Effectiveness of silver nitrate application on plant growth and bioactive compounds in Agastache rugosa (Fisch. & C.A.Mey.) kuntze

The objective of this study was to determine the optimal dose of silver nitrate (AgNO₃) for plant growth and to increase the main bioactive compounds in <i>A. rugosa</i> cultivated in a hydroponic system. The application of soaked diniconazole (120 μmol mol^-1) to all plants at 7 days after transplanting (DAT) for dwarfing plant height, optimizing cultivation space in the plant factory. Subsequently, plants were soaked with 50, 100, 200, and 400 μmol mol^-1 AgNO₃ for 10 min at 25 DAT and harvested at 39 DAT. The results indicated that 200 and 400 μmol mol^-1 treatments tended to severely decrease plant growth parameters compared to treatments with lower concentrations. The net photosynthetic rate was significantly reduced by the 200 and 400 μmol mol^-1 treatments compared to treatments with other concentrations. The 400 μmol mol^-1 treatment led to the lowest concentrations of chlorophyll <i>a</i>, chlorophyll <i>a</i>/b, total carotenoid, chlorophyll <i>b</i>, and the total chlorophyll. However, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was considerably increased in 50, 100, 200, and 400 μmol mol^-1 compared to that of the control plants. A higher rosmarinic acid (RA) concentration in the whole plant was noticed with the 400 μmol mol^-1 treatment compared with that of the untreated plants. The 100 μmol mol^-1 treatment exhibited the highest concentration and content of tilianin in the whole plant. Concentration of acacetin 1 significantly increased in the whole plant with 100 and 200 μmol mol^-1 treatments compared with that of the untreated plants. Concentrations of acacetin 2 and 3 in the whole plant were the highest with 100 and 200 μmol mol^-1 treatments, respectively. The results demonstrated that 100 μmol mol^-1 treatments can be used to increase bioactive compounds without severely limiting the plant growth and reducing chlorophyll concentrations of <i>A. rugosa</i>. Implementing this optimal dose can enable growers and researchers to cultivate <i>A. rugosa</i> more efficiently, enhancing bioactive compound content and overall plant performance, thus harnessing the potential health benefits of this valuable plant species.