Abstract: A replacement series experiment was carried out to analyze the effects of moderateintensity harvesting on interspecific competition between Elodea nuttallii and Potamogeton crispus. Competition indices such as aggressivity, relative yield, relative competitive intensity and relative crowding coefficient showed that E. nuttallii was the stronger competitor before and after harvesting. P. crispus outcompeted E. nuttallii significantly (P<0.05) in coverage in both the monoculture and the mixed culture before harvesting. However, harvesting resulted in a significant reduction in coverage of P. crispus by 33.5% in the monoculture and 45.3% (P<0.05) in the mixed culture, respectively, and a significant increase in coverage of E. nuttallii (P<0.05). The result showed that E. nuttallii surpassed slightly over P. crispus in terms of coverage. The mean dry weight per plant of P. crispus was greater than that of E. nuttallii in both the monoculture and the mixed culture before harvesting (P<0.05). However, the mean dry weight per plant of P. crispus was obviously lower than that of E. nuttallii after harvesting in both the cultivation modes (P<0.05). The moderateintensity harvesting produced inhibition effects on P. crispus but promotion effects on E. nuttallii in branching and dry matter accumulation in layers of 0-25 cm and above, which would be beneficial for E. nuttallii to win the competition with P. crispus. In addition, the results also showed that root growth was less affected by the interspecific competition.

Key words: sand-binding plant, life form, water source, root distribution