Does elevated atmospheric CO₂ allow for sufficient wheat grain quality in the future?

Abstract

To identify future impacts on biomass production and yield quality of important C₃ crops, spring wheat was grown in association with 13 weed species in a Mini-FACE (free-air carbon dioxide (CO₂) enrichment) system under ambient (375 μl l^-1) and elevated (526 μl l^-1) CO₂ concentrations. Wheat productivity was assessed at maturity and grain yield was subjected to various chemical analyses and baking quality tests.
CO₂ enrichment acted as carbon ‘fertiliser’ and increased the aboveground biomass production of wheat by 18.8% as there was a trend towards higher stem biomass. Although not statistically significant, wheat grain yield was increased by 13.4% due to a significant establishment of more grains per unit ground area. At the same time, thousand grain weight was non-significantly shifted towards smaller grain size classes, which may result in negative consequences for the crop market value. As a result of the CO₂- induced physiological and biochemical modifications, concentration of total grain protein was significantly decreased by 3.5%, reducing the wheat grain quality with potentially far-reaching impacts on the nutritional value and use for processing industry. Although often not significant, the concentrations of amino acids per unit of flour were decreased by 0.2 to 8.3% due to elevated CO₂ thereby affecting the composition of proteinogenic amino acids.
Furthermore, gluten proteins tended to decline. Within the significant decreased gliadins, α- and ω5-gliadins were significantly reduced under CO₂ enrichment; there was also a negative trend for ω1,2- and γ-gliadins. Changes in certain essential minerals were found as well, although not statistically significant. Concentrations of sodium, calcium, phosphorus and sulphur were slightly lowered and those of potassium and magnesium were slightly increased due to CO₂ enrichment. The micro-element molybdenum was increased, while concentrations of iron, zinc, copper, manganese and aluminium were decreased. With regard to rheological and baking parameters defining the cereal quality for industrial processing, the resistance of the dough was significantly reduced by about 30%, while the extensibility was non-significantly increased by 17.1% under CO₂ enrichment. Moreover, the bread volume was decreased non-significantly by about 9%. Elevated CO₂ is obviously affecting grain characteristics important for consumer nutrition and health, industrial processing and marketing. Experimental evidence for these changes is still poor but deserves further attention.