Abstract:The marine nitrogen cycling is one major component in Earth’s element cycle. The marine nitrogen cycling is a biochemical process composed of a series of redox reactions. Nitrogen fixation and nitrogen assimilation supplies critical bioavailable nitrogen (ammonium) to ecosystems. Nitrification can further convert ammonium into nitrates, while denitrification can convert nitrate into nitrogen. Different nitrogen forms are converted through the nitrogen cycle in the ocean. Studying marine nitrogen cycling could help understand the mechanism of interaction and co-evolution between marine organisms and Earth environment. It may also better protect the Earth’s ecological environment. By employing the published genome-scale metabolic network models based on key microorganisms involved in nitrogen cycling, researchers can study the efficiency of different nitrogen cycle processes and their influencing environmental factors, and disclose the mechanism of the nitrogen cycle and biological network, so as to help further study the mechanism of marine nitrogen conversion. This article mainly reviews the main microorganisms involved in each transformation process in the marine nitrogen cycle and applications of genome-scale metabolic network models in the analysis of the nitrogen cycle.