Exogenous Melatonin Compensates for Moderate Nitrogen Reduction in Upland Rice by Optimizing Leaf Nitrogen Allocation...

Area of Science:

• Agricultural Science
• Plant Physiology
• Agronomy

Background:

• Moderate nitrogen (N) reduction in upland rice can decrease costs but may impair photosynthesis, N assimilation, and yield.
• Melatonin's role in regulating plant photosynthesis and nutrient metabolism is known, but its effect on N allocation under reduced N fertilization is unclear.

Purpose of the Study:

• To investigate if melatonin application improves the effectiveness of reduced N rates in upland rice by altering functional leaf N allocation.
• To evaluate the impact of melatonin on photosynthetic performance, N metabolism, and grain yield under varying N application rates.

Main Methods:

• A two-year field experiment (2024-2025) with four N rates (0, 120, 160, 200 kg N ha⁻¹) and two foliar treatments (water or 100 μmol L⁻¹ melatonin).
• Assessment of photosynthetic parameters, functional leaf N allocation, N metabolism enzymes (NR, GS), and grain yield.
• An additional experiment using p-chlorophenylalanine (p-CPA) to inhibit endogenous melatonin.

Main Results:

• Melatonin significantly improved photosynthetic rates (Pn, Vcmax, Jmax) and grain yield, particularly at 160 kg N ha⁻¹ (N2M1 treatment).
• At 160 kg N ha⁻¹, melatonin increased the proportion of N allocated to photosynthetic functions (73.55% to 86.79%) and enhanced photosynthetic N-use efficiency (PNUE) by 11.10%.
• Melatonin application boosted nitrate reductase (NR) and glutamine synthetase (GS) activities, improving N metabolism and N fertilizer-use efficiency.

Conclusions:

• Exogenous melatonin application effectively compensates for moderate N reduction in upland rice, especially at 160 kg N ha⁻¹.
• Melatonin enhances photosynthetic capacity, optimizes functional N allocation, and improves N assimilation, leading to maintained or increased grain yield.
• Combining melatonin with a 20% reduction in N fertilizer presents a viable strategy for sustainable upland rice production.