Effects of dual inoculation with arbuscular mycorrhizal fungi and rhizobia on Acacia senegal (L.) Willd. seedling growth and soil enzyme activities in senegal

Abstract

Acacia senegal (L.) Willd. is a multipurpose legume that is economically and ecologically important in Sahelian areas, especially in Senegal. It has long been used for arabic gum production. However, drought and overexploitation lead to decreased soil fertility and tree productivity. An experiment was conducted to examine the response of A. senegal seedlings to inoculation with mixed arbuscular mycorrhizal fungi (Glomus fasciculatum, Rhizophagus irregularis and Glomus verriculosum) and rhizobial strains (ORS 3574, ORS 3593, ORS 3607 and ORS 3628) in glasshouse conditions. After 6 months of culture under non-sterilized field soil from Dahra (northern part of Senegal), plant height, arbuscular mycorrhizal root colonization rate and soil acid phosphatase activity were significantly enhanced by the combined inoculation of arbuscular mycorrhizal fungi (AMF) and rhizobia. However, plant biomass, soil spore density and hyphal length were significantly improved by the single inoculation with mycorrhizal or rhizobial strains. The number of nodules was higher for rhizobial inoculated plants. No significant increase in shoot nutrient contents was observed after inoculation. The microbial inoculation enhances the soil acid phosphatase activity whereas no positive effect was noticed on soil total microbial activity. These results indicate that the single inoculation with AMF or rhizobia improves A. senegal seedling growth under this non-sterilized field soil better than the dual inoculation. It is suggested that, for the success of a dual inoculation, a careful selection of effective combinations of microsymbionts is necessary to enhance plant growth and soil bio-functioning and for restoration of soil fertility in a given environment.