The quantum yield as a fundamental parameter controlling vertical photosynthetic profiles of phyto plankton in lake constance europe
Archiv fur Hydrobiologie, Supplementband 69(2): 169-198
ISSN/ISBN: 0365-284X Accession: 006745308
Vertical shifts in quantum yields of phytoplankton photosynthesis were analyzed in meso-eutrophic Lake Constance. Both seasonal and diel variations in photosynthetic responses to light were apparent. Near the lake surface where light saturation and light inhibition occurs, quantum yields were generally low. At depths where light was limiting, maximum values were attained. Plateaus of maximum quantum yields in deep water as postulated from theory were only observed when thermal stability was low or absent (spring, autumn). During summer, quantum yields either increased or decreased with depth. Also in the diurnal course significant changes in photosynthetic light responses by algae were observed. The seasonal range of mid-day maximum quantum yields was 0.022-0.092 moles C assimilated per mole PAR [photosynthetically absorbed radiation] absorbed. Over the course of a day, maximum quantum yields varied 3-fold. These results are discussed in view of existing methodological problems for estimating quantum yields as well as changes in algal light-shade adaptation and species composition.