Effect of eucalyptus (Eucalyptus camaldulensis) and maize (Zea mays) litter on growth, development, mycorrhizal colonization and roots nodulation of Arachis hypogaea

In Senegal, farmers often cultivate groundnut in association with eucalyptus plantations to increase their incomes. However eucalyptus plantations produce large amounts of litter, which impact on groundnut has not been clearly elucidated yet. In order to investigate litter accumulation effect on growth, development, and groundnut root infection by arbuscular mycorrhizal fungi (AMF) and rhizobia, a greenhouse experiment was performed. The effect of eucalyptus litter was compared to that maize litter effect at three litter amendments (0, 1 and 5%). Chemical analysis showed that eucalyptus litter differed essentially from maize litter by its high polyphenols content and lower pH. At high amendment (5%), root nodulation and mycorrhizal colonization were significantly reduced with eucalyptus litter whereas no significant differences were observed with maize litter. In addition, groundnut growth, number of flowers per plant, pods yield and leaf mineral contents (N and C) were significantly lower for plant grown in soil highly amended with eucalyptus litter. Plants showed deficiency of chlorophyll content in leaves and were less vigorous compared to treatments without amendment and those amended at 1% level. For all parameters measured, plants grown in soil lowly amended (1%) and plants grown in control treatment did not significantly differ.Key words: Litter, Eucalyptus, Arachis hypogaea, Mycorrhizal symbiosis, Rhizobia

Comparative Study of the West African Continental, Coastal, and Marine Atmospheric Profiles during the Summer of 2006

We used sounding data of the Multidisciplinary Analysis of the African Monsoon experience in summer 2006 at continental and coastal sites of West Africa, respectively, to analyze the vertical profiles of relative humidity, temperature, dew point, and speed and wind direction for the JJAS rainy period. The vertical gradient method is applied to the profiles of some thermodynamic parameters estimated from sounding data to do a comparative study of the structure and thermal properties, moisture, and static stability of the atmospheric boundary layer of inland, coastal, and marine sites to show consistent differences related to geographic factors. In vertical profiles of relative humidity, the intensity is higher in Dakar than in Niamey particularly in the core of the season. There are dry intrusions in the low levels at the beginning and end of the season in Dakar, which do not exist in Niamey. The mixing layer on the continent during the day can reach a height greater than 1100 m, and the inversion layer height can exceed 1700 m. Therefore, the maximum thickness of the boundary layer is observed on the continent during the day, while at night the marine boundary layer is the thickest. The diurnal evolution shows that the mixing layer thickness decreases during the night over the continent but increases at the coast and at sea. In the night at the continental site there is a division of the mixing layer with a consistent residual mixing layer. Continental boundary layer is more unstable during the day, while at night it is the marine boundary layer that is more unstable than the coastal and inland ones

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

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Effets d’application sur le long terme de fertilisants organiques et minéraux sur l’agrégation et les activités microbiennes d’un sol tropical sableux au Burkina Faso

