Photosynthetic oxygen evolution rates of D. chodatii were measured under increasing photon flux densities from 0 to 1580 μmol photons m−2 s−1 according to Karsten et al. (2010b (link)) and Prelle et al. (2019 (link)). Presens Fibox3 oxygen optodes (Presens, Germany) and 4 × 3 mL thermostatic acrylic chambers DW1 (Hansatech Instruments, UK) combined with magnetic stirrers were used at an ambient temperature of 20 °C. The O2 production per photon flux density and time was normalized to the amount of total chlorophyll a per sample. After photosynthesis-irradiance (P-I) curve measurements, the cell suspension was filtered onto Whatman GF/F glass fiber filters (Whatman, Dassel, Germany). Chlorophyll a was extracted with 90% aqueous ethanol (v/v) overnight at 4 °C and quantified according to Ritchie (2008 (link)). P-I curve data were calculated and fitted by the mathematical photosynthesis model of Walsby (1997 (link)) with the SOLVER-function from Excel (Microsoft Office 365) which allowed the calculation of the three parameters: α (positive slope at limiting photon flux densities), IC (light compensation point), and IK (initial value of light-saturated photosynthesis).
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