Maximum ammonium uptake rates of Scenedesmus quadricauda (Chlorophyta) and Microcystis novacekii (Cyanobacteria) grown under nitrogen limitation and implications for competition

We measured maximum ammonium uptake rates of the green alga Scenedesmus quadricauda (Turpin) Bre-bisson and the blue-green alga Microcystis novacekii (Kom.) Comp. grown in nitrogen (ammonium)-limited chemostats. Maximum uptake rates per cellular carbon were larger in S. quadricauda than in M. novacekii. These rates increased with increased specific growth rates. Maximum uptake rates per cellular nitrogen were also larger in S. quadricauda than in M. novacekii. The maximum uptake rates per cellular nitrogen were nearly constant against increased cellular N:C ratios under nitrogen-limited conditions. The higher maximum uptake rates indicate that S. quadricauda had higher uptake abilities for ammonium than M. novacekii when grown under nitrogen limitation. We examined the competition between both species under two distinct nutrient supply modes, using measured maximum uptake values and computer simulations, Microcystis novacekii prevailed in the small-pulse, high-frequency nutrient supply mode, whereas S. quadricauda became competitively superior in the large-pulse, low-frequency nutrient supply mode. These results indicate that we could control nuisance blooms of blue-green algae in lakes and reservoirs by changing the nutrient supply modes.