[African agriculture faced with global changes: researches and innovations based on ecological sciences]. / L'agriculture africaine face aux changements globaux : recherches et innovations basées sur les sciences de l'écologie.

In the context of environmental and socio-economic changes, the agriculture of Sub-Saharan African countries will have to ensure food security of the population, while reducing its environmental footprint. The biophysical and social systems of agricultural production are complex. Innovative agricultural practices will be based on an intensification of ecological processes that determine the functioning of the soil-plant system, farmers' fields and agro-ecosystems. This ecological engineering approach is useful to take up the challenge of Sub-Saharan agricultures in the future, as shown in researches conducted by IESOL International Joint Lab "Intensification of agricultural soils in West Africa" (ISRA, UCAD, TU, OU, INERA, IRD).

Response of native soil microbial functions to the controlled mycorrhization of an exotic tree legume, Acacia holosericea in a Sahelian ecosystem.

Fifty years of overexploitation have disturbed most forests within Sahelian areas. Exotic fast growing trees (i.e., Australian Acacia species) have subsequently been introduced for soil improvement and fuelwood production purposes. Additionally, rhizobial or mycorrhizal symbioses have sometimes been favored by means of controlled inoculations to increase the performance of these exotic trees in such arid and semiarid zones. Large-scale anthropogenic introduction of exotic plants could also threaten the native biodiversity and ecosystem resilience. We carried out an experimental reforestation in Burkina Faso in order to study the effects of Acacia holosericea mycorrhizal inoculation on the soil nutrient content, microbial soil functionalities and mycorrhizal soil potential. Treatments consisted of uninoculated A. holosericea, preplanting fertilizer application and arbuscular mycorrhizal inoculation with Glomus intraradices. Our results showed that (i) arbuscular mycorrhizal (AM) inoculation and prefertilizer application significantly improved A. holosericea growth after 4 years of plantation and (ii) the introduction of A. holosericea trees significantly modified soil microbial functions. The results clearly showed that the use of exotic tree legume species should be directly responsible for important changes in soil microbiota with great disturbances in essential functions driven by microbial communities (e.g., catabolic diversity and C cycling, phosphatase activity and P availability). They also highlighted the importance of AM symbiosis in the functioning of soils and forest plantation performances. The AM effect on soil functions was significantly correlated with the enhanced mycorrhizal soil potential recorded in the AM inoculation treatment.