Sustainable phosphorus (P) use to meet the global food demand is a major challenge for agriculture. A number of soil microorganisms may influence the plants’ ability to utilize different chemical forms of phosphorus in the rhizosphere. Inoculating phosphate-solubilizing microorganisms together with rock phosphates (RP) has intrigued researchers for over a century. However, microbe-mediated mobilization mechanisms for use of RP remain seldomly comprehensively addressed. This study aimed at elucidating these mechanisms driven by mono- versus mixed-inoculation with a phosphate-solubilizing bacterium (PSB) Pseudomonas corrugata (strain SP77) and arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis (strain EEZ58) at the vegetative (Veg) and flowering (Flo) stage of Medicago truncatula cv. Jemalong. Multivariate analysis of combined physiological and symbiotic parameters, nutrients concentrations, and transcriptional changes of P metabolism related genes, showed distinct patterns for the phenological stages. At the Veg stage, P-related mechanisms were inoculation-type dependent (mono- versus mixed-inoculation), whereas, at the Flo stage they were exclusively AMF inoculation-dependent. Competition for resources under mixed-inoculation seems important at the Veg stage. However, positive interactions between the microbial inoculants appear at the Flo stage. Variability of differentially expressed genes related to P transporters, carotenoid dioxygenase genes, strigolactones and abscisic acid (ABA) concentration allowed us to elucidate the crosstalk among the organisms at the Veg and Flo stage. Understanding the interactions of plants with soil microbes allows development of an effective microbial management in agriculture.
The research reported in this publication was supported by a scholarship from the University of Carthage, Tunisian Ministry of Higher Education and Scientific Research and the Institute of Agricultural Research and Higher Education of Tunisia (IRESA)