Effects of plant species diversity and density of Acorus calamus and Reineckea carnea on nitrogen removal and plant growth in constructed wetlands during the cold season

Plant species diversity is an important factor affecting nitrogen (N) removal in constructed wetlands (CWs), but these effects are poorly understood for the cold season. The potential effect of plant density on ecosystem function is also understudied. This study set up a two-factor experiment to explore the effects of plant species diversity and density on N removal and plant growth in CWs during the cold season. The results showed that: (1) Plant species richness positively affected plant aboveground N pool but had no significant effect on N removal efficiency or plant aboveground biomass. (2) Across plant density treatments, Acorus calamus monocultures had significantly higher plant belowground biomass and N pools than Reineckea carnea monocultures. (3) The increase in plant planting density not only increased plant biomass and plant N pool of R. carnea monoculture, but also improved the removal efficiency of nitrate nitrogen (NO3--N) 3 --N) and total inorganic nitrogen (TIN) in R. carnea monoculture. These results showed that plant species diversity had a limited effect on N removal in CWs during the cold season, but more N could be removed by increasing planting density and harvesting specific plants, such as A. calamus. .