Spectral photosynthesis, quantum yield and blue-green light enhancement of productivity rates in the diatom Chaetoceros gracile and the prymnesiophyte Emiliania huxleyi

Abstract

The photosynthetic properties of white and blue-green light grown cultures of a diatom, Chaetoceros gracile, and a prymnesiophyte, Emiliania huxleyi, were compared. The aim of the study was to quantify chromaticity effects on the spectral properties of chromophytes which significantly impact bio-optical predictions of in situ primary production. The comparisons emphasized the spectral dependency of cell pigmentation, absorption, quantum yield and rates of photosynthesis. Concentrations of chlorophylls and carotenoids were similar for the white light cultures of C. gracile and E. hrudeyi. While the absorption spectra for the chromophytes were similar, E. huxleyi exhibited a higher quantum efficiency and hence a higher photosynthetic rate, than C gracile. The pattern of blue-green light adaptation was quite distinct for the 2 phytoplankters. The &atom exhibited little change in pigmentahon, but relative quantum yleld increased slightly as did overall rates of photosynthesis. In the prymnesiophyte, total cell pigmentation was reduced by half, lowerlng cell absorption while increasing in situ chlorophyll-specific rates of photosynthesis. Carbon action spectra were made with and without background blue-green light in order to assess the potential errors produced by restricted 'Emerson enhancement effects' which are inherent in the measurement of photosynthetic action spectra. Rates of photosynthesis increased 17 to 36 % when enhancement effects were taken into account. These direct measures of photosynthesis were in good agreement with bio-optlcal model predictions based on the spectral properties of chron~ophytes.