Plant Species Richness Affected Nitrogen Retention and Ecosystem Productivity in a Full-Scale Constructed Wetland

The effects of plant species richness (SR; i.e., 1, 2, 4, 8, and 16 species per plot) on substrate nitrate and ammonium retention and ecosystem productivity in a full-scale constructed wetland (CW) with high nitrogen (N) input were studied. Substrate nitrate (0.116.4?mg?kg-1) and ammonium concentrations (1.39.2?mg?kg-1) in this study were higher than those in other comparable biodiversity experiments. Substrate nitrate concentration significantly increased while ammonium concentration significantly decreased with the increase of plant SR (p?=?0.008 and 0.040, respectively). The response of ecosystem productivity to increasing SR was unimodal with four species per plot achieving the greatest productivity. Transgressive overyielding, which was compared to the most productive of corresponding monocultures, did not occur in most polycultures. We conclude that substrate N retention was enhanced by plant SR even with high N input, and plant SR could be managed to improve the efficiency of N removals in CWs for wastewater treatment.