Does elevated atmospheric carbon dioxide concentration increase wheat nitrogen demand and recovery of nitrogen applied at stem elongation?

The effect of elevated carbon dioxide concentration ([CO2]) on fertilizer nitrogen (N) recovery in wheat grown under open-air conditions in the North China Plain has not been reported. Winter wheat (Triticum aestivum L. cv. Zhongmai 175) was grown to maturity under ambient (415 ± 16 μmol mol−1) and elevated (550 ± 17 μmol mol−1) [CO2] at the free-air carbon dioxide enrichment (FACE) facility in a semi-arid region in northern China. We applied 15N-enriched (10.22 at.%) granular urea to microplots at either 25 or 95 kg N ha−1 at the stem elongation stage of wheat. Elevated [CO2] increased wheat biomass (29%) and grain yield (23%), but had no significant effect on grain protein concentration. The [CO2]-induced N demand (19%) was satisfied mostly by increased uptake of indigenous N (19%). Elevated [CO2] had no significant effect on the recovery of fertilizer 15N (applied at stem elongation) by the plant or on the amount that remained in the soil. Of the fertilizer 15N assimilated by the whole plant, the allocation to grain increased from 62% under ambient [CO2] to 72% under elevated [CO2]. High N application did not increase wheat biomass, grain protein concentration, or fertilizer N recovery in the plant, irrespective of [CO2]. The results suggest that current fertilizer practice in a wheat cropping system such as in the North China Plain will have to be adjusted in a CO2-rich world.