Elodea nuttallii and Hydrilla verticillata are very similar in morphology and growth mode. Their growth responses to substrates with different fertilities and their competitive relationship were studied in controlled tank experiments. A replacement series experiment was set up to evaluate their competitive ability at two levels of soil fertility, and a year-round experiment was carried out to investigate the long-term competitive result of E. nuttallii and H. verticillata when they were grew together. The r...