Caractérisation et Evolution du Peuplement Ligneux du Bois de Boulogne du Centre Nationale de Recherches Agronomiques (CNRA) de Bambey (Diourbel/Sénégal)

Le Sénégal à l’instar des autres pays sahéliens, est confronté à la dégradation de ses espaces forestiers dû à un ensemble de facteurs tels que : les défrichements agricoles, les feux tardifs, l’exploitation anarchique, etc. Des travaux d’inventaires ont été réalisés dans la formation boisée (Bois de Boulogne) du Centre National de Recherches Agronomiques de Bambey. L’étude vise à évaluer le potentiel ligneux du Bois soumis à forte pression anthropique dans le but de donner des recommandations. Un inventaire systématique sur 103 placettes de 50 X 50 m est réalisé en 2018. Les paramètres recherchés sont : la richesse spécifique, la densité, la surface terrière, le volume, le couvert aérien, la régénération, la structure horizontale et verticale, les observations sur l’émondage, le vieillissement, etc. Ainsi, 28 espèces de 13 familles ont été recensées. Mimosaceae et Combretaceae domine la végétation. Pour les individus adultes, la densité est de 98 individus/ha, dominée par Acacia seyal, tandis que la régénération s’élève à 581 plantules/ha, dominée par Combretum aculeatum. La surface terrière du peuplement est estimée à 2,12 m2/ha, le couvert aérien (3223,08 m2/ha) et le volume (13,83 m3/ha). La distribution du peuplement par classe de diamètre et de hauteur révèle la prédominance de la strate arbustive. Les observations ont montré la présence de pratiques anthropiques. Cette étude a permis de recenser la flore du Bois, d’évaluer le potentiel ligneux et de remarquer l’anthropisation, d’où la nécessité de mettre en place une stratégie de gestion pour la conservation et la restauration du couvert végétale.   Senegal, like other Sahelian countries, is faced forest degradation due to a combination of factors such as: agricultural clearings, late fires, uncontrolled logging, etc. Inventory work has been carried out in the woodland formation (Bois de Boulogne) of the Centre National de Recherches Agronomiques de Bambey. The aim of the study was to assess the woody potential of the Bois, which is under heavy human pressure, with a view to making recommendations. A systematic inventory on 103 plots of 50 X 50 m is carried out in 2018. The parameters sought are: species richness, density, basal area, volume, aerial cover, regeneration, horizontal and vertical structure, observations on pruning, ageing, etc. A total of 28 species from 13 families were recorded. Mimosaceae and Combretaceae dominate the vegetation. Adult density is 98 individuals/ha, dominated by Acacia seyal, while regeneration is 581 seedlings/ha, dominated by Combretum aculeatum. Stand basal area is estimated at 2.12 m2/ha, aerial cover (3223.08 m2/ha) and volume (13.83 m3/ha). Stand distribution by diameter and height class reveals the predominance of the shrub layer. Observations revealed the presence of anthropogenic practices. This study enabled us to survey the flora of the wood, assess its woody potential and note its anthropization, hence the need to implement a management strategy for the conservation and restoration of the plant cover

Caractérisation de la Dynamique des Peuplements Ligneux du Centre Nationale de Recherches Agronomiques de Bambey (Diourbel/Sénégal)

