Can Organisms Regulate Global Biogeochemical Cycles?
Résumé
Global biogeochemical cycles are being profoundlyaffected by human activities; therefore, it is criticalto understand the role played by organisms in theirregulation. Autotrophic organisms can regulatenutrient abundance at local scales through resourceconsumption, but most resources are inaccessible tothem at global scales, either because of physicalbarriers or because of the presence of non-assimil-able chemical forms of nutrients. Here we present ageneric model of resource access limitation andapply it to the oceanic cycles of iron, phosphorus,and silicon to examine whether phytoplankton canregulate the concentrations of these key nutrients.Our model predicts that autotrophs cannot at thesame time strongly impact accessible nutrients andexert perfect regulation on inaccessible nutrients.We show that the ability of organisms to regulateinaccessible nutrient pools strongly depends onpassive physical and chemical flows, and on thefraction of the system that is accessible to organ-isms. Components of global climate change such asincreasing water column stratification might resultin a further decrease of the biotic regulation ofinaccessible nutrients in freshwater and marinesystems.