The Importance of Considering Levels of P and N Fertilization to Promote Beneficial Interaction between Rapeseed and Phosphate-Solubilizing Bacteria

International audience

إنجليزي. Biointrants constitute a promising opportunity to lower mineral input on rapeseed, characterized by high nutrient requirements. As bio-inoculants, phosphate-solubilizing bacteria (PSB) could increase the amount of available P in a soil solution. However, the deployment of these bioinoculants in fields is not always successful. Disentangling the factors conditioning their reliability is necessary. Because the activities of microorganisms are particularly subject to nutrient availability, the N fertilization level could represent a key factor for the success of PSB inoculation in the early stages of plant growth. In this study, Pfaba (Pseudomonas sp.), a promising plant growth-promoting rhizobacteria (PGPR) strain isolated from soil, was inoculated on rapeseed grown in rhizotrons under two N fertilization levels (N160 or N80) in P labile or P complexed conditions. Pfaba confirmed its PSB potential to solubilize recalcitrant P complexed forms for the benefit of plant growth, but only when the N supply is adequate (N80). In a P complexed environment, Pfaba tended to increase root and shoot biomass (respectively, from 2.17 ± 0.47 g for control modality to 2.88 ± 0.85 g, and from 6.06 ± 1.67 g for control modality to 8.33 ± 1.70 g), increase the P and N contents in roots (respectively, from 0.15 ± 0.09 mg for control modality to 0.70 ± 0.51 mg, and from 37.90 ± 11.09 mg for control modality to 41.34 ± 14.16 mg), and restore root length at a comparable level than plants supplemented with labile P. Conversely, these positive effects were inhibited with lower levels of N fertilization. Our results highlight the importance of nutrient availability to promote beneficial interaction between plants and microorganisms. These findings could also contribute to ensuring the successful deployment of microbial biointrants.