Marine Phytoplankton Photosynthesis as a Function of Light Intensity: A Comparison of Methods

Abstract

An apparatus is described in which the constant for exponential algal growth has been determined as a function of light at controlled temperature. Studies were made of bacteria-free cultures of Skeletonema costatum and Dunaliella tertiolecta grown at the optimum temperature for cell division in media with and without adequate nitrate and phosphate. Less complete studies were made of the behaviour of Monochrysis lutheri and Amphidinium carteri. In all experiments the growth constants were determined at known light intensities, expressed in the energy units, langlies/minute, using light of a known spectral distribution similar to sunlight shining through a few metres of coastal sea water.Growth constants were determined for the following processes: increase of cellular carbon, chlorophylls a, b or c, carotenoids, cell numbers and photosynthesis measured both by oxygen evolution (net and gross) and by the uptake of C-14 labelled carbonate.The rate of maximum photosynthesis occurred when the illumination reached about 0.1 ly/min and little or no light inhibition occurred when the intensity was increased to as high as 0.4 ly/min. Respiration was about 10% of maximum gross photosynthesis. This fraction increased when cells were nitrogen deficient but decreased in phosphate deficient cultures because a phosphate shortage inhibited respiration more severely than photosynthesis.Gross photosynthesis at low light intensities was proportional to the total number of molecules of all plant pigments added together, irrespective of species or of culturing conditions. By contrast, the rate of maximum gross photosynthesis was poorly related to pigment composition, the best correspondence being with the amount of chlorophyll a in the cultures.The uptake rate of C-14 varied with time. There was an apparent "leakage" of labelled organic matter which eventually reached a near-equilibrium with 14CO2 uptake, after which the C-14 method measured the production of particulate carbon but not necessarily net or gross photosynthesis. The rate of particulate carbon production was the same as that of cell division but about 40% less than net photosynthesis in cultures of Skeletonema. Agreement between C-14 rates and net photosynthesis was better in cool-white fluorescent light than in the imitation submarine sunlight used in this work. At high light intensities there was apparently no excretion from Dunaliella "shade" cells but when these became changed to "sun" cells they behaved more like Skeletonema.Various observations are recorded of the effect of growth conditions on cell composition, especially with regard to pigments.The relatively low C-14 rates found with Skeletonema costatum may be explicable in part by an abnormally low counting efficiency for this species even when present as a "weightless" source but the problem requires further study.

The place of diatoms in the biofuels industry

“…This has not only been repeatedly demonstrated in laboratory cultures under optimal conditions [31][32][33], but in environmental samples from different locations [30]. In a comparative study, diatoms grew faster under low light conditions than competing algae [34].…”

Variation in Rubisco and other photosynthetic parameters in the life cycle of Haematococcus pluvialis

“…P/R has been suggested as an important index in evaluating the significance of productivity measurements (Humphrey, 1975). The ratio is known to vary with many factors including growth phase (Ryther, 1954) and nutrient levels (McAllister et al, 1964). When cells were deprived of nutrients, they were transformed into cysts as a resting stage, coinciding with a decreasing P/R ratio (Fig.3), slower rate of cell division, expansion of cell volume, thickening of the cellulose wall and accumulation of astaxanthin (Wang et al, 2004).…”

Periphyton metabolism along a nutrient gradient in a desert river (Truckee River, Nevada, USA)

“…In August, community respiration (CR) of periphyton responded to the enhanced nutrient supply with a signifi cant increase (from 2.8 to 10.1 g O 2 m -2 d -1 ), and about 82% of the variation in CR could be explained by the variation in GPP (linear regression), indicating a close link between respiration and primary production. Periphyton respiration includes algal respiration, which is often assumed to be 10-50% of gross primary production (McAllister et al, 1964;Whittaker and Likens, 1975) and respiration of heterotrophic organisms located at the surface or in the biofi lm matrix. In contrast to primary production, measurements of periphyton respiration provide limited information with respect to respiration at the ecosystem level since hyporheic respiration of open-canopied streams is known to contribute between 40-90% to ecosystem respiration (Grimm and Fisher, 1984;Naegeli and Uehlinger, 1997).…”