The concentration of carbon dioxide in seawater may affect phytoplankton physiology and ecology and their role in marine biogeochemical cycles. In order to assess the effects of CO 2 on the elemental composition of marine phytoplankon, carbon, nitrogen, and phosphorus quotas were measured in 4 species of marine phytoplankton acclimated to 150 to 1500 ppm CO 2 (5 to 50 μM) in semi-continuous cultures. Nitrogen quotas declined steeply with increasing CO 2 in the centric diatoms Thalassiosira pseudonana and T. weissflogii acclimated to 150 to 380 ppm (5 to 13 μM), but more slowly as the CO 2 increased from 380 to 1500 ppm (13 to 50 μM). Nitrogen demand varied little with CO 2 in the pennate diatom Phaeodactylum tricornutum, but was positively correlated with CO 2 over the range of 150 to 770 ppm in the prymnesiophyte Isochrysis galbana. Based on the nitrogen-CO 2 trends in centric diatoms, relief from carbon-nitrogen colimitation could lead to 2-fold larger cells as CO 2 increases from 150 to 380 ppm, but only 15% larger cells from 380 to 770 ppm CO 2. Phosphorus quotas in the 3 diatoms decreased as CO 2 increased from 150 to 380 ppm. As previously observed in these and other species, C:N, C:P, and N:P ratios increased with increasing CO 2, but the present results show that much of this variation was due to differences in nitrogen and phosphorus rather than carbon quotas. Marine phyto - plankton could provide a negative feedback against increasing CO 2 over the pCO 2 range of 150 to 380 ppm by supporting larger cells or higher biomass, but would support a smaller carbon sink as atmospheric CO 2 rises above 380 ppm.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Aquatic Science
- Carbon dioxide