Abstract: Denitrification and emission of greenhouse gases and oxygen are all important biochemical processes occurring in aquatic ecosystems. To define extent of the impact of aquatic plants, relative to type, on these processes, dynamics of N₂, CH₄ ,O₂ ,CO₂ and N₂O emissions from eutrophied waters in Caohai of Lake Dianchi, rank with emergent plants (Acorus calamus), floating-leaved plants (Nymhaea tetragona, Nelumbo nucifera), floating plants (Eichhornia crassipes) and submerged plants (Myriophyllum verticillatum, Hydrilla verticillata) and in control (waters without plants) were studied in July and August, 2012. Gases released from the waters were in-situ collected using a self-developed bubble trapping device, while water temperature, dissolved oxyen(DO), oxidative redox potential(ORP) and pH were also measured. Results show that the gas emitted from the waters with or without aquatic plants, were composed mostly of N₂, CH₄ and O₂, and the rest of CO₂ and N₂O. The submerged plants obviously improved O₂ releasing process via photosynthesis, resulting in higher gas emission rate and higher emission fluxes of various fractions of gass. The leaves of Nymhaea tetragona, Nelumbo nucifera, and Eichhornia crassipes created shadow over the water surface, thus decreasing photosynthetic capacity of algae in the water, and consequently the gas emission rate of the water, with its median being even lower than that in the control. Moreover, the shadow also reduced emission fluxes of various fractions of gases. No significant difference was found in CH₄ concentration in emitted gas between the experimental plots, while the concentration of N2 in the gas emitted from the waters grown with Acorus calamus or Nymhaea tetragona was significantly higher than that from the control. The study provides a new method and idea for studying how different aquatic plants affect the gas releasing process in waters.  

Key words: aquatic plant, denitrification, greenhouse gas, eutrophied waters