The provided data represent maximum growth rates of the temperate diatom Thalassiosira rotula obtained from the Harder Lab (University of Bremen; strain T. rotula_S16) and the polar diatom Thalassiosira gravida was obtained from the Norwegian culture collection of algae (NORCCA strain number UIO 478). Data were assessed in a nanocosm (microtiter-plate) 7-day multi-stressor laboratory experiment conducted in November 2022. The experimental design includes different combinations of temperature (4°C; 9°C; 13.5°C), photoperiod (4:20; 16:8; 24:0) and microbiome presence (xenic; axenic) at which growth was assessed to evaluate interactive effects of abiotic factors (temperature & photoperiod) and biotic facors (interactions with microbiome bacteria). Moreover, the code to process the data for statistical analysis is provided.

Diatom cultures were pre-acclimatized to experimental conditions for 7 days by inoculating 40 ml batch cultures with 500 cells ml^-1 (2000 cells ml^-1 for treatments with 4h photoperiod to obtain sufficient biomass) which were grown at each of the nine treatment conditions to allow acclimatization of fluorophores. The actual subsequent multifactorial experiment was conducted in white 96-well plates (Greiner, Germany) with 300 µl experimental units and 48 replicates per treatment. After chlorophyll-a fluorescence of the acclimatized stock cultures was measured with a photo-spectrometric plate reader (ClarioStar Plus BMG Labtech, excitation 440 nm, emission 680 nm) plates were inoculated at twice the initial fluorescence units of the blank values measured in the growth medium. To maintain sterile conditions, the 96-well plates were sealed with a gas-permeable membrane (Breathe-Easy, Sigma-Aldrich, United States). Plates were incubated in climate cabinets at the respective experimental temperature and were placed onto LED tables emitting 50 µmol m^-2 s^-1 under the photoperiod settings above. Fluorescence intensity was measured daily at the same time after 5 minutes of dark acclimation and the experiment was terminated after seven days. After blank values of fluorescence in the growth medium were subtracted from the experimental fluorescence data, maximum growth rates (µ_max) were calculated for each experimental unit by fitting non-linear models to the data using the “growthrates” package (Petzoldt, 2020).

The dataset (plateassay_growthrates.xlsx) can be opened with Excel and the code for running the statistical analysis is an R script (giesler23.r).