Mechanisms of light control of the quantum yield of in situ phytoplankton fluorescence as studied by pulsed laser fluorometry

The mechanisms of the effect of natural illuminance on the initial $(\Phi^0)$ and maximum $(\Phi^{max})$ quantum yields of phytoplankton fluorescence and the efficiency of the initial stages of photosynthesis were studied. Remote measurements of $\Phi^0$ and $\Phi^{max}$ in phytoplankton samples were performed using the double-beam laser method. It was found that the principal mechanisms of control of the fluorescence yield by the light are the "energy-dependent" fluorescence quenching that occurs at illuminances about 5-20 klx and the photoinhibition of the initial stages of photosynthesis at illuminances of 30-100 klx.