Letter to the Editor Re: Yu Qing, Wang Hai-Jun, Wang Hong-Zhu, Li Yan, Liang Xiao-Min, Xu Chi, Jeppesen Erik Does the responses of Vallisneria natans (Lour.) Hara to high nitrogen loading differ between the summer high-growth season and the low-growth season? Science of the Total Environment 601-602(2017)1513-1521.

Yu et al.'s paper showed very interesting effects of high nitrogen (N) on the submerged macrophytes Vallisneria natans: active growth in the growing season enabled the macrophytes partly to overcome the ammonium stress. This result was evident in an experiment using ten pond ecosystems; however, their conclusion that shading induced by high phytoplankton biomass together with the toxicity of high ammonium contributed to the decrease of macrophytes growth was not strongly supported by the data provided in the paper. Three factors influencing how submerged macrophytes respond to high ammonium, not addressed by Yu et al.'s paper, are toxicity of ammonium/ammonia (NH/NH), the precise extent of shading in water and species-specific characteristics of macrophytes. In conclusion, a comprehensive consideration of abiotic and biotic factors that involve in the responses of submerged macrophytes to high N is urged in future studies of the role of high N on the growth of submerged macrophytes.