Search results for "ABONDANCE"
showing 10 items of 12 documents
Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates
2012
Marine N<sub>2</sub> fixing microorganisms, termed diazotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen (N<sub>2</sub>) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic …
Variations spatiales et temporelles des communautés adventices des cultures annuelles en France
2007
Although arable weed species are particularly well adapted to habitats characterised by high levels of disturbance(ploughing, harvest), the degree and rate at which agro-ecosytems have been transformed in the last 50 years in Europe(use of chemicals, changes in crop rotations) has led to profound changes in the composition and diversity of arable weedcommunities. This thesis provides an update on the composition and diversity of weed communities that can be foundacross the main crop types and regions of France. It also addresses two objectives i) applying (community) ecologytheories for the analysis and interpretation of spatial and temporal variations in weed communities and ii) using the …
Direct seeding mulch-based cropping increases both the activity and the abundance of denitrifier communities in a tropical soil
2009
International audience; This study evaluated the impact of direct seeding mulch-based cropping (DMC), as an alternative to conventional tilling (CT), on a functional community involved in N cycling and emission of greenhouse gas nitrous oxide (N2O). The study was carried out for annual soybean/rice crop rotation in the Highlands of Madagascar. The differences between the two soil management strategies (direct seeding with mulched crop residues versus tillage without incorporation of crop residues) were studied along a fertilization gradient (no fertilizer, organic fertilizer, organic plus mineral fertilizers). The activity and size of the denitrifier community were determined by denitrifica…
Utilization of microbial abundance and diversity as indicators of the origin of soil aggregates produced by earthworms
2013
This study aimed at testing the capability of microbial community structure and abundance to be used as bioindicators of the origin of earthworm cast aggregates. Compact surface casts produced by Amynthas khami and surrounding aggregates lacking visible signs of biological activity (control) were left to disaggregate by natural rainfall and separated into four size classes (5-2, 2-0.5, 0.5-0.25 and <0.25 mm). The genetic structure and the abundance of the bacterial and fungal communities were characterized using B- and F-ARISA fingerprinting approach and quantitative PCR directly from DNA extracted from soil. Bacteria and to a lesser extent fungi were more abundant in casts than in control …
La Grive à Pieds Jaunes, Turdus lherminieri (Turdidés): une espèce méconnue à valeur patrimoniale.
2013
10 pages; National audience; Les départements et régions d’Outre-Mer présentent une biodiversité remarquable et un fort taux d’endémisme,mais cet endémisme a pour conséquence une plus grande fragilité et un plus grand risque d’extinction. Les enjeuxde conservation de la biodiversité sont alors importants et l’élaboration de mesures de gestion se heurte biensouvent à une profonde méconnaissance de la biologie des espèces. Dans ce contexte, la Grive à Pieds Jaunes,oiseau endémique de quatre îles des Petites Antilles (statut vulnérable, UICN) est un modèle de choix dans la miseen place de mesures de gestion et de conservation. Les premiers résultats d’un programme d’étude dédié à cetteespèce o…
Indicateurs pour l'évaluation de l'impact de produits phytosanitaires sur la composante microbienne de la qualité biologique des sols
2011
National audience
Variations spatiales et temporelles de communautés adventices des cultures annuelles en France
2010
Résumé de thèse; National audience
Biovigilance flore adventice le point dans trois bassins de production de colza
2013
EA SPE EcolDur; National audience
Connaître les sols français pour mieux les gérer
2012
National audience
Gestion territoriale des adventices : effets des propriétés du paysage sur les communautés adventices et sur leur régulation par les carabidae
2015
Landscape-scale management is known to affect pest and biodiversity levels in agroecosystems. Here, we focus on the lanscape drivers of arable weeds, first by reviewing evidence of direct landscape effects on weed species richness and abundance and then by analyzing current knowledge on landscape effects on carabids, which are well-known weed seed predators that contribute to the biological regulation of weeds. Our analysis shows that (i) heterogeneous landscapes usually harbor higher species richness and more diversified communities than simple ones, (ii) total weed and carabid abundances appear seldomly affected by the landscape context of arable fields and (iii) weed seed predation in fi…