Diel oscillations of the photosynthesis-irradiance (P-I) relationship in natural assemblages of phytoplankton |
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Authors: | L W Harding Jr B B Prézelin B M Sweeney J L Cox |
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Institution: | (1) Oceanic Biology Group, Marine Science Institute and Department of Biological Sciences, University of California at Santa Barbara, 93106 Santa Barbara, California, USA;(2) Present address: Chesapeake Bay Institute, The Johns Hopkins University, 4800 Atwell Road, 20764 Shady Side, Maryland, USA |
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Abstract: | 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 ( ) and asymptote (P
max) 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 (P
max). Diatom-rich samples collected during an upwelling event and those dominated by dinoflagellates both had midday to early afternoon maxima in and P
max. Samples from other locations had peak photosynthetic activity later in the afternoon. The relationship between and P
max 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 and P
max are closely coupled for a variety of natural phytoplankton assemblages. |
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