Elevated atmospheric CO 2 concentration triggers redistribution of nitrogen to promote tillering in rice.

Elevated atmospheric CO 2 concentration (eCO 2 ) often reduces nitrogen (N) content in rice plants and stimulates tillering. However, there is a general consensus that reduced N would constrain rice tillering. To resolve this contradiction, we investigated N distribution and transcriptomic changes in different rice plant organs after subjecting them to eCO 2 and different N application rates. Our results showed that eCO 2 significantly promoted rice tillers (by 0.6, 1.1, 1.7, and 2.1 tillers/plant at 0, 75, 150, and 225 kg N ha -1  N application rates, respectively) and more tillers were produced under higher N application rates, confirming that N availability constrained tillering in the early stages of growth. Although N content declined in the leaves (-11.0 to -20.7 mg g -1 ) and sheaths (-9.8 to -28.8 mg g -1 ) of rice plants exposed to eCO 2 , the N content of newly emerged tillers on plants exposed to eCO 2 equaled or exceeded the N content of tillers produced under ambient CO 2 conditions. Apparently, the redistribution of N within the plant per se was a critical adaptation strategy to the eCO 2 condition. Transcriptomic analysis revealed that eCO 2 induced less extensive alteration of gene expression than did N application. Most importantly, the expression levels of multiple N-related transporters and receptors such as nitrate transporter NRT2.3a/b and NRT1.1a/b were differentially regulated in leaf and shoot apical meristem, suggesting that multiple genes were involved in sensing the N signal and transporting N metabolites to adapt to eCO 2 . The redistribution of N in different organs could be a universal adaptation strategy of terrestrial plants to eCO 2 .