Wheat grain quality under enhanced tropospheric CO2 and O3 concentrations

It is expected that the progressive increase of tropospheric trace gases such as CO2 and O3 will have a significant impact on agricultural production. The single and combined effects of CO2 enrichment and tropospheric O3 on grain quality characteristics in soft red winter wheat (Triticum aestivum L.) were examined in field studies using 3 m in diam. open-top chambers. Wheat cultivars 'Massey' (1991) and 'Saluda' (1992) were exposed to two CO2 concentrations (350 vs. 500 μmol CO2 mol-1 ; 12 h d-1) in combination with two O3 regimes (charcoal-filtered air vs. ambient air + 40 ± 20 nmol O3 mol-1, 7 h d-1 ; Monday to Friday) from late March until maturity in June. Grain quality characteristics investigated included : test weight, milling and baking quality, flour yield, protein content, softness equivalent, alkaline water retention capacity, and cookie diameter. In general, exposure of plants to either elevated CO2 or weekly chronic O3 episodes caused only small changes in grain quality. Milling and baking quality score were not significantly changed in response to treatments in both years. Flour yield was increased by elevated CO2 but this increase was counteracted when elevated CO2 was combined with chronic O3 exposure. Flour protein contents were increased by enhanced O3 exposure and reduced by elevated CO2. Softness equivalent was increased by 2.4% by enhanced O3 exposure but unaffected by O3 under elevated CO2. Although the single effect of either CO2 enrichment or chronic O3 exposure had some impact on grain quality characteristic, it was noted that the combined effect of these gases was minor. It is likely that the concomitant increase of CO2 and O3 in the troposphere will have no significant impact on wheat grain quality.