| The collection of phytoplankton and in situ incubation experiment were conducted in September, 2003 and September, 2004 respectively in Changjiang estuary to investigate the characteristics of phytoplankton population and the nutrient absorption and growth variation of phytoplankton under the control of the coupling between different phosphorus concentration and different irradiance. The results show as following:1. Dominant species of diatom and green alga, which were born in the flasks containing f/2 culture media, were very obvious.2. In situ irradiance, the uptake rates of phosphate silicate and nitrate were accelerated under high phosphorus concentration, the same as the growth rate of nanophytoplankton. On the contrary, picoeukphytoplankton had a high growth rate under low phosphorus concentration. The cell density of Synechococcus sp. less increased under high phosphorus concentration which always decreased under low or middle phosphorus concentration.3. In simulating TM irradiance, the uptake rates of phosphateN silicate and nitrate were restrained under high phosphorus concentration, the same as the growth rate of nanophytoplankton, picoeukphytoplankton also had a high growth rate under low phosphorus concentration, the growth rate of Synechococcus sp. under different phosphorus concentration in simulating TM irradiance were also higher than that under high phosphorus concentration with in situ irradiance. In addition, the growth period of nano pico and syn were prolonged.4. In the dark, denitrification happened obviously, the addition of phosphate didn't affect the release rates of both phosphate and nitrite which showed lineal increase, and the growth rates of phytoplankton showed exponential decrease.5. The uptake rates of phosphate silicate and nitrate under low or middle phosphorus concentration in simulating TM irradiance is higher than that in situ irradiance which happed under high phosphorus concentration on the contrary.
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