Mixotrophy everywhere on land and in water: the grand écart hypothesis
Résumé
There is increasing awareness that many terrestrial and aquatic organisms are not strictly heterotrophic or autotrophic but rather mixotrophic. Mixotrophy is an intermediate nutritional strategy, merging autotrophy and heterotrophy to acquire organic carbon and/or other elements, mainly N, P or Fe. We show that both terrestrial and aquatic mixotrophs fall into three categories, namely necrotrophic (where autotrophs prey on other organisms), biotrophic (where heterotrophs gain autotrophy by symbiosis), and absorbotrophic (where autotrophs take up environmental organic molecules). Here we discuss their physiological and ecological relevance since mixotrophy is found in virtually every ecosystem and occurs across the whole eukaryotic phylogeny, suggesting an evolutionary pressure towards mixotrophy. Ecosystem dynamics tend to separate light from non-carbon nutrients (N and P resources): the biological pump and water stratification in aquatic ecosystems deplete non-carbon nutrients from the photic zone, while terrestrial plant successions create a canopy layer with light but devoid of non-carbon soil nutrients. In both aquatic and terrestrial environments organisms, face a grand-écart (dancer’s splits, i.e. i.e. the need to reconcile two opposing needs) between optimal conditions for photosynthesis versus gain of non-C elements. We suggest that mixotrophy allows adaptation
of organisms to such environmental gradients, ultimately explaining why mixotrophic behaviors are widespread
Origine : Fichiers produits par l'(les) auteur(s)
Licence : Domaine public
Licence : Domaine public