Polycyclic Aromatic Hydrocarbon Pollution Stress Impairs Soil Enzyme Activity and Microbial Community

Polycyclic aromatic hydrocarbons (PAHs) are widely prevalent harmful organic pollutants. Enzymatic activities (such as those of dehydrogenases, catalase, protease and urease), as well as the microbial community structure and assembly (through 16S and ITS amplicon sequencing), were evaluated 90 days after PAH contamination and compared to those in normal soils. Microbial activity, as indicated by soil urease, catalase, and protease activities, was inhibited under PAH stress. Furthermore, PAH stress exerted significant impacts on the soil microbial community structure. Notably, PAH stress reduced soil bacterial and fungal biomass and inhibited the abundance of microbial taxa involved in soil carbon and nitrogen cycling (e.g., Marmoricola, Pedobacter, and Streptomyces), along with the majority of predicted responsive metabolic functions, particularly those related to amino acid and carbohydrate metabolism. PAH stress enriched PAH-degrading microorganisms, including Pseudomonas, Mycobacterium, Bacillus, Cycloclasticus, and Flavobacterium. The niche breadth of bacterial and fungal communities decreased significantly under PAH stress (51.5 and 14.1, respectively) compared to that in normal soil (63.7 and 22.3), which was further supported by Beta Nearest Taxon Index and co-occurrence network analysis. PAH stress increased the contribution of heterogeneous selection to soil microbial assembly (100%) compared to that in normal soil (80%). Thus, the majority of microbial community responses to PAH stress were adversely affected. These results suggest that PAH contamination may profoundly affect the soil quality by restricting the survival space of bacteria and fungi.