Dataset: Series 5: pCO2 as one of multiple stressors for Thalassiosira weissflogii - cell characteristics: Chl. a: C ratio

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