Growth and saikosaponin production of the medicinal herb Bupleurum chinense DC. under different levels of nitrogen and phosphorus

Dried roots of Bupleurum spp. have been used medicinally in China for over 2000 years. The roots, which are called Bupleuri Radix, are used in at least 66% of the formulations/prescriptions in traditional Chinese medicine and Kampo medicine. Demand for Bupleuri Radix is increasing and B. chinense is one of the most important Bupleurum spp. in China. We conducted a 2-year pot experiment to investigate the effect of nitrogen (N) and phosphorus (P) fertilizer on biomass production and root saikosaponin a (SSa) and saikosaponin d (SSd) content of B. chinense. The experiment included seven combinations of N and P fertilizer. The results showed that medium levels of N and P fertilizer significantly increased the biomass and SSa content of B. chinense roots, but had no significant effect on root SSd content. The application of moderate amounts of N or P fertilizer increased total SSa and SSd yield significantly compared to the unfertilized control, but the greatest increase in total SSa and SSd yield occurred when N and P were applied together. This suggests that N and P have a synergistic effect on B. chinense growth and saikosaponin production. When high amounts of N and P fertilizer were used total SSa and SSd yields declined. This implied that there was a nutrient supply threshold for the biosynthesis of saikosaponins. Total SSa and SSd yields were greater in treatments which received only P fertilizer compared to treatments that received only N fertilizer. Our results reinforce the importance of soil testing and the application of recommended amounts N and P fertilizers for the cultivation of B. chinense.