Effects of nitrogen reduction combined with molybdenum trioxide and zinc oxide nanoparticles on the growth and quality of Glycyrrhiza glabra

In licorice cultivation, excessive nitrogen fertilizer application has led to increasingly prominent issues, such as diminished quality and inadequate medicinal potency. Under 50% nitrogen reduction, this study used molybdenum trioxide (MoO 3 ) and zinc oxide (ZnO) nanoparticles (NPs) at three concentration levels (0, 50, and 100 mg/L) in both single and combined application treatments to systematically investigate their effects on Glycyrrhiza glabra growth and quality. The results indicated that 50% nitrogen reduction significantly inhibited the growth of G. glabra and root nodule formation, while promoting the accumulation of glabridin, glycyrrhizic acid, liquiritin, glycyrrhetinic acid, and isoliquiritigenin in roots and enhancing the nitrogen-fixing capacity of root nodules. Notably, application of MoO 3 NPs and ZnO NPs effectively alleviated the growth inhibition of G. glabra induced by nitrogen reduction, among which the 100 mg/L combined NPs treatment performed best: it not only significantly promoted aboveground growth of G. glabra , improved photosynthetic performance, increased the activity of key nitrogen-metabolizing enzymes, strengthened biological nitrogen fixation, and optimized root architecture, but also facilitated the accumulation of key secondary metabolites, with its efficacy even surpassing that of the full-nitrogen control (CK). Field experiments further verified that this optimal treatment increased per-hectare yield of G. glabra by 25.35% and total accumulation of key secondary metabolites by 20.34%–126.81% compared with CK. This study provides theoretical and practical bases for the sustainable and efficient cultivation of G. glabra under nitrogen reduction and the application of NPs in the green production of Chinese medicinal materials. • Nitrogen reduction inhibited licorice growth but promoted medicinal quality. • Co-treatment with MoO₃ and ZnO NPs mitigated growth suppression and amplified metabolite biosynthesis. • PLS-PM revealed NPs enhanced growth and metabolites via photosynthesis and nitrogen fixation. • Field trials showed NPs improved yield by 25.35% and key metabolites by 20.34%–126.81%.