THE RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND LIGHT FOR NATURAL ASSEMBLAGES OF COASTAL MARINE PHYTOPLANKTON¹

Abstract

SUMMARY In a series of 188 experiments on the, light‐saturation curve for natural assemblages of phytoplankton at 3 stations in Nova Scotia coastal waters, it was found that both the initial slope (α) of the curve and the assimilation number (PmB) varied about 5‐fold throughout the year. No differences could be detected between stations, but both α and PmB decreased with depth. The mean value of α for all the experiments was 0.21 mg C[mg Chl a]−1· h−1· W−1· m2 with a range from 0.03 to 0.63. An explanation is offered for the nonconstancy of a in terms of the effect of cell‐size and shape on self‐shading. An estimate is made from first principles of the physiological maximum‐attainable value of α. This estimate corresponds, within the limits of experimental error, to the highest values of α observed in the study. It is deduced that on the average the phytoplankton were photosynthesizing at only 44% maximum capacity. The mean value of PmB for all experiments was 4.9 mg C[mg Chl a]−1· h−1, with a range from 0.73 to 24.8. In the matrix of partial correlation coefficients, α and PmB were positively correlated with each other; α was correlated with mean solar radiation averaged over the 3 days prior to the experiment, but uncorrelated with temperature; PmB was correlated strongly with temperature but uncorrelated with recent solar radiation. The results show that PmB could be estimated from α and temperature using an empirical multiple regression equation, independent of depth. It is suggested that α and PmB are both correlated with some other factor not measured in the study, perhaps the mean cell‐size of the populations, or the nutrient status of the cells. The predictability of primary production is discussed in the light of this evidence.

Comparison of photosynthetic responses in diploid and haploid life-cycle phases of Emiliania huxleyi (Prymnesiophyceae)

“…If coccoliths served such a function, then 2 possible effects might be observed (Nanninga & Tyrrel 1996): (1) the irradiance at which P chl a max is attained (E sat ) would be higher in cal- . Also shown are the associated fitted P-E models for the haploid (Platt et al 1980) and diploid (Webb et al 1974) stages (Student's paired t-test: p < 0.001, 35 < n < 30, 0.82 < r 2 < 0.95) Table 1. Characteristics of haploid (N) vs. diploid (2N) phases of Emiliania huxleyi cultures: growth rate (μ), the ratio of chl a concentration over cell concentration (chl a/cell).…”

“…P-E curves were fitted for cultures of both life-cycle phases by non-linear parametric estimation according to the model of Platt et al (1980): where according to Sakshaug et al (1997), P chl a is the photosynthetic rate, α chl a is the maximum light-utilization coefficient, β chl a is the photoinhibition parameter, and P chl a s is the potential maximum photosynthetic rate if there was no photoinhibition.…”

“…The maximum photosynthetic rate (P chl a max ) and the light-saturation parameter (E k ) are defined as follows (Platt et al 1980): E k in this study corresponds to the irradiance at which photosynthesis was optimal, whereas E sat , employed notably by Nanninga & Tyrrel (1996), is the irradiance at which the maximal rate of photosynthesis is first attained.…”

Irradiance Regulation of Photosynthesis and Respiration in Modern Marine Microbialites Built by Benthic Cyanobacteria in a Tropical Lagoon (New Caledonia)

“…When photoinhibition occurred, the model of Platt et al [38] was used. Parameters of photosynthesis following the nomenclature and definitions of Sakshaug et al [42] were obtained from the fitted P vs I curves as follows:…”

An in vivo fluorescence method for the continuous in situ estimation of phytoplankton photosynthetic characteristics

“…Photosynthesis versus irradiance measurements were made on water samples from the first 3 depths, using the photosynthetron (Lewis & Smith 1983). Parameters aB, P : , , Ik and I, of the photosynthesis versus irradiance curves were estimated using the model of Platt et al (1980). These parameters were calculated using I4C uptake values standardized per unit chlorophyll a (B).…”