DYNAMICS OF MICROCYSTIS AERUGINOSA AND SCENEDESMUS OBLIQUUS IN CULTURE SYSTEMS WITH DIFFERENT PHOSPHORUS CONCENTRATION

The specific growth of Microcystis aeruginosa and Scenedesmus obliquus was studied on the condition of pure culture and different mixed cultures with different phosphorus concentration in laboratory,and P half saturation constant of each algae in different culture conditions was calculated.As a result,within the setting scope of phosphorus concentration,it is shown that the growth rates of the two algae both became greater as raising phosphorus concentration,with a greater influence on Scenedesmus obliquus than on Microcystis aeruginosa.The growth rate of Microcystis aeruginosa was greater than that of Scenedesmus obliquus in 1∶1 mixed culture when phosphorus concentration is lower than 100 μg/L;the facts pointed to a contrary conclusion if the phosphorus concentration was higher than 100 μg/L.Both the growth rates and the maximum amounts of the two species were affected by different inoculation densities-the growth rates of Microcystis aeruginosa increased with the decrease of inoculation densities while Scenedesmus obliquus had a contrary law.Scenedesmus obliquus got the maximum specific growth rate in the 10∶1 mixed culture,and Microcystis aeruginosa was at its minimum specific growth rate in the 10∶1 mixed culture.P half saturation constant of Microcystis aeruginosa decreased with the reduction of its proportion and got a minimum value of 10.35 μg/L,but the P half saturation constant of Scenedesmus obliquus did not show a distinct law,the constant getting the minimum value of 19.82 μg/L in the 1∶10 mixed culture.No matter which culture system was used,P half saturation constant for Microcystis aeruginosa growth was lower than that of Scenedesmus obliquus.So Microcystis aeruginosa is easier to win in the competition in comparative low nutrition environment.