The synthesis and secretion of key substances in the flavonoid metabolic pathway responding to different nitrogen sources during early growth stages in Robinia pseudoacacia

from mineral nitrogen and symbiotic nitrogen; however, the regulatory mechanisms by which legume plants respond to various nitrogen sources are still unclear. Methods Here, the flavonoid metabolism profiles of Robinia pseudoacacia (black locust)in response to different nitrogen sources during the early growth stages were performed using the hydroponics method. Results The flavonoids were accumulated specifically responding to different nitrogen sources (symbiotic nitrogen and NO3 ?)in the roots and root exudates of R. pseudoacacia and showed growth-stage-dependent changes in the plant growth process. More flavonoids were synthesized and secreted under nitrogen deficiency. The differential flavonoids among different treatments were significantly enriched in the flavone and flavonol biosynthesis pathway and isoflavonoid biosynthesis pathway. Liquiritigenin, naringenin, apigenin and kaempferol were not only the metabolic nodes of these two metabolic pathways but also the key nodes in the differential flavonoid network. Therefore, these four flavonoids may be the key flavonoids of R. pseudoacacia responding to different nitrogen sources. Conclusion Our findings provide an important insight into the adaptability of legumes to different nitrogen environments and are of great significance for understanding the molecular mechanisms underlying nitrogen utilization in legumes and will contribute to the development of sustainable agricultural practices and crop production.