Combined Transcriptomics and Metabolomics Uncover the Potential Mechanism of Plant Growth-Promoting Rhizobacteria on the Regrowth of Leymus chinensis After Mowing

Mowing significantly influences nutrient cycling and stimulates metabolic adjustments in plants to promote regrowth. Plant growth-promoting rhizobacteria (PGPR) are crucial for enhancing plant growth, nutrient absorption, and stress resilience; however, whether inoculation with PGPR after mowing can enhance plant regrowth capacity further, as well as its specific regulatory mechanisms, remains unexplored. In this study, PGPR <i>Pantoea eucalyptus</i> (B13) was inoculated into mowed <i>Leymus chinensis</i> to evaluate its effects on phenotypic traits, root nutrient contents, and hormone levels during the regrowth process and to further explore its role in the regrowth of <i>L. chinensis</i> after mowing. The results showed that after mowing, root nutrient and sugar contents decreased significantly, while the signal pathways related to stress hormones were activated. This indicates that after mowing, root resources tend to sacrifice a part of growth and prioritize defense. After mowing, B13 inoculation regulated the plant's internal hormone balance by reducing the levels and signal of JA, SA, and ABA and upregulated the signal transduction of growth hormones in the root, thus optimizing growth and defense in a mowing environment. Transcriptomic and metabolomic analyses indicated that B13 promoted nutrient uptake and transport in <i>L. chinensis root</i>, maintained hormone homeostasis, enhanced metabolic pathways related to carbohydrates, energy, and amino acid metabolism to cope with mowing stress, and promoted root growth and regeneration of shoot. This study reveals the regenerative strategy regulated by B13 in perennial forage grasses, helping optimize resource utilization, increase yield, and enhance grassland stability and resilience.