Abstract
We investigated for factors possibly affecting dominance of Microcystis species. Microcystis cells collected in Lake Suwa were cultured under conditions with changes in the concentration of nutrients, temperature and light intensity. In the series with the change in concentration of potassium nitrate and sodium nitrate, the composition of the three species apparently changed. M. aeruginosa became dominant at a relatively high concentration, whereas M. viridis did so at a relatively low one. In Lake Suwa, the decrease in dissolved inorganic nitrogen (DIN) concentration corresponded well to the decrease in M. aeruginosa and the increase in M. viridis. Accordingly, nitrogen concentration may be a factor possibly affecting the dominance. With the change in light intensity, M. aeruginosa and M. wesenbergii could grow well at a higher light intensity than M. viridis. Light intensity may also be a possible factor. However, temperature did not affect the dominance of the species.
