Effects Of Benzo(a)pyrene Multiple-time Superimposed Pollution On Microbial Community Diversity In Soil

B[a]P?Benzo?a?pyrene?is one of the most polluted and most harmful PAHs?Polycyclic aromatic hydrocarbons?pollutants in the environment.And more than90%of the PAHs in the environment are carried by the soil.To reveal the impact of accumulated pollution of B[a]P on functional diversity of soil microbial community,B[a]P was added to soil by low-dose superposition method to simulate the cumulative pollution of B[a]P in natural soil,and the effects of different ways of B[a]P pollution on microbial community functions in soil was investigated by the Biolog-ECO method.B[a]P Polluted soil microbial species diversity was studied by using the CFU?Colony forming units?to determine the number of viable bacteria in B[a]P contaminated soils.Denaturing gradient gel electrophoresis?DGGE?was used to overcome the problem that most of microorganisms are unculturable and investigate the microbial commnity structures from a molecular biology perspective.The main research findings are listed as follows:?1?The extractble and available B[a]P contents in soil declined quickly in the first28 days and then decreased slowly from 28 to 56 days under the one-time and accumulated pollution conditions.The descending rates of the content of B[a]P?the extractable state and available content?decreased at the early stage?1-28d?are 2.40?g·?kg·d?^-1,13.25?g·?kg·d?^-1,0.16?g·?kg·d?^-1,0.26?g·?kg·d?^-1;The descending rates of the content of B[a]P?the extractable state and available content?decreased at the late stage?1-28d?are 0.55?g·?kg·d?^-1,2.00?g·?kg·d?^-1,0.08?g·?kg·d?^-1,0.05?g·?kg·d?^-1.?2?AWCD,reflecting the soil microbial metabolic activity,presented the law of L>CK-Y>Y>CK-L at the beginning of incubation period?1 d?,and presented the law of Y>CK-Y>CK-L>L at the 7th day,then the law of AWCD during the rest of incubation period?8-56 d?was the same as the law of the 7th day.Moreover,shannon and simpson index showed similar change rules with the AWCD under the one-time and accumulated pollution conditions.Compared with CK-L and CK-Y,accumulated pollution promoted the functional diversity?1 d?and then inhibited microbial activities?7-56 d?,one-time pollution treatment inhibited the functional diversity?1 d?and then stimulated microbial activities?7-56 d?.?3?Besides,there was more higher positive correlations between the contents of B[a]P and microbial community functional diversity index in the accumulated pollution soil than in one-time pollution soil,which indicated that the low-dose superposition method was appropriate to reflect environmental risk of B[a]P in soil.?4?Under accumulated and one-time pollution modes,the number of culturable microbial colonies?bacteria,fungi and actinomycetes?in the polluted soils was always greater than that in one-time pollution.The diversity of the accumulated polluted microorganisms was greater than that of the one-time pollution treatment.The cumulative pollution treatment was less than one-time pollution treatment.The accumulated pollution significantly increased the number of soil bacteria during the whole incubation period,reduce the number of fungi and actinomycetes;one-time pollution reduced the number of bacteria and actinomycetes in the initial stage of incubation period,and increased the number of fungi.The inhibition rate of accumulated pollution on soil microbial activity was from large to small:actinomycetes>fungi>bacteria;the inhibition rate of one-time pollution on soil microbial activity was as follows:actinomycetes>bacteria>fungi.?5?Under the one-time pollution condition,there was a negative correlation between the number of culturable actinomycetes in soil and the contents of B[a]P;Under accumulated and one-time pollution modes,there was a negative correlation betweenthe number of culturable actinomycetes in soil and indexs of microbial functional diversity in soil.And actinomycetes can be used as a biological indicator of polycyclic aromatic hydrocarbon contaminants contaminated soil.?6?In the early stage?1d?,bacterial community structures of soil polluted by cumulative B[a]P and its control treatment were the most similar and community structure similarity reached 60%.With time going on,soil bacterial community structure of control pollution treatments of accumulated and one-time pollution were the most close and the soil bacterial community structure similarity was 83%when 56days.In addition,soil bacterial community structure similarity reached 79%among accumulated pollution and control treatments of accumulated and one-time pollution.