Coccolithophorid Emiliania huxleyi to elevated pCO2 under nitrate limitation

The effects of a partial pressure of CO2 (pCO2) increased from 400 to 700 ppm on
nitrogen-limited growing cells of the coccolithophore Emiliania huxleyi were studied.
Nitrogen limitation was obtained within NO3-limited continuous cultures renewed at
the rate of 0.5 d−1 and submitted to saturating light level. pCO2 was controlled by bubbling
CO2-rich or CO2-free air in the cultures. It is shown that the increase of pCO2
has a rapid effect on cell physiology taking place within the 2 cell divisions occurring
after the perturbation. Net calcification rate (C) was depressed from approximately
25%, and, as opposed to what has been reported by previous studies on N-replete cultures,
net community production (NCP) was depressed in the same proportion. These
results therefore suggest that the increase of pCO2 had not noticeable effect on the
calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited.