Elevated CO2 in semi-arid cropping systems: A synthesis of research from the Australian Grains Free Air CO2 Enrichment (AGFACE) research program

Abstract

Climate change impacts to crop production are likely to be greatest in semi-arid regions already constrained by marginal growing conditions. The response of temperate grain crops (wheat, field pea and lentil) to elevated CO 2 (eCO 2 ) (550 μmol mol − 1 ) under semi-arid field conditions was studied over 11 years in the Australian Grains Free Air CO 2 Enrichment (AGFACE) research program. This review synthesizes key outcomes and implications for crop adaptation in a semi-arid environment. Across all crops and environments, eCO 2 increased mean yields (16–58%) compared to current ambient (aCO 2 ) concentrations. Wheat yields increased by 18% and 29% under rainfed and supplemental irrigation, respectively resulting in yield increases of 6.1 (aCO 2 ) and 14.1 (eCO 2 ) kg ha − 1 mm − 1 of additional water. Wheat grain [N] declined (~ 7%) under eCO 2 across cultivars, resulting in reduced grain protein and bread baking quality, and this was not reversed by additional fertilizer N. Of several tested crop traits favorable for dryland cropping of wheat under eCO 2 , a transpiration efficiency trait increased yields under eCO 2 representing a path for adaptation in semi-arid environments. The rates and amounts of N 2 fixation in legumes were increased by eCO 2 but were greater under higher soil water content. Barley yellow dwarf virus incidence increased by 10.6% due to changes in epidemiology under eCO 2 . Results from AGFACE suggest that maximizing the advantages of eCO 2 requires synergistic development of adapted management systems, innovative genetics and removing physiological bottlenecks. This systems approach will increase the potential to maintain agricultural production in new combinations of environments for longer than if changes are piecemeal.