What was done
Three varieties of winter wheat (Emma, Martina and Mezofold) were grown in controlled environment chambers under ambient (375 ppm) and elevated (750 ppm) CO2 at a min, max and mean temperature regime of 10,12 and 10.7°C, respectively.  In addition, twelve days after the average heading date, several plants were subjected to fifteen days of elevated temperatures (min/max/mean of 20, 35 and 25.2°C ) in an effort to assess the combined effects of elevated CO2 and temperature on wheat growth and yield.

What was learned
The temperature treatment accelerated the aging process in the three wheat varieties, but concurrent atmospheric CO2 enrichment generally helped them maintain a higher and longer level of photosynthetic activity during grain-filling and maturation.  As a result, the authors report that the CO2-enriched plants "suffered less damage from heat stress and produced a higher yield than at the ambient level."  What is more, in the case of the Emma cultivar, the extra CO2 supplied to the plants meant the difference between life and premature death, since by the end of the 15-day high-temperature treatment, the plants growing in ambient air were dead, while the plants growing in elevated CO2 were able to survive for a few more days.

What it means
In a future world of higher atmospheric CO2 concentrations, wheat crops should be better able to withstand the stress of high temperature, suffering less damage and producing greater yields.