Abrupt and acclimation responses to changing temperature elicit divergent physiological effects in the diatom Phaeodactylum tricornutum

Summary Growth rates and other biomass traits of phytoplankton are strongly affected by temperature. We hypothesized that resulting phenotypes originate from deviating temperature sensitivities of underlying physiological processes. We used membrane‐inlet mass spectrometry to assess photosynthetic and respiratory O 2 and CO 2 fluxes in response to abrupt temperature changes as well as after acclimation periods in the diatom Phaeodactylum tricornutum . Abrupt temperature changes caused immediate over‐ or undershoots in most physiological processes, that is, photosynthetic oxygen release (), photosynthetic carbon uptake (), and respiratory oxygen release (). Over acclimation timescales, cells were, however, able to re‐adjust their physiology and revert to phenotypic ‘sweet spots’. Respiratory CO 2 release () was generally inhibited under high temperature and stimulated under low‐temperature settings, on abrupt as well as acclimation timescales. Such behavior may help mitochondria to stabilize plastidial ATP : NADPH ratios and thus maximize photosynthetic carbon assimilation.