Foliar application of selenium nanoparticles enhance quality and mitigate negative plant-soil feedback in Panax notoginseng by modulating plant-microbiota interactions.

Developing a practical strategy to enhance the quality of medicinal herb while alleviating negative plant-soil feedback (NPSF) is critical for agriculture. In this study, we investigated the effects of selenium nanoparticles (SeNPs) on Panax notoginseng through a two-year field experiment. Four treatments were established: a control (SeNPs_0) and three SeNPs concentrations (3, 5, and 10 mg/L), which were foliar-sprayed every 15 days for a total of six applications. We evaluated physiological characteristics, saponin accumulation, root rot incidence, and integrated metabolomics and microbiomics to elucidate the mechanisms of interaction between the aboveground and belowground parts of the plant. Results demonstrated that SeNPs significantly enhanced the total saponin content in the flowers (15.68% - 17.17 %), stems (11.44 % - 16.93 %), and roots (12.07 % - 17.34 %) of P. notoginseng. At a concentration of 5 mg/L, SeNPs significantly reduced root rot incidence by 71.43 % in Year 1 and 66.67 % in Year 2. Mechanistically, SeNPs activated flavonoid and terpenoid biosynthesis pathways, promoting saponin production (e.g., notoginsenoside Ft1 and Rb1). These metabolites enriched beneficial Trichoderma in the rhizosphere, which antagonized pathogens (Fusarium and Ilyonectria), thereby alleviating NPSF. Our study demonstrates that foliar application of SeNPs regulate plant-microbiota crosstalk, offering a dual-benefit solution for enhancing quality of medicinal component and controlling soil-borne diseases in perennial herbs.