Abstract:

In this experiment,pH ranges (7 and 9) were carefully controlled to distinguish the effect of the unionised NH3 and the NH+4 ion.The objective was to find the effect of total ammonia nitrogen concentration and pH on growth of Ceratophyllum demersumThe results showed that relative growth rates (RGR) varied between -010 and 003 per day.The toxicity of total ammonia to C.demersum was a result of the effect of both ionised and unionised forms at low NH3 concentrations (<0.22 mg/L).Relative growth rates of C.demersum decreased linearly with increasing NH3 concentrations up to a maximum level (4.39 mg/L),above which C.demersum died.As the time of ammonia stress prolonged and ammonia content increased,these ammonia additions decreased carbontonitrogen ratios and Chlorophyll contents of C.demersum.At the same time,these ammonia additions weakened photosynthesis and decreased relative growth rate of C.demersumAccording to the test results，the scientific basis can be taken to improve water quality by using C.demersumAnd the result also can provide reference for studying the living condition of submersed macrophytes under the stress of the unionised NH3.