Jeudi 2 juin - The long unnoticed marine diazotrophs and their current biogeochemical impact
Jun 02, 2016
from 11:00 AM to 12:00 PM
Sophie Rabouille, LOV
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Laboratoire d'Océanographie de Villefranche (LOV)
Title : The long unnoticed marine diazotrophs and their current biogeochemical impact.
Diazotrophic organisms are able to fix atmospheric nitrogen (N2) and use it for growth, which makes them virtually independent from the nitrogen resource. The democratization of molecular techniques in the past two decades has revealed how diverse diazotrophs were in the natural environment. Cyanobacteria are currently seen as the main nitrogen fixers in the marine environment. As in situ abundance data are made available, their biogeochemical role is getting widely acknowledged. Diazotrophic cyanobacteria participate in both carbon and nitrogen input. Conceptualy, they represent an important link in the coupling of oceanic carbon and nitrogen cycles. Nonetheless, a large uncertainty still remains on the actual numbers: how much nitrogen is fixed in the global ocean? The process of N2 fixation is still unsung, because non trivial to quantify. Combining theory and laboratory experiments are an efficient way to picture the control that forcing conditions exert on the metabolism, and hence on populations, at different spatial and/or temporal scales. Examples will be developed on the growth efficiency of marine, diazotrophic cyanobacteria and their consequent carbon and nitrogen fluxes at the scale of the population. The information acquired on growth processes is then gathered into models, whose implementation and simulations draw a mechanistic understanding and representation of the growth dynamics. Models can then be used to infer and quantify the responses under a very wide range of environmental conditions.