Effects of Exogenous Methyl Jasmonate on Metabolism and Soil Activity in Chrysanthemum morifolium

Challenges significantly hinder the sustainable cultivation of tea chrysanthemum, leading to imbalances in soil nutrients, the accumulation of allelopathic phenolic acids, reduced enzymatic activity, and disruptions in rhizosphere microbial communities. To explore potential mitigation strategies, this study systematically evaluated the integrative effects of exogenous methyl jasmonate (MeJA, 0-400 (μmol L^-1)) on both soil environmental parameters and plant growth performance under continuous cropping conditions. The results revealed that treatment with 100 (μmol L^-1) MeJA significantly enhanced plant height, canopy width, flower number, and fresh flower weight. Concurrently, it improved soil organic matter content, the available nitrogen levels, and redox stability while increasing the activity of key enzymes, including polyphenol oxidase, urease, and catalase. Notably, this treatment markedly reduced the accumulation of allelopathic phenolic acids, such as p-hydroxybenzoic acid and vanillic acid. High-throughput sequencing further demonstrated that 100 (μmol L^-1) MeJA optimized the composition of soil microbial communities, increasing the abundance of beneficial taxa, such as nitrogen-fixing and phosphate-solubilizing bacteria, while suppressing pathogenic fungi. Metabolomic analysis showed that this concentration of MeJA activated stress-resistance metabolic pathways involving flavonoids and terpenoids while downregulating degradation-related processes, thereby supporting enhanced plant resilience at the metabolic level. Collectively, these findings demonstrate that an appropriate concentration of exogenous MeJA can effectively alleviate continuous cropping obstacles in Chrysanthemum morifolium, providing both theoretical insights and practical guidance for its eco-friendly and efficient cultivation.