Soil Microbial Community Structure And Utilization Mechanism Of Petroleum Hydrocarbon Components In Oil Production Area Of Northern Shaanxi

Soil pollution in oil field area is one of the important ecological and environmental problems to be solved urgently in China.Northern Shaanxi is an important energy and chemical industry area in China,and petroleum exploitation brings great toxicity risk to the local soil ecological environment.In this paper,we collected the soil near the oil field in 10 different districts and counties in northern Shaanxi Province,measured the physical and chemical properties of the soil and the structural diversity of the microbial population,and explored the effect of oil stress on the structure and diversity of the soil microbial community.The biodegrading functional bacteria were enriched and screened from oil-contaminated soil,the composition and structure of biodegrading functional bacteria were determined,and the differences of biodegrading functional bacteria composition and structure in contaminated soil were compared.¹³C-cetane was selected as the model compound of petroleum hydrocarbon components,and the utilization of petroleum hydrocarbon components by soil microorganisms was investigated by measuring the carbon isotope values of phospholipid fatty acids in soil.Through the research,the following conclusions are drawn:(1)Proteobacteria and Actinobacteria were the main bacterial phyla in clean soil of 10 districts and counties in northern Shaanxi.Bacteria genera mainly include Pseudomonas,Saccharibacteria?genera?incertae?sedis,Sphingomonas,Ncardioides,Marinobacter,Gemmatimonas,Arthrobacter and Acinetobacter,etc.The Ace index,Chao1 index,Shannon index and Simpson index ranged from 1072 to 8121,1220 to2033,3.69 to 7.24 and 0.06558 to 0.0024 respectively.The mycophyla mainly includes Ascomycota and Basidiomycota.Fungus genera mainly included Mortierella,unclassified?Fungi,unclassified?Hypocreales,Ochroconis,unclassified?Ascomycota,Epicoccum,Fusarium and Alternaria,etc.The Ace index,Chao1 index,Shannon index and Simpson index of soil fungi ranged from 250 to 816,246 to 798,2.73 to 4.30 and0.0330 to 0.2631.Soil microbial community composition and diversity were mainly affected by geographical orientation,soil physical and chemical properties and climatic conditions in the sampling area.From north to south,the richness and evenness of soil bacterial community increased,as did the richness of soil fungal community,but the distribution of evenness was not obvious.The higher the soil water content and total nitrogen content,the smaller the C/N ratio,and the better the diversity of soil bacterial community structure.The smaller the total organic carbon and the ratio of carbon to nitrogen,the greater the annual average rainfall and the less the annual sunshine duration in the sampling area,the better the diversity of soil fungal community structure.(2)Compared with the clean soil,there was no significant change in the bacterial community richness in the soil contaminated by oil at 12867?50200 mg/kg.However,it would decrease the evenness of soil bacterial community(the correlation coefficient between the difference of Shannon index and Simpson index between oil-contaminated soil and clean soil and petroleum hydrocarbon content was-0.659 and 0.929,respectively).The effects of oil pollution on the richness and evenness of soil fungal community were not significant.(3)Derivative characteristics of biodegrading functional bacteria showed that at the phylum level,the structural composition of biodegrading functional bacteria was similar to that of total bacteria in the soil,which mainly consisted of Proteobacteria,Bacteroidetes and Actinobacteria.At the genus level,the structural composition of degrading functional bacteria was different from that of total bacteria in the soil.Petroleum degrading bacteria were mainly Acinetobacter,Pseudomonas,Olivibacter,Sphingobacterium,Ochrobactrum and Chryseobacterium.The main alkane-degrading bacteria were Stenotrophomonas,Acinetobacter,Klebsiella,Olivibacter,Pandoraea,Elizabethkingia,Neorhizobium,Pseudomonas and Rahnella.The PAH-degrading bacteria were mainly Pseudomonas,Klebsiella and Achromobacter.(4)¹³C-hexadecane(4837?4936 mg/kg)was added into the clean soil as the model compound of petroleum hydrocarbon components for artificial pollution,and the contaminated soil was respectively added with potassium nitrate and organic fertilizer for remediation.On the 30th day of remediation,the degradation rate of cetane increased from 3.22%to 6.49%and 7.81%,respectively,adding potassium nitrate and organic fertilizer could promote the degradation of cetane in the soil.Adding cetane to the soil could increase soil organic carbon content,but adding potassium nitrate had little effect on soil organic carbon content.When the soil is contaminated with cetane,The content of bacteria,fungi,actinomycetes and other microorganisms decreased,adding potassium nitrate had little effect on the contents of various microbial communities.However,application of organic fertilizer significantly increased the contents of various microbial communities in soil.(5)In all the treated soils,the PLFA monomers with higher content were common bacteria 16:00 and 18:00,G⁺bacteria i15:0,a15:0,i16:0,i17:0,i17:0,a17:0,a17:0,and a17:0,G^-bacteria 16:1?5c,16:1?7c,cy17:0?7c,18:1?5c,18:1?7c,cy19:0?7c,fungi18:1?9c,and actomycetes 16:0(10Me),17:0(10Me),18:0(10Me),17:1(10Me),17:1(10Me),17:1(10Me),17:1?7c(10Me).The main microbial communities utilizing¹³C-cetane were common bacteria 16:00,G⁺bacteria i15:0,a15:0,G^-bacteria 16:1?5c,16:1?7c,fungi 18:1?9c and actinomycetes 16:0(10Me).When potassium nitrate and organic fertilizer were added into the soil for 30 days,the proportion of labeled exogenous carbon in different phospholipid fatty acid monomers increased from0.85%?3.83%to 1.03%?5.00%and 1.54%?7.02%,respectively,indicating that when remediation of organic contaminated soil was carried out,The application of potassium nitrate and organic fertilizer as biological stimulants can promote the degradation of organic pollutants by soil microorganisms to a certain extent.