Le Sénégal, à l’instar des autres pays sahéliens, est confronté à la dégradation de ses espaces forestiers due à un ensemble de facteurs tels que : les défrichements agricoles, les feux tardifs, l’exploitation anarchique, etc. Ce phénomène est plus accentué dans la région de Diourbel où l’un des très rares poumons verts se trouve dans le site du Centre National de Recherches Agronomiques de Bambey (CNRA). Cette étude avait comme objectifs de caractériser et d’estimer le potentiel des ligneux dans cette formation forestière dans le but de donner formuler des recommandations. Un inventaire systématique sur 103 placettes de 50 X 50 m a été réalisé en 2018. Les paramètres recherchés ont été : la richesse spécifique, la densité du peuplement, la surface terrière, le volume de bois, le couvert aérien, la régénération, la structure horizontale et verticale, les observations sur l’émondage, le vieillissement, etc. Ainsi, 28 espèces appartenants à 13 familles ont été recensées. Les familles des Mimosaceae (28,57%) et des Combretaceae (17,86%) dominent la végétation. Pour les individus adultes, la densité est de 98 individus/ha, dominée par Acacia seyal, tandis que la régénération s’élève à 581 plantules/ha, dominée par Combretum aculeatum. La surface terrière du peuplement est estimée à 2,12 m2/ha, le couvert aérien (3223,08 m2/ha) et le volume (13,83 m3/ha). La distribution du peuplement par classe de diamètre et de hauteur révèle la prédominance de la strate arbustive. Les observations ont montré la présence de pratiques anthropiques qui pourraient contribuer à la régression de la dynamique du peuplement par la diminution du couvert végétal et la disparition de certaines espèces (Deterium microcarpum, Pterocarpus erinaceus et Sterculia setigera) constatée dans cette formation.  Ces résultats montrent l’urgence de mettre en place une stratégie de gestion en étroite collaboration avec les communautés pour la conservation et la restauration du couvert végétale de cette formation boisée de 149 ha.   Senegal, like other Sahelian countries, is faced with the degradation of its forest areas due to a combination of factors such as agricultural clearing, late fires, uncontrolled logging, etc. This phenomenon is more pronounced in the Diourbel region, where one of the very few green lungs is located on the site of the Centre National de Recherches Agronomiques Bambey (CNRA). This phenomenon is more pronounced in the Diourbel region, where one of the very few green lungs can be found on the site of the “Centre National de Recherches Agronomiques de Bambey” (CNRA). The objectives of this study were to characterize and estimate the potential of woody species in this forest formation, to formulate recommendations. A systematic inventory of 103 50 x 50 m plots was carried out in 2018. The parameters investigated were: species richness, stand density, basal area, wood volume, aerial cover, regeneration, horizontal and vertical structure, observations on pruning, aging, etc. A total of 28 species belonging to 13 families were inventoried. Among these families, Mimosaceae (28,57%) and Combretaceae (17,86%) dominate the vegetation. The density of adult trees is 98 individuals/ha, dominated by Acacia seyal, while regeneration amounts to 581 seedlings/ha, dominated by Combretum aculeatum. The basal area of the stand is estimated at 2.12 m2/ha, the aerial cover (3223.08 m2/ha), and the volume (13.83 m3/ha). The distribution of the stand-by diameter and height class reveals the predominance of the shrub layer. Observations revealed the presence of human practices that could be contributing to the decline in stand dynamics through the reduction in plant cover and the disappearance of certain species (Deterium microcarpum, Pterocarpus erinaceus, and Sterculia setigera) observed in this formation. These results show the urgent need to implement a management strategy in close collaboration with the communities to conserve and restore the plant cover of this 149 ha woodland formation

Symbiotic Performance of Diverse Frankia Strains on Salt-Stressed Casuarina glauca and Casuarina equisetifolia Plants

Symbiotic nitrogen-fixing associations between Casuarina trees and the actinobacteria Frankia are widely used in agroforestry in particular for salinized land reclamation. The aim of this study was to analyze the effects of salinity on the establishment of the actinorhizal symbiosis between C. glauca and two contrasting Frankia strains (salt sensitive; CcI3 vs. salt tolerant; CeD) and the role of these isolates in the salt tolerance of C. glauca and C. equisetifolia plants. We show that the number of root nodules decreased with increasing salinity levels in both plants inoculated with CcI3 and CeD. Nodule formation did not occur in seedlings inoculated with CcI3 and CeD, at NaCl concentrations above 100 and 200 mM, respectively. Salinity also affected the early deformation of plant root hairs and reduced their number and size. In addition, expression of symbiotic marker Cg12 gene, which codes for a subtilase, was reduced at 50 mM NaCl. These data suggest that the reduction of nodulation in C. glauca under salt stress is in part due to inhibition of early mechanisms of infection. We also show that prior inoculation of C. glauca and C. equisetifolia with Frankia strains CcI3 and CeD significantly improved plant height, dry biomass, chlorophyll and proline contents at all levels of salinity tested, depending on the Casuarina-Frankia association. There was no correlation between in vitro salt tolerance of Frankia strains and efficiency in planta under salt-stressed conditions. Our results strongly indicate that increased N nutrition, photosynthesis potential and proline accumulation are important factors responsible for salt tolerance of nodulated C. glauca and C. equisetifolia

Permanent Draft Genome Sequences for Mesorhizobium sp. Strains LCM 4576, LCM 4577, and ORS3428, Salt-Tolerant, Nitrogen-Fixing Bacteria Isolated from Senegalese Soils

The genus Mesorhizobium contains many species that are able to form nitrogen-fixing nodules on plants of the legume family. Here, we report the draft genome sequences for three Mesorhizobium strains. The genome sizes of strains LCM 4576, LCM 4577, and ORS3428 were 7.24, 7.02, and 6.55 Mbp, respectively

Permanent Draft Genome Sequence of Rhizobium sp. Strain LCM 4573, a Salt-Tolerant, Nitrogen-Fixing Bacterium Isolated from Senegalese Soils

