Dataset: G. huxleyi cell count data from RCC874 and RCC914 N amendment laboratory-based culture experiment

G. huxleyi strains RCC874 and RCC914 were obtained from the Roscoff Culture Collection (RCC). The cultures were transferred from the maintenance stock into artificial seawater (40 g Instant Ocean® Sea Salt per L Milli-Q® water) amended with nutrients, trace metals, and vitamins according to the L1 recipe (https://ncma.bigelow.org/algae-media-recipes) without silica (herein reported as L1-Si). The temperatures were selected to simulate no heat stress (18°C), moderate heat stress (22°C), and high heat stress conditions (25°C and 28°C for RCC874 and RCC914, respectively). The cultures were acclimated to the temperature conditions under a 14:10 light/dark cycle for approximately 10 days prior to the start of the experiment.

Following acclimation, cultures were transferred in triplicate into 2.8 L Fernbach flasks at an initial concentration of 1.0 ✕ 10⁵ cells mL⁻¹. The cultures were divided into two conditions: nitrogen-replete (N replete; L1-Si with standard 8.82 ✕ 10⁻⁴ M NaNO₃) and nitrogen-limited (N limited; L1-Si with 8.82 ✕ 10⁻⁵ M NaNO₃). Cell abundances and optical properties were measured daily using flow cytometry with a BD Accuri C6 Plus equipped with a C-Sampler (BD, USA).