Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few 'hyperdominant' species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region.
ISSN: 2041-1723

hal-01204225
https://hal.archives-ouvertes.fr/hal-01204225
DOI : 10.1038/ncomms7857
PRODINRA : 305614
PUBMED : 25919449

Éditeur(s) : HAL CCSD Landes Bioscience
Résumé : International audience
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
Autophagy

hal-00735751
https://hal.archives-ouvertes.fr/hal-00735751
PUBMED : 22966490

Éditeur(s) : HAL CCSD
Résumé : Eight drill cores cutting through the Mn-carbonate bearing black shales from the Bangombé Plateau were studied. Mn-carbonates (up to 80 m thick) are underlain by laminated pyrite rich shales with organic carbon contents of about 4 wt. % and MnO contents of about 6 wt. %. Mn and Fe, S poor shales are intercalated. Mn-carbonate rich shales (20-29 wt. % MnO) have low contents of phyllosilicates, but are rich in organic carbon (about 7 wt. %) with moderate S contents (about 2 wt. %). All shale facies were deposited in a closed basin through suspension settling and precipitations under anoxic conditions. The Mn-carbonates, towards the top, were formed most likely under suboxic conditions. Pyrite and Mn-carbonates are characterized by bacteriomorphous structures. The latter are composed of micrometric carbonates finely intergrown with clays, quartz and organic matter. They formed around and corroded the dolomite and/or organic matter. Mn-carbonates and pyrite both form also several tenths of micrometer large agglomerates and sub-automorphous grains. The agglomerates can be attributed to evolving diagenesis. Carbonate chemistry varies mainly from rhodochrosite to dolomite. The present results point to primary microbial Mn-carbonate formation. No signs for a Mn-oxide precursor were detected. Slumping and shearing structures, distortion and disruption of thin pyrite beds indicate synsedimentary deformations.
13th Biennial SGA Meeting
Nancy, France

hal-01356155
https://hal.archives-ouvertes.fr/hal-01356155