Elevated atmospheric [CO2] can dramatically increase wheat yields in semi‐arid environments and buffer against heat waves

Wheat production will be impacted by increasing concentration of atmospheric CO₂ CO₂], which is expected to rise from about 400 μmol mol^?1 in 2015 to 550 μmol mol^?1 by 2050. Changes to plant physiology and crop responses from elevated CO₂] (eCO₂]) are well documented for some environments, but field‐level responses in dryland Mediterranean environments with terminal drought and heat waves are scarce. The Australian Grains Free Air CO₂ Enrichment facility was established to compare wheat (Triticum aestivum) growth and yield under ambient (~370 μmol^?1 in 2007) and eCO₂] (550 μmol^?1) in semi‐arid environments. Experiments were undertaken at two dryland sites (Horsham and Walpeup) across three years with two cultivars, two sowing times and two irrigation treatments. Mean yield stimulation due to eCO₂] was 24% at Horsham and 53% at Walpeup, with some treatment responses greater than 70%, depending on environment. Under supplemental irrigation, eCO₂] stimulated yields at Horsham by 37% compared to 13% under rainfed conditions, showing that water limited growth and yield response to eCO₂]. Heat wave effects were ameliorated under eCO₂] as shown by reductions of 31% and 54% in screenings and 10% and 12% larger kernels (Horsham and Walpeup). Greatest yield stimulations occurred in the eCO₂] late sowing and heat stressed treatments, when supplied with more water. There were no clear differences in cultivar response due to eCO₂]. Multiple regression showed that yield response to eCO₂] depended on temperatures and water availability before and after anthesis. Thus, timing of temperature and water and the crop's ability to translocate carbohydrates to the grain postanthesis were all important in determining the eCO₂] response. The large responses to eCO₂] under dryland conditions have not been previously reported and underscore the need for field level research to provide mechanistic understanding for adapting crops to a changing climate.