Nutrient removal by Rotala rotundifolia: a superior candidate for ecosystem remediation at low temperatures

Temperature is an extremely important factor affecting the nutrient (mainly nitrogen and phosphorus) removal of aquatic macrophytes. A novel submersed Rotala rotundifolia was separately cultivated at room and low temperatures to investigate its ability for nutrient removal. The physiological metabolism was analyzed to explore the mechanism of removing nutrients under a wide temperature range. The results showed that the removal efficiency (RE) of nutrients at low temperature was competitive with that obtained at normal temperature, demonstrating that temperature exerted no obvious influence on the nutrient removal by R. rotundifolia. The root vitality at 5 °C rose from the initial 0.26 to 1.5 mg g^-1 h^-1, whereas it fell by 38.66% at 10 °C, 28.74% at 20 °C and 5.15% at 30 °C. The peroxidase (POD) activity at 5 °C showed the maximum value on day 7 followed by a notable decline on day 21. All the peak values of soluble sugar and protein as well as MDA showed up at 5 °C and they were 5.5, 437.9 and 10.1 mg g^-1, respectively. Chlorophyll a and b reached 8.4 and 4.4 mg g^-1 on day 28, respectively, with a total chlorophyll content (a plus b) of 12.4 mg g^-1 at 5 °C, all of which were higher than that at 30 °C. These results validated that R. rotundifolia could be a superior candidate suitable for in situ application.