Manioc : Portail | resultats 21 - 40 pour la recherche: nitrogen-fixation

Projet de décret portant modifications à la réglementation minière de la Guyane française
Auteur(s) : Gouvernement de la Guyane française
Année de publication :

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La Guadeloupe. Renseignements sur l'Histoire, la Flore, la Faune, la Géologie, la Minéralogie, l'Agriculture, le Commerce, l'Industrie, la Législation, l'Administration. Tome II - 1715-1774
Auteur(s) : Ballet, Jules (1825-1904)
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L'agriculture pratique des pays chauds : Cultures - Elevage, Productions Naturelles, Végétales et Animales. Cinquième année
Auteur(s) : France. Ministère des colonies (1894-1946)
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L'Amérique angloise, ou Description des isles et terres du roi d'Angleterre, dans l'Amérique. Avec de nouvelles cartes de chaque isle & terres
Auteur(s) : Blome, Richard (16..-1705)
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Bulletin officiel de la Guyane française
Année de publication :

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Intriguing diversity among diazotrophic picoplankton along a Mediterranean transect: a dominance of rhizobia
Auteur(s) : Le Moal, Marc Collin, H. Biegala, Isabelle C.

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : The Mediterranean Sea is one of the most oligotrophic marine areas on earth where nitrogen fixation has formally believed to play an important role in carbon and nitrogen fluxes. Although this view is under debate, the diazotrophs responsible for this activity have still not been investigated in the open sea. In this study, we characterised the surface distribution and species richness of unicellular and filamentous diazotrophs across the Mediterranean Sea by combining microscopic counts with size fractionated in situ hybridization (TSA-FISH), and 16S rDNA and nifH genes phylogenies. These genetic analyses were possible owing to the development of a new PCR protocol adapted to scarce microorganisms that can detect as few as 1 cell ml(-1) in cultures. Low concentrations of diazotrophic cyanobacteria were detected and this community was dominated at 99.9% by picoplankton hybridized to the Nitro821 probe, specific for unicellular diazotrophic cyanobacteria (UCYN). Among filamentous cyanobacteria only 0.02 filament ml(-1) of Richelia were detected in the eastern basin, while small (0.7-1.5 mu m) and large (2.5-3.2 mu m) Nitro821-targeted cells were recovered at all stations with a mean concentration of 3.5 cell ml(-1). The affiliation of the small Nitro821-targeted cells to UCYN-A was confirmed by 16S and nifH phylogenies in the western Mediterranean Sea. In the central and the eastern Mediterranean Sea no 16S rDNA and nifH sequence from UCYN was obtained as cells concentration were close to, or below PCR detection limit. Bradyrhizobium sequences dominated nifH clone libraries from picoplanktonic size fractions. A few sequences of gamma-proteobacteria were also detected in the central Mediterranean Sea. While low phosphate and iron concentrations could explain the absence of Trichodesmium sp., the factors that prevent the development of UCYN-B and C remain unknown. We also propose that the dominating picoplankters probably developed specific strategies, such as associations with protists or particles, and/or photosynthetic activity, to acquire carbon for sustaining diazotrophy.
Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2011 , Vol. 8 , N. 3 , P. 827-840

Droits : Author(s) 2011. CC Attribution 3.0 License.
http://archimer.ifremer.fr/doc/00133/24392/22416.pdf
DOI:10.5194/bg-8-827-2011
http://archimer.ifremer.fr/doc/00133/24392/

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