Effect Of Temperature,Irradiance And Population Interaction On The Growth Of Phytoplankton Of East China Sea

Ten species of typical phytoplankton of the East China Sea (Skeletonema costatum, Prorocentrum donghaieuse, Alexandrium tamarense, Pseudo-nitzschia pungens, Chaetoceros curvisetus, Chaetoceros Debilis, Gymnodinium sp., Nitzschia closterium, Heterosigma akashiwo Hada, Platymonas helgolanidica) were chosen to test the effect of temperature and irradiance on their growth behavior. The effect of different irradiance on physiological character of Skeletonema costatum and Prorocentrum donghaieuse and the effect on population competition of Skeletonema costatum and Prorocentrum donghaieuse based on the competitive model of Lotka-Volterra were also explored.1. The effect of temperature, irradiance on the growth of phytoplankton According to the environmental conditions in the East China Sea, a series of testsunder different temperature (15, 20, 25 and 30℃) and irradiance (30, 80 and 140μmol·s-1·m-2), representing 12 condition combinations in laboratory, were designed. Batch culture experiment was conducted to study the effect of temperature and irradiance on the growth of phytoplankton. The statistical analysis results showed that the growth ratios of each species were affected significantly or most significantly by temperature under the experimental conditions. The growth ratios of Pseudo-nitzschia pungens were not significantly different under different irradiance (30, 80 and 140μmol·s-1·m-2), neither was Nitzschia closterium . On the contary, the growth rations of the other 8 species were significantly different. In this test, the optimal temperature for these ten phytoplankton was 20 ℃ or 25 ℃, the optimal irradiance for the ten phytoplankton was 140μmol·s-1·m-2.2. The effect of irradiance on the growth and physiological character of phytoplanktonIn laboratory at 20℃, a series of irradiance (30, 80 and 140 μmol·s-1·m-2) was designed to test the effect of irradiance on the growth and physiological character ofSkeletonema costatum and Prorocentrum donghaieuse. The results showed that the maximum density of the two phytoplankton increased distinctly with the increasing of the irradiance, that was to say, the increasing of irradiance had a stimulative effect on the growth of phytoplankton. The content of protein and carbohydrate in cells of Skeletonema costatum reached to the maximum at the irradiance of 80μmol·s-1·m-2. The content of carbohydrate in cells of Prorocentrum donghaieuse also reached to the maximum at the irradiance of 80μmol·s-1·m-2 and the content of protein reduced with the increase of irradiance. The ratios of the content of protein and that of carbohydrate in the cells of the two phytoplankton under the faintest irradiance (30 μmol·s-1·m-2) were both much more than that under the higher irradiance (80μmol·s-1·m-2 and 140μmol·s-1·m-2), the ratios reduced with the increasing of irradiance. 3. The effect of population competition on the growth of Skeletonema costatum and Prorocentrum donghaieuseIn laboratory, under the condition of the same temperature, irradiance, radiant cycle and enough inorganic nutrients composition, batch culture experiment which made use of pure culture and mixed culture at different initial cell densities of Skeletonema costatum and Prorocentrum donghaieuse (the ratios of the initial cell densities were 1:4, 1:1, 4:1) was conducted to study the effect of population competition on the growth of phytoplankton. The result showed that initial cell density had obvious effect on the growth curves of the two phytoplankton. Along with the increasing of initial cell density, the intrinsic growth rates (r) of the two phytoplankton all increased. The carrying capacity of the environment (K) of Skeletonema costatum reduced with the increasing of initial cell density, the carrying capacity of the environment (K) of Prorocentrum donghaieuse increased with the increasing of initial cell density. Skeletonema costatum predominated absolutely in mixed culture, its maximum densities of 3 different initial cell densities in mixed cultures were all bigger than those in pure culture, the competitive parameters were all negative, that was to say, Prorocentrum donghaieuse had a stimulative effect on the growth of Skeletonema costatum. The growth of Prorocentrum donghaieuse was inhibited distinctly in mixed culture, not only Prorocentrum donghaieuse's maximumdensity was far less than that in pure culture, but also the population of Prorocentrum donghaieuse disappeared 8 days later.The effect of ecosystem factors on the growth and succession of phytoplankton population are all important. This paper systematically studied the effect of temperature, irradiance and population competition on the growth of phytoplankton. It is expected to offer scientific basis for the growth and succession of phytoplankton and the causation of red tide.