Fertilization of Phaseolus vulgaris with the Tunisian rock phosphate affects richness and structure of rhizosphere bacterial communities

- This work addressed short-lived effects of P fertilization on bacterial community.
- Significant difference in richness and bacterial structure between TRP and TSP.
- TRP at low P level showed an increase in copiotrophic taxa.
- Proteobacteria (Beta) and Actinobacteria were stimulated by TRP at low P level.
- Some TRFs affiliated to Rhizobiaceae were inhibited by TSP.

Tunisian rock phosphate (TRP) extracted from the region of Gafsa is one of the most promising rock phosphates for soil fertilization. Its appropriate use as a source of phosphate nutrition can substitute chemical fertilizers for sustainable agriculture. The main objective of this study is to investigate the impact of P fertilizers on soil bacterial communities in the rhizosphere of bean (Phaseolus vulgaris). Application of chemical triple superphosphate (TSP) or TRP at similar P rates induced a significant increase in alkaline phosphatase and fluorescein diacetate hydrolysis activities. T-RFLP analysis of 16S rDNA revealed that P fertilization affected soil bacterial richness. Application of TRP at the same P rate as TSP was characterized by the stimulation of Actinobacteria both in the rhizosphere and in the uncultivated soil. Some of these Actinobacteria are known by their ability to produce organic acids thus promoting the dissolution of calcium and phosphore. Another important feature was the stimulation of 'mycorrhiza helper bacteria' like Comamonadaceae, Bradyrhizobacteriaceae and Oxalobacteraceae and other plant growth promoting bacteria such as Enterobacteriaceae and Pseudomonodaceae. These bacteria may contribute to the solubilization of phosphate through the production of organic acids (i.e., citric acid) and phytohormones (i.e., indol acetic acid) that stimulate plant root development and help P uptake by increasing the absorptive surface area. However, many putative plant growth promoting bacteria (mainly Sphingomonadaceae and Rhizobiaceae) were found to be inhibited by the chemical TSP fertilizer.