| Summary: | Phytoplankton are the basis of marine food webs, and affect biogeochemical cycles. As CO2 levels increase, shifts in the frequencies and physiology of ecotypes within phytoplankton groups will affect their nutritional value and biogeochemical function. However, studies so far are based on a few representative genotypes from key species. Here, we measure changes in cellular function and growth rate at atmospheric CO2 concentrations predicted for the year 2100 in 16 ecotypes of the marine picoplankton Ostreococcus. We find that variation in plastic responses among ecotypes is on par with published between-genera variation, so the responses of one or a few ecotypes cannot estimate changes to the physiology or composition of a species under CO2 enrichment. We show that ecotypes best at taking advantage of CO2 enrichment by changing their photosynthesis rates most should increase in relative fitness, and so in frequency in a high-CO2 environment. Finally, information on sampling location, and not phylogenetic relatedness, is a good predictor of ecotypes likely to increase in frequency in this system. (Figure1) Photosynthesis (measured as oxygen evolution rates) for 16 Ostreococcus ecotypes at ambient and elevated pCO2 This file contains oxygen evolution data per cell per hour for all ecotypes in both CO2 treatments as measured with a Clark-type electrode. Note that these are means for biological (n=3-6) and technical (n=3) replicates. Also, the ppm CO2 given are the pCO2 we aimed to reach. For the actual values and detailed carbonate chemistry, please see our SI files, which are available from nature climate change. DatadryadPS.xlsx (Figure1)Growth rates of 16 Ostreococcus ecotypes at ambient and elevated CO2 levels This file contains growth rate data for 16 Ostreococcus ecotypes, measured as OD and verified on an Accuri (AWI) and a FACS Calibur (Edinburgh) flow cytometre. DatadryadGrowth.xlsx (Figure1) CN ratio of five representative ecotypes of Ostreococcus at ambient and elevated pCO2 levels This file contains ...
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