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The mining company IAMGOLD aims to reduce the environmental footprint of its Essakane project (Burkina Faso) through soil restoration projects. Mining activities generate important physical, chemical and biological impacts on the ecosystem. The main solid wastes produced (tailings and overburden), are often biologically dead substrates and contain excess contaminants such as cyanide (CN) and arsenic (As). The ecosystem restoration should be done with ecologically adapted native plant species. For this reason, studies of symbiotic interactions between these endemic taxa and associated symbionts are essential for enhanced reclamation and for promoting sustainable development of these disturbed soils. An evaluation of rhizobial and mycorrhizal inoculum potentials and of physico-chemical properties of materials with different degradation levels (tailings, waste rock, two sites reclaimed in 2009 and a natural site outside the mine) was carried out on Essakane’s mine.
The results of this study showed an absence of ectomycorrhizal fungi and a very low presence of rhizobia and arbuscular mycorrhizal (AM) fungi on all materials. For AM fungi, the two disturbed sites showed lower spore density (less than 1 spore/100 g of soil) and root colonisation rate than the non-disturbed sites. This low presence of symbiotic microorganisms can be explained by high alkalinity (pH = 9) and low carbon content of these soils. Concomitantly, a greenhouse experiment was conducted to test different symbiotic inocula and substrates on Acacia senegal seedlings. The symbiotic inocula were the rhizobium strain ORS 3588 (from Senegal) and two strains of AM fungi (Glomus aggregatum, from Senegal; and a Canadian commercial product, Glomus irregulare) used alone or combined.
The three substrates with different content of manure and sand (50:50; 25:75; 0:100) were tested to determine the ones that promote the best symbiotic colonisation. After 75 days, morphometric data on plants were analysed. The dry mass was significantly higher on substrates with manure. No effect of inoculation was observed except for the shoot dry mass, on the substrate without manure. In the 100% sand, shoot dry mass of plants inoculated with Glomus aggregatum was significantly higher from that of plants inoculated with Glomus irregulare, Rhizobium or without inoculum. All treatments with Glomus aggregatum are not significantly different. The non-Rhizobium inoculation effect yielded low rate of nodulation.
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