Chapitre 8. Dynamique de stockage du carbone dans les sols du Sénégal

Introduction Au Sénégal, la dynamique de stockage du carbone dans les sols est souvent estimée par des approches de modélisation (Tschakert et al., 2004 ; Parton et al., 2004 ; Woomer et al., 2004 ; Lufafa et al., 2008 ; Stoorvogel et al., 2009 ; Dièye et al., 2012 ; Touré et al., 2013 ; Loum et al., 2014). Quelques études expérimentales ont également été réalisées (Elberling et al., 2003 ; Manlay et al., 2002 ; Masse et al., 2004). La teneur des sols en carbone est généralement faible, de mo..

Carbone des sols en Afrique

Les sols sont une ressource essentielle à préserver pour la production d’aliments, de fibres, de biomasse, pour la filtration de l’eau, la préservation de la biodiversité et le stockage du carbone. En tant que réservoirs de carbone, les sols sont par ailleurs appelés à jouer un rôle primordial dans la lutte contre l’augmentation de la concentration de gaz à effet de serre. Ils sont ainsi au centre des objectifs de développement durable (ODD) des Nations unies, notamment les ODD 2 « Faim zéro », 13 « Lutte contre le changement climatique », 15 « Vie terrestre », 12 « Consommation et production responsables » ou encore 1 « Pas de pauvreté ». Cet ouvrage présente un état des lieux des sols africains dans toute leur diversité, mais au-delà, il documente les capacités de stockage de carbone selon les types de sols et leurs usages en Afrique. Il propose également des recommandations autour de l’acquisition et de l’interprétation des données, ainsi que des options pour préserver, voire augmenter les stocks de carbone dans les sols. Tous les chercheurs et acteurs du développement impliqués dans les recherches sur le rôle du carbone des sols sont concernés par cette synthèse collective. Fruit d’une collaboration entre chercheurs africains et européens, ce livre insiste sur la nécessité de prendre en compte la grande variété des contextes agricoles et forestiers africains pour améliorer nos connaissances sur les capacités de stockage de carbone des sols et lutter contre le changement climatique

Correlation between soil erosion and satellite data on areas of current desertification : a case study in Senegal

International audienceThe purpose of the study is to verify whether some correlation exists between soil erodibility (i.e. K factor mentioned in RUSLE model) and data obtained from satellite images. This piece of work represents a first attempt towards a model that would predict the risk for soil erosion, from information contained in satellite images. Ouarchoch is a rural community in Ferlo Region, Senegal. It lies in a Sahelian typical arid zone and is affected by desertification processes. Ouarchoch site was the pilot area on which the test was performed. K factor was calculated by using soil textural data (sand, silt and clay) in the top (0 &8211; 5 cm) soil layer (data obtained from the web). Landsat7 satellite images represented different seasonal snapshots ("cool" dry season, warm dry season, rainy season, end of rainy season or beginning of dry season) of the same year, 2014. Calculation used Bands 1 to 7 and Normalized Difference Vegetation Index (NDVI). The choice of data, calculation and analysis are detailed. Some positive moderate correlation exists between soil erodibility on the one hand, and NDVI index displayed during the dry season (images in January and May), as well as Band 5 radiations displayed at the beginning of the dry season (post-harvest, image in October) on the other hand

SNPs on ABC Transporters and in vivo Malaria Parasite Non Clearance after Chloroquine Treatment in Malian Children

Background: pfcrt K76T mutation was demonstrated to play a central role in the P. falciparum resistance to chloroquine. Aim: To find any association between mutant alleles of pfcrt K76T, pfmdr1 N86Y, pfG30 and pfG47 and the in vivo parasite non clearance after chloroquine treatment in Mali. Methodology: We carried out a chloroquine efficacy study in 196 children suffering from uncomplicated malaria in a rural village of Kollé, Mali, using WHO protocol. Subjects were treated with standard dose of chloroquine and followed for 14 days. Parasite DNA was extracted from finger prick blood blotted onto filter paper and genotypes were analyzed by different PCR methods. Results: The mutant alleles pfcrt 76T and pfmdr1 86Y were associated with parasite non clearance with p=0.00001 and 0.03 respectively. However, the association of SNPs on pfG30 and pfG47 genes with parasite non clearance was not statistically significant, p =0.43 and 0.57 respectively. The logistic regression analysis showed that the mutant allele pfmdr186Y contributed positively to the pfcrt 76T parasites non clearance (p=0.02). Conclusion: These findings have shown that pfcrt76T and pfmdr1 86Y alleles are associated with the in vivo parasite non clearance, but not SNPs on the new putative transporters genes

