MARCONE, SONIA (2026) USE OF PHOSPHATE-SOLUBILIZING MICROORGANISMS (PSMs) AS BIOFERTILIZERS IN CROP PRODUCTION. [Tesi di dottorato]

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Abstract

The increasing need to reduce dependence on synthetic fertilizers and improve nutrient use efficiency has stimulated interest in sustainable agricultural practices based on beneficial microorganisms. Among these, phosphate-solubilizing microorganisms (PSMs) represent a promising strategy to enhance phosphorus (P) availability, one of the most limiting nutrients for crop production due to its low bioavailability in soils. This PhD research investigated the potential of selected bacterial strains belonging to the genera Bacillus and Pseudomonas as biofertilizers capable of improving phosphorus mobilization and plant growth. An integrated approach combining phenotypic, physiological, metabolomic, and agronomic analyses was adopted to characterize the functional traits of six bacterial strains and evaluate their performance under both in vitro and in vivo conditions. The bacterial isolates were assessed for salt tolerance, siderophore production, antagonistic activity against phytopathogenic fungi, and phosphate-solubilizing ability using insoluble phosphorus sources, including tricalcium phosphate and rock phosphate. Quantitative assays confirmed the superior phosphorus-solubilizing capacity of Pseudomonas putida RPT12, Bacillus pumilus FBP01, and Bacillus megaterium FBM09. Metabolomic profiling by GC–MS revealed that phosphorus mobilization was associated not only with medium acidification but also with strain-specific metabolic reprogramming involving the production of organic acids, phenolic compounds, and nitrogen-containing metabolites. The agronomic effectiveness of the selected strains was evaluated on wheat (Triticum aestivum L.) and tomato (Solanum lycopersicum L.) plants. Microbial inoculation significantly improved plant growth, biomass accumulation, and phosphorus uptake, particularly when combined with rock phosphate under phosphorus-limited conditions. In tomato, the application of B. pumilus FBP01 and B. megaterium FBM09 enhanced fruit yield, quality parameters, and phosphorus accumulation, demonstrating their ability to increase the agronomic value of poorly soluble phosphorus sources. Overall, the results highlight the potential of phosphate-solubilizing bacteria as sustainable bioinoculants capable of improving phosphorus use efficiency and reducing reliance on chemical fertilizers. This study provides new insights into the physiological and metabolic mechanisms underlying phosphorus mobilization and offers a scientific basis for the development of innovative microbial-based fertilization strategies aimed at enhancing the sustainability and resilience of modern agricultural systems.

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