Temperature responses of different functional traits in Arctic phytoplankton

This study was conducted in autumn/winter 2021/2022 at the laboratory of the Alfred-Wegener-Institute Bremerhaven. To assess temperature response patterns of various functional traits in Arctic phytoplankton species, we cultivated Thalassiosira hyalina, Phaeocystis pouchetii, Micromonas pusilla and Nitzschia frigida at a temperature gradient of 0°C to 14°C under saturating light of 100 µmol photons m-2 s-1 (T. hyalina, P. pouchetii, M. pusilla) or 30 µmol photons m-2 s-1 (N. frigida) and replete nutrient conditions (micronutrients following F/2; 100 µmol L-1 nitrate, 100 µmol L-1 silicate, 6 µmol L-1 phosphate) in dilute batch cultures. Culture bottles were aerated with air containing a pCO2 of 400 µatm ensure a stabilized carbonate chemistry and to avoid sedimentation. After an acclimation period of >7 generation or >10 days, respectively, various functional traits were obtained: specific growth rate, quotas of particulate organic carbon (POC) and nitrogen (PON) as well as chlorophyll a (Chl a), photo-physiology using fast repetition rate fluorometry. Furthermore, the following parameters were calculated from the obtained data: POC:PON, Chl a:POC, POC production rate, photosystem II quantum yield, absolute electron transport rates at in-situ irradiance and maximal irradiance, light use efficiency, light acclimation indices, lifetime of PSII reopening and absorption cross section.