Root-exuded benzoxazinoids can alleviate negative plant-soil feedbacks

Plants can suppress the growth of other plants by modifying soil properties. These negative plant-soil feedbacks are often species-specific, suggesting that some plants possess resistance strategies. However, the underlying mechanisms remain largely unknown. Here, we investigated if and how benzoxazinoids, a class of dominant secondary metabolites that are exuded into the soil by maize and other cereals, influence plant-soil feedbacks. We find that three out of five tested crop species suppress maize (Zea mays) performance via negative plant-soil feedbacks relative to the mean across species. This effect is partially alleviated by the capacity of maize plants to produce benzoxazinoids. Soil complementation with purified benzoxazinoids is sufficient to restore the protective effect for benzoxazinoid-deficient mutants. Sterilization and re-inoculation experiments suggest that benzoxazinoid-mediated protection acts via changes in soil biota. Substantial variation of the protective effect between experiments and soil types illustrates that its magnitude is context-dependent. In summary, our study demonstrates that plant secondary metabolites can confer resistance to negative plant-soil feedbacks. These findings expand the functional repertoire of plant secondary metabolites and reveal a mechanism by which plants can resist negative soil feedbacks. The uncovered phenomenon may represent a promising avenue to stabilize plant performance in crop rotations in the future.