Intraspecific variability in cell size and nutrient uptake-related traits of Chaetoceros affinis in different nutrient regimes

Intraspecific trait variability can determine how phytoplankton species respond to environmental changes, and ultimately can influence the food web structure in aquatic ecosystems. In this study, we individually incubated each of nine genotypes of the diatom Chaetoceros affinis in seven different nitrate regimes, spanning a gradient from nitrate limitation (2.5N:1P) over Redfield ratio to phosphate limitation (40N:1P). After seven days, we measured cell size, cellular carbon (POC) and nitrogen (PON) contents, stoichiometry (nitrogen to phosphorus ratio, N:P, and carbon to nitrogen ratio, C:N) as well as their potential correlations in each treatment. The aim was to investigate, if changes in cell size along the nitrate gradient determined variations in cellular nutrients and stoichiometry at two intraspecific levels, i.e. the inter- and intragenotypic level. According to preliminary results, cell size correlated positively with C:N at both levels of intraspecific variability, positively with POC at the intergenotypic level, and negatively with PON at the intragenotypic level. This translated into larger cells accumulated more C than N under stoichiometrically N-limited conditions. These findings add insights on the importance of intraspecific cell size variability on cellular nutrients and stoichiometry along nutrient gradients, highlighting the need to study intraspecific dynamics both among and within genotypes.