The adaptability of a wetland plant species Myriophyllum aquaticum to different nitrogen forms and nitrogen removal efficiency in constructed wetlands

Abstract

Constructed wetlands (CWs) cultivated with Myriophyllum aquaticum showed great potential for total nitrogen (TN) removal from aquatic ecosystems in previous studies. To evaluate the growth characteristics, photosynthetic pigment content, and antioxidative responses of M. aquaticum, as well as its TN removal efficiency in CWs, M. aquaticum was treated with different levels of ammonium (NH₄⁺) and nitrate (NO₃⁻) for 28 days. The results indicated that M. aquaticum had strong nitrogen stress tolerance and was more likely to be suppressed by high levels of NH₄⁺ than NO₃⁻. High levels of NH₄⁺ also led to inhibition of synthesis of photosynthetic pigments and increased peroxidase activity in plant leaves, which was not found in the NO₃⁻ treatments. High levels of both NH₄⁺ and NO₃⁻ generated obvious oxidative stress through elevation of malondialdehyde content while decreasing superoxide dismutase activity in the early stage. A sustainable increase of TN removal efficiency in most of the CWs indicated that M. aquaticum was a candidate species for treating wastewater with high levels of nitrogen because of its higher tolerance for NH₄⁺ and NO₃⁻ stress. However, the increase of TN removal efficiency was hindered in the late stage when treated with high levels of NH₄⁺ of 26 and 36 mmol/L, indicating that its tolerance to NH₄⁺ stress might have a threshold. The results of this study will enrich the studies on detoxification of high ammonium ion content in NH₄⁺-tolerant submerged plants and supply valuable reference data for proper vegetation of M. aquaticum in CWs.