Arbuscular mycorrhizal fungi associated with the rhizosphere of Piliostigma reticulatum and Guiera senegalensis shrubs in Senegal

Piliostima reticulatum and Guiera senegalensis shrubs constitute \u201cislands of soil fertility\u201d in the rhizosphere, with better availability of water and more intense biological activity in the Sudano-Sahelian agro-ecosystems. There is, however, paucity of information on diversity of arbuscular mycorrhizal fungi (AMF) fungi, which have a wide ecological range of associations with a variety of vegetation. The purpose of this study was to identify the types of AMF in the rhizospheres of P. reticulatum and G. senegalensis shrubs in Senegal. Soil samples were collected from around the shrubs in Keur Matar Arame and Keur Ndary Ndiaye in 2019 after a rainy season. Arbuscular mycorrhizae fungi spores were isolated by the wet sieving method and identified based on their morphological characteristics (shape, size, colour, attached hyphae, and spore ornamentation). Four types of AMF were identified, namely Glomus aggregatum, Sclerocystis rubiformis, Gigaspora margarita and Scutellospora gregaria. In addition, the density of spores was more abundant in the soil outside the shrub canopy compare to the soil beneath the shrub.Les arbustes Piliostima reticulatum et Guiera senegalensis constituent des \uab \ueelots de fertilit\ue9 \ubb dans la rhizosphere des sols, avec une meilleure disponibilit\ue9 en eau et une activit\ue9 biologique plus intense dans les agro-\ue9cosyst\ue8mes soudano-sah\ue9liens. Cependant, Il y a peu d\u2019informations sur la diversit\ue9 des champignons mycorhiziens arbusculaires (CMA) qui peuvent s\u2019associer avec une large vari\ue9t\ue9 de plantes. Le but de cette \ue9tude est d\u2019identifier les types de CMA dans les rhizosph\ue8res des arbustes P. reticulatum et G. senegalensis au S\ue9n\ue9gal. Des \ue9chantillons de sol ont \ue9t\ue9 collect\ue9s autour des arbustes \ue0 Keur Matar Arame et Keur Ndary Ndiaye en 2019 apr\ue8s la saison des pluies. Les spores de champignons mycorhiziens arbusculaires ont \ue9t\ue9 isol\ue9es par la m\ue9thode de tamisage humide et identifi\ue9es en fonction de leurs caract\ue9ristiques morphologiques (forme, taille, couleur, hyphes attach\ue9s et ornementation des spores). Quatre types de CMA ont \ue9t\ue9 identifi\ue9s, \ue0 savoir Glomus aggregatum, Sclerocystis rubiformis, Gigaspora margarita et Scutellospora gregaria. De plus, la densit\ue9 des spores \ue9tait plus abondante dans les sols hors couvert que dans les sols sous-couvert des arbustes

Agroforesterie et services écosystémiques en zone tropicale

Respectueux de l’environnement et garantissant une sécurité alimentaire soutenue par la diversification des productions et des revenus qu’ils procurent, les systèmes agroforestiers apparaissent comme un modèle prometteur d’agriculture durable dans les pays du Sud les plus vulnérables aux changements globaux. Cependant, ces systèmes agroforestiers ne peuvent être optimisés qu’à condition de mieux comprendre et de mieux maîtriser les facteurs de leurs productions. L’ouvrage présente un ensemble de connaissances récentes sur les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers. Il concerne, d’une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, de régions tropicales humides en Amérique du Sud, en Afrique de l’Est et du Centre, d’autre part les parcs arborés et arbustifs à base de cultures vivrières, principalement de céréales, de la région semi-aride subsaharienne d’Afrique de l’Ouest. Il synthétise les dernières avancées acquises grâce à plusieurs projets associant le Cirad, l’IRD et leurs partenaires du Sud qui ont été conduits entre 2012 et 2016 dans ces régions. L’ensemble de ces projets s’articulent autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent

Temporal microbial response to wetting-drying cycles in soils within and outside the influence of a shrub in the Sahel

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, ?-glucosidase activity, microbial biomass carbon (MB C ), and available nitrogen ( NH+4 ; 3NO-3 ) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MB C increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal respiration, microbial biomass carbon, available nitrogen, and bêta-Glucosidase activity resulted in a tight clustering in the beneath shrub soil samples. Soils incubated for more than 30 days after DRW cycles had higher available nitrogen content than soils incubated for less than 30 days. Soil from beneath the shrub canopy significantly improved soil resilience based on bêta-glucosidase activity. Soil from beneath the shrub canopy also had higher nutrient levels and greater microbial activity even when subjected to DRW cycles, potentially improving the ability of crops to withstand in-season drought when they are adjacent to shrubs. The work should bring our scientific community into a more comprehensive assessment of potential effects of a crop-shrub intercropping that may allow for increased crop yields in semi-arid ecosystems under drought conditions

Impact of simulated drought stress on soil microbiology, and nematofauna in a native shrub + millet intercropping system in Senegal

Drought stress strongly affects soil biota and impairs crop production, which under climate change will be exacerbated in semi-arid cropping regions such as the Sahel. Hence soil management systems are needed that can buffer against drought. In West Africa, field studies have found intercropping of millet with the native shrub Piliostigma reticulatum improves soil-plant-water relations, microbial activity and diversity, and suppress parasitic nematodes, which can significantly increase crop yield. However, little information is available on its beneficial or negative effects on soils or crops during water stress. Therefore, the objective was to investigate the impact of P. reticulatum in moderating water stress effects on soil properties and pearl millet (Pennisetum glaucum [L.] R. Br.) productivity. In the greenhouse, soil chemical and microbial properties and millet growth were investigated with a factorial experiment of varying levels of soil moisture (favorable, moderately stressed, or severely stressed water conditions) that was imposed for 55 days on soils containing sole P. reticulatum or millet, or millet + P. reticulatum. The results showed that the presence of P. reticulatum did not buffer soils against water stress in relation to soil chemical and microbial properties measured at the end of the experiment. Severe water stress did significantly decrease the height, number of leaves, and aboveground biomass of millet plants. Additionally, respiration, nematofauna trophic structure and abundance decreased as water stress increased. Lastly, bacterial feeders and plant parasitic nematodes were the most sensitive to severe water stress while fungal feeding nematodes remained unaffected. The results suggested that the intensity of water stress had more negative effects on soil basal respiration rather than soil microbial biomass

Agroforesterie et services écosystémiques en zone tropicale : recherche de compromis entre services d'approvisionnement et autres services écosystémiques

Basé sur des cas d'étude au Sénégal, ce chapitre dresse le bilan de 15 années de recherches sur le fonctionnement des sols d'agrosystèmes associant plantes cultivées (mil-arachide) et arbustes natifs au Sahel. Les travaux, publiés pour la plupart, ont montré que Guiera senegalensis et Piliostigma reticulatum redistribuent l'eau dans le sol, stimulent les microorganismes du sol et génèrent des îlots de fertilité au bénéfice de la culture associée. Ainsi, les rendements des cultures sont augmentés, y compris en absence de fertilisants : jusqu'à +137 % pour le mil en présence de P. reticulatum à Nioro-du-Rip. Cela justifie l'intérêt de maintenir ces arbustes dans les champs en appliquant une gestion agroécologique