Effect of Sulfate Availability on Phytoplankton Stoichiometry

Abstract

SummarySulfur is a key element in multiple metabolic pathways of phytoplankton cells. The effect of environmental S availability on phytoplankton elemental quotas and stoichiometry has been addressed in few studies, using a limited number of species and with contradictory results.Using high-temperature combustion oxidation and X-ray fluorescence methods, we measured the concentrations of micro- and trace elements in monocultures of 20 phytoplankton species, grown with different sulfate concentrations representing those of early and modern oceans.The red lineage species, with higher S requirement and metabolic S fluxes, have higher S content than those of the green lineage, resulting in lower C:S (93) and higher S:P (1.06) than the green lineage species (226 and 0.76, respectively). Zn was the only trace element affected by the environmental concentration of sulfate.Phytoplankton cells respond to different sulfate availability by either increasing Zn or decreasing P quotas, where the P response is more characteristic in the red lineage, and the Zn response is independent of genotypic constraints or plastid type. This study sheds light on a metabolic basis for the expansion of the red lineage algae and their current dominance in ocean waters.Plain language summaryMicroalgae assimilate dissolved sulfate as a source of sulfur, an element that takes part in multiple biochemical pathways and cellular functions. Changes in the concentration of dissolved sulfate in the environment have an effect on the cellular dynamics of several essential biological elements, essencially phosphorus and zinc. The results of this study help to understand the biogeochemical cycling of these elements in the ocean and the dominance of certain phytoplankton lineages.