Diel oscillations of the photosynthesis-irradiance (P-I) relationship in natural assemblages of phytoplankton
- Cite this article as:
- Harding, L.W., Prézelin, B.B., Sweeney, B.M. et al. Marine Biology (1982) 67: 167. doi:10.1007/BF00401282
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Diel oscillations in the photosynthesis-irradiance (P-I) relationship are described for marine phytoplankton assemblages at 6 stations in an upwelling area off the southern California coast (USA) between May and August 1980. The initial slope (α) and asymptote (Pmax) of P-I curves changed significantly over the day; both parameters were in phase and had similar changes in amplitude. The diel oscillations in photosynthesis appeared unrelated to changes in chlorophyll a concentrations. Amplitudes of daily variations in photosynthesis ranged from approximately 3 to 9, as measured by the maximum to minimum ratio for photosynthetic capacity (Pmax). Diatom-rich samples collected during an upwelling event and those dominated by dinoflagellates both had midday to early afternoon maxima in α and Pmax. Samples from other locations had peak photosynthetic activity later in the afternoon. The relationship between α and Pmax was consistent in all phytoplankton samples analyzed, with a surprisingly high correlation considering the spatial and temporal scales encompassed in this study. These results indicate that the photosynthesis-irradiance (P-I) relationship is time-dependent and, moreover, that changes in α and Pmax are closely coupled for a variety of natural phytoplankton assemblages.