The genus Rhizobium contains many species that are able to form nitrogen-fixing nodules on plants of the legume family. Here, we report the 5.5-Mb draft genome sequence of the salt-tolerant Rhizobium sp. strain LCM 4573, which has a G+C content of 61.2% and 5,356 candidate protein-encoding genes

Permanent draft genome sequence of Ensifer sp. strain LCM 4579, a salt-tolerant, nitrogen-fixing bacterium isolated from Senegalese soil

The genus Ensifer (formerly Sinorhizobium) contains many species able to form nitrogen-fixing nodules on plants of the legume family. Here, we report the 6.1-Mb draft genome sequence of Ensifer sp. strain LCM 4579, with a G+C content of 62.4% and 5,613 candidate protein-encoding genes

Three-way relationships between gut microbiota, helminth assemblages and bacterial infections in wild rodent populations

Despite its central role in host fitness, the gut microbiota may differ greatly between individuals. This variability is often mediated by environmental or host factors such as diet, genetics, and infections. Recently, particular attention has been given to the interactions between gut bacteriota and helminths, as these latter could affect host susceptibility to other infections. Further studies are still required to better understand the three-way interactions between gut bacteriota, helminths and other parasites, especially because previous findings have been very variable, even for comparable host-parasite systems. In our study, we used the V4 region of the 16S rRNA gene to assess the variability of gut bacteriota diversity and composition in wild populations of a small mammal, the bank vole Myodes glareolus. Four sites were sampled at a regional geographical scale (100 km) along a North-South transect in Eastern France. We applied analyses of community and microbial ecology to evaluate the interactions between the gut bacteriota, the gastro-intestinal helminths and the pathogenic bacteria detected in the spleen. We identified important variations of the gut bacteriota composition and diversity among bank voles. They were mainly explained by sampling localities and reflected the North/South sampling transect. In addition, we detected two main enterotypes, that might correspond to contrasted diets. We found geographic variations of the Firmicutes/Bacteroidetes ratio, that correlated positively with body mass index. We found positive correlations between the specific richness of the gut bacteriota and of the helminth community, as well as between the composition of these two communities, even when accounting for the influence of geographical distance. The helminths Aonchotheca murissylvatici, Heligmosomum mixtum and  the bacteria Bartonella sp were the main taxa associated with the whole gut bacteriota composition. Besides, changes in the relative abundance of particular gut bacteriota taxa were specifically associated with other helminths (Mastophorus muris, Catenotaenia henttoneni, Paranoplocephala omphalodes and Trichuris arvicolae) or pathogenic bacteria. Especially, infections with Neoehrlichia mikurensis, Orientia sp, Rickettsia sp and P. omphalodes were associated with lower relative abundance of the family Erysipelotrichaceae (Firmicutes), while coinfections with higher number of bacterial infections were associated with lower relative abundance of a Bacteroidales family (Bacteroidetes). These results emphasize complex interlinkages between gut bacteriota and infections in wild animal populations. They remain difficult to generalize due to the strong impact of the environment on these interactions, even at regional geographical scales. Abiotic features, as well as small mammal community composition and within host parasite coinfections, should now be considered to better understand the spatial variations observed in the relationships between gut bacteriota, gastro-intestinal helminths and bacterial infections

Parasites and invasions: changes in gastrointestinal helminth assemblages in invasive and native rodents in Senegal

Understanding why some exotic species become widespread and abundant in their colonised range is a fundamental issue that still needs to be addressed. Among many hypotheses, newly established host populations may benefit from a parasite loss ("enemy release" hypothesis) through impoverishment of their original parasite communities or reduced infection levels. Moreover, the fitness of competing native hosts may be negatively affected by the acquisition of exotic taxa from invaders ("parasite spillover") and/or by an increased transmission risk of native parasites due to their amplification by invaders ("parasite spillback"). We focused on gastrointestinal helminth communities to determine whether these predictions could explain the ongoing invasion success of the commensal house mouse (Mus musculus domesticus) and black rat (Rattus rattus), as well as the associated decrease in native Mastomys spp., in Senegal. For both invasive species, our results were consistent with the predictions of the enemy release hypothesis. A decrease in overall gastrointestinal helminth prevalence and infracommunity species richness was observed along the invasion gradients as well as lower specific prevalence/abundance (Aspiculuris tetraptera in Mus musculus domesticus, Hymenolepis diminuta in Rattus rattus) on the invasion fronts. Conversely, we did not find strong evidence of GIH spillover or spillback in invasion fronts, where native and invasive rodents co-occurred. Further experimental research is needed to determine whether and how the loss of gastrointestinal helminths and reduced infection levels along invasion routes may result in any advantageous effects on invader fitness and competitive advantage