Influence of Phosphorus and Silicon on Competitive Interaction between Microcystis aeruginosa and Cyclotella sp. by Monoculture and Competitive Biculture Experiments

Abstract

In Lake Teganuma, the shift of dominant species from blue-green algae (Microcystis aeruginosa [M. aeruginosa]) to diatoms (Cyclotella sp.) has been observed since 2000 as a result of the discharge of Tone River water into Lake Teganuma through the North-chiba Water Conveyance Channel. In this study, the influence of phosphorus fluctuation under relatively high silicon concentration, reflecting the condition in Lake Teganuma after 2000, on the shift of dominant species was experimentally examined through individual monoculture and competitive biculture experiments. The results from monoculture experiment showed that the half-saturation constant and uptake rate of phosphorus for M. aeruginosa was respectively lower and faster than that for Cyclotella sp., representing that M. aeruginosa possesses much higher growth potential than Cyclotella sp. under the phosphorus limited condition. The outcome of competitive biculture experiment obviously reflected these results, i.e., dominance of M. aeruginosa with a proportion of 99 % in total cell. Therefore, phosphorus fluctuation under the high silicon concentration could be interpreted as a minor factor for the shift of dominant species, from M. aeruginosa to Cyclotella sp. as observed in Lake Teganuma.