Phosphate concentration parameters in the water column; Plankton abundance per unit volume of the water column; Dissolved inorganic nitrogen concentration in the water column; Phytoplankton growth; Metadata parameters; Phytoplankton taxonomic volume in water bodies; Air temperature; Experiment state variables

This dataset comprises laboratory culture experiments investigating the effects of temperature and nutrient stoichiometry on eukaryotic plankton physiology and metabolism. Experiments examined growth rates, biovolume, body size changes, cellular chlorophyll-a, particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphorus (POP), primary production, and respiration. The interactive effects of temperature (3 vs 6 °C) and nitrogen-to-phosphorus (N:P) ratios (16:1 vs 10:1) were assessed in five polar phytoplankton isolates under exponential and stationary growth conditions. The five polar strains were: Arctic Thalassiosira nordenskioeldii CCAP 1085/31, obtained from the Culture Collection of Algae and Protozoa (CCAP, Oban – UK), Antarctic Fragiliariopsis nana K0637 and Antarctic Fragiliariopsis cylindrus CCMP1102 were provided by Thomas Mock (University of East Anglia – UK), Arctic Isochrysis galbana RCC5353 and Arctic Rhodomonas sp RCC5322 from Roscoff Culture Collection (RCC, Roscoff-France). These experiments were conducted in several different laboratories at the National Oceanography Centre in Southampton in 2023. The culture media (F/2 or L1) consisted of 0.2 µm filtered seawater enriched with macronutrients, trace metals and vitamins. Media was modified to adjust the nitrate initial concentration to get a 16:1 or 10:1 N:P ratio (0.57 mmol NO3-1 L-1 and 0.35 mmol NO3-1 L-1, respectively). Triplicate cultures were maintained in 100-250 mL Erlenmeyer conical glass flasks at two different temperatures (3 and 6 °C) inside growth chambers. Light was supplied with white-fluorescent lamps adjusted with a blue LEE filter (209 0.3ND) providing 97-104 μmol quanta m−2 s−1 on a 12:12 h light:dark incubation cycle. Therefore, monoclonal culture experiments were run at two different temperature-nutrient ratio combinations, as a representation of i) today’s conditions (3 °C, 16:1 N:P), ii) effect of warming (6 °C, 16:1 N:P), iii) effect of a decrease in N:P ratio only (3 °C, 10:1 N:P), and iv) warming plus decrease in N:P ratio imitating “future” conditions (6 °C, 10:1 N:P). An initial culture of each species was grown at the four different treatments for a full growth phase before the culture was split into triplicates for each treatment (12 experimental flask per strain). Cultures were monitored daily, or over 2-day periods, by counting cells under the microscope and were maintained at semi-continuous growth by diluting cultures with fresh media when they were reaching stationary conditions. Cultures were acclimated for at least 10 generations before the experiments. Polar regions are warming 2–5 times faster than the global average, affecting the balance of carbon and key nutrients such as nitrogen and phosphate. Temperature and nutrient availability are major drivers of plankton growth, size, and metabolism (primary production and respiration), but their interactive effects on polar phytoplankton remain unclear and so the aim of these experiments is to increase the understanding of these affects. This dataset was generated by scientists at the National Oceanography Centre, Southampton under the National Environment Research Council (NERC) Grant Reference: NE/W004933/1.

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