The effects of cell size on the C:N:P of phytoplankton

Abstract

Phytoplankton are the primary producers of the global ocean and their elemental stoichiometry (C:N:P) is a central feature of their ecology and biogeochemistry. Understanding the underlying mechanics of phytoplankton C:N:P variation is a key focus of marine biogeochemistry study. We used four diatom species of different sizes, Thalassiosira pseudonana, Thalassiosira weissflogii, Odontella mobiliensis, and Stephanopyxis palmeriana, to investigate how intracellular C:N:P varies with cell volume and determine the biochemical basis of that variation. To do this, we measured the main macromolecular components of C, N, and P in addition to the cellular quotas for these element in all four species during growth at near-optimal, nutrient replete conditions. This study found a negative relationship of C:P and N:P to cell volume that is supported by clear macromolecular mechanisms. This relationship is reflected by larger size-scaling exponents of P relative to C and N. As cell volume increased, species allocated relatively more N and P to residual pools and less to biosynthesis as represented by protein, RNA, and chl a. This study demonstrates that C:N:P variation and P-allocation across a size spectrum reflects a tradeoff between biosynthesis and storage.