Comparative studies of the response of sensitive and tolerant submerged macrophytes to high ammonium concentration stress.

Three submerged macrophytes, Ceratophyllum demersum (CD), Myriophyllum spicatum (MS) and Myriophyllum aquaticum (MA), were treated with various concentrations of ammonia for different lengths of time. Ammonium ions (NH₄⁺) in the medium severely inhibited plant growth and led to a reduction in total chlorophyll (chl a and b) in CD and MS. The addition of ammonia significantly decreased the soluble protein content and increased the free amino acid content of CD and MS in treatments with high concentrations of NH₄⁺, but MA showed no significant physiological response. The antioxidant enzyme system of MA was activated, which in turn reduced the peroxidation level in the plant and maintained the plant's normal physiological activities when the ammonia nitrogen in the culture fluid increased. The study continued to use higher concentrations (25, 50, 100, 200 and 400 mg/L) of ammonium nitrogen to treat and observe the peroxidation level and corresponding enzyme production for this species of MA in vivo to explore its resistance mechanism. The experiments show that MA can normally live for a period of time in a high-ammonia environment of up to 100 mg/L. The results of the present study will assist in studies of the detoxification of high ammonium ion contents in submersed macrophytes and the selection of plants suitable for macrophyte recovery.