Variability in cellular elemental stoichiometry among several major lineages of marine eukaryotic phytoplankton

Marine biota has a strong influence on the biogeochemical cycling of the macronutrient elements carbon, nitrogen and phosphorus (C,N,P). Previous data suggest that eukaryotic phytoplankton lineages that thrive in cold water environments, like diatoms, have low C:P_cell and N:P_cell in comparison with lineages that inhabit warmer waters. We asked how the elemental composition of 30 photosynthetic eukaryotes isolated from several lineages of marine phytoplankton that grow in multiple biogeographical provinces, is linked to phylogeny, growth rate, temperature, and cell size. Although the data suggest wide stoichiometric variability within specific classes, our model indicated that growth rate and temperature had significant negative and positive relationships, respectively, with C:P_cell, and N:P_cell, and that cell size only had a significant effect on C:N_cell. The C:P_cell and N:P_cell of Prymnesiophyceae was significantly higher than those of Mamiellophyceae (P < 0.05), but in general, our data suggest that these elemental ratios were not significantly different among the classes of phytoplankton analyzed, in contrast to prior findings. For all isolates, mean C:P_cell, (107.5), N:P_cell (16.3) and C:N_cell (6.7) were close to Redfield ratios. Overall, our data support current hypotheses that predict how temperature and growth rate might affect cellular elemental stoichiometry of eukaryotic phytoplankton.