3.2 Relative distribution change of N to new-born tillers under eCO2

Higher N application rate increased N content in both leaf and sheath, regardless of CO2 condition (Fig. 2 A and B). However, eCO2 reduced the N content consistently under all N application rates, compared to the ambient CO2treatments. It is worthy to mention that under the ambient CO2 condition, N content reached a plateau at the N10 treatment, whereas under the eCO2 it still increased at the N15, regardless of tissue type (leaf or sheath). This further showed that N application rate was more a constraint to rice growth at the eCO2 than at the ambient CO2 condition.
Contrary to the reductions of N contents in the leaf and sheath of rice plant, the new-born tillers under the eCO2 tended to have higher N content than under the ambient CO2 (Fig. 2C). Further comparison of their relative changes clearly demonstrated, contrasting to the dramatic decrements of N content in both leaf and sheath, the new-born tillers under the eCO2 showed a slight increment (Fig. 2D), suggesting distribution favored the new-born tillers. A plausible explanation was that a higher proportion of N distributed to the new-born tillers under eCO2 than under ambient CO2 condition.