Background
The authors note that "the function and structure of the photosynthetic apparatus of many algal species resembles that of higher plants (Plumley and Smidt, 1984; Brown, 1988; Plumley et al., 1993)," and that "unicellular green algae demonstrate responses to increased CO2 similar to those of higher plants in terms of biomass increases (Muller et al., 1993)."  They also note, however, that "little is known about the changes to their photosynthetic apparatus during exposure to high CO2," which deficiency they begin to correct via a new experiment.

What was done
Batches of the unicellular green alga Scenedesmus obliquus (wild type strain D3) were grown autotrophically in liquid culture medium for several days in a temperature-controlled water bath of 30°C at low (55 µmol m^-2 s^-1) and high (235 µmol m^-2 s^-1) light intensity while they were continuously percolated with air of either 300 or 100,000 ppm CO2.

What was learned
It was determined that exposure to air of 100,000 ppm CO2 produces, in the words of the authors, a "reorganization of the photosynthetic apparatus" that "leads to enhanced photosynthetic rates, which ... leads to an immense increase of biomass."  After five days under low light conditions, for example, the CO2-induced increase in biomass was approximately 300%, while under high light conditions it was approximately 600%.

What it means
Like their land-locked cousins (see Growth Response to Very High CO2 Concentrations), unicellular green algae appear to thrive on vastly higher-than-current atmospheric CO2 concentrations, which suggests they should do very well indeed as the air's CO2 content continues to climb.

References
Brown, J.S.  1988.  Photosynthetic pigment organization in diatoms (Bacillariophyceae).  Journal of Phycology 24: 96-102.

Muller, C., Reuter, W. and Wehrmeyer, W.  1993.  Adaptation of the photosynthetic apparatus of Anacystis nidulans to irradiance and CO2-concentration.  Botanica Acta 106: 480-487.

Plumley, F.G. and Smidt, G.W.  1984.  Immunochemical characterization of families of light-harvesting pigment-protein complexes in several groups of algae.  Journal of Phycology 20: 10.

Plumley, F.G., Marinson, T.A., Herrin, D.L. Ideuchi, M. and Schmidt, G.W.  1993.  Structural relationships of the photosystem I and photosystem II chlorophyll a/b and a/c light-harvesting apoproteins of plants and algae.  Photochemistry and Photobiology 57: 143-151.