MEPS 146:207-223 (1997)  -  doi:10.3354/meps146207

Estimation of the photosynthetic action spectrum: implication for primary production models

Kyewalyanga MN, Platt T, Sathyendranath S

A simple method for estimating the photosynthetic action spectrum is developed. The method uses the shape of the absorption spectrum of phytoplankton pigments, scaled to the magnitude of the initial slope of the photosynthesis-light curve as established for broad-band illumination. The method was tested by comparing the estimated action spectra with those measured during a cruise in the North Atlantic, in the fall of 1992. The agreement between the constructed and the measured spectra was good. Both the measured and constructed action spectra were then used to compute daily water-column primary production (PZ,T)using a spectrally resolved model. The results showed that, at most of the stations, the PZ,T computed using the constructed action spectrum was not significantly different from PZ,T calculated using the measured spectrum. Daily water-column primary production was also computed at each station using the average shape of the measured action spectra (spectra averaged over all stations), scaled to the magnitude of broad-band initial slope at that station. The results were similar to the PZ,T values computed using the action spectra constructed for individual stations. The errors that may affect the constructed action spectrum are assessed through a sensitivity analysis. The analysis suggests that, for our data, the presence of photosynthetically inactive pigments causes negligible errors in the computed PZ,T. An assessment of the effects of random errors in the action spectrum showed that the error in the computed primary production was on average 1.5% (under the conditions chosen for the computation), when random errors of up to ±20% were introduced into the action spectrum. However, given similar conditions, systematic errors of similar magnitude in the action spectrum cause an average error of about 6% in the computed water-column primary production.

Photosynthesis · Action spectrum · Absorption spectrum · Phytoplankton · Primary production

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