Enhanced Degradation of Diesel in the Rhizosphere of Lupinus luteusafter Inoculation with Diesel‐Degrading and Plant Growth‐Promoting Bacterial Strains

The association of plants and rhizospheric bacteria provides a successful strategy to clean up contaminated soils. The purpose of this work was to enhance diesel degradation in Lupinus luteusrhizosphere by inoculation with selected bacterial strains: a diesel degrader (D), plant growth–promoting (PGP) strains, or a combination (D+PGP). Plants were set up in pots with the A or B horizon of an umbric Cambisol (ACamband BCamb) spiked with diesel (1.25%, w/w). After 1 mo, the dissipation of diesel range organics (DRO) with respect to t= 0 (i.e., 1 wk after preparing the pots with the seedlings) concentration was significantly higher in inoculated than in noninoculated (NI) pots: The highest DRO losses were found in ACambD+PGP pots (close to 15–20% higher than NI) and in BCambD pots (close to 10% higher). The water‐extractable DRO fraction was significantly higher at t= 30 d (15–25%) compared with t= 0 (<5%), probably due to the effects of plant root exudates and biosurfactants produced by the degrader strain. The results of this experiment reflect the importance of the partnerships between plants and bacterial inoculants and demonstrate the relevance of the effect of bacterial biosurfactants and plant root exudates on contaminant bioavailability, a key factor for enhancing diesel rhizodegradation. The association of lupine with D and PGP strains resulted in a promising combination for application in the rhizoremediation of soils with moderate diesel contamination. Biostimulated rhizodegradation of diesel contaminated soils was applied.The synergy between plants and microorganisms (diesel‐degraders and PGP) was exploited.Biosurfactants and root exudation highly influenced contaminant bioavailability.