Results

The following results were obtained:

Population Size:

Our results (Fig. 1) indicate that the populations cultured in 370 and 750ppm CO₂ experienced significantly greater population growth (P < .01) throughout the duration of the experiment than the culture incubated in 100ppm CO₂.   The most prolific growth at current concentrations of atmospheric CO₂ (370ppm), whereas those populations cultured in abnormally low CO₂ concentrations (100ppm) experienced the most limited growth.  On the last day of the experiment, the population of all three cultures was significantly different from each other (100 vs. 370ppm, P<.001; 100 vs. 750ppm, P<.001; 370 vs. 750ppm, P<.01) with the most prolific growth occurring at current concentrations of atmospheric CO₂ (370ppm).

pH of Culture Medium:

The results of this analysis (Fig. 2) reveal that the culture medium incubated in 100ppm CO₂ was more basic than the 370ppm CO₂ culture, which, in turn, was more basic than the culture maintained at 750ppm CO₂.

Photopigment Concentrations:

Fluorescence:

Analysis of the fluorescence of chlorophyll (Fig. 3) showed a steady increase throughout the experiment in all culture conditions.  The data suggests, however, that there is no difference in the fluorescence of the chlorophyll between the cultures incubated in 370ppm and 750ppm CO₂.  The populations in these two culture conditions do, however, appear to have more chlorophyll fluorescence than the diatom population maintained at 100ppm CO₂^.

Direct Photopigment Analysis:

Our data shows that chlorophyll a is the most abundant photopigment (58%), followed by carotinoid (35%), and chlorophyll c (7%).  Within each culture condition (100ppm, 370ppm, and 750ppm CO₂) chlorophylls a and c behaved similarly over the course of the experiment with both steadily increasing in concentration except for the 750ppm culture where no increase in chlorophyll a was recorded on the last day of the experiment (Figs. 4&5, respectively).  Additionally, the concentration of chlorophyll a on the last day of the experiment was significantly higher in the 100ppm culture than the 750ppm culture (P<.05).  There was, however, no statistically significant difference in the concentrations of chlorophyll c between the culture conditions.

Carotinoid concentrations increased over the course of the experiment in all culture conditions (Fig. 6).  On the last day, the concentration of carotinoids in the 750ppm culture was significantly higher than that found in the 100ppm culture (P<.05).

The total photopigment concentration was highest in cultures maintained at 100ppm CO₂ and lowest in the 750ppm culture.

Inorganic Nutrient Concentrations:

The concentrations of inorganic nutrients (nitrate, phosphate, and silicate) in the 100ppm CO₂ culture decreased at a gradual rate for the duration of the experiment (Figs. 7, 8, and 9).  The concentrations of nitrate, phosphate, and silicate in the 370ppm and 750ppm CO₂ cultures, however, decreased rapidly to zero during the first four days of the experiment.  After this point, nitrate recovered slightly to approximately 40ppm (Fig. 9).

Carbonic Anhydrase Activity:

The results of the experiment reveal that carbonic anhydrase (CA) activity varied inversely with the concentration of CO₂ in the culture medium, with the 100ppm culture having the most CA activity and the 750ppm culture having the least amount of CA activity (Fig. 10).