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Title: Light effects and diel variations of nitrate reductase activity in phytoplankton from the northwest Africa upwelling region
Authors: Martinez, Rosa
Packard, Theodore T. 
Blasco, Dolors
UNESCO Clasification: 251001 Oceanografía biológica
Issue Date: 1987
Publisher: 0198-0149
Journal: Deep-Sea Research, Part A: Oceanographic Research Papers 
Abstract: Light kinetics and diel cycles of nitrate reductase (NR) activity were studied in the upwelling ecosystem off northwest Africa. The activity of the enzyme showed a strong response to light at low intensities but became saturated at light intensities above 15–30% of the incident light intensity. At higher irradiances, NR activity showed photoinhibition. At sea surface irradiances an average inhibition of 32% in the NR activity was observed. Diel cycles of NR activity exhibited the following characteristics: a low pre-dawn value (0.03–0.009 μmol NO3−N (μg Chl α)−1), a rapid increase with the onset of daylight, a maximum before noon (tripling the dark value), a secondary maximum in the early afternoon, and an afternoon-evening decrease that coincided with the decrease in sunlight. To simulate these characteristics a continuous polynomial function of light and time was developed
ISSN: 0198-0149
DOI: 10.1016/0198-0149(87)90034-3
Source: Deep Sea Research Part A, Oceanographic Research Papers [ISSN 0198-0149], v. 34, p. 741-753
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