Photosynthesis of phytoplankton studied with three different incubation methods

Abstract

In natural environments, algal cells that constitute the phytoplankton continuously experience light variations because of the vertical displacement within the water column due to hydrodynamics. The common method for determination of phytoplankton primary production is the static incubation, when photosynthesizing cells are exposed to constant light conditions. The in situ and laboratory measurement of planktonic primary production in Lake Balaton has been made so far only by static incubation. Therefore we compared the static and the dynamic incubation methods of the measurement of primary production in Siófok-basin of Lake Balaton in August 2007. The dynamic incubation was performed by an elevator operated with a stepper-motor. In sunny weather the natural UV radiance inhibited the photosynthesis of phytoplankton, therefore the laboratory incubation without UV radiation overestimated the primary production. In cloudy weather, however, the lower natural UV radiance stimulated photosynthesis. Signifcant differences have not been found between the results of the in situ dynamic and in situ static incubation. According to our results, the laboratory incubation method is suitable to estimate the algal primary production, however the in situ dynamic method is the best way to measure it, if the determination of photosynthesis-irradiance curve is not required.