Abstract. The elemental stoichiometry of marine phytoplankton plays
a critical role in global biogeochemical cycles through its impact on
nutrient cycling, secondary production, and carbon export. Although
extensive laboratory experiments have been carried out over the years to
assess the influence of different environmental drivers on the elemental
composition of phytoplankton, a comprehensive quantitative assessment of the
processes is still lacking. Here, we synthesized the responses of P:C and
N:C ratios of marine phytoplankton to five major drivers (inorganic
phosphorus, inorganic nitrogen, inorganic iron, irradiance, and temperature)
by a meta-analysis of experimental data across 366 experiments from 104
journal articles. Our results show that the response of these ratios to
changes in macronutrients is consistent across all the studies, where the
increase in nutrient availability is positively related to changes in P:C
and N:C ratios. We found that eukaryotic phytoplankton are more sensitive to
the changes in macronutrients compared to prokaryotes, possibly due to their
larger cell size and their abilities to regulate their gene expression
patterns quickly. The effect of irradiance was significant and constant
across all studies, where an increase in irradiance decreased both P:C and
N:C. The P:C ratio decreased significantly with warming, but the response to
temperature changes was mixed depending on the culture growth mode and the
growth phase at the time of harvest. Along with other oceanographic
conditions of the subtropical gyres (e.g., low macronutrient availability),
the elevated temperature may explain why P:C is consistently low in
subtropical oceans. Iron addition did not systematically change either P:C
or N:C. Overall, our findings highlight the high stoichiometric plasticity
of eukaryotes and the importance of macronutrients in determining P:C and
N:C ratios, which both provide us insights on how to understand and model
plankton diversity and productivity.
A meta-analysis on environmental drivers of marine phytoplankton C : N : P