Abstract: To understand the effects of plant diversity on the nitrogen removal and nitrification in constructed wetlands,  simulated constructed wetlands with monoculture and mixed planting of four kinds of plants were constructed, and ammonium nitrogen was taken as the sole inflowing nitrogen loading. In the mixed planting system, both the effluent inorganic nitrogen concentration and the effluent ammonium nitrogen concentration were lower than those in the monoculture system (3.41 mg·L^-1 vs. 7.20 mg·L^-1, and 1.35  mg·L^-1 vs. 4.11 mg·L^-1, respectively;P<0.05), but the ratio of NO₃^-/NH₄+ concentration was greater than that in the monoculture system (1.55 vs. 0.80, P<0.05), indicating that mixed planting enhanced the nitrification in the simulated constructed wetlands. The substrate inorganic nitrogen accumulation in the mixed planting system was lower than that in the monoculture system (1455 mg·m^-2 vs. 2235 mg·m^-2, P<0.05), suggesting that the complementary resource use might occur in the mixed planting system. Based on the mass-balance approaches, the plant nitrogen uptake in the mixed planting system had a greater contribution rate to the total inorganic nitrogen removal than in the monoculture system (48% vs. 31%, P<0.05), and the nitrogen removal by the plant aboveground parts also presented the similar trend (33% vs. 20%, P<0.05). The substrate nitrogen accumulation had an opposite trend to  the plant nitrogen uptake,  with 5% in mixed planting system and 9% in monoculture system (P<0.05). As compared with those in monoculture system, the denitrification, ammonia volatilization, and microbial nitrogen immobilization in the mixed planting system had lower contribution rates to the nitrogen removal.

Key words: advection-aridity model, actual evapotranspiration, spatiotemporal variation, trend-analysis, sensitivity analysis.