In March 2023, cell densities of the Arctic diatom Thalassiosira gravida (isolated from the Central Arctic Ocean) were determined to calculate its growth rates at different temperatures and photoperiods in the presence and absence of its natural microbiome. Therefore, a full-factorial experimental design was chosen with two levels of temperature (9°C; 13.5°C) and photoperiod (16h; 24h), to which axenic and xenic diatom cultures were acclimated for one week in climate cabinets prior to the start of the actual growth experiment at a light intensity of 50 µmol photons m-2 s-1. With an initial cell density of 1500 cells/ml, axenic and xenic diatoms were grown under the respective experimental conditions until a cell density of approximately 15000 cells/ml was reached. Cell densities were determined microscopically using an inverted light microscope, following the procedure described in detail in Giesler et al. (2023, 10.3389/fmars.2023.1244639).
This dataset comprises dissolved organic carbon (DOC) concentrations from axenic and xenic cultures of Thalassiosira gravida that were cultivated at the Alfred-Wegener-Institute (Bremerhaven, Germany) in March, 2023. After a cell density of ~ 15.000 cells * mL-1 was reached, cultures were filtered through a 0.2 µm polycarbonate (PC) filter (Whatman) that was cleaned by soaking in 10 % hydrochloric acid (HCl, Merck suprapure) for at least 12 h and subsequently rinsing with ultrapure water (Merck Millipore MilliQ). DOC was quantified by high temperature catalytic oxidation with a Shimadzu TOC analyzer (VCPN-TOC, Shimadzu) according to Garzón-Cardona et al. 2024; doi: 10.1016/J.JMARSYS.2023.103893. Cultures were grown under two temperatures (9 °C, 13.5 °C) and two photoperiods (16:8 h, 24:0 h light:dark). The aim was to investigate responses of algal extracellular release and bacterial DOC transformation to marine heatwave-like conditions.
This dataset comprises dissolved organic matter (DOM) composition from axenic and xenic cultures of Thalassiosira gravida that were cultivated at the Alfred-Wegener-Institute (Bremerhaven, Germany) in March, 2023. After a cell density of ~ 15.000 cells * mL-1 was reached, cultures were filtered through a 0.2 µm polycarbonate (PC) filter (Whatman) that was cleaned by soaking in 10 % hydrochloric acid (HCl, Merck suprapure) for at least 12 h and subsequently rinsing with ultrapure water (Merck Millipore MilliQ). Cultures were grown under two temperatures (9 °C, 13.5 °C) and two photoperiods (16:8 h, 24:0 h light:dark). 2 mL of the sample were filtered through a 0.2 µm regenerated cellulose (RC)-membrane syringe filter (Sartorius) after defrosting. Molecular composition data were acquired with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled to a reversed-phase liquid chromatography (RPLC) with negative electrospray ionization (ESI) according to Lechtenfeld et al., 2024 (doi: 10.1021/acs.est.3c07219). Measurements were performed on on a solariX XR, Bruker Daltonics, Billerica, U.S.A. at the Helmholtz Centre for Environmental Research (UFZ; Leipzig, Germany). Molecular formulas were assigned and filtered using UltraMassExplorer (Leefmann et., 2019; doi: 10.1002/rcm.8315). If the Total ion chromatogram (TIC) was much higher and/or different in certain retention time windows compared to other samples of the same treatment, the sample was excluded from the dataset. The aim of this study was to investigate responses of algal extracellular release and bacterial DOM transformation to marine heatwave-like conditions.
This dataset encompasses maximum growth rates derived from photoperiod reaction norm experiments conducted on Arctic and temperate strains of the diatoms Thalassiosira gravida and Thalassiosira rotula, respectively. The study aimed to investigate the growth response of these strains to varying photoperiods, specifically 1h, 4h, 8h, 16h, and 24h light cycles. The experiments were performed using four Arctic strains of T. gravida at the University of Oslo (from 2022-02-15 to 2022-03-02) and four temperate strains of T. rotula at the University of Trondheim (from 2022-07-09 to 2022-07-18). Prior to the experiment, cultures were maintained in climate chambers under controlled conditions, with Arctic strains kept at 4°C and temperate strains at 15°C, both under a light intensity of 30 µmol photons m⁻²s⁻¹ and a photoperiod of 16:8h light:dark. The photoperiod reaction norms assays were conducted in nanocosm well-plate photobioreactors, allowing for high replication and well-specific programmed light settings. The experimental temperature was set to 9°C for Arctic strains and 16°C for temperate strains, representing the lowest optimum temperatures among the studied genotypes. Cultures were acclimated for seven days before the actual growth experiments, with daily measurements of chlorophyll-a fluorescence intensity using a photo-spectrometric plate reader. The growth rates were calculated using the growthrates package after subtracting the mean blank value of the medium from the measured fluorescence values. The dataset provides valuable insights into the photoperiodic growth responses of T. gravida and T. rotula, which can be crucial for understanding the ecological adaptability of these diatom species.