Effect of water hyacinth on N2O emission through nitrification and denitrification reactions in eutrophic water
凤眼莲对富营养化水体硝化、反硝化脱氮释放N2O的影响

Direct uptake of nitrogen (N) by floating macrophytes was widely studied with the aim of removing nitrogen from eutrophic water, while the contribution of nitrification and denitrification process was ignored in the past studies. In this study, an innovative method of collecting N2O released from water cultivated with the floating macrophyte, water hyacinth (Eichhonia crassipes), was developed to study the effect of Eichhonia crassipes on N2O emission through the nitrification and denitrification reactions in eutrophic water. It was found that cultivation of Eichhonia crassipes stimulated the nitrification, denitrification and coupled nitrification-denitrification reactions. Under the conditions of this experiment, concentrations of N2O released from water with cultivation of Eichhonia crassipes ranged 453~4055 nL·L-1, and the N2O-N loss accounted for 1.36% of the total N removal (in treatment without addition of nitrification inhibitor). This proportion was 4.31 times higher than that in water without cultivation of Eichhonia crassipes. During the experiment, the amount of N2O-N loss was significantly (p<0.05) correlated with the changes of NH4+ or NO3- concentration in water with cultivation of Eichhonia crassipes, indicating that N2O emission was influenced by the change of NH4+ or NO3- concentration. The quantity of nitrifying and denitrifying bacteria in water was increased by cultivation of Eichhonia crassipes, but was still much lower than that attached to Eichhonia crassipes roots. However, there was no significant correlation between quantity of nitrifying or denitrifying bacteria in water and concentration of N2O released from water. This may indicate that bacteria attached to Eichhonia crassipes roots were the major contributor to stimulate N2O emission through nitrification and denitrification reactions in water.