ABSTRACT
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 A. holosericea mycorrhizal inoculation on the soil nutrient content, microbial soil functionalities and mycorrhizal soil potential. Treatments consisted of uninoculated A. holosericea, pre-planting fertilizer application and arbuscular mycorrhizal inoculation with Glomus intraradices. Our results showed that (i) AM inoculation and pre-fertilizer application significantly improved A. holosericea growth after 4 year's 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.

Key words: arbuscular mycorrhizal symbiosis; functional diversity; mycorrhizal soil potential; Acacia holosericea, Glomus intraradices; soil microbial communities, exotic tree species