Synergistic optimization of yield, quality, and nitrogen use efficiency in indica rice: Influence of nitrogen management and C-N metabolism linkages

Abstract

Context

Currently, indica rice cultivation faces significant challenges in achieving coordinated enhancement of high yield, superior quality, and nitrogen use efficiency (NUE). Carbon-nitrogen (C-N) metabolic coordination is recognized as a pivotal trait for attaining this goal.

Objective

This study aims to systematically analyze the dynamic characteristics of C-N metabolism under nitrogen (N) regulation and clarify their mechanistic roles in synergistically improving the yield-quality-NUE relationship.

Methods

In this study, the indica rice cultivar Quanliangyou 851 was used with nine N regulation treatments (78.75–292.5 kg ha⁻¹) established through dynamic allocation of basal, tillering, supplementary, and panicle fertilizers. This approach shaped distinct C-N metabolic patterns across the growth cycle.

Results

Treatments under phased insufficient N supply conditions always exhibited low yield and poor rice appearance quality, treatments with a total N application of 225 kg ha⁻¹ achieved yield increases (9.50–10.35 × 10³ kg ha⁻¹) through supplementary or panicle fertilization. Notably, appropriate dosage and application period of nitrogen (N6 treatment, panicle fertilizer applied at the 13th leaf stage) significantly increased the total spikelet number and stem-sheath non-structural carbohydrate (NSC) translocation rate, thereby achieving higher yield and partial factor productivity of nitrogen (PFPN). Furthermore, its optimization of carbon-dominated assimilate allocation during grain filling mitigated the negative impact of excessive protein accumulation on rice taste value, ultimately demonstrating optimal yield-quality-NUE synergy through balanced carbon-nitrogen metabolism. A comprehensive evaluation of yield-quality-NUE based on the Analytic Hierarchy Process (AHP) model revealed strong correlations between comprehensive evaluation scores and C-N metabolism indicators. Stepwise regression modeling further validated that SPAD decay rate (β=-0.4), the ratio of stem-sheath NSC accumulation (NSCA) to stem-sheath N accumulation (NA) at heading (NSCA/NA) (β= 0.62), and the ratio of LAI to SPAD value at heading stage (LAI/SPAD) (β=1.20) collectively explained 87.1 % of the synergistic variation (R²=0.871). This demonstrates that efficient C-N metabolic coordination is crucial for synergistic yield-quality-NUE improvement.

Conclusion

The synergistic improvement in yield, quality, and NUE achieved by applying panicle fertilizer at the 13th leaf stage (225 kg ha⁻¹) is fundamentally underpinned by the regulated balance of C-N metabolism. This balance optimizes sink strength, assimilate allocation, and nitrogen remobilization. Furthermore, NSCA/NA, LAI/SPAD, and SPAD decay rate are validated as key diagnostic indicators for guiding this precision management.

Implications

The findings are expected to provide a theoretical basis for varietal selection and cultivation practices aimed at achieving high yield, good quality, and high nitrogen use efficiency in indica rice.