Freshwater Salinization Mitigated N<sub>2</sub>O Emissions in Submerged Plant-Covered Systems: Insights from Attached Biofilms
Yongxia Huang, Min Deng, Lu Li, Zezheng Wang, Kang Song, Fengchang Wu
Abstract
Submerged plants (SMPs) play a critical role in improving water quality and reducing N 2 O greenhouse gas emissions. However, freshwater salinization represents a major environmental challenge in aquatic systems. To investigate the impact of salinization on N 2 O emissions, this study conducted indoor mesocosm experiments simulating SMP and nonsubmerged plant (Non_SMP) areas in freshwater lakes. The objective was to explore the effects and microbial mechanisms of the attached biofilm on N 2 O emission in freshwater salinization. Salinization systems (700–1500 μS cm –1 ) reduced N 2 O flux by 37.0 and 40.5% compared to freshwater systems (<700 μS cm –1 ) of SMPs and Non_SMPs, respectively. Kinetic experiments showed that the reduction in N 2 O emissions was mainly attributed to the attached biofilm rather than the sediment or water. The N 2 O net emission rates of the attached biofilm decreased by 47.1 and 71.8% in salinization systems of SMPs and Non_SMPs, respectively, compared with freshwater systems. Additionally, biofilms in salinization systems exhibited lower denitrification rates. Furthermore, salinization reduced the N 2 O production potential (( nirS + nirK )/( nosZI + nosZII )), thereby further decreasing N 2 O emissions. This study provides valuable insights into the role and mechanisms of biofilms in mitigating N 2 O emissions in salinized freshwater lakes.