WHEAT-GRAIN QUALITY UNDER ENHANCED TROPOSPHERIC CO2 AND O-3 CONCENTRATIONS

It is expected that the progressive increase of tropospheric trace gas es such as CO2 and O-3 will have a significant impact on agricultural production. The single and combined effects of CO2 enrichment and trop ospheric O-3 on grain quality characteristics in soft red winter wheat (Triticum aestivum L.) were examined in held studies using 3 m in dia m. open-top chambers. Wheat cultivars 'Massey' (1991) and 'Saluda' (19 92) were exposed to two CO2 concentrations (350 vs. 590 mu mol CO2 mol (-1); 12 h d(-1)) in combination with two O-3 regimes (charcoal-filter ed air vs. ambient air + 40 +/- 20 nmol O-3 mol(-1), 7 h d(-1) Monday to Friday) from late March until maturity in June. Grain quality chara cteristics investigated included: test weight, milling and baking qual ity, flour yield, protein content, softness equivalent, alkaline water retention capacity, and cookie diameter. In general, exposure of plan ts to either elevated CO2 or weekly chronic O-3 episodes caused only s mall changes in grain quality. Milling and baking quality score were n ot significantly changed in response to treatments in both years. Flou r yield was increased by elevated CO2 but this increase was counteract ed when elevated CO2 was combined with chronic O-3 exposure. Flour pro tein contents were increased by enhanced O-3 exposure and reduced by e levated CO2. Softness equivalent was increased by 2.4% by enhanced O-3 exposure but unaffected by O-3 under elevated CO2. Although the singl e effect of either CO2 enrichment or chronic O-3 exposure had some imp act on grain quality characteristic, it was noted that the combined ef fect of these gases was minor. It is Likely that the concomitant incre ase of CO2 and O-3 in the troposphere will have no significant impact on wheat grain quality.