Abstract:Planktonic algae have the considerable periodicity in species composition and abundance, and this seasonal succession pattern is the important characteristic of algae fluctuations. The mechanisms by which environmental factors affect algae succession are complex. Besides, algae succession varies in lakes or reservoirs of different limnological features and trophic state. Although hypotheses of algae succession have been stated in some researches, there is uncertainity for specific lake and specific species. Based on planktonic algae succession in Qiandao Lake during 2009-2010, the effect of nitrogen and phosphorus ratitos on the growth of cyanobacteria and chlorophyta under the laboratory conditions is studied in order to further verify the impact of nutrients on the succession pattern. The main results and conclusions are as follows:Under the laboratory conditions, we set five N/P ratio treating groups (N/P=307.06, N/P=153.53, N/P=76.77, N/P=15.35 and N/P=3.84) based on the BG-11 cultures to explore the effects of different N/P ratio on blue-green algae (Microcystis flos-aquae, Dactylococcopsis sp.) and chlorophyta (Chlorella sp., Scenedesmus quadricauda) growth. The results indicated that the logistic model can well describe the growth of four kinds of algae. Microcystis flos-aquae grew better with the decrease of N/P ratio (the maximum biomass K and the specific growth rate r increased significantly). Scenedesmus quadricauda had the higher value of K and r with the increase of N/P ratio. Dactylococcopsis sp. favored the relative high N/P ratio cultures and the highest value of r at N/P=15.35 group which was close to Redfield ratio. Chlorella sp.presented algal bloom in N/P=15.35 and N/P=3.84 groups. At the end of the experiment, the accumulated TN concentration of Microcystis flos-aquae was the significantly lower in N/P=307.06 and N/P=153.53 groups than that in others (P<0.05), Scenedesmus quadricauda had the lower TN concentration per cell in N/P=3.84 group than that in others (P<0.05). TP concentration per cell in four kinds of algal body significantly increased with the decrease of N/P ratio (P<0.05).
