Genotype and Phosphorus Availability Shape Chickpea Symbiotic Efficiency and Rhizosphere Microbiome Composition, Driving Contrasting Agro-Physiological Responses.

Co-inoculation of grain legumes, including chickpea, with nitrogen-fixing and phosphate-solubilising bacteria (PSB) improves symbiotic efficiency and plant productivity under low-P availability. However, the extent of chickpea's responsiveness to inoculation and their reliance on symbiotic nitrogen (N) fixation remains intricately influenced by plant genotypic diversity and the associated rhizosphere microbiome under different P levels. This study evaluated the agro-physiological, symbiotic and microbial traits of two Moroccan winter chickpea (Cicer arietinum) varieties (Arifi and Bochra) under low-P conditions represented by three rock-P levels (0, 25, 50 and 75 kg P₂O₅ ha^-1) and co-inoculation with Mesorhizobium ciceri and Rhanella aceri (PSB). Results showed that inoculation at rock-P levels ≥ 50 kg P₂O₅ ha^-1, significantly improved symbiotic traits, plant biomass and nutrient uptake in both varieties, with Bochra exhibiting superior performance. At 75 kg P₂O₅ ha^-1 of rock-P, Bochra exhibited a strong correlation between root morphological traits and P-related rhizosphere traits. Results further highlighted Bochra's robust response to inoculation under 75 kg P₂O₅ ha^-1 rock-P, driven by its ability to shape the rhizobacterial community composition, where Mesorhizobium dominated and significantly influenced plant and rhizosphere traits. More notably in Bochra than Arifi, rhizobacterial species richness and community composition correlated strongly with nodule traits, plant traits and rhizosphere P-related parameters. These findings elucidate the significant contribution of the rhizosphere bacterial community to the symbiotic performance of Mesorhizobium-inoculated chickpea, which remains both genotype- and P-dependent.