Hormetic Effects Of Cd And Pb On Bacteria、fungi And Actinomycetes In Soils Of Chongming Dongtan Wetland

The Hormetic effect is the effect of a chemical at high concentrations,which produces the opposite effect at low concentrations.In recent years,the study of heavy metal distribution and its influence in different ecosystems has become more and more important.People pay more attention to the Hormetic effect of heavy metals.Although previous studies have made important progress,most of these studies are based on the biological individual,and the corresponding research on the biological population is not enough.In this paper,soil samples were collected from Chongming Dongtan wetland.We added different concentrations of Cd and Pb into the soil samples.We used plate colony counting and Miseq two generation high-throughput sequencing to study the characteristics of the quantity,community structure and abundance of bacteria,fungi and actinomycetes under the action of Cd and Pb.We revealed the magnitude of stimulus effect,the dose interval,and the response of microbial groups to provide theoretical basis for risk assessment and remediation of heavy metal pollution in soil.The main results and conclusions are as follows:(1)Cd had significant Hormetic effect on the number of bacteria,fungi and actinomycetes.The amplitude of stimulation were 14.29~29.35 %,14.29~38.89 %,12.50~17.65 %,and the dose interval were 0.004~0.16 mg/kg and 2.4~4 mg/kg,1.2~2.4 mg/kg and 10 mg/kg,0.004~0.08 mg/kg,respectively.Different from the classical inverted U curve,the Hormetic effect curve of Cd on the three species of microorganisms showed "double inverted U type".From the initial response concentration,the sensitivity of bacteria(0.004 mg/kg)to Cd was significantly higher than that of fungi(1.2 mg/kg).In comparison,the stimulation amplitude of Pb to the number of bacteria,fungi and actinomycetes were 15.58~45.00 %,14.71~60.58 %,10.65~25.93 %,and the dosage interval were 160~240 mg/kg,160~240 mg/kg,280~340mg/kg,respectively.The difference is that the initial part of the effect curve is suppressed.From the initial response concentration,the sensitivity of bacteria(160 mg/kg)and fungi(160 mg/kg)to Pb was similar.The maximum rates of Cd and Pb for microbial populations were as follows: fungi > bacteria > actinomycetes.(2)Combined action of Cd and Pb had Hormetic effect on three kinds of microorganisms.Compared with the single action of Cd,the stimulation amplitude of the number of bacteria,fungi and actinomycetes increased under the combined action.The phenomenon of “Double inverted U type” disappeared.The stimulation amplitude of the number of bacteria,fungi and actinomyces were 10.33~34.86%,5.56~41.67%,9.17~50.00%,respectively.The stimulation dose interval of Cd to three kinds of microorganisms were expanded to 0.004~0.6 mg/kg,0.2~10 mg/kg,0.2~10 mg/kg,respectively.Compared with the single action of Pb,the stimulation amplitude of the number of actinomycetes increased under the combined action.The stimulation amplitude of the number of bacteria and fungi decreased under the combined action.The stimulation dose interval of Pb to three kinds of microorganisms was expanded to 80~300 mg/kg.(3)The major microbial groups that produce Hormesis responses to Cd are Bacillus,Podospora,Streptomyces and Micromonospora.The major microbial groups that produce Hormesis responses to Pb are Pontibacter,Hypocreales,Periconia and Streptomyces.The major microbial groups that produce Hormesis responses to the combination of Cd and Pb are Bacillus,Micromonosporaceae and Streptomycetaceae.Coincidentally,both Bacillus and Streptomyces produce Hormesis responses to Cd and Pb.We found that the bacteria stimulated by heavy metals were gram positive bacteria.The bacteria that inhibited by heavy metals were gram negative bacteria.This indicated that gram positive bacteria had better resistance and adaptability to heavy metals.