Metabonomics Analysis Reveals the Influence Mechanism of Three Potassium Levels on the Growth, Metabolism and Accumulation of Medicinal Components of Bupleurum scorzonerifolium Willd. (Apiaceae)

<i>Bupleurum scorzonerifolium</i> Willd. is a commonly used bulk Chinese herbal remedy. Due to the large-scale mining of wild <i>Bupleurum scorzonerifolium</i> Willd., its natural resources are gradually exhausted. In addition, there are some problems in <i>Bupleurum scorzonerifolium</i> Willd. cultivation, such as lack of guidance, excessive application of fertilizers and so on, which lead to the yield and quality of <i>Bupleurum</i> to be below the standard value. Therefore, it is significant to clarify the regulation of quality and yield under different levels of fertilizers. In this study, three different levels of potassium fertilizer were applied; then, the metabolites in different parts of <i>Bupleurum</i> were analyzed by gas chromatography-mass spectrometry (GC-MS) to detect the alterations in the metabolic spectrum and recognize both the accumulation and distribution of key metabolites in response to each level of potassium fertilizer. The contents of various mineral elements, such as sodium, calcium, potassium, magnesium, manganese, zinc, iron, and copper, in different parts of <i>Bupleurum</i> under different potassium levels were determined. Potassium fertilizer had a significant impact on the absorption and distribution of these mineral elements. There were synergistic and antagonistic effects between each element and K⁺. The results showed that low and high potassium levels could promote the progression of main shoots and roots, but inhibited the accumulation of dry matter in lateral shoots and flowers. Low potassium levels stimulated the content of saikosaponin a in all plant parts, while high potassium levels inhibited the accumulation of most saikosaponin a,c and d. A total of 77 metabolites were identified by GC-MS, of which glycerol, d-glucose, silane and copper phthalocyanine were highlighted as the key metabolites in response to potassium fertilizer. The abovementioned metabolites are mapped into insulin signaling pathways, streptomycin biosynthesis, galactose metabolism and other metabolic pathways, sustaining the metabolic regulation of <i>Bupleurum scorzonerifolium</i> Willd.