Dynamic nutrient removal potential of a novel submerged macrophyte Rotala rotundifolia, and its growth and physiological response to reduced light available.

Rotala rotundifolia is a novel submerged macrophyte able to survive across the winter under temperature as low as 4 °C. Dynamic nutrient removal potential of R. rotundifolia was estimated using the Eco-tank system simulating natural eutrophic waters. The growth and physiological response of R. rotundifolia by cutting and division propagation to light (100%, 60%, and 20% natural light) were investigated. The results showed that R. rotundifolia was superior in removing N and P from eutrophic waters. As influent concentrations of NH4+-N and total phosphorus (TP) were 4.81-5.87 and 0.61-0.78 mg L-1, effluent concentrations of NH4+-N, total nitrogen (TN), and TP were separately 0.06-1.10, 0.40-1.59, and 0.05-0.17 mg L-1, with removal efficiencies of 93.6%, 84.6%, and 82.5% at a flow rate of 200 L d-1. The growth and morphology of the plant under two propagation patterns were influenced by light and the responses were quite different. The biomass of the plant by cutting was higher at low light conditions, and the plant allocated more biomass on above ground. However, there was no significant difference in the height. By division, the plant preferred to high light. The biomass and height were significantly higher at 100% natural light. The peroxidase (POD), superoxide dismutase (SOD) and root activities of plant by cutting showed a trend of decrease and followed by an increase with light reduction, while by division, they increased with reduced light available. Variations of chlorophyll and soluble protein of the plant by cutting and division were contrary to the changes of POD activity. These results suggest that R. rotundifolia can be used to effectively remove nitrogen and phosphorus in eutrophic waters, and high light promotes the growth of the plant by division, while suitable shade is needed for the plant by cutting.