Objectif: L’objectif a été d’étudier l’effet d’une application sur le long terme d’intrants organiques et minéraux sur la formation d’agrégats stables et les activités microbiennes d’un sol tropical sableux du Burkina Faso.Méthodologie et résultats: Ce travail a été réalisé dans l’observatoire de longue durée de la station agronomique de Saria au Burkina Faso. Dans cet essai, les parcelles en monoculture de sorgho (Sorghum bicolor) ont été soumises à des apports ou non d’intrants organiques (Fumier à 10 t ha-1 an-1 et Paille 83 t. ha-1 an-1) et minéraux (Urée à 60 kg N. ha-1 an-1) pendant 27 années. Les teneurs en C, N et P, les agrégats formés, le potentiel de respiration du sol, les activités de la chitinase et la longueur des hyphes fongiques ont été déterminés. Les résultats ont montré que l’apport sur le long terme des résidus organiques entraine une augmentation de la quantité des macro-agrégats (> 2000 μm) comparé au sol témoin. Cependant, cette augmentation ne dépend pas de la qualité des résidus organiques. Les résultats montrent que les macro-agrégats > 2000 μm sont corrélés aux hyphes fongiques, mais pas à l’activité chitinase. L’apport de N minéral exogène entraine une diminution de la macro-agrégation qui résulterait d’une complexation des polyphénols, agents agrégeants dans le processus d’agrégation pour le long terme.Conclusion et application des résultats: Cette étude à long terme confirme nos premiers résultats obtenu sur le cours terme et qui stipulent que la formation des macro-agrégats ne dépend pas de la qualité de résidus organiques. La mesure des hyphes fongiques semble plus déterminante dans la formation des macro-agrégats à long terme, par opposition aux activités fongiques dans le court terme.Mots clés: résidus organiques, N minéral, agrégation, activités fongiques, LixisolEnglish Title: Long-term effect of organic residues and mineral fertilizers on soil aggregation and microbial activities in a tropical sandy soil in Burkina FasoEnglish AbstractObjective: The objective was to study the effect of the long-term application of organic amendments and inorganic fertilizers on the formation and stability of soil aggregates and microbial activities in a tropical sandy soil in Saria (Burkina Faso). The relationships between aggregation, microbial activities and the amendments were discussed.Methodology and results: This study was performed in a long-term (27 years) experimental field in Saria (Burkina Faso) with a continuous sorghum (Sorghum bicolor) cropping system. A randomized block experiment comprising organic amendment (unamended control, straw at 83 t ha−1, manure at 10 t ha−1) coupled with mineral (no urea, urea at 60 kg ha−1) was sampled. Chemical parameters (C, N and P), the formation of aggregates, C mineralization, fungal hyphae length, and chitinase activity were measured in soil. The results showed that there were more macroaggregates (>2000 μm) in soils amended withresidues. However, the formation of macro-aggregates was not significantly affected by the quality of residues. The results showed that the macro-aggregates were correlated to fungal hyphae, but not to chitinase activity. The addition of exogenous mineral N reduced the macro-aggregation that would result from complexation of polyphenols that have been considered to be a primary factor in the aggregation process for the long-term experiment.Conclusions and application of the results: This long-term study confirms our previous results obtained on the short term incubation of soil amended with residues which showed that the formation of macroaggregates was not affected by the quality of residues. The measurement of fungal hyphae seems to be the most pertinent indicator associated with aggregation in a long-term experiment, as opposed to fungal activity in the short-term experiment.Keywords: residue quality, mineral N, aggregation, fungal activity, lixiso

Rainfall distribution over the Fouta Djallon — Guinea

International audienceThe main goal of the present paper is to discuss the asymmetry of the rainfall distribution over the mountain range of the Fouta Djallon — Guinea — in relation with orography and local atmospheric circulation. The Fouta Djallon is the main West African hydrographic source area. The two principal rivers (Niger and Senegal) take birth in this region where, in addition, one of the highest cumulative rain heights in the world (> 10 m) is observed. The data used are images of the Meteosat satellite, reanalyses of NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) and ECMWF (European Centre for Medium-Range Weather Forecasts), and observations from ground-based raingauge networks. Over the Fouta Djallon, the convective activity is found to increase in frequency and intensity due to the orographic forcing of water vapor in an area of convergence between monsoon and Harmattan fluxes; heavy rain is released over the southwest side of the range. A conceptual model is proposed suggesting that convective systems developing over or east of the range are advected westward of the generating area, resulting in a strong pluviometric contrast and a maximum offshore

Soil bio-functioning under Acacia nilotica var. tomentosa protected forest along the Senegal River

Acacia nilotica var. tomentosa trees from the Diarra protected forest located in the Senegal River valley were identified for the assessment of both biological nitrogen fixation, using the natural abundance method, and soil bio-functioning parameters (nodulation, root biomass, total microbial biomass, and potential N mineralization). The presence and the genetic diversity of indigenous rhizobia nodulating A. nilotica var. tomentosa was also investigated, taking into account distance from the trunk (0, 1, 2, and 3 m) and depth (0-25, 25-50, and 50-75 cm). Surprisingly, no nodules on the trees root systems were found, whereas under laboratory conditions the presence of indigenous rhizobia nodulating A. nilotica var. tomentosa was demonstrated in the analyzed soils (90% of the nodules harvested on the trapped plants were occupied by the same Inter-Genic Spacer (IGS) group, IGS1). There was no significant influence of trees and/or depth on total microbial biomass and potentials of nitrogen mineralization. Some assumptions were formulated on the possible combined effect of flooding, which usually occurs annually during 4-7 months, and the clayey soils in the Diara forests. Although a deeply natural nodulation of A. nilotica var. tomentosa trees by indigenous rhizobia is not excluded, but it still remains to be demonstrated