Characteristics of Grain Yield, Dry Matter Production and Nitrogen Uptake and Transport of Rice Varieties with Different Grain Protein Content

Grain protein content (GPC) is an important index affecting rice quality and nutrition, and there is a large difference in the GPC among varieties. However, the differences in the grain yield, dry matter production, and nitrogen uptake and transport among varieties with a different GPC and their relationships with the GPC are still unclear. In this study, three japonica varieties with high GPC (H-GPC) and three japonica varieties with low GPC (L-GPC) were compared for their grain yield, dry matter production, and nitrogen uptake and transport, in field experiments under the same nitrogen application level in 2020 and 2021. The results showed that the grain yield of the L-GPC type was 26.87% higher in 2020, and 25.98% higher in 2021 than that of the H-GPC type at the same nitrogen rate, which might be related to the higher spikelet per panicle and larger sink capacity of the L-GPC type. Moreover, the varieties with L-GPC showed more dry matter production and total nitrogen content compared with the varieties with H-GPC at the heading stage and maturity, but the nitrogen uptake during the grain-filling period (NUP-GF) of the L-GPC varieties was lower than that of the H-GPC varieties. The leaf nitrogen translocation amount (L-NTA) of the L-GPC type was significantly higher than that of the H-GPC type. There was no significant difference in the leaf nitrogen translocation efficiency (L-NTE) between the different GPC types. The GPC was mainly determined by the amount of nitrogen available for developing the grain per unit sink capacity (NAV) and had a significant positive correlation with the NAV, indicating that sufficient NAV is necessary to obtain a high GPC. The direct restriction effect of the sink capacity on the NAV was the largest, and the leaf nitrogen content at the heading stage (LNC-H) had the largest direct promotion effect on the NAV, but the indirect restriction effect of the LNC-H on the NAV was also the strongest. The direct and indirect path coefficients of the NUP-GF to the NAV were both positive, indicating that increasing the NUP-GF can promote the improvement of the NAV.