A reduction in metabolism explains the tradeoffs associated with the long-term adaptation of phytoplankton to high CO 2 concentrations.

Phytoplankton are responsible for nearly half of global primary productivity and play crucial roles in the Earth's biogeochemical cycles. However, the long-term adaptive responses of phytoplankton to rising CO ₂ remains unknown. Here we examine the physiological and proteomics responses of a marine diatom, Phaeodactylum tricornutum, following long-term (c. 900 generations) selection to high CO ₂ conditions. Our results show that this diatom responds to long-term high CO ₂ selection by downregulating proteins involved in energy production (Calvin cycle, tricarboxylic acid cycle, glycolysis, oxidative pentose phosphate pathway), with a subsequent decrease in photosynthesis and respiration. Nearly similar extents of downregulation of photosynthesis and respiration allow the high CO ₂ -adapted populations to allocate the same fraction of carbon to growth, thereby maintaining their fitness during the long-term high CO ₂ selection. These results indicate an important role of metabolism reduction under high CO ₂ and shed new light on the adaptive mechanisms of phytoplankton in response to climate change.
(© 2021 The Authors. New Phytologist © 2021 New Phytologist Foundation.)