Growth, Yield and Water Use of Wheat under Elevated Carbon Dioxide

In 2007, two free air carbon dioxide (CO₂) enrichment facilities were established to simulate the future environments under which crops will be grown by raising the CO₂ level under otherwise field conditions. Averaged for six seasons, wheat grown under high CO₂ saw 15 to 50% increases in yield. This increase occurred irrespective of the sowing time or year, but was strongly influenced by temperature and water supply. There were smaller, but significant, yield increases even under hot and dry conditions. The harvest index of these six wheat crops—the proportion of growth that goes to grain—was not reduced with high CO₂ so the plants were actually operating more efficiently with the extra carbon available to them in the atmosphere. The yield response suggests that CO₂ will help reduce the impact of higher temperatures and lower rainfalls, even in the low rainfall regions of Australia. However, higher yields come with lower grain protein content which is part of a physiological adaptation to having more CO₂. Reductions in grain mineral content and changes in other aspects of grain quality were also noticed.

The research also identified interactions between N, P and S supply, and these data indicate that adequate P is important in enabling crops to use the added carbon. Sulfur supply, balanced with N supply is important to ensure wheat baking quality. Our research also found that current varieties vary in their response to elevated CO₂, probably because of changing N allocations, differences in transpiration efficiency, variation in stress response and differences in inherent physiological features. Understanding these differences will allow targeted selection of wheat cultivars better adapted to future warmer, drier and carbon-rich environments. It will also identify regions and management practices where yield response to elevated CO₂ can be maximized. In the future, we will investigate strategies to improve N use efficiency under elevated carbon dioxide using variety differences, agronomic practice and enhanced efficiency fertilizers. ANZ-02