Soil structures built by litter-feeding termites are one of the main soil translocation processes in dry tropical savanna. Runways (soil sheeting) made of soil particles cemented with salivary secretions covering the dead plant pieces collected on the ground surface represent the main soil structures. The aim of this study was to determine the impact of this soil engineering activity on the microbially-mediated N transformations (nitrification and denitrification) associated with termite sheeting. We investigated the hypothesis that the physicochemical and microbial properties of termite soil sheeting depend on (i) the termite species and (ii) the type of organic substrate consumed. Soil sheeting built by two of the main savanna species, Macrotermes subhyalinus and Odontotermes nilensis, were sampled on field plots treated with three different types of litter (Acacia leaves, millet straw, both whole and ground (< 500 µm), and cattle manure). The soil's organic C, total N, inorganic N, microbial biomass, potential CO 2 respiration, nitrification and denitrification were measured. For both termite species and all types of litter, the soil sheeting was enriched in organic C and inorganic N, resulting in an increase in soil respiration, whereas the microbial biomass was unchanged with respect to the reference soil. With the exception of the soil nitrification potential, the type of organic substrate did not significantly affect the properties of the soil sheeting measured. However, the nitrogen cycle was affected differently by the two termite species. In O. nilensis sheeting, the denitrification potential was reduced with respect to the reference soil, whereas the nitrification potential was inhibited in M. subhyalinus sheeting. The changes in the nitrogen cycle processes resulted in an increase in NH 4 + and NO 3 − in the termite soil sheeting, increasing the availability of nitrogen to plants. This study reinforces the importance of termites as a keystone savanna group whose building activities have an effect on tropical soil mineralization.
Tel (221) 77 569 80 01RÉSUMÉ L'objectif de cette étude est d'évaluer l'activité antifalcémiante d'extraits de racines de Leptadenia hastata sur des hémoglobines falciformes et d'identifier les principes actifs à l'origine de cette activité. La méthode employée étudie la réversibilité des drépanocytes, en fonction du temps d'incubation des extraits par rapport aux témoins (eau physiologique, phénylalanine et arginine) sur des échantillons de sang de patients drépanocytaires homozygotes. Des concentrations de 0,05; 0,5; 5 et 10 mg/ml de quatre extraits (méthanol, hexane, acétate d'éthyle et méthanol résiduel) ont été mises en contact avec des drépanocytes de type SS après avoir provoqué leur falciformation avec une solution à 2% de métabisulfite de sodium. L'évaluation a été effectuée toutes les 30 minutes pendant 120 minutes. Les différents extraits ont montré une activité dosedépendante sur la réversibilité de la falciformation des globules rouges avec plus de 80% d'inversion en 120 minutes pour l'extrait méthanolique, le plus actif. Un screening phytochimique a permis de faire une corrélation entre les flavonoïdes et l'activité antifalcémiante des extraits de Leptadenia hastata.
This paper provides an early assessment of the effects of the COVID-19 outbreak and of subsequent response measures on milk production, collection, processing, marketing and consumption in Africa. We focus on the period surrounding the first wave of the outbreak (from February to June 2020), during which the number of cases surged and many steps were taken to curb the epidemic. The paper is based on reports from four countries covered by the Africa-Milk Research Project: Burkina Faso, Kenya, Madagascar and Senegal. Data was collected primarily from nine dairy processors located in those countries. Major conclusions of the study are: (1) Dairy farmers were negatively affected by COVID-19 measures when the health crisis coincided with the peak of the milk production season, and when governments did not take steps to support milk production. (2) Small and informal milk collectors were also affected by traffic restrictions as they could not obtain traffic permits. (3) Milk powder importation remained unaffected during the outbreak. (4) Dairy processors (particularly small ones) faced many challenges restricting their operation. Travel restrictions led to temporary interruptions of milk supply, and because of employee protection and safety measures, processing costs increased. (5) Many small retailers were affected by bans on public transport and reduced their purchases of artisanal dairy products; meanwhile, spoilage of dairy products increased during long curfews coupled with poor storage conditions. Supermarkets were able to increase their market share during the pandemic thanks to their connections with industrial dairy processors and wholesalers. (6) A majority of consumers decreased their consumption of dairy products due to a decrease of purchasing power. In some cases, an increase in consumption occurred (due to Ramadan month and dry season high temperatures) and consumption shifted towards long-life dairy products. (7) Overall, the consequences of the health crisis affected more small and informal dairy supply chains than the larger ones, which are more formal, better organised and finally more resilient to face this kind of global crisis.
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