Abstract
Submerged plant (SP) restoration is a crucial strategy for restoring aquatic ecosystem. However, the effect of SP on nitrous oxide (N(2)O) emissions remains controversial, and the impact of SP-attached biofilms on N(2)O emissions is often overlooked. In this study, SP and non-submerged plant (NSP) systems were set up and operated continuously for 189 days, revealing that SP reduced N(2)O flux by 42.4 %. By comparing the N(2)O net emission rates from water, sediment, and biofilms, we identified biofilms as the primary medium responsible for the reduction in N(2)O emissions in both SP and NSP systems. Further analysis of N(2)O metabolic rates from nitrification, denitrification, and abiotic processes under light and dark conditions confirmed that counter-diffusion of dissolved oxygen and nutrients in SP biofilms plays a key role in reducing denitrification-driven N(2)O emissions. Additionally, SP-attached biofilms increased nosZII-type denitrifiers (e.g., Bacillus) and reduced N(2)O production potential ((nirS+nirK)/(nosZI+nosZII)). Notably, the establishment of a SP restoration project in a typical eutrophic freshwater lake demonstrated that SP could reduce N(2)O fluxes by 61.5 %. This study provides significant insights for strategies aimed at mitigating N(2)O emissions.