Revisiting the microbial nitrogen-cycling network: bibliometric analysis and recent advances

The nitrogen (N) cycle, a complex reaction network driven by microbial communities, controls the stock, distribution, and transformation of N. Here, we analyzed current research hotspots in the microbial N cycle and summarized the hotspots where these processes occur and influencing factors to update our understanding of the N cycle. Bibliometric analysis revealed that the research in this area focused on nitrification, denitrification, anaerobic ammonia oxidation (anammox), and dissimilatory nitrate reduction to ammonia (DNRA). The effects of emerging pollutants on microbial communities have become a hot topic, especially in agriculture. Global N budget revealed denitrification activities occur in N-rich organic soils under warm well-drained conditions. Notably, elevated temperatures stimulated nitrous oxide (N2O) emissions and further aggravated global warming. Biochar as an electron shuttle participated in the extracellular electron transfer between microorganisms and can mitigate greenhouse gas emissions. The changes in microbial community, functional gene expression, and enzyme activities were the main microbial mechanisms by which microplastics affect N cycle. Finally, future work should focus on emerging pollutant impacts, multifactorial interactions, long-term effects of influencing factors, microbial relationships, and underlying mechanisms.