The Optimum Resource Ratio (N:P) for the Growth of Microcystis Aeruginosa with Abundant Nutrients

Redfield ratio about 16N:1P indicates the atomic ratio of the average elemental composition of phytoplankton, and the initial ratio of resource availability in a system provides the capacity to support algae biomass. Field and laboratory studies, focusing on the natural aquatic environment without disturbance, obtain regular growth of Microcystis aeruginosa with varied Redfield ratios. However, whether there are similar rules of M. aeruginosa under severely disturbing conditions remains unclear. In this study, we reported the growth of M. aeruginosa under conditions with excessive input of nitrogen and phosphorus, which may serve as clues to the control of M. aeruginosa blooming. Growth of M. aeruginosa was monitored in semi-continuous cultures with abundant supply of nitrogen and phosphorus. Effect of nitrogen, phosphorus and their ratio on growth of M. aeruginosa was examined, and the uptake of nitrogen and phosphorus under different nutrient conditions was compared. The effect of N:P ratio depended on the concentration of nitrogen and phosphorus. When initial nitrogen concentration was at 10 mg l-1 and the N:P ratio of 16, the algae growth displayed the highest maximum cell yield and the longest exponential growth. The maximum uptake of nitrogen and phosphorus reached at the N:P ratio of 16, consistent to the maximum yield. On the other hand, when initial phosphorus concentration was around 1 mg l-1, the highest maximum cell yield and the longest exponential growth occurred at the N:P ratio of 40. The ratio of 40 also favored the uptake of phosphorus, while the uptake of nitrogen increased with the increase of nitrogen concentration.