On each sampling day, samples for cellular particulate organic carbon and nitrogen (POC and PON, respectively, μg L−1), dry weight (DW, mg L−1) and total lipids (% w/w) were taken.
For POC and PON analyses, duplicate samples were filtered onto acid-washed and precombusted Whatman GF/F glass fibre filters and dried at room temperature in darkness. The samples were analyzed with a Roboprep/Tracermass mass spectrometer (Europa Scientific, UK). From the results, C/N weight ratios were obtained.
For DW determinations, duplicate samples were filtered onto precombusted (450 °C, 4 h) and preweighed Whatman GF/F glass fibre filters and stored at room temperature in darkness. The filters with the samples were weighed after drying them at 60 °C overnight.
For total lipid analyses, cells were harvested (i.e. 0.1‒0.4 mg of wet weight) by centrifugation, and the pellets were stored at −80 °C prior to the analyses. The total lipid content (% mg/mg DW) of the samples was determined by disrupting the cells and extracting the fatty acids with chloroform. The fatty acids were determined using transmethylation and gas chromatography (GC) with flame ionization detector (FID) according to Spilling et al. (2013 (link)). The total lipid concentrations (mg L−1) were obtained by multiplying the total lipid contents (% w/w) by the analyzed DW (mg L−1) values.
For POC and PON analyses, duplicate samples were filtered onto acid-washed and precombusted Whatman GF/F glass fibre filters and dried at room temperature in darkness. The samples were analyzed with a Roboprep/Tracermass mass spectrometer (Europa Scientific, UK). From the results, C/N weight ratios were obtained.
For DW determinations, duplicate samples were filtered onto precombusted (450 °C, 4 h) and preweighed Whatman GF/F glass fibre filters and stored at room temperature in darkness. The filters with the samples were weighed after drying them at 60 °C overnight.
For total lipid analyses, cells were harvested (i.e. 0.1‒0.4 mg of wet weight) by centrifugation, and the pellets were stored at −80 °C prior to the analyses. The total lipid content (% mg/mg DW) of the samples was determined by disrupting the cells and extracting the fatty acids with chloroform. The fatty acids were determined using transmethylation and gas chromatography (GC) with flame ionization detector (FID) according to Spilling et al. (2013 (link)). The total lipid concentrations (mg L−1) were obtained by multiplying the total lipid contents (% w/w) by the analyzed DW (mg L−1) values.