Effects Of Hexachlorocyclohexane On Bacterial Community Diversity And Structure In Agricultural Soil

Hexachlorocyclohexane,a highly effective organochlorine insecticide,was widely used in agricultural production.It played an important role in controlling diseases and pests hence improving agricultural yield.Hexachlorocyclohexane is stable under high temperature,sunlight and acid conditions,thus difficult to degrade together with biotransformation between different isomers,it can still be detected in some farmland and woodland soils even though was banned in the 1980s.Soil microbial community is the driving force of soil material transformation,such as nitrogen fixation,denitrification,nitrification,and transformation of other elements.Hexachlorocyclohexane residues in soil can reduce the diversity of soil bacterial community,destroy the community structure,seriously threaten the safety of soil micro-ecological environment and human health through the food chain.Because hexachlorocyclohexane is banned,there are few studies of its influence on soil bacterial community different types of soil crops system.In this study,wheat and rice were planted in red soil and purple soil polluted by hexachlorocyclohexane to investigate the residue in the soils.PCR-DGGE and high-throughput sequencing were used to analyze the changes of bacterial community structure in soil,the response relationship between the concentration of hexachlorocyclohexane and the microbial community in different types of soil,and the structure and diversity of soil bacterial community.The results provide a theoretical basis for understanding the microecological effects of hexachlorocyclohexane contaminated soil.The main research results are as follows.1.Revealed the degradation and residue law of hexachlorocyclohexane in different types of soilThe pot experiment was used to reveal the residual dynamics of HCH in different types of soil.The red paddy soil from Yingtan City,Jiangxi Province and the purple paddy soil from Yanting County of Sichuan Province were used as potting soils with different physicochemical properties.High concentration of HCH affected the growth of crops;During the wheat culture period,91 days after application,γ-HCH residue was less than 10%,β-HCH residue was between 12%and 27%,The results showed that the initial residue of HCH in red soil was higher than that in purple soil.The results further showed that the residue of HCH in rice treatment was lower than that in dryland soil;HCH in paddy soil had been completely degraded on the 56th day,and the degradation rate of HCH was faster than that in soil planted with wheat.2.PCR-DGGE was used to analyze the effects of HCH on the diversity and structure of bacterial communities in different types of soilThe diversity of bacterial community was rich in soil planted with wheat and rice by DGGE analysis.The similarity index table showed that with the increase of HCH concentration in wheat soil and paddy soil,the similarity between HCH and control group decreased gradually,and the similarity index of red soil was greater than that of purple soil.In wheat soil,HCH increased the diversity index of bacterial community in red soil for a short time.HCH had little effect on the diversity of bacterial community in purple wheat soil and paddy soil.Compared with red soil,the bacterial community structure in purple soil was more stable.On the 42nd day,the diversity of bacterial community in paddy soil gradually returned to the normal level.3.High throughput sequencing technology was used to analyze the response of bacterial communities in different types of soil to HCH pollutionHigh throughput sequencing confirmed that the bacterial community richness of purple soil was higher than that of red soil.Alpha diversity analysis showed that HCH could temporarily increase the Chaol index and Shannon index of soil bacterial community in red soil wheat soil and red soil paddy soil.The values of 600 and 1500 g/ha HCH treatments were increased by 9.1%and 14.7%in red soil There was no significant difference in the diversity index of red soil planted with rice.The diversity of bacterial community in purple soil planted with wheat and rice decreased with HCH,but there was no significant difference compared with the control group.The difference of bacterial community structure caused by different concentrations of HCH was not similar.In red soil,the relative abundance of Proteobacteria decreased under HCH treatments,the relative abundances of Chloroflex increased In purple soil,the relative abundance of Proteobacteria increased under HCH treatment,HCH could decrease the relative abundance of Nitrospira,Nitrosospira,Pirellula and Pseudonocardia,and increase the relative abundance of Sphingomonas and Pseudomonas.