Carbon metabolism responses in acclimated and perturbed emiliania huxleyi cultures under ocean acidification conditions

12th International Phycological Congress, 22-26 March 2021Carbon metabolism related variables in Emiliania huxleyi show variable responses to ocean cidification (OA). However, most of the studies converge on the statement that OA has negative effects on alcification. In this study we hypothesize that carbon metabolic responses to OA differ between CO2 acclimated and perturbed phytoplankton cultures. Hence, responses of Emiliania huxleyi cultures acclimated to future CO2 concentrations (1000 ppmv, High Carbon: HC) and present CO2 concentrations (406 ppmv, Low Carbon: LC, Control) were assessed under acclimated and perturbed conditions, the last one promoted by stopping the CO2 supply in the culture media for 4 hours. Gene expression of three genes related to CCMs (Carbonic anhydrase (CA): αca1, αca2) and carbon fixation (RuBisCO: rbcL) were quantified as well as rates of photosynthetic carbon incorporation, DOC release and calcification. The results revealed two different patterns in both, molecular and physiological responses, depending on culture conditions and CO2 treatment: acclimated conditions performed a down-regulation of the carbon metabolism in HC cells compared to LC cells while under perturbed conditions, HC cells showed an up-regulation of most of the photosynthetic carbon metabolic pathways studied. In addition, the calcification rates under HC concentrations revealed a more conservative response than the other tested variables and always showed lower values than under LC conditions. These results highlight the relevance of considering previous growth conditions to appropriately interpret the response of calcifying phytoplankton to future OA scenariosThis work has been funded by the Spanish Ministry of Economy, Industry and Competitiveness and by the Xunta de GaliciaN