Research on the Response of Key Processes of Soil N-cycling Mediated by Microorganisms to Oil Contamination

Soil oil pollution alters the structure and function of microbial communities, thereby significantly influencing microbial-mediated nitrogen cycling processes. Although recent studies have examined the characteristics of petroleum hydrocarbon pollution and the community structure of hydrocarbon-degrading microorganisms, limited attention has been paid to soil nitrogen cycling dynamics and the underlying mechanisms of functional microbial shifts under exposure of oil contamination. This review synthesizes the effects of petroleum hydrocarbons on key microbial- mediated nitrogen cycling processes and the associated microbial communities. Findings indicate divergent conclusions regarding the impacts of oil contamination on nitrogen fixation process. Petroleum hydrocarbons inhibit nitrification process primarily due to their biotoxicity to soil microbes, though the degree of inhibition varies among hydrocarbon components. Conversely, petroleum hydrocarbons can serve as substrates for denitrifying microorganisms, thus enhancing the denitrification process. However, competition between the denitrifying microorganisms and sulfate-reducing microorganisms for petroleum hydrocarbons may occur. The dissimilatory nitrate reduction to ammonium (DNRA) process is influenced by multiple environmental factors, particularly the soil C/N ratio, with higher ratios favoring DNRA. This review concludes with future research directions, aiming to provide a critical foundation for further studies on the ecological effects of petroleum pollution on soil nitrogen cycling process.