Abstract: To understand the effects of plant diversity on ecosystem functioning in constructed wetlands which were used for treating wastewater with a high nitrogen concentration, a microcosm experiment with simulating constructed wetlands was conducted. Three common plants (Juncus effusus, Rumex japonicus,and Phalaris arundinacea) were selected to establish the monocultures of the three species and a threespecies mixture. At the intermediate stage (with hydraulic retention time of four days) and the late stage (eight days) after wastewater was supplied, nitrous oxide (N₂O) emission and the effluent nitrogen concentration in each microcosm were measured. Results showed that N₂O emission from the mixtures was lower than the average value of three monocultures in the intermediate stage but not in the late stage. The average N₂O emission from monocultures in the intermediate stage was higher than that in the late stage, but it was not the case in the mixture. The nitrogen removal efficiency from the mixture was lower than that averaged across the three monocultures in the intermediate stage, but not in the late stage. In the intermediate stage, the average nitrogen removal efficiency from the monoculture of P. arundinacea was higher than that from the other monocultures or the mixtures, but not in the late stage. Our results suggest that the N₂O emission from the mixtures was lower than that from the monocultures but it was contrary for nitrogen removal efficiency.

Key words: seedling and sapling, ground diameter-tree height model, regeneration, natural broad-leaved forest, mixed effect