Synergistic regulation of mycorrhizal symbiosis and bacteria in winter nitrogen removal of constructed wetlands: Performance and metabolism.

Winter temperature decline impairs nitrogen removal performance in constructed wetlands (CWs). Arbuscular mycorrhizal fungi (AMF) are known to enhance plant physiological functions and modulate rhizosphere microbial communities. In this study, two constructed wetlands (Control group; AMF-inoculated group) were established to investigate the regulatory mechanisms of AMF on nitrogen removal and ecosystem stability in winter. Results indicated that AMF improved nitrogen removal efficiency: the total nitrogen (TN) removal efficiency increased by 2.11%, and ammonia nitrogen (NH4+-N) removal efficiency in the AMF group was 17.34% higher than in the CK group. Moreover, AMF exhibited potential for reducing N2O emissions in constructed wetlands. The AMF colonization rate in plant roots reached 62.50%, confirming successful symbiosis. Mycorrhizal symbiosis boosted plant photosynthesis, root activity, nitrogen uptake, and activated the plant antioxidant system. Microbial community analysis revealed that the relative abundance of nitrifying bacteria Nitrospira increased by 2-3 fold. Functional gene prediction further suggested that relative abundances of nitrification-related genes were upregulated. Meanwhile, genes involved in assimilatory and dissimilatory nitrate reduction were enriched. Overall, this study demonstrated that AMF regulated nitrogen metabolism in winter CWs through coordinated plant-microbe interactions.