Coordinating Postanthesis Carbon and Nitrogen Metabolism of Hybrid Rice through Different Irrigation and Nitrogen Regimes

We sought to explore the role of postanthesis carbon and nitrogen (C-N) metabolism of hybrid rice in increasing yield and nitrogen utilization efficiency (NUE). We used the 13C and 15N dual-isotope tracer method and physiological/biochemical analysis and established different irrigation and nitrogen fertilization (W-N) regimes to investigate the relationship of C-N metabolism characteristics, yield, and NUE. The results showed that W-N regimes had significant effects on postanthesis absorption and translocation of N and photosynthate, yield and NUE. Aerobic irrigation combined with the N fertilization regime 30% base, 30% tillering, 40% booting was the best W-N coupling regime for rice yield and NUE increase. The regime enhanced flag leaf photosynthesis rate and the activities of ribulose 1,5-diphosphate carboxylase/oxygenase (RuBPCase), glutamine synthetase (GS), and other key enzymes of C-N metabolism, and improved the total accumulations of photoassimilates (0.97–21.57 mg 13C plant−1) and N (1.55–23.36 mg 15N plant−1), respectively. Correlation analysis showed that, under the W-N interaction, C-N metabolism enzymes promoted the positive synergistic effect between 13C and 15N accumulation in panicles (r = 0.825). In addition, the change in C/N ratio can be used as an indicator of the simultaneous improvement in yield and NUE in hybrid rice.