Abstract
This study was conducted to obtain fundamental information to elucidate the transition of the dominant species from green alga Scenedesmus quadricauda to blue-green alga Microcystis aeruginosa. Monoculture and monoxenic culture experiments for both species were conducted under nitrogen-limited conditions (monoculture, NO3-N = 0.1-5.0 mg/L; monoxenic culture, NO3-N = 0.5-5.0 mg/L) with a phosphorus concentration of 1.55 mg/L. Monoculture experiment results demonstrated that the Δ N/ Δ Chl.a value was ca. 5–7 times greater value for M. aeruginosa than for S. quadricauda at NO3-N = 0.5, 1.0, 2.5, and 5.0 mg/L. These findings imply that S. quadricauda possesses better ability for nitrogen productivity than that of M. aeruginosa. Monoxenic culture experiment results show that M. aeruginosa and S. quadricauda were respectively dominant at NO3-N = 0.5 mg/L and 1.0-5.0 mg/L. Furthermore, monoxenic culture experiment results suggest that a switching point of the N:P ratio for the dominance of S. quadricauda or M. aeruginosa exists in the range of 0.3 (NO3-N = 0.5 mg/L) to 0.6 (NO3-N = 1.0 mg/L).
