Removal of metals and their pools in plant in response to plant diversity in microcosms of floating constructed wetlands

Plant species diversity could enhance nitrogen and phosphorus removal efficiencies in constructed wetlands (CWs). However, the effects of plant diversity on other pollutants removal efficiencies in CWs are still unknown. In this study, we conducted a microcosm experiment simulating floating CWs using four common early spring species to set up four species richness (1, 2, 3, and 4) and fifteen species compositions to explore the effects of plant diversity on the removal efficiencies of calcium (Ca), potassium (K), and magnesium (Mg) and their pools in plants. Results showed that (1) plant species richness had no effect on Ca, K, and Mg removal efficiencies; however, it increased plant K and Mg pools; (2) among the four monocultures, the Ca removal efficiency and plant Ca pool of the Rumex japonicus monoculture was the highest; the K removal efficiencies and plant K pools of Oenanthe javanica or R. japonicus monoculture were significantly higher than those of other two species monocultures; (3) the presence of R. japonicas increased the Ca removal efficiency and belowground plant Ca pool; however, the presence of Phalaris arundinacea decreased the Ca removal efficiency and belowground plant Ca pool; (4) the presence of O. javanica increased the K removal efficiency and plant (aboveground and belowground) K pool; however, the presence of P. arundinacea decreased the K removal efficiency and belowground plant K pool; and (5) no difference in Mg removal efficiency was found among species compositions. Assembling proper plant species composition in CWs might be more important than simply increasing species richness for increasing Ca and K removal efficiencies.