The effects of elevated [CO₂] on growth, nitrogen (N) uptake and fertilizer-¹⁵N recovery by spring wheat (Triticum aestivum L. cv. Yitpi) were investigated under ambient (380 mmol mol^–1) and elevated (550 mmol mol^–1) [CO₂] at the Australian Grains Free-Air Carbon dioxide Enrichment (AGFACE) experiment in southern Australia over a 2-year period. ¹⁵N-enriched (10.22 atom%) granular urea was applied to PVC microplots at 50 kg N ha^–1 at rainfed and supplementary irrigated conditions for three experimental periods (2008 normal sowing (2008NS), 2008 late sowing (2008LS) and 2009 normal sowing (2009NS)). Elevated [CO₂] increased the total biomass of wheat grown at 2008NS and rainfed plots of 2009NS by 27-58% and a concurrent total N uptake by 19-44%, while tissue N concentration remained unchanged. At these growth periods, the amount of plant N derived from soil increased by 20-50% under elevated [CO₂], but that derived from fertilizer remained unchanged. At late sowing (warmer and drier), elevated [CO₂] had no effect on wheat biomass, tissue N concentration and N uptake. In general, elevated [CO₂] did not alter the percentage of fertilizer recovery in plant and in soil for any experimental periods. Supplementary irrigation increased grain yield by 94 and 37% for 2008LS and 2009NS, respectively. These results indicate that higher fertilizer application rate will be necessary in this wheat field under future [CO₂] environments, whereas yield gains in future hotter and drier climates will be lower than in higher rainfall zones.

 

Keywords

Free-air carbon dioxide enrichment (FACE), supplementary irrigation, nitrogen uptake, nitrogen fertilizer recovery, wheat