3.4 Soil Microbial community composition
In the whole data set, 1947305 bacterial sequences and 2631038 fungal sequences obtained from 30 soil samples were classified as 17295 and 1681 ASVs, respectively. On average, 98.11% of the sequences in each sample were classified as bacteria and only 1.89% were classified as archaea. For bacteria, Proteobacteria accounted for the highest proportion among the 30 samples, accounting for 77.79% of the total on average. Other dominant bacteria include Bacteroidetes (5.02%), Actinobacteria (3.95%), Firmicutes (3.04%), and Gemmatimonadetes (2.15%). Among the fungal sequence, the average is 100% fungi. Ascomycota predominated these samples, accounting for an average of 82.58% of the total sequence. The other prevalent phyla were Mortierellomycota (10.61%) and Basidiomycota (1.88%).
At the phylum level (Fig. 5 ), compared with the control, the relative abundance of Proteobacteria were increased, and that of Gemmatimonadetes and Bacteroidetes were decreased. In the fungal community, the relative abundance of Ascomycota and Chytridiomycota increased. In contrast, the relative abundances of Basidiomycota, Mortierellomycota, and Zoopagomycota decreased after short-term petroleum contamination (p <0.05) compared with Control. After long-term petroleum pollution, the relative abundance of Ascomycota was raised, while that of Chytridiomycota and Zoopagomycota were decreased (p <0.05).
Among the top 20 identified bacterial genera (Fig. 5 ),Ralstonia , Pseudomonas , Sulfurimonas ,Oleibacter , and Marinobacter were most bounteous. Compared with Control, relative abundances of Ralstonia ,Acinetobacter , Lysobacter , Kaistobacter ,Stenotrophomonas , Bacillus , Lactobacillus , andSphingomonas were significantly decreased in PS samples. Conversely, relative abundances of Pseudomonas ,Sulfurimonas , Oleibacter , Marinobacter ,Marinobacterium , Arcobacter , Halomonas ,Pseudidiomarina , and Shewanella were increased (p <0.05); Relative abundances of Ralstonia ,Marinobacter , Acinetobacter , Lysinibacillus , andLactobacillus were significantly decreased in OS samples, conversely, relative abundances of Oleibacter ,Alcanivorax , Sediminibacter , Thiobacillus ,Nitrosopumilus , and Candidatus _Portiera were increased (p <0.05). For fungi, Fusarium ,Mortierella , Pseudallescheria , Alternaria andOchroconis were most abundant. Compared with Control, relative abundances of Mortierella , Alternaria ,Cladosporium , Syncephalis were decreased in PS samples. Conversely, relative abundances of Fusarium , Ochroconis , and Nigrospora were increased (p <0.05); Relative abundances of Mortierella , Alternaria ,Cladosporium , Syncephalis , and Aspergillus were decreased in OS samples, whereas that of Fusarium andOchroconis were increased (p <0.05).