Effects of Periodic Nitrogen Top Dressing on Root Hypertrophy and Cell Wall Related Gene Expression in Panax ginseng

Background: Although nitrogen (N) is a critical nutrient for the growth of Panax ginseng, its excessive application often induces physiological disorders. To establish an effective fertilization strategy, in this study, we investigated how periodic N topdressing affects root hypertrophy and cell wall-related gene expression. Methods and Results: We performed a 26-week pot experiment on 2-year-old ginseng plants treated with various urea concentrations (0, 2.5, 5.0, and 10.0 ㎏/10 a). In addition, we performed a field trial on 3-year-old ginseng plants from July to October (12 weeks) to compare split application frequencies. In the pot experiment, the 10.0 ㎏/10 a N treatment delayed leaf senescence and increased root weight by 28.5% compared to the control. In the field, split application (i.e., six times at 2-week intervals) was more efficient than less frequent application, increasing the yield and root hardness by 23.7% and > 10%. Real-time qPCR analysis performed using samples from the pot experiment revealed that N treatment rapidly upregulated EXPB3 and CESA6 within 24 h, indicating activated cell wall loosening and secondary wall synthesis. Conclusions: Periodic N topdressing promoted secondary growth and improved root quality in P. ginseng by activating cell wall-related genes without causing salt injury. Split application of urea has been suggested as an optimal nutrient management strategy for maximizing ginseng yield and quality.