Mild Drought Promotes Biomass Accumulation and Increases Diosgenin Content in Rhizomes of Dioscorea nipponica

<i>Dioscorea nipponica</i> is an important medicinal and edible plant in northern China, and its extract dioscin is an important raw material for the modern pharmaceutical industry. To investigate the key environmental factors influencing diosgenin accumulation in the rhizomes of <i>D. nipponica</i> and their action mechanism, we collected wild <i>D. nipponica</i> plants from 60 plots on Zhongtiao Mountain and analyzed the effects of environmental conditions on both plant growth and diosgenin synthesis. Additionally, physiological parameters of <i>D. nipponica</i> were investigated under different intervals of watering treatments: control (CK, 3 days), mild drought (MID, 5 days), moderate drought (MD, 8 days) and severe drought (SD, 10 days). The results showed that the water content of rhizome was the main factor affecting the diosgenin content, and soil nutrients, especially nitrogen, played an important role in the growth of <i>D. nipponica</i>. The results of a drought stress gradient test showed that diosgenin increased significantly under mild drought compared to the control, reaching 103.19 ± 2.63%. SD inhibited the growth of plants, and the indexes decreased by 10.08 ± 0.03-34.94 ± 5.60% compared with MID but increased the proliferation rate of rhizomes (83.33%), which is the reproductive strategy of <i>D. nipponica</i> when faced with drought stress. It provides a scientific basis for imitation of wild cultivation of <i>D. nipponica</i>.