There are few reports on the effects of atmospheric carbon dioxide concentration ([CO2]) on fertilizer N recovery by crops under open-air conditions. This study was conducted at the Australian Grains Free-Air CO2 Enrichment (AGFACE) facility in southern Australia to investigate the effects of elevated [CO2] (550 mu mol mol(-1)) on growth, N uptake and fertilizer N-15 recovery by spring wheat (Triticum aestivum L. cv. Yitpi) over a 2-year period. N-15-enriched (10.22 atom%) granular urea was applied to microplots at 50 kg N ha(-1) at varying seasonal rainfall and temperature scenarios (simulated by supplementary irrigation and late sowing) for three experimental periods [2008 normal sowing (2008NS), 2008 late sowing (2008LS) and 2009 normal sowing (2009NS)]. Elevated [CO2] increased wheat biomass (27-58%), N uptake (18-44%) and amount of plant N derived from soil (20-50%) at 2008NS and 2009NS (rainfed), but the effect was not apparent at 2008LS (hotter and drier) and supplementary irrigated plots for 2009NS (above-average rainfall). Tissue N concentration and N derived from fertilizer were unaffected by elevated [CO2] in any experimental period. Irrespective of [CO2], grain yield and whole plant fertilizer N uptake was 37-94 and 13-609%, respectively, higher under supplementary irrigated plots than that in rainfed counterparts. These results indicate that more fertilizer N will need to be applied to this wheat production zone under future [CO2] environments, and yield gains in hotter and drier climates will be lower than those in higher rainfall zones.
