Effects of excessive and deficient nitrogen fertilizers on triptolide, celastrol, and metabolite profile content in Tripterygium wilfordii Hook F.

Tripterygium wilfordii Hook F. is a traditional medicinal plant known for its valuable secondary metabolites, including triptolide and celastrol, and can potentially be developed into pharmaceuticals. However, the production of these secondary metabolites in Tripterygium wilfordii is influenced by various environmental factors, making it essential to optimize fertilization techniques. This study aimed to measure the content of triptolide and celastrol in the above-ground and under-ground sections of Tripterygium wilfordii during three years of experiments in three types of growth media. Additionally, untargeted metabolomics analysis was conducted on Tripterygium wilfordii roots under five levels of nitrogen fertilizer rates. Excessive nitrogen fertilizer significantly increased the fresh shoot weight of Tripterygium willfordii and decreased the plant height and fresh root weight, whereas nitrogen fertilizer deficiency significantly decreased the fresh shoot and root weight, as well as the plant height. Additionally, both excessive and deficient nitrogen fertilizer levels limited the accumulation of triptolide and celastrol in Tripterygium wilfordii roots and shoots, with higher content observed at a moderate fertilizer level. This study also identified a total of 197 alkaloids, 216 flavonoids, 12 lignans, 25 coumarins, 227 phenolic acids, 13 tannins, 147 terpenoids, and 43 other secondary metabolites. Notably, alkaloids were up-regulated at a moderate nitrogen fertilizer level (30–60 g N/pot), whereas flavonoids were down-regulated at a higher nitrogen level (90–120 g N/pot). These findings emphasize the value of nitrogen fertilizer and controlled growth conditions in enhancing the production of secondary metabolites in Tripterygium wilfordii.