On the production of particulate organic carbon by heterotrophic processes in sea water

The refractive index of phytoplankton is calculated from its metabolite composition. The mean index of the algal dry mass, relative to the index of water, seems to vary from 1.146 for green algae to 1.167 for coccolithophonds. This difference of 0.021 reduces to 0.007 and 0.003 when the partial water volumes of the algae are 0.6 and 0.8, respectively. The most important factor for the variation of the refractive index is the algal water content. If a reasonable average range of the partial water volume is 0.6 ± 0.2, the corresponding range of the refractive index relative to sea water becomes 1.06 ±0.04. This result is in excellent agreement with estimates based on optical measure- ments of pure algal cultures. The normal dispersion of the refractive index is negligible, but anoma- lous dispersion in the vicinity of strong absorption bands may be of importance for the light scattering properties of small phytoplankton.

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Refractive index of phytoplankton derived from its metabolite composition

SUMMARY

Biomass-specific, dark respiration rates of microalgae vary by almost two orders of magnitude from 0.01 to 0.6 d−1. In general, dark respiration rates increase with growth rates in both intraspecitic and interspecific comparisons, but the precise relationship between respiration and growth rate varies. Under optimal conditions, respiration rates are about 20-30% of growth rates, but the ratio of respiration to growth increases under suboptimal conditions. The intercept of plots of respiration rate vs. growth rate varied from < 0.01 to 0.4 d1, and the slopes of these relationships varied from < 0.1 to 1.0. Minimum maintenance metabolic rates of about 0.01 d 1 have been estimated for some microalgae by extrapolation of the initial slope of the light curve for growth to a hypothetical negative growth rate in darkness. The dimensionless total energy cost of synthesis and maintenance for heterotrophie growth of microalgae using either endogenously or exogenously supplied carbohydrates is typically 0.4-1.2 for growth with ammonia or urea as a nitrogen source and 0.7-1.4 for growth with nitrate as the nitrogen source.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1989.tb00321.x

Respiration and microalgal growth: a review of the quantitative relationship between dark respiration and growth

Dissolved organic carbon, nitrogen and phosphorus in the sea

Following exposure in situ for periods of 3 to 24 h of samples of lake or sea waters to which $^{14}$C-bicarbonate had been added, radioactivity was found in dissolved organic matter in the water as well as in the cells of phytoplankton. The amount in the water was between 7 and 50% of the total carbon fixed in the photic zone of the water column. This production of extracellular $^{14}$C-labelled organic matter was found under a wide variety of conditions and with many different types of phytoplankton community. It thus seems likely that the widely used method, in which fixation of $^{14}$C in particulate matter only is determined, under-estimates total primary productivity. The labelled organic substances in the water are probably liberated by intact photosynthesizing cells rather than by breakage of cells during filtration. Glycollic acid is likely to be one of the principal substances concerned. Over a wide range of light intensities liberation of extracellular products by a given phytoplankton population was proportional to the amount of carbon fixed in the cells, except that it tended to be relatively greater at low light intensities ( 50 kilolux), when as much as 95% of the total organic $^{14}$C might be extracellular. Population density, period of exposure to $^{14}$C-bicarbonate and species differences also affect the extent of excretion. The implications of extensive liberation by phytoplankton of extracellular products of photosynthesis for our understanding of the trophic relationships in aquatic habitats seem to be considerable.

Extracellular products of phytoplankton photosynthesis.

1. An oxidative assimilation of acetic add and glucose in darkness has been demonstrated in the green alga, Chlorella pyrenoidosa . From manometric experiments it has been shown that 1 mol (CH2O) per mol acetic add and 5 mols (CH2O) per mol glucose are produced.

2. The time required for complete utilization of a limited amount of acetic acid or glucose is not affected by illumination in the absence of carbon dioxide.

3. The time required for complete utilization of a limited amount of glucose is not affected by the simultaneous occurrence of photosynthesis. It must therefore be concluded that the accumulating product of photosynthesis cannot be glucose but must be some slowly respirable (storage) material.

4. Possible interrelationships between oxidative assimilation and photosynthesis may be further studied by following, in darkness and in light, the time course of oxidative assimilation of substrates which are possible intermediates in the two processes.

/pdf/oxidative-assimilation-in-relation-to-photosynthesis-in-1ofsof57p8.pdf

Oxidative assimilation in relation to photosynthesis in chlorella

In studies on the algae remarkably little attention has been paid to those details of metabolism which have proved essential in understanding the physiology of other microbial forms. On the carbon and nitrogen balance, for instance, there is little available information. Krogh, Lange, and Smith (3) obtained a carbon balance on a culture of Scenedesmus which showed that 95% of the carbon was retained by the cells under the usual conditions of algal culture. Barker (1) made tests for but failed to find soluble photosynthate which might be excreted by diatoms. One report of excreted photosynthate is that of Uhvtts (11) who found that very small amounts of acetaldehyde of the order of 10e to IO5 moles could be obtained from 200 to 700 ml. of algal suspension (C. pyrenoidosa) when bisulfite had been added to the medium. It is also common observation that algal cultures develop small amounts of bacterial growth even in completely inorganic media. More complete information on the carbon and nitrogen balance is needed.

James A. Johnston

Papers

Oxidative assimilation in relation to photosynthesis in chlorella

Carbon and nitrogen balance of chlorella during growth.