Drought-tolerant rhizobacterial consortia with diverse plant growth promoting traits enhance wheat and faba bean growth under water and low-P availability promising multi-traits.

Staple crops like wheat and faba bean are increasingly subjected to multiple and simultaneous stresses, resulting in substantial yield reduction. Although vast available knowledge about the role of root-rhizosphere microbes in enhancing crop tolerance to single stress, few is known about the potential of bacterial consortia rationally assembled from strains with defined and complementary ecological functions to improve crop tolerance to combined drought and phosphorus (P) deficiency. This study evaluated wheat (Triticum durum) or faba bean (Vicia faba) morpho-physiological response to three functionally diverse drought-tolerant bacterial consortia (C7, C8, C9), in greenhouse conditions, under low-P well-watered conditions (rock phosphate (RP), 80% field capacity (FC)) or low-P drought conditions (RP, 40% FC). Assessment of agro-physiological parameters identified consortium C8 as particularly effective, leading to significant increases in root biomass, leaf area, and shoot inorganic P content, of both wheat and faba bean plants under combined drought and low-P availability. This improvement is likely driven by bacterial traits related to drought tolerance, increased root biomass allocation, and enhanced rhizosphere P availability, as indicated by enhanced physiological traits related to leaf area, photosynthetic efficiency (Fv/Fm ratio), and chlorophyll content. Additionally, soil P availability and acquisition improved in response to bacterial inoculation that positively influenced faba bean nodulation, indicating that these bacterial consortia plausibly increased faba bean symbiotic effectiveness through optimizing P use efficiency as a potential mechanism among others. Additionally, the ability of bacterial consortia to produce phytohormones (e.g. Auxins) could partially explain induced root development and nodulation under water stress, given the key role of these phytohormones in root growth and rhizobia-legume symbiosis establishment. Our findings provide consistent evidence on the effectiveness of bacterial consortia - comprising functionally diverse PGP traits - in enhancing plant growth and nutrient acquisition under stressful conditions.