Legume choice matters: different effects on Brassica napus agronomic performance and root-associated bacterial communities in intercropping systems

Background and Aims Brassica napus L., an oilseed crop, is one of the three major crop groups contributing to global food production. It is generally grown as a monoculture and is very demanding in terms of nitrogen inputs. To meet the nutritional needs of B. napus and to reduce the excessive use of chemical inputs, intercropping with legumes plays an important role in agricultural ecosystems. This study aims to assess how different intercropping systems with two forage legumes (Medicago sativa L. and Hedysarum coronarium L.) affect the biometric parameters of B. napus and influence the associated bacterial communities in the rhizosphere and root compartments. Methods A two-year field experiment was conducted to assess how M. sativa L. and H. coronarium L. intercropping influences B. napus biometric parameters and bacterial communities in both rhizosphere and root compartments, with particular emphasis on inter-annual variability and temporal dynamics of plant–microbe interactions. Results Our results showed that the agronomic parameters varied among the different cultivation systems and between the two growing seasons (2022 and 2023). H. coronarium proved to be the best legume to be used in intercropping with B. napus, particularly under drought conditions. Thus, this legume demonstrated high potential for supporting oilseed production when water availability is limited, highlighting its value for climate-resilient cropping systems. The intercropped legume species also shaped the bacterial communities in both the rhizosphere and B. napus roots, with Vicinamibacterales and Caulobacterales orders that increased in legume-canola intercropping systems. Conclusion This study demonstrates that in intercropping with legumes, the promotion of B. napus growth depends on the legume species choice. Moreover, intercropping practice affects bacterial composition, particularly in B. napus roots, suggesting different microbial recruitment mediated by the presence of a specific legume.