3.3 Carbohydrate accumulation promoted by the eCO2

Under the ambient CO2 condition, soluble sugar content reduced significantly when N application rate increased from N0 to N5 and N10. Further enrichment to N15 significantly increased the soluble sugar content. However, the starch content was relatively stable (Fig. 3A, B, C and D). Likewise, under the eCO2, enrichment of N from N0 to N5 reduced soluble sugar, but further N enrichment to N10 or N15 increased soluble sugar content. In contrast, the starch content under the eCO2 was consistently high under all N application rates (Fig. 3E, F, G and H). The new-born tillers under the eCO2 had higher contents of both soluble sugar and starch than the ambient CO2, implying that relative higher distribution of N content in them was not a result of carbohydrate drainage. Overall, under the eCO2condition, all tissues contained higher carbohydrate content than the ambientCO2, regardless of N application rate.