Temperature and the biogeography of algal stoichiometry

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AbstractAimThe average carbon‐to‐nitrogen‐to‐phosphorus ratio (C:N:P) of marine algae is known to be tightly coupled to that of the inorganic pools of C, N and P in the ocean interior (i.e. the Redfield ratio), and therefore plays a key role in regulating the C and N cycles in the ocean. The C:N:P ratio of algae also varies substantially, both within and among taxa, in response to variation in the abiotic environment, raising the possibility that biogeochemical controls on the marine C and N cycles may shift as a result of climate change. However, the role of temperature in driving phenotypic variation in stoichiometry within algal taxa, as well as biogeographic variation in particulate C, N and P among oceanic regions, remains largely unresolved.LocationGlobal.MethodsTo assess the extent to which temperature controls algal stoichiometry we performed two complementary meta‐analyses. First, we characterized the global temperature dependence of algal stoichiometry by analysing field data that encompassed 767 estimates of C:N:P from 22 oceanic sites spanning over 130° of latitude. Second, we characterized the within‐species acclimation responses of C:N:P stoichiometry to temperature by analysing data that encompassed 17 experiments, 9 species and 4 taxonomic classes.ResultsThe geographic analyses demonstrated that the N:P and C:P ratios of marine algae were best predicted by latitudinal variation in average sea‐surface temperature, and that both ratios increased 2.6‐fold from 0 to 30 °C. These global‐scale temperature responses, which largely reflect geographic variation in the species compositions of algal assemblages, were of similar magnitude to the average within‐species response of the N:P and C:P ratios to experimental temperature manipulations.Main conclusionsThe congruence between field and experimental observations suggests that temperature‐dependent physiological mechanisms operating at the subcellular level play an important role in determining the stoichiometry of algae in the world's oceans.