Compositional homeostasis of the dinoflagellate Protoceratium reticulatum grown at three different pCO2.

In the CO2-richer world that awaits us, the impact of elevated pCO2 on the allocation of resources in phytoplankton may have profound repercussions on the physiology of the microalgae and on the ecology of the ecosystems of which they are part. We studied the overall physiology and cell composition of the potentially toxic dinoflagellate Protoceratium reticulatum subjected to a medium-term increase of CO2. The physiological responses investigated were growth rates, cell size, photosynthetic and respiratory rates, and key enzyme activities. Cell composition was assessed by conventional analytical methods and FTIR spectroscopy. After 3 generations of incubation at current atmospheric, high and very high pCO2 (380, 1000, 5000ppm CO2), growth, photosynthesis, and dark respiration rates increased significantly, but the internal composition was only slightly affected. We propose the homeostasis of cell composition as a strategy that organisms can use to tackle environmental perturbations, especially when they are of relatively short duration.