Balanced ammonium–nitrate nutrition enhances photosynthetic efficiency, micronutrient homeostasis, and antioxidant networks via ROS signaling in Glycyrrhiza glabra across soil and soilless systems

Licorice (Glycyrrhiza glabra L.) is a high-value medicinal crop; its slow soil-based cultivation limits yield and risks root loss or contamination. We evaluated how nitrogen form [nitrate (NO₃⁻), ammonium (NH₄⁺), and ammonium nitrate (NH₄NO₃)] affects licorice physiology in four culture systems: aeroponic, nutrient film technique (NFT), substrate hydroponics (cocopeat: perlite 1:1), and soil. Seedlings (21 days old, 10 cm tall) were transferred into each system in a completely randomized design with three replications and fertigated with modified Hoagland solution (10 mM total N) from day 80 to harvest at day 120. We measured root and shoot Fe, Mn, Zn, and Cu by atomic absorption spectroscopy; chlorophyll fluorescence indices (F_0, Fm, Fv, Fv/Fm, PI_aβs, PI_tot) using a Pocket PEA fluorimeter; and superoxide dismutase (SOD) and catalase (CAT) activities spectrophotometrically. Across all systems, NH₄NO₃-fed plants showed the highest root and shoot micronutrient concentrations, maximal PSII photochemical efficiency (F_v/F_m), and performance indices (PI_aβs, PI_tot). Sole NH₄⁺ reduced chlorophyll fluorescence parameters but induced the greatest SOD and CAT activities, indicating oxidative stress. NO₃⁻ alone produced intermediate responses, while differences between NH₄NO₃ and NO₃^- were modest, suggesting that mixed nutrition stabilizes pH and energy balance during assimilation.Our findings support the hypothesis that balanced NH₄⁺:NO₃⁻ nutrition enhances photosynthetic efficiency, micronutrient uptake, and antioxidant capacity in licorice irrespective of the cultivation system. Implementing combined N fertilization in soilless and soil systems can accelerate licorice production and improve root quality for pharmaceutical use.