Dataset: Growth, carbon fixation, and nitrogen fixation rates of Trichodesmium erythraeum GBRTRLIN201 and Synechococcus WH8012 from laboratory culture experiments under temperature and nutrient limitation treatments

Culturing Methods

Synechococcus WH8012 and Trichodesmium erythraeum GBRTRLIN201 were isolated from the Sargasso Sea and the North Great Barrier Reef Lagoon, respectively (Waterbury et al. 1986; Bell et al. 2005). Thermal performance curves were established by stepwise acclimation of stock cultures from 28 °C to target temperatures, with approximately 3–4 days of acclimation between sequential transfers to minimize transient stress responses. Synechococcus was grown from 15 to 34 °C and Trichodesmium from 20 to 34 °C, both at 2–3 °C intervals. Triplicate cultures were grown in 0.2 µm-filtered, microwave-sterilized artificial seawater under nutrient-replete (100μM nitrate; 10μM phosphate; 125nM Fe- 25μM EDTA) and N- (7μM nitrate), P- (0.4μM phosphate), or Fe-limited (5nM Fe-25μM EDTA)  conditions (Synechococcus), or replete(10μM phosphate; 250nM Fe- 25μM EDTA), P- (0.4μM phosphate), and Fe-limited (10nM Fe-25μM EDTA) conditions (Trichodesmium). Light was provided at ~40 µmol photons m⁻² s⁻¹ (Synechococcus) and ~150 µmol photons m⁻² s⁻¹ (Trichodesmium) on a 12:12 h light: dark cycle. Cultures were maintained in semi-continuous exponential growth for at least one month, and measurements were conducted after steady-state growth was achieved (Jiang et al., 2018; Qu et al., 2019).

Physiological Analyses

Specific growth rates. Daily growth rates were determined from in vivo chlorophyll a fluorescence measured with a Turner Designs 10-AU fluorometer. Specific growth rates were calculated as µ = ln[N(T1)/N(T0)] / (T1– T0).

Carbon and nitrogen fixation rates. Carbon fixation rates were measured using the 14C-labeled bicarbonate method. Triplicate 30 mL subsamples were incubated for 24 h with added H14CO3- alongside dark controls, then filtered onto GF/F filters, and analyzed by liquid scintillation counting (Beckman LS 6000; Qu et al. 2019). Nitrogen fixation rates were measured by acetylene reduction: 30 mL subsamples were incubated in 75 mL sealed bottles with 2 mL acetylene for 4 h, and ethylene production was quantified by gas chromatography (Shimadzu GC-8A). Procedural blanks were subtracted from all values. Carbon and Nitrogen fixation rates were normalized to particulate organic carbon (POC) and nitrogen (PON), respectively, collected on pre-combusted GF/F filters and analyzed with a Costech elemental analyzer using acetanilide calibration standards (Yang et al., 2021).

This experiment was conducted from March 2024 to April 2025. This period does not include the date when the culture was originally isolated from the field.