| Summary: | <p>The increase in partial pressure of CO2 (pCO2) is causing ocean acidification, which impacts the<br /> growth rates and elemental composition of phytoplankton. Here, shifts in growth rates and cell<br /> quotas of Thalassiosira weissflogii grown under a variety of different temperatures, irradiances,<br /> and pCO2 conditions are discussed. The presented data suggest that acclimatization times of<br /> exponentially growing diatoms to environmental perturbations may be weeks to months, rather<br /> than days to weeks. The response of acclimatized T. weissflogii to pCO2 depended on irradiance<br /> and temperature and was highly interactive, non-linear, and non-uniform. A very significant<br /> negative effect of pCO2 was observed under growth conditions that were light-, and<br /> temperature-limited; a smaller, but still significant negative response was seen under<br /> light-limiting growth conditions, whereas pCO2 did not affect growth rates of T. weissflogii under<br /> light-saturated growth conditions. Cell quotas of organic carbon, nitrogen, or chlorophyll a were<br /> linked to growth rate. The cell-normalized production of transparent exopolymer particles (TEP)<br /> was positively correlated with POC cell quotas, with some minor impact of irradiance and pCO2<br /> on the relationship. This correlation of TEP production with carbon cell quotas is consistent with<br /> the hypothesis that extracellular release is an inherent component of cell metabolism. Results<br /> suggest that elevated pCO2 functions as an (additional) metabolic stressor for T. weissflogii and<br /> that the interaction of different stressors determines growth rates and cell characteristics in a<br /> complex, non-linear relationship.</p>
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