Elevated Atmospheric CO₂ Concentration Has Limited Effect on Wheat Grain Quality Regardless of Nitrogen Supply

Elevated atmospheric CO₂ concentrations (e[CO₂]) can decrease the grain quality of wheat. However, little information exists concerning interactions between e[CO₂] and nitrogen fertilization on important grain quality traits. To investigate this, a 2-year free air CO₂ enrichment (FACE) experiment was conducted with two CO₂ (393 and 600 ppm) and three (deficiency, adequate, and excess) nitrogen levels. Concentrations of flour proteins (albumins/globulins, gliadins, and glutenins) and key minerals (iron, zinc, and sulfur) and baking quality (loaf volume) were markedly increased by increasing nitrogen levels and varied between years. e[CO₂] resulted in slightly decreased albumin/globulin and total gluten concentration under all nitrogen conditions, whereas loaf volume and mineral concentrations remained unaffected. Two-dimensional gel electrophoresis revealed strong effects of nitrogen supply and year on the grain proteome. Under adequate nitrogen, the grain proteome was affected by e[CO₂] with 19 downregulated and 17 upregulated protein spots. The downregulated proteins comprised globulins but no gluten proteins. e[CO₂] resulted in decreased crude protein concentration at maximum loaf volume. The present study contrasts with other FACE studies showing markedly stronger negative impacts of e[CO₂] on chemical grain quality, and the reasons for that might be differences between genotypes, soil conditions, or the extent of growth stimulation by e[CO₂].