Abstract: In order to study the mitigation possibility of methane (CH₄) emission in constructed wetlands for waste water treatment, a controlled microcosm experiment was conducted. The effects of plant species richness and identity on CH₄ emission, nitrogen removal and related parameters were analyzed. Three hygrophilous plants (Rumex japonicus, Oenanthe javanica and Phalaris arundinacea) were applied to establish the monocultures of three individual species and a 3species mixture. The microcosms were filled with fine sand (particle diameter 0.25-1 mm) and supplied with simulated wastewater. The results showed that plant species richness increased CH₄ emission (P<0.05), but had no excessive emission effect (P>0.05). Species richness had no significant effect on nitrogen removal (P>0.05). Plant species identity surpassed species richness as a key driver of CH₄ emission and nitrogen removal. Microcosms with P. arundinacea monoculture had the lowest CH₄ emission and the highest nitrogen removal (P<0.05). These results suggested that assembling P. arundinacea monoculture is more conducive to reduce CH₄ emission and enhance nitrogen removal in constructed wetland simultaneously than improving species richness. This study can provide a reference for plant species selection and plant diversity assemblage in constructed wetlands.

Key words: conservation tillage, straw recycling, microbial biomass C, microbial activity, soil respiration, respiratory quotient.