Photosynthetic Algae, Thalassiosira weissflogii, Response to CO2 Change

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This project simulated the natural marine environment in order to study the ability of a marine diatom, Thalassiosira weissflogii, to fix carbon dioxide during photosynthesis. Diatom cultures were grown under three different CO₂ concentrations. The cultures grown at the highest CO₂ concentration had the highest cell counts and produced more chlorophyll and carotinoid pigments than the cells grown at the lower CO₂ levels. This is to be expected because cells under high CO₂ levels likely had higher photosynthetic rates which would allow greater cell growth rates. However, by day six of the experiment, cell counts were similar between the three cultures indicating that some nutrient, other than CO₂, was limiting the diatom population growth.

Surprisingly, cells grown under higher CO₂ concentrations showed more carbonic anhydrase activity than those grown at lower CO₂ levels, just the opposite of what had been hypothesized. In this experiment, very high cell counts were obtained, and this may be attributable to very high nutrient levels in the seawater used for the cultures. Possibly the high cell numbers depleted the CO₂ readily available to them, then began producing carbonic anhydrase to convert bicarbonate into usable CO₂. This would explain the higher enzyme activity seen at higher CO₂ concentrations.

Investigation of those variables which influence carbon uptake by diatoms and phytoplankton is important in studying global warming because these organisms, which make up about 1% of the Earth's biomass, are responsible for approximately 50% of the Earth's photosynthesis. They play an important role in the flow of carbon between the atmosphere, the ocean, and ocean sediments.