In the monocultures of two algal species, i.e., Phaeodactylum tricornutum (Bacillariophyceae; strain MACC/B254) and Prorocentrum minimum (Dinophyceae; strain HYESL63), we investigated responses of lipid biomarkers (sterols and fatty acids (FAs)) to different temperatures (12, 18 and 24℃), nitrogen and phosphorus concentrations and their molar ratios (N:P ratios) of 10:1, 24:1 and 63:1. Algal cells were counted daily with an improved Neubauer hemacytometer (Glaswarenfabrik Karl Hecht GmbH) under a microscope (Olympus CX41). To analyze particulate organic carbon (POC), sterols and FAs, algal cells at steady-state conditions were harvested on pre-combusted GF/F filters (Whatman) after filtering 15-30 mL of cultures depending on cell density in the culture flask and the parameters to be determined. Samples were kept at − 80℃ after filtration. POC was determined by an elemental analyzer (Thermo Flash 2000) (Sharp 1974, https://doi.org/10.4319/lo.1974.19.6.0984). Sterols and FAs were analyzed according to the methods in Eglinton et al. (1996 https://doi.org/10.1021/ac9508513), Galy et al. (2011, https://doi.org/10.1016/j.epsl.2011.02.003) and Zhao et al. (2006, https://doi.org/10.1016/j.orggeochem.2005.08.022). The trimethylsilyl ether derivatives of sterols and fatty acid methyl esters (FAMEs) were analyzed in a gas chromatograph (Agilent Technologies 8890A) equipped with a flame ionization detector, and a HP-1 column (50 m, 0.32 mm i.d., 0.17 μm film; Agilent J&W) and a SP-2560 column (100 m, 0.25 mm i.d., 0.20 μm film; Supelco) for sterol and FAME analysis, respectively. The identification of sterols was performed by gas chromatography-mass spectrometry (GC-MS) analysis at 70 eV using an Agilent 7890B GC (HP-5MS column; 30 m, 0.25 mm i.d., 0.25 μm film; Agilent J&W) connected to an Agilent MSD 5977B mass selective detector (ion source temperature 230℃). Sterols were identified be comparison of the mass spectra of their trimethylsilyl ether derivatives to those of published GC-MS values (Lisboa et al. 1982, https://doi.org/10.1016/0305-0491(82)90281-4; Taipale et al. 2016, https://doi.org/10.3389/fpls.2016.00212), based on the molecular ion and prominent ions. The following sterols were identified: brassicasterol/epi-brassicasterol,and dinosterol. FAs were identified with reference to the standard Supelco 37 component FAME mixture. C-normalized (on a per POC basis; μg mg C-1) and per-cell (pg cell-1) contents of sterols and FAs were presented, and FA proportions (% of total fatty acids (TFAs)) were also reported in the dataset.

This study was financially supported by Laoshan Laboratory (grant number LSKJ202204005) and the National Natural Science Foundation of China (grant numbers 41876118).