| Organochlorine pesticides?OCPs?and plastic film mulching have been widely used as different farm management measures,in which OCPs threaten the ecological security due to their refractory nature,although most organochlorine pesticides have been banned,high concentrations of organochlorine pesticides can still be detected in many places,the plastic film mulching could change the soil properties besides warming and moisturizing effect.Soil microbes play an important role in soil geochemical cycles such as nutrient conversion,organic matter decomposition,pollutant degradation and remediation,and respond to changes in soil conditions,so they can be used as indicators of soil environmental changes.In this study,the plastic film mulching was combined with the typical organochlorine pesticide?-HCH pollution,and the 16S rRNA sequencing of the cultured potted rhizosphere soil was carried out by greenhouse pot experiment.We analyzed the soil physicochemical properties,bacterial community structure and soil carbon and nitrogen cycle-ralated bacterial abundance and its metabolic pathways,and the following results have been obtained:?1?The richness and diversity of bacterial community in rhizosphere soil decreased at lower concentration(50 ng·g-1)?-HCH,plastic film mulching could increase the richness of bacterial community and diversity in rhizosphere soil without?-HCH.It was found that the richness of bacterial community in rhizosphere soil decreased when there was?-HCH,and the rhizosphere soil has the lowest bacterial diversity at lower concentration of?-HCH;the mulching treatment can increase the abundance of bacterial communities in the rhizosphere soil without?-HCH and higher concentration of?-HCH(500 ng·g-1),while enhancing rhizosphere soil bacterial diversity at no?-HCH and lower concentrations of?-HCH.In the rhizosphere soil under different treatment methods,Proteobacteria and Actinobacteria are the most in the level of the phylum,and Sphingomonas,Nocarda,Nocardioides,Iamia are the most in the level of the genus.Some bacteria involved in carbon degradation and nitrogen cycle in different concentrations of?-HCH and plastic film mulching were found to be positively correlated with the contents of soil organic carbon and soil total nitrogen by RDA analysis.?2?Plastic film mulching increased the relative abundance of bacteria involved in carbon degradation without?-HCH,while?-HCH reduced some of the bacteria involved in carbon degradation in the rhizosphere soil.Plastic film mulching and?-HCH had no significant effect on the relative abundance of bacteria involved in carbon sequestration and methane oxidation,the plastic film mulching increased the content of bacteria involved in carbon degradation?Pseudomonas,Cellvibrio,Bacillus,Achromobacter?at no?-HCH?P<0.05?,and the content of bacteria involved in carbon degradation?Pseudomonas?at lower concentration of?-HCH?P<0.05?,while the film mulching had no significant change of soil carbon degrading bacteria in the higher concentration of?-HCH?P>0.05?;?-HCH could significantly reduce the abundance of some of the bacteria involved in carbon degradation in the rhizosphere soil?no mulching:Streptomyces,Mycobacterium,plastic film mulching:Pseudomonas,Achromobacter??P<0.05?.Plastic film mulching and lower concentrations?-HCH could promote the carbon fixation in photosynthetic organisms,methane metabolism,and some of the carbohydrate metabolism.?3?Plastic film mulching could increase the relative abundance of some bacteria involved in the nitrogen cycling in the rhizosphere soil,while higher concentration?-HCH will reduce the relative abundance of some bacteria involved in the nitrogen cycling in the rhizosphere soil under the plastic film mulching.Plastic film mulching could increase the relative abundance of nitrogen-fixing bacteria?Rhizobium?,nitrofication?Nitrospira?and denitrification?Bacillus,Pseudomonas?in the rhizosphere soil at no?-HCH?P<0.05?,and increased the relative abundance of some bacteria involved in denitrification?Pseudomonas,Flavisolibacter??P<0.05?at lower concentration?-HCH;and the plastic film mulching could increase the relative anbundance of individual bacteria involved in nitrogen fixation?Anabaena,Azospirillum?and nitrification?Nitrosospira?at higher concentration of?-HCH?P<0.05?.The?-HCH increased the contents of Mesorhizobium which involved in nitrogen fixation in rhizosphere soil?P<0.05?,but higher concentration of?-HCH decreased the relative abundance of Nitrosomonas and Pseudomonas involved in nitrification and denitrification?P<0.05?.Plastic film mulching and?-HCH had no significant effect on nitrogen metabolism in rhizosphere soil. |
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