Effects of Increasing Organic Fertilizer Application on the Growth, Photosynthetic Characteristics, and Saponin Content of Panax notoginseng

Purpose To investigate the effects of organic fertilizer (OF) application on the growth, photosynthetic characteristics, and saponin content of the shade-demanding rhizomatous medicinal plant Panax notoginseng (Burk.) F. H. Chen (PN), providing a theoretical basis for the rational OF application in its ecological cultivation.

Methods Using two-year-old and three-year-old PN as experimental materials, five OF treatments were established at 15000 kg/hm² (100% OF), 18750 kg/hm² (125% OF), 22500 kg/hm² (150% OF), 26250 kg/hm² (175% OF), and 30000 kg/hm² (200% OF). The growth indicators, photosynthetic characteristics, and saponin content of PN under each treatment were measured.

Results Under 150% OF treatment, the main root length and width of three-year-old PN were the largest, while OF had no significant effect on the dry weight of main root and rhizome, and main root economic yield of PN. With the increase of organic fertilizer application, the net photosynthetic rate of 2-year-old PN showed a trend of first increasing and then decreasing, but there was no significant change in chlorophyll content. Under 200% OF treatment, the net photosynthetic rate, stomatal conductance, and intercellular CO₂ concentration of 2-year-old PN were all lower than those under 100% OF treatment; and the above indicators of 3-year-old PN were all below 150% OF treatment. The maximum quantum yield of photosystemⅡ photochemistry (F_v/F_m) of 2-year-old PN treated with 200% OF was significantly higher than that treated with 150% OF; the thermal dissipation and electron transport rate of 2-year-old PN were both optimized with 125% OF treatment; the antioxidant enzyme activity of PN treated with 200% OF was much lower than that treated with 100% OF. With the increase of OF application, the overall content of various saponins in 2-year-old PN showed an increasing trend.

Conclusion Applying OF can promote the growth of the underground root system of PN to a certain extent, and increase the accumulation and distribution of biomass. In soils with medium to high organic matter content, increasing the application of OF to 30000 kg/hm² can improve the quality of 2-year-old PN, while increasing the application of OF to 22500 or 30000 kg/hm² can enhance the economic yield of main root of 3-year-old PN.