Notice of Retraction Effects of Ammonium Nitrogen on the Growth of Ceratophyllum demersum

In this paper, pH ranges (7 and 9) were carefully controlled to distinguish between the effects of the un-ionized ammonia(NH3) and the ionized ammonia(NH4+). The objective was to find the effects of ammonium nitrogen concentration and pH on the growth of Ceratophyllum demersum. The results showed that the relative growth rate(RGR) of C. demersum varied between -0.10 and 0.03 per day. When un-ionized NH3 concentration was <;0.22mg/L, the toxicity of ammonium nitrogen to C. demersum was a result of the effect of both ionized and un-ionized forms. When the un-ionized NH3 concentration reached the maximum level(4.39mg/L), the relative growth rates of C. demersum reduced prominently till it died. Along with the increase of ammonium nitrogen's concentration and extension of stress time, for the C. demersum, the carbon-to-nitrogen ratio declined, the chlorophyll contents dropped, the photosynthesis weakened, and the RGR declined. The experimental results provide scientific basis to improve water quality by rational usage of C. demersum, as well as references for studying the stress effect of un ionized NH3 on submersed macrophytes.