Critical Light Intensities for Microcystis aeruginosa, Scenedesmus quadricauda and Cyclotella sp. and Competitive Growth Patterns under Different Light:N:P Ratios

ABSTRACT

Critical light intensities for Microcystis aeruginosa, Scenedesmus quadricauda, and Cyclotella sp. were calculated, and patterns of growth and competition were analyzed under different light:N:P conditions in the laboratory. The growth of all three species was limited at a light intensity of 14 μmol.m⁻².^s-1, M. aeruginosa was in general the dominant competitor. At a light intensity of 54 μmol.m⁻².^s-1, N:P was the key factor controlling the competitive outcome. When light intensity was 108 μmol.m⁻².^s-1, light controlled the competitive outcome. Under constant light intensity conditions, S. quadricauda attained dominance only at low N:P ratios and moderate light intensity conditions. M. aeruginosa dominated under critical light intensity, moderate or high N:P ratio, or high light intensity. Under conditions of fluctuating light intensity, the densities of M. aeruginosa, S. quadricauda, and Cyclotella sp. in monoculture and mixed culture were lower than those under conditions of constant light intensity.