EXUDATES - PHYTOPLANKTON BACTERIOPLANKTON INTERACTIONS IN PLUSSEE

Phytoplankton from Plubetasee were investigated with regard to photosynthetic activity and the simultaneously occurring release of extracellular organic compounds (EOC). rhe chemical properties, as well as the quantity of EOC, differ considerably depending on the community's seasonally varying composition and on individual physiological status. EOC constituted up to 99.9% (minimum 30.5%, mean 65.9%) of the phytoplankton's primary production. EOC quality seemed to be decisive for uptake as a carbon source utilized first by aquatic bacteria. In early summer, EOC were rapidly incorporated by microorganisms and represented an important contribution to their biomass production. In contrast, the exudates released during late summer (August and September) predominantly consisted of components slowly incorporated by bacteria. These exudates were compounds of presumably high molecular weight.