclusions are as follows:(1)The contents of lead in four forms and total lead in soil had significantly differed among the samples(P< 0.05).We observed that the content of four forms of Pb was higher after multiple-time contamination than after one-time contamination.The residue lead content(56.26～521.84 mg/kg)in soil was the highest,followed by reducible lead(42.73～249.70 mg/kg),and acid soluble lead(10.22～231.59 mg/kg).The content of oxidizable lead(1.94～14.03 mg/kg)was the lowest.Pb contamination reduced the content of soil organic carbon,and the content of soil organic carbon was higher after multiple-time contamination than after one-time contamination.The soil p H decreased as Pb concentration increased in both contamination modes,whereas soil water content increased as Pb concentration increased.(2)Lead contamination inhibited the microbial activity of tea garden soil.The microbial activity decreased as Pb concentration increased,and the microbial activity was higher after multiple-time contamination than after one-time contamination.The contents of microbial biomass C and N in Pb-contaminated soil were decreased.Soil microbial biomass C was higher after the high concentration lead treatment in the multiple-time contamination mode,and microbial biomass N was higher after the high concentration lead treatment in the onetime contamination mode.The soil respiration intensity and metabolic entropy decreased as Pb concentration increased in both contamination modes.Lead contamination reduced the activities of urease,sucrase and acid phosphatase in the soil,and their enzyme activities were higher after multiple-time contamination than after one-time contamination.Lead contamination enhanced the activities of polyphenol oxidase and catalase in the soil,and their enzyme activities were higher after one-time contamination than after multiple-time contamination.Dehydrogenase activity was increased in the lead multiple-time contamination,and decreased in the medium and high lead concentration treatments of the one-time contamination.(3)The results of plate culture showed that the effects of different contamination methods and concentrations on culturable bacteria,fungi and actinomycetes were significantly different,and Pb contamination significantly reduced the number of culturable soil bacteria,fungi,and actinomycete communities(P< 0.05).Culturable fungi were more resistant to Pb contamination.The number of culturable bacteria was higher after high Pb concentration.The number of actinomycetes decreased as Pb concentration increased,and was higher after multiple-time contamination than after one-time contamination.(4)The results from Biolog-ECO Plate indicated that the capacity of soil culturable microorganisms to metabolize carbon source increased as Pb concentration increased,and the capacity of soil microorganisms to metabolize carbon was higher after multiple-time contamination than after one-time contamination.After multiple-time contamination,the culturable microorganisms mainly increased the utilization ratio of amine carbon source,and the utilization ratio of amine in low concentration,medium concentration,and high concentration increased by 90.90%,136.36%,and 81.82%,respectively.After one-time contamination,the utilization ratio of phenolic acid carbon source was mainly increased,and the utilization ratios of phenolic acid in low concentration,medium concentration,and high concentration increased by 200%,190%,and 110%,respectively.(5)After multiple-time Pb contamination,the bacterial abundance and diversity were highest in high Pb contaminated soils.The abundance and diversity of bacteria in other leadtreated soils were lower than those in control soils,and were higher after one-time contamination than after multiple-time contamination.The redundancy analysis showed that lead was the environmental factor with the greatest impact on soil microorganisms,followed by soil C/N ratio.The dominant bacterial phyla in the soil included Firmicutes,Chloroflexi,Actinobacteria and Proteobacteria.The abundance of Chloroflexi significantly differed among the samples,and were highest in the soil samples treated with high Pb concentrations.The organic carbon and reducible lead strongly affected Chloroflexi.The dominant bacterial genera in the soil included Tumebacillus,Bacillus,Thermosporothrix and Nitrospira.The abundance of Thermosporothrix significantly differed among the samples,and were highest in the soil samples treated with high Pb concentrations.The oxidizable lead strongly affected Thermosporothrix.Bacterial genes involved in amino acid transport and metabolism exhibited the highest abundance,followed by those involved in translation,ribosomal structure and biogenesis,general function,energy production and conversion,carbohydrate transport and metabolism,coenzyme transport and metabolism,transcription,cell wall/membrane/envelope biogenesis,and inorganic ion transport and metabolism.These functions were less abundant in high lead contaminated soil.(6)Fungal abundance and diversity were higher in Pb contaminated soils than in control soils,and were highest in high Pb contaminated soils.In addition,bacterial abundance and diversity were higher after one-time contamination than after multiple-time contamination.The dominant fungal phyla in soil included Ascomycota,Basidiomycota,Mortierellomycota and Mucoromycota.The abundance of Basidiomycota significantly differed among the samples,and were highest in the soil samples treated with high Pb concentrations.The soil C/N ratio strongly affected Basidiomycota.The dominant fungal genera in soil included Trichoderma,Talaromyces,Coniosporium,Rhodotorula and Fusarium,and the abundance of those fungal genera significantly differed among the samples.The abundance of Trichoderma,Talaromyces and Fusarium were highest in the soil samples treated with high Pb concentrations,and the residual and oxidizable lead strongly affected them.The soil p H strongly affected Coniosporium and Rhodotorula.The functional nutritional types of fungi were mainly pathotrophic-saprotrophic,saprotrophic and pathotrophic-saprotrophicsymbiotrophic.The abundance of pathotrophic-saprotrophic fungi decreased as Pb concentration increased.The abundance of saprotrophic fungi and pathotrophicsaprotrophic-symbiotrophic fungi increased as Pb concentration increased. |
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