Objective This study investigates the effects of different concentrations of manganese stress on the growth, physiological and biochemical characteristics and accumulation of medicinal components of Pogostemon cablin seedlings. It aims to clarify the physiological and metabolic response of P. cablin to manganese stress, thereby providing a theoretical foundation for stress-resistant cultivation and quality regulation of P. cablin in acidic soil regions of southern China.

Method A hydroponic experiment was conducted to systematically evaluate the response differences of P. cablin to manganese stress in growth, physiology, biochemistry and medicinal components by setting different manganese concentrations〔1.5(CK), 15, 150, 1 000 μmol/L Mn²⁺〕.

Result Low concentration of manganese stress (15 μmol/L) significantly promoted the root development of P. cablin after 16 days, and the root dry weight, total root length and root-shoot ratio were increased by 55.04%, 47.91% and 19.93%, respectively, compared with the control. However, high concentration of manganese stress (1 000 μmol/ L) treatment for 32 d significantly inhibited the growth of plants, and the chlorophyll a, b and total amount of leaves decreased by more than 43%. Treatment with low-concentration manganese stress (15 μmol/L) for 16 d significantly promoted the root development of P. cablin. Specifically, root dry weight, total root length, and the root-to-shoot ratio increased by 55.04%, 47.91%, and 19.93%, respectively, compared to the control. Conversely, high-concentration manganese stress (1 000 μmol/L) treatment for 32 days significantly inhibited plant growth, and the dry weight of shoots decreased by 25.35%, and the contents of chlorophyll a, chlorophyll b, and total chlorophyll in leaves decreased by more than 43%. High manganese stress induced oxidative stress, which showed that the activities of SOD and POD in leaves increased significantly, while the activity of CAT was significantly inhibited, which was 72.70% lower than that of the control. The manganese content in each part of the plant increased significantly with the increase of treatment concentration, accompanied by a continuous increase in the translocation factor, indicating that P. cablin had strong manganese tolerance and transport capacity. The contents of the medicinal components pogostone and patchouli alcohol displayed a trend of increasing initially and then decreasing with rising manganese concentrations. Both peaked after 32 days of treatment at 15 μmol/L, increasing by 21.42% and 16.78% compared to the control, respectively, but decreased significantly under high manganese stress (1 000 μmol/L).

Conclusion An appropriate manganese concentration promotes the growth of P. cablin seedlings and the accumulation of medicinal components, whereas high manganese stress inhibits growth and induces oxidative damage.