Abstract: Hydroponic microcosms of constructed wetlands were used to study the effects of plant species richness on nitrogen removal and some other ecosystem functions. Multiple functions were integrated to assess the net greenhouse effect in response to plant diversity. Microcosms with mono and mixed culture of four plant species (Oenanthe javanica, Rumex japonicus, Phalaris arundinacea, Reineckia carnea) were established and supplied regularly with simulated wastewater in which nitrate (NO₃^--N) was the sole nitrogen form. Results showed that the effluent inorganic nitrogen concentration was significantly lower in the mixed microcosms than in the monocultures, indicating that high plant species richness enhanced the nitrogen removal efficiency. The aboveground and total biomass in the mixed microcosms were higher than those in the monocultures. Denitrification was the major contributor to nitrogen removal in the monocultures, while plant nitrogen uptake was the major contributor in the mixed microcosms. Microcosms with mixed planting of four species had higher CH₄ and N₂O emissions. However, high species richness could enhance the reduction in CO₂ emission through enhancing plant biomass, which could be used as biofuel to replace the fossil fuels. After synthesizing CO₂, CH₄ and N₂O emissions, we found that high plant species richness reduced the net global warming potential (GWP) of the systems.

Key words: mulching soil, soil layer, Danjiangkou Reservoir area., nitrogen mineralization rate