Chlorophyll Fluorescence as a Biological Indicator of Primary Productivity

Abstract

The traditional technique of using radioisotopes to measure primary productivity is dependable but has its limitations. Technological developments in phytoplankton fluorescence have led to the introduction of instruments which utilize fluorescence as a basis for determining rates of carbon assimilation. Whether the productivity values calculated from chlorophyll fluorescence are comparable to those produced by traditional bottle incubation methods remains unclear. To test the relationship between these two techniques, photosynthesis vs. irradiance curves were produced for water samples collected on several cruises on Monterey Bay during summer 1997 and compared to pulsed amplitude modulation (PAM) fluorometer data that was measured from the same samples. Measurements of carbon assimilation rates vs. irradiance were performed using 14C-labeled bicarbonate water collected from 0-5m. Chlorophyll fluorescence was measured using a PAM-100 fluorometer, wherein a mirrored cuvette containing the sample was subjected to short saturating pulses of light. Fv/Fm was calculated from these readings, effectively producing a yield via the fluorescence method that could be compared to the quantum yield of carbon as determined by the traditional radioisotope technique.