Effects Of 3-bromocarbazole And 1,3,6,8-tetrabromocarbazole On Soil Microbial Community Structure And Function

As a new type of organic pollutants,polyhalogenated carbazoles(PHCZs)have been widely detected in soils all over the world,its soil ecological risk remains unclear.To research its soil ecological risks,we take 3-bromocarbazole(3-BCZ)and 1,3,6,8-tetrabromocarbazole(1,3,6,8-TBCZ),as the representative,studied theirs influences on soil microbial numbers,diversity,community structure,gene abundance of nitrogen and carbon cycle function and soil enzyme activity.Besides,we used 16 S r DNA and ITS high-throughput sequencing technology to determine the alteration of soil bacterial community structure and function,and used Q-PCR technology to determine the expression of 16 S r DNA,ITS,nif H,nar G,AOA-amo A,AOBamo A and cbb L genes,and used colorimetric method to determine the expression of dehydrogenase,urease,acid phosphatase and ?-glucosidase activity changes.The integrated biomarker Response Index(IBR)method was used to evaluate the toxicity of different pollutants at different exposure concentrations.The effects of PHCZs on soil microbial ecology were as follows:(1)3-BCZ exposure increased the number and species diversity of soil fungi.1,3,6,8-TBCZ exposure decreased the number of soil fungi and also increased species diversity.The number of bacteria decreased significantly under PHCZs exposure.In terms of community structure,the soil fungal community structure after 3-BCZ and 1,3,6,8-TBCZ exposure showed some differences from the control,while the bacterial community structure did not show significant differences.The relative abundance of Bradyrhizobium,Bryobacter,Ilumatobacter Reyranella,Mortierella,Trichoderma,and Cercophora were decreased,while the relative abundance of Gemmatimonas,RB41,Filobasidium,Archaeorhizomyces Aspergillus and Botryotrichum were increased.(2)PHCZs significantly affected the interaction network between bacteria and fungi.The average degree and density of the network increased.0.1 mg/kg 3-BCZ significantly increased the proportion of positive correlation between bacteria,and promoted the symbiotic relationship between bacteria in soil.However,0.1 mg/kg 1,3,6,8-TBCZ significantly increased the proportion of negative correlation between bacteria,and increased the competitive and mutually exclusive reaction between bacteria.The positive correlation ratio of 0.1 mg/kg 1,3,6,8-TBCZ fungi increased,which promoted the interaction and symbiosis between fungi in soil.(3)In terms of soil microbial ecological functions,3-BCZ and 1,3,6,8-TBCZ had potential inducing effects on biological processes related to soil nitrogen cycle and carbon cycle,such as methanol oxidation,methylotrophy,hydrocarbon degradation and potential inhibiting effects on soil nitrogen fixation,nitrification,denitrification,carbon dioxide fixation,and aerobic chemoheterotrophy processes.1,3,6,8-TBCZ alone had promoting effects on methanol oxidation,methanotrophy,and fibrinolysis.In terms of fungal functions guild,Dung Saprotroph and Undefined Saprotroph dominated the saprotrophs,as well as 3-BCZ and 1,3,6,8-TBCZ significantly changed the functional characteristics guild of fungal nutrients(Dung Saprotroph,Soil Saprotroph,and Wood Saprotroph etc.).3-BCZ and 1,3,6,8-TBCZ had no significant effect on acid phosphatase and ?-glucosidase,and some inhibition of dehydrogenase.1,3,6,8-TBCZ inhibited urease activity.(4)After 80 days of exposure to two PHCZs,the IBR comprehensive toxicity index of soil microorganisms including 16 S r DNA,ITS,nif H,nar G,AOA-amo A,AOB-amo A,cbb L,dehydrogenase and urease were calculated.The results showed that 16 S r DNA and nar G were the two most sensitive indexes.The IBR index of 1,3,6,8-TBCZ to soil microorganisms was greater than that of 3-BCZ.In conclusion,the number of soil microbial bacteria decreased significantly after exposure to both PHCZs.The nitrogen and carbon cycling functions were inhibited.Soil enzyme activities were relatively stable.The comprehensive toxicity of 1,3,6,8-TBCZ to soil microorganisms was greater than that of 3-BCZ.Through the above studies,we clarified the toxic effects of PHCZs on soil microorganisms from different perspectives,which enriched PHCZs research data and provided data support for soil ecological risk assessment of PHCZs.