Search results for "Tree"
showing 10 items of 1841 documents
Biodiversity and characterization of arbuscular mycorrhizal fungi at the molecular level
1994
Biodiversity within a biological group provides the basis for distinguishing members into genera and species according to taxonomic criteria, and between individuals within a species depending on more detailed differences at the genetic level. Diversity between species occurs after a genetic barrier has been created either by a geographic or genetic impedance of gene flow. Divergence can continue by nucleotide substitutions and by mutations in a broader sense (deletions, translocations, duplications), and resulting diversity can be evaluated at the molecular level and used as a phylogenetic character. Diversity at the subspecies level is a function of both mutation rates and gene flow betwe…
Biological nitrogen fixation for the 21st century
1998
The biodiversity of nitrogen-fixing organisms is huge. Taxonomic and phylogenetic research is needed to structure this diversity, to facilitate communication among scientists, and to increase our understanding of the evolution and biology of diazotrophs. Molecular tools for taxonomic and biodiversity studies of diazotrophic rhizobia, frankiae, cyanobacteria and bacilli are presented in sections 2 to 5. Sections 6 to 9 focus on problems with genus and species assignment.
Characterization of a novel selenium methyltransferase from freshwater bacteria showing strong similarities with the calicheamicin methyltransferase
2004
A novel group of Se-methyltransferases is presented. The genetic determinant, named mmtA, which revealed this group was isolated from selenite and selenate-resistant freshwater bacteria. E. coli expressing mmtA and grown with a Se supplement emitted dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Phylogenetic analysis divided MmtA-like bacterial sequences into two clusters, one grouping MmtA with S- and O-methyltransferases, and one grouping UbiE C-methyltransferases. Se methylation by some of these MmtA phyletic neighbours was investigated.
Microbial Community Structure and Density Under Different Tree Species in an Acid Forest Soil (Morvan, France)
2005
Overexploitation of forests to increase wood production has led to the replacement of native forest by large areas of monospecific tree plantations. In the present study, the effects of different monospecific tree cover plantations on density and composition of the indigenous soil microbial community are described. The experimental site of "Breuil-Chenue" in the Morvan (France) was the site of a comparison of a similar mineral soil under Norway spruce (Picea abies), Douglas fir (Pseudotuga menziesii), oak (Quercus sessiflora), and native forest [mixed stand dominated by oak and beech (Fagus sylvatica)]. Sampling was performed during winter (February) at three depths (0-5, 5-10, and 10-15 cm…
Phylogenetic comparison of symbiotic (nodC and nifH) and 16S rRNA genes in strains of Rhizobium, Mesorhizobium and Bradyrhizobium isolated from Astra…
2000
Various studies reported different conclusions on the phylogenetic relationship between symbiotic (nod and nif) and chromosomal (16S rRNA) genes in rhizobia (Haukka et al, 1998). Some studies suggested that the phylogeny of nod genes could be related with the host plant (Ueda et al., 1995). In a previous study, rhizobia (44 isolates) from Astragalus, Oxytropis and Onobrychis pp have been classified into 14 distinct 16S rRNA gene types independently of their host plant and geographic origin. The majority of isolates were classified within the genus Mesorhizobium, and few within Rhizobium and Bradyrhizobium genera (Laguerre et al., 1997). The aim of the present study was to determine the dive…
Simplification d’un modèle complexe pour le développement d’un modèle d’aide à la décision pour la gestion agroécologique de la flore adventice
2019
National audience; Afin de réduire l’utilisation d’herbicides, nous avons besoin de nouveaux outils pour aider à concevoir des stratégies de gestion des adventices économes en herbicides. Dans ce but, nous avons développé un Outil d'Aide à la Décision (OAD) pour la conception de systèmes de culture réconciliant protection des cultures et respect des écosystèmes. La démarche fait intervenir en parallèle le développement de la structure de l’outil en interaction avec les futurs utilisateurs (conseillers et agriculteurs) et une sim-plification du contenu biophysique du modèle FLORSYS concernant les impacts des systèmes de culture et des adventices. FLORSYS est une « parcelle virtuelle », où so…
A mathematical method for determining genome divergence and species delineation using AFLP.
2002
The delineation of bacterial species is presently achieved using direct DNA-DNA relatedness studies of whole genomes. It would be helpful to obtain the same genomically based delineation by indirect methods, provided that descriptions of individual genome composition of bacterial genomes are obtained and included in species descriptions. The amplified fragment length polymorphism (AFLP) technique could provide the necessary data if the nucleotides involved in restriction and amplification are fundamental to the description of genomic divergences. Firstly, in order to verify that AFLP analysis permits a realistic exploration of bacterial genome composition, the strong correspondence between …
Stratégies de lutte contre le charançon rouge du palmier
2018
La communauté scientifique internationale (source : publication FAO d’avril 2017) s’accorde sur l’importance de la combinaison des mesures de lutte en fonction des niveaux d’infestation par le charançon rouge du palmier. Plusieurs mesures de lutte sont disponibles ou envisageables : assainissement mécanique, application d’insecticides à titre préventif ou curatif, piégeage de masse et biocontrôle (lutte biologique sensu stricto). Il est à noter que plusieurs expérimentations sur le biocontrôle sont en cours.Dans la perspective d’améliorer les stratégies de lutte contre le charançon rouge du palmier, il est demandé : 1) d’identifier les stratégies de lutte (en tant que combinaison de différe…
The rebirth of streetcars in the United-States and France
2014
International audience
Towards automated and operational forest inventories with T-Lidar
2011
International audience; Forest inventory automation has become a major issue in forestry. The complexity of the segmentation of 3D point cloud is due to mutual occlusion between trees, other vegetation, or branches. That is why, the applications done until now are limited to the estimation of the DBH (Diameter at Breast Height), the tree height and density estimation. Furthermore other parameters could also be detected, such as volume or species of trees (Reulke and Haala) . . . This paper presents an effective approach for automatic detection, isolation of trees and DBH estimation. Tree isolation is achieved using an innovative approach based on a clustering methodology followed by a skele…