Abstract: By the methods of pure culture and mixed culture in laboratory, this paper studied the effects of different substrate nitrogen and phosphorus concentrations on the population growth and interspecific competitive parameters of two kinds of microalgae, Skeletonema costatum and Prorocentrum donghaiens. With the increasing concentrations of substrate nitrogen and phosphorus, the maximum biomass of the two kinds of microalgae increased, and their specific growth rate was higher in pure culture than in mixed culture. In mixed culture, S. costatum was dominant at the beginning, while P. donghaiensebecame dominant later. The time period when this change happened was related to the nutritional conditions, and the inflection point forS. costatum and P. donghaiense was about 0-2.6 and 0.5-4.9 d, respectively. Under the test nutritional conditions, the competitive parameter of P. donghaienseto S. costatum (β) was higher than that of S. costatum toP. donghaiense (α). When the substrate nitrogen and phosphorous concentrations were 128 μmol N·L^-1  and 32 μmol P·L^-1, the competitive capability of P. donghaiense was 3.8 times of that of S. costatum, presenting the most obvious difference.

Key words: nutrition, competitive parameter, Prorocentrum donghaiense, Skeletonema costatum.