Ammonium nitrogen (NH4+-N) at high concentrations is toxic to plants. In order to explore the NH4+-N tolerance of Myriophyllum aquaticum (M. aquaticum) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH4+-N levels (70, 210, 420 mg·L-1) to incubate M. aquaticum for 21 d. The characteristics of plant physiology and N and P uptake of M. aquaticum were measured. At NH4+-N of 70 mg·L-1, M. aquaticum grew healthily, and shoot height and biomass linearly increased with the increase incubation time. Relative shoot height and biomass of M. aquaticum were 40.56 cm and 17.82 g·hole-1 on day 21, respectively. Compared to the control with 70 mg·L-1 ammonium, malondialdehyde (MDA) content of M. aquaticum was significantly increased; chlorophyll and soluble sugar contents were also high at NH4+-N of 210 mg·L-1. M. aquaticum suffered from the NH4+-N stress. However, the stress of 210 mg·L-1 NH4+-N did not affect its normal growth and there was no significant difference in the relative growth rate of the shoot height and biomass compared with the control. At NH4+-N of 420 mg·L-1, MDA contents of M. aquaticum doubled and the shoot height and biomass growth rate were only 27.4% and 17.9% of those for 70 mg·L-1 NH4+-N, indicating that M. aquaticum was subjected to serious stress that caused unhealthy growth or even death. At three NH4+-N levels, the ranges of N and P content of M. aquaticum were 30.7-53.4 mg·g-1 and 3.8-7.7 mg·g-1, respectively, which indicated that M. aquaticum had a high uptake capacity of N and P. M. aquaticum is an ideal wetland plant that has a good application prospect for constructed wetlands in biological treatment of high-ammonia wastewater.
Keywords: Myriophyllum aquaticum; ammonium; nitrogen; phosphorus; stress.