Effects of alkalinity variations on photosynthetic activity and exopotysaccharides of Chlorella pyrenoidosa

Effects of bicarbonate (HCO3-) alkalinity on the photosynthetic performance of Chlorella pyrenoidosa was investigated in present study. Photosynthetic activity, pigments, MDA and ultrastructure of Chlorella pyrenoidosa were measured for when they were cultured at two different alkalinities including 2.3mmol/L (ALK2.3) and 12.4mmol/L (ALK12.4), respectivily. At ALK2.3, photosynthetic activity was stimulated at the prophase of culture and then inhibited at the anaphase. At ALK 12.4, it represented the same phenomenon, but inhibition effects were weaker than those at ALK2.3. Ratios of Chl.b/Chl.a was increased, but Caro/TChl ratios was decreased at elevated alkalinities. The contents of MDA increased at ALK2.3 and decreased at ALK12.4. In addition, secretion of glycocalix-like layer was remarkably stimulated at elevated alkalinities. These results showed that elevated alkalinities promoted algae carbon assimilation and stimulated secretion of glycocalix-like layer. Carbohydrate could alleviate stresses at elevated alkalinities. Secretion of glycocalix-like layer could decrease the synthesis of excess products of photosynthesis and relieve feedback inhibition, which will increase the stress tolerance of C. pyenoidosa at elevated alkalinities