Abstract: To investigate the effects of plant species identity and diversity on nitrous oxide emission and functional gene abundance under moderate effluent C/N ratio, we constructed a vertical flow constructed wetlands in the laboratory. Three plant species, Phragmites australis, Lythrum salicaria ,and Pontederia cordata,which are commonly used in constructed wetlands and with good landscape effects, were selected to establish the monocultures of each species and one threespecies mixture. Results showed that nitrous oxide emissions from the mixtures (24597.0 μg N₂O·m^-2·d^-1) were higher than the mean values of the three monocultures (11744.8 μg N₂O·m^-2·d^-1) (P<0.001). Similarly, the absolute abundances of amoA (6.33×10⁷ copies·g^-1 soil) and nirS (1.92×10⁶ copies·g^-1 soil) from the mixtures were also higher than the mean values of the monocultures (5.70×10⁷ and 1.58×10⁶ copies·g^-1 soil). In addition, the effluent NO₃^--N concentrations in the mixtures were lower than that in the three monocultures (P<0.01), but there was no significant difference in the NH₄⁺-N concentration, microbial biomass and plant biomass between the mixtures and the mean values of monocultures (P>0.05). There were significant differences in the nitrous oxide emission, absolute abundance of amoA, absolute abundance of nirS, effluent NH₄⁺-N concentration, microbial biomass and plant biomass among the three monocultures,but with no significant difference in the effluent NO₃^--N concentration among the three monocultures.The effects of plant richness on nitrous oxide emission, amoA absolute abundance and nirS absolute abundance were greater than those of species identity, whereas the effects of plant species identity on effluent NO₃^--N concentration were greater than that of plant richness.

Key words: Kouhe River basin, water environmental capacity, ecological compensation, mechanism and policy.