Role of nitrogen cycling functional genes and their key influencing factors in eutrophic aquatic ecosystems

The nitrogen cycle, essential for the transformation and circulation of nitrogen, involves key processes such as nitrogen fixation, nitrification, denitrification, and ammonification. Microorganisms are crucial in these processes, influencing water quality through energy conversion and nitrogen cycling. Eutrophication, driven by human activities, increases exogenous nitrogen input, accelerating nitrogen cycling and loss, boosting greenhouse gas emissions, and impacting aquatic ecosystems. Functional genes in the nitrogen cycle, such as amoA (nitrification), nirS, nirK, nosZ (denitrification), and hzs and hzo (anaerobic ammonium oxidation), are indicators of nitrogen transformation in sediments. Environmental factors like temperature, dissolved oxygen (DO), organic matter content, nitrogen levels, pH, and salinity significantly influence these genes' expression and regulation. For example, temperature changes can affect nitrifying and denitrifying bacteria activities, DO levels impact microbial growth and metabolism, and higher organic matter content stimulates the expression of nitrogen cycle genes. Understanding how these environmental factors affect nitrogen cycling genes is crucial for addressing eutrophication in aquatic ecosystems. This review focuses on the adaptability and responses of nitrogen-associated functional microorganisms and genes environmental changes, offering theoretical insights and practical guidance for sustainable ecosystem management.