Aquatic plants promote denitrification and inhibit ammonia volatilization: A meta-analysis

To elucidate the regulatory effects of aquatic plants on denitrification and ammonia volatilization in sha-llow water ecosystems and the underlying mechanisms, we evaluated the regulatory effects of aquatic plants on denitrification and ammonia volatilization and their key driving factors using meta-analysis based on 421 sets of experimental data from 35 publications published between 2007 and 2024. The results showed that aquatic plants significantly promoted denitrification (by 99.2%) through root exudation of organic matter, improvement of sediment environment, and provision of microbial habitat matrix. Shallow lakes and floating plants exhibited the strongest effects, increasing by 265.4% and 213.6%, respectively. Aquatic plants significantly inhibited ammonia volatilization (by 31.8%) through root absorption of NH₄⁺-N, formation of physical barriers, and secretion of organic acids. The constructed wetlands and submerged plants exhibited the strongest inhibitory effects, reducing ammonia volatilization rates by 38.7% and 60.9%, respectively. The regulatory effects of aquatic plants on denitrification and ammonia volatilization were significantly influenced by environmental factors. Neutral to weakly alkaline pH (7-8), higher temperature (>20 ℃), higher concentration of NO₃^--N (>1 mg·L^-1), and high concentration of dissolved organic carbon (DOC) (>10 mg·L^-1) significantly enhanced the promoting effect of aquatic plants on denitrification. High concentration of NH₄⁺-N (>50 mg·L^-1), high concentration of dissolved oxygen (DO) (>5 mg·L^-1), low concentration of NO₃^--N (<1 mg·L^-1), and lower concentration of DOC (2-10 mg·L^-1) signi-ficantly weakened such effect. The inhibitory effect of aquatic plants on ammonia volatilization was significantly enhanced at higher temperatures (>20 ℃), and significantly weakened under acidic conditions (pH<7), lower temperatures (<20 ℃), and lower concentration of NH₄⁺-N (<50 mg·L^-1). In summary, aquatic plants in sha-llow water ecosystems can significantly promote denitrification and inhibit ammonia volatilization through multiple mechanisms, and are regulated by environmental factors. These results could provide a scientific basis for nitrogen pollution control and ecological restoration of water bodies.