VERTICAL AND SEASONAL-VARIATIONS OF INORGANIC CARBON ALLOCATION INTO MACROMOLECULES BY PHYTOPLANKTON POPULATION IN A BROWN-COLORED AND A CLEAR-WATER LAKE

The aim of this study was to assess vertical and seasonal variations o f inorganic carbon allocation into macromolecules by phytoplankton pop ulation in an humic and acidic lake (Lake Vassiviere) and in a clearwa ter lake (Lake Pavin). Biochemical fractionation was done by consecuti ve differential extractions in order to separate proteins, polysacchar ides, lipids and low molecular weight compounds (LMW) by virtue of the ir relative solubilities in different extraction solvents. Independent of depth and season, the principal photosynthetic end products were p olysaccharides followed by proteins, LMW and lipids. However, inorgani c carbon allocation into macromolecules varied, in these two lakes, wi th depth and with the taxonomic composition of phytoplankton. Carbon a llocation into polysaccharides decreased with increasing depth, especi ally in the brown-colored humic lake, and Diatoms showed high C incorp oration into polysaccharides.