Metabolic Characteristics of PGPR-Induced Growth Promotion in Alfalfa (Medicago sativa L.)

Background/Objectives: Plant growth-promoting rhizobacteria (PGPR) have demonstrated potential for enhancing plant growth; existing research inadequately characterizes the metabolic underpinnings of PGPR-induced plant phenotypes. Methods: A deeper investigation into the impact of PGPR on plant metabolic pathways is crucial for a comprehensive understanding of their growth-promoting mechanisms and for the development of more effective biofertilizers and plant protection strategies. Results: To clarify the core metabolic pathways targeted by PGPR strains, we selected alfalfa as the research object, employed two Pseudomonas combinations, and utilized a broad-targeted metabolomics approach to investigate the metabolic characteristics of alfalfa roots. Through the analysis of primary and secondary metabolites, a total of 2694 metabolites were identified, among which lipids were the main nutrients during the growth of alfalfa. The L-citrulline and L-arginine contents were significantly upregulated, thereby affecting nitrogen metabolism and ultimately promoting plant growth. In addition, different branches of the isoflavonoid biosynthesis pathway showed differential regulation, indicating their close relationship with plant growth promotion. Conclusions: This study provides a new perspective for a deeper understanding of the molecular mechanisms by which PGPR promotes plant growth and lays a theoretical foundation for the future development of PGPR-based agricultural biological agents.