Functional diversity of soil microbial community, rock phosphate dissolution and growth of Acacia seyal as influenced by grass-, litter- and soil-feeding termite nest structure amendments

We tested termite mound materials belonging to different feeding groups: Cubitermes (soil-feeder), Trinervitermes (grass-feeder) and Macrotermes (litter-feeder), as natural microbial inoculum to promote plant growth and increase nutrient supplies from soil organic matter and inorganic amendments (rock phosphate), through their effects on soil microoganisms (functional diversity of soil microflora, arbuscular mycorrhizal fungi. rhizobia. fluorescent pseudomonads, actinomycetes and saprophytic fungi). Experiments were made in a pot experiment with Acacia seyal, a leguminous tree abundant in West Africa, with a sandy soil amended or not with rock phosphate. Results indicated a stimulation of plant growth with Cubitermes and Trinervitermes mound powder (plant height and shoot biomass), similar to what was obtained with rock phosphate alone. Leaf content in N was also increased in the termite treatments (except in Macrotermes soil), whereas mycorrhizal colonization was inhibited as compared to the control. The development of saprophytic fungi was significantly higher in the soils amended with rock phosphate and this effect was hypothesized to be related to the production of large quantities of oxalic acid by fungal populations. The fluorescent pseudomonad populations notably increased in the soils dually amended with mound powders and rock phosphate., and this could be due to the fact that some species of this bacterial group are able to dissolve rock phosphate. The organic and inorganic amendments decreased the soil catabolic evenness in all the mound powder treatments. Among the mound materials tested, Cubitermes mound powder had the most promising effect, especially on SIR response to oxalate. It is concluded that soils amended both with rock phosphate and Cubitermes mound soil could promote the development of microbial communities, which could help to metabolize this compound and consequently enhance plant growth. (C) 2004 Elsevier B.V. All rights reserved