Interactive influences of intercropping by nitrogen on flavonoid exudation and nodulation in faba bean

In order to address the question of how flavonoids affected root nodulation of faba bean in a wheat and faba bean intercropping system, we set up soil and hydroponic experiments comprising two cropping pattern treatments (intercropped and monocropped) and three nitrogen (N) supply treatments at the deficient (50% N), adequate (100% N), and excessive (150% N) levels with three replicates in a randomized complete block design. Across the three N treatments and two experiments, it was frequently observed that intercropping increased but N fertilization decreased the nodule number and nodule dry weight of faba bean. Six types of flavonoids were detected in the faba bean root secretion, but only genistein, hesperetin, and naringenin often had significant correlations with the nodule number and nodule dry weight. Intercropping increased faba bean root secretions of genistein, hesperetin, and naringenin compared to monoculture only at the deficient and adequate N supply levels. The differences in flavonoids of faba bean caused by the intercropped patterns, N supply levels, and their interactions were mainly significant at flowering stage. In conclusion, interspecies and N supply interactively altered the contents and proportions of flavonoids in faba bean root exudations under wheat and faba bean intercropping. These findings provide insight into flavonoids-nodule-yield interactions in cereal and legume intercropping systems.