Grain mineral contents under elevated carbon dioxide

Wheat (Triticum aestivum L. cv. Yitpi) was grown under field conditions in the Australian Grains Free-Air Carbon Dioxide Enrichment (AGFACE) facility during the 2008 and 2009 growing seasons. Current ambient CO₂ (384 µmol/mol) and elevated CO₂ (550 µmol/mol) were combined with two different times of sowing (TOS): A “normal sowing” date (TOS1) contrasted with “late sowing” (TOS2) to investigate the CO₂ interaction with TOS which provide different grain filling temperature on grain quality. Grain physical and chemical properties were investigated. Thousand-kernel weight (TKW) was increased at elevated CO₂, while the size distribution shifted towards larger grains. Grain protein concentration (dry grain basis) was 15.3% (2008) and 15.5% (2009) under ambient CO₂ and 13.4% (2008) and 13.5% (2009) under elevated CO₂, showing a 12.5% and 13.1% reduction at elevated CO₂ in both years. The largest reduction in grain protein concentration at elevated CO₂ relative to ambient CO₂ was observed at TOS2. Regardless of growth CO₂ concentration, overall grain protein concentration was higher at TOS2 in both years (16.87%, 15.63%) than at TOS1 (11.83%, 13.41%), and the magnitude of protein concentration increase at TOS2 was 42.6% and 16.6% in 2008 and 2009, respectively. Large changes in mineral nutrient composition were also observed under elevated CO₂, showing a decline in concentration of several minerals. At elevated CO₂ the reduction in grain mineral concentrations of Fe (10.6%), Ca (8.8%), Cu (11.7%), P (8.8%), S (9.9%), Mg (8.3%), Zn (12%), and Na (48%) were observed. Large reduction in grain Zn and Fe was observed in both 2008 and 2009. Reduction in grain protein was well correlated with Fe, Zn, and S concentration, suggesting that elevated CO₂ is likely to exaggerate worldwide Fe and Zn malnutrition for those on grain-based diets. ANZ-05