Elevated CO₂ alters grain quality of two bread wheat cultivars grown under different environmental conditions

Bread wheat (Triticum aestivum L. cv. Yitpi and cv. Janz) was grown under field conditions in the Australian Grains Free-Air CO₂ Enrichment (AGFACE) facility. Ambient [CO₂] (a[CO₂], ~384μmolmol^-1) and elevated [CO₂] (e[CO₂], ~550μmolmol^-1) were combined with two soil water levels (rain-fed and irrigated) and two times of sowing (TOS) in three consecutive years to provide six environments (2007-TOS₁, 2007-TOS₂, 2008-TOS₁, 2008-TOS₂, 2009-TOS₁, 2009-TOS₂). Grain samples were assessed for a range of physical, nutritional and dough rheological properties. The effect of e[CO₂] on thousand grain weight (TGW) was significantly different in each growing environment: TGW was significantly increased under e[CO₂] only at 2007-TOS₂ (by 5%), 2009-TOS₁ (by 5%) and 2009-TOS₂ (by 15%) but not significantly changed under other conditions. The magnitude of reduction of grain protein concentration at e[CO₂] differed among the growing environments but was highly correlated with the percentage yield stimulation under e[CO₂] (r²=0.91) suggesting that grain protein concentration under e[CO₂] was diluted by increased yield. Across all treatments, grain nutrient concentration was significantly reduced by e[CO₂] for Fe (3.9%, 6.2%), Cu (2.2%, 3.4%), Zn (5.9%, 5.7%), Ca (5.6%, 7.3%), Mg (5.6%, 5.8%), Na (21.2%, 30.4%), S (4.4%, 4.4%), P (4.1%, 3.2%) in cv. Yitpi and Janz, respectively. Effects of e[CO₂] on grain Zn, Mg and Na concentrations were dependent on the growing environment. Relative reduction of grain S, Fe, Mg, Zn, P at e[CO₂] were significantly correlated with grain yield stimulation at e[CO₂]. Reductions of these nutrients under e[CO₂] were not fully explained by biomass dilution as the relationships differed for each nutrient. Under e[CO₂], flour yield of cv. Janz was increased but that of cv. Yitpi was not changed. Even though grain protein concentrations of both cultivars were similar at e[CO₂], bread volume as inferred indirectly by dough rheology parameters was 12% greater for cv. Janz (185±5cm³) than cv. Yitpi (162±4cm³) at e[CO₂]. This disparity may be related to the compositional changes in wheat flour protein at e[CO₂], suggesting that future breeding and adaptation strategies to improve the grain quality under e[CO₂] should consider the prevailing hydro-thermal conditions.