Light is essential for plants and plays a vital role in their growth and development. Light irradiation affects the physiological characteristics and synthesis of secondary metabolites in plants. As a semi-shade perennial plant, Panax ginseng C.A. Mey. is sensitive to changes in the light environment. Different light irradiations significantly affect the secondary metabolic processes of P. ginseng. However, few studies have investigated the changes in ginsenoside content in P. ginseng under different light irradiation conditions. In this study, 3-year-old P. ginseng was cultured under white (CK) light, blue (B) light, red (R) light, green (G) light, and natural light (NL) to explore the effects of light irradiation on the physiological characteristics and ginsenoside secondary metabolism of P. ginseng. The B and CK treatments significantly increased the photosynthetic level in P. ginseng leaves. The total saponin content under blue and red light treatments increased by 28.81% and 21.64%, respectively, compared with the CK treatment. Blue and red light improved the transcription levels of ginsenoside biosynthetic pathway genes. Blue light upregulated the expression of HMGR, SS, SE, DS, CYP716A52, and CYP716A47, and the expression of HMGR, SS, SE, DS, and CYP716A47 under red light treatment was significantly upregulated in P. ginseng roots. Principal component and correlation analyses revealed that the physiological and ecological processes of P. ginseng exhibited different responses to light irradiation. The total saponin content in the roots was positively correlated with the content of protopanaxatriol -type ginsenosides and water use efficiency in leaves. Our study indicates that light conditions can be improved by blue and red light or by blue and red film covering to facilitate the accumulation of saponin during the ecological cultivation of P. ginseng.

Ginseng is regarded as the “king of herbs” in China, with its roots and rhizomes used as medicine, and it has a high medicinal value. In order to meet the market demand, the artificial cultivation of ginseng emerged, but different growth environments significantly affect the root morphology of garden ginseng. In this study, we used ginseng cultivated in deforested land (CF-CG) and ginseng cultivated in farmland (F-CG) as experimental materials. These two phenotypes were explored at the transcriptomic and metabolomic levels so as to understand the regulatory mechanism of taproot enlargement in garden ginseng. The results show that, compared with those of F-CG, the thickness of the main roots in CF-CG was increased by 70.5%, and the fresh weight of the taproots was increased by 305.4%. Sucrose, fructose and ginsenoside were significantly accumulated in CF-CG. During the enlargement of the taproots of CF-CG, genes related to starch and sucrose metabolism were significantly up-regulated, while genes related to lignin biosynthesis were significantly down-regulated. Auxin, gibberellin and abscisic acid synergistically regulated the enlargement of the taproots of the garden ginseng. In addition, as a sugar signaling molecule, T6P might act on the auxin synthesis gene ALDH2 to promote the synthesis of auxin and, thus, participate in the growth and development of garden ginseng roots. In summary, our study is conducive to clarifying the molecular regulation mechanism of taproot enlargement in garden ginseng, and it provides new insights for the further exploration of the morphogenesis of ginseng roots.