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ABSTRACT Winter wheat ( Triticum aestivum L., cv. Mercia) was grown in chambers under light and temperature conditions similar to the UK field environment for the 1990/1991 growing season at two levels each of atmospheric CO 2 concentration (seasonal means: 361 and 692 μmol mol −1 ), temperature (tracking ambient and ambient +4°C) and nitrogen application (equivalent to 87 and 489 kg ha −1 total N applied). Total dry matter productivity through the season, the maximum number of shoots and final ear number were stimulated by CO 2 enrichment at both levels of the temperature and N treatments. At high N, there was a CO 2 ‐induced stimulation of grain yield (+15%) similar to that for total crop dry mass (+12%), and there was no significant interaction with temperature. This contrasts with other studies, where positive interactions between the effects of increases in temperature and CO 2 have been found. Temperature had a direct, negative effect on yield at both levels of the N and CO 2 treatments. This could be explained by the temperature‐dependent shortening of the phenological stages, and therefore, the time available for accumulating resources for grain formation. At high N, there was also a reduction in grain set at ambient +4°C temperature, but the overall negative effect of warmer temperature was greater on the number of grains (‐37%) than on yield (‐18%), due to a compensating increase in average grain mass. At low N, despite increasing total crop dry mass and the number of ears, elevated CO 2 did not increase grain yield and caused a significant decrease under ambient temperature conditions. This can be explained in terms of a stimulation of early vegetative growth by CO 2 enrichment leading to a reduction in the amount of N available later for the formation and filling of grain.
Mitchell et al. (Tue,) studied this question.