The Essential oil of Eucalyptus alba L. Growing on the Salt Zone of Fatick (Senegal) as a Source of 1,8Cineole and Their Antibacterial Activity

Members of the genus Eucalyptus are potential sources of number of commercial essential oils and aromachemicals. In present study, the essential oils isolated by hydrodistillation from the leaves of Eucalyptus alba were analyzed by GC-FID and GC-MS. Essential oil yields ranged from 2.41 to 4.35%. In total 18 constituents were identified, accounting for 99.0 to 99.7% of the total compositions. 1,8-cineole was present in all samples as the major component (76.5-88.1%). In addition to this compound, others that were found including limonene (3.8–8.6%), α-terpineol (1.4–2.8%), globulol (1.3–6.3%) and α-pinene (1.5–1.8%). The essential oil showed a strong antibacterial activity against S. aureus ATCC 29213 which is translated by an MIC of 1.25 mg/mL and good activity against E. coli ATCC 25922 (6.25 mg/mL) and E. faecalis ATCC 29212 (6.25 mg/mL). To our knowledge, our study is the first report of E. alba essential oils characterized by a high 1,8-cineole content (>76.5%). They may have potential applications in food and pharmaceutical products. Keywords: Eucalyptus alba, essential oils, antibacterial activity, 1,8-cineole and GC-S

Grass Physiognomic Trait Variation in African Herbaceous Biomes

International audienceAfrican herbaceous biomes will likely face drastic changes in the near future, due to climate change and pressures from increasing human activities. However, these biomes have been simulated only by dynamic global vegetation models and failing to include the diversity of C 4 grasses has limited the accuracy of these models. Characterizing the floristic and physiognomic diversity of these herbaceous biomes would enhance the parameterization of C 4 grass plant functional types, thereby improving simulations. To this end, we used low-ermost and uppermost values of three grass physiognomic traits (culm height, leaf length, and leaf width) available in most floras to identify several grass physiognomic groups that form the grass cover in Senegal. We then checked the capacity of these groups to discriminate herbaceous biomes and mean annual precipitation domains. Specifically, we assessed whether these groups were sufficiently generic and robust to be applied to neighboring (Chad) and distant (South Africa) phytogeographic areas. The proportions of two phys-iognomic groups, defined by their lowermost limits, delineate steppe from savanna and forest biomes in Senegal, and nama-karoo, savanna, and grassland biomes in South Africa. Proportions of these two physiognomic groups additionally delineate the mean annual precipitation domains 600 mm in Senegal, Chad, and South Africa, as well as the 1000 mm domains in South Africa. These findings should help to identify and parameterize new C 4 grass plant functional types in vegetation models applied to West and South Africa

Low infectivity of Plasmodium falciparum gametocytes to Anopheles gambiae following treatment with sulfadoxine-pyrimethamine in Mali

Sulfadoxine-pyrimethamine (SP) treatment increases the rate of gametocyte carriage and selects SP resistance-conferring mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS), raising concerns of increased malaria transmission and spread of drug resistance. In a setting in Mali where SP was highly efficacious, we measured the prevalence of DHFR and DHPS mutations in P. falciparum infections with microscopy-detected gametocytes following SP treatment, and used direct feeding to assess infectivity to Anopheles gambiae sensu lato. Children and young adults presenting with uncomplicated malaria were treated with SP or chloroquine and followed for 28 days. Gametocyte carriage peaked at 67% 1 week after treatment with a single dose of SP. Those post-SP gametocytes carried significantly more DHFR and DHPS mutations than pre-treatment asexual parasites from the same population. Only 0.5% of 1728 mosquitoes fed on SP-treated gametocyte carriers developed oocysts, while 11% of 198 mosquitoes fed on chloroquine-treated gametocyte carriers were positive for oocysts. This study shows that in an area of high SP efficacy, although SP treatment sharply increased gametocyte carriage, the infectiousness of these gametocytes to the vector may be very low. Accurate and robust methods for measuring infectivity are needed to guide malaria control interventions that affect transmission