Effects of Elevated CO 2 Concentration and Nitrogen Application Levels on the Accumulation and Translocation of Non-Structural Carbohydrates in Japonica Rice

Non-structural carbohydrates (NSC) play an important role in yield formation. In this paper, the relationships of NSC accumulation and translocation with yield formation were investigated under elevated CO 2 concentrations ([CO 2 ]) and nitrogen (N) application rates. A japonica rice ( Oryza sativa L.) cultivar, “Nanjing 9108,” was grown at three [CO 2 ]—Ambient (T0), ambient + 160 μmol·mol −1 (T1), and ambient + 200 μmol·mol −1 (T2)—in open-top chambers (OTC), with three levels of N fertilizer application rates—10 gN·m −2 (N1), 20 gN·m −2 (N2), and 30 gN·m −2 (N3)—Which were set in OTCs using pot experiments. The results showed that the concentration of NSC (C NSC ) and the total mass of NSC stored in stems (TM NSC ) under T1 and T2 were higher than those in the T0 treatment, and the C NSC and TM NSC of N3 were lower than those of N1 and N2 at the heading stage. The C NSC and the TM NSC were significantly positively correlated with the stem biomass during the growth period and were notably negatively correlated with the N content in leaves (N leaf ) at the heading and filling stages. The seed setting rate was significantly positively related to the apparent transferred mass of NSC from stems to grains (ATM NSC ) at the filling stage, while the relationship between yield and the ATM NSC was not statistically significant. Although there was no difference in the apparent contribution of transferred NSC to grain yield (AC NSC ) between treatments, NSC stored in stems further accumulated obviously during the late filling stage, implying that the grain yield of “Nanjing 9108” was predominantly sink-limited. We concluded that elevated [CO 2 ] improved the concentration of NSC at the rice heading stage. The interaction between elevated [CO 2 ] and N fertilizer rates significantly influenced the concentration of NSC at the filling stage. Rice stems NSC reaccumulated at the late grain filling stage, which implies a restriction on NSC transference to grain.