Response of wheat growth, grain yield and water use to elevated CO₂ under a Free‐Air CO₂ Enrichment (FACE) experiment and modelling in a semi‐arid environment

Abstract

The response of wheat crops to elevated CO 2 (eCO 2) was measured and modelled with the Australian Grains Free‐Air CO 2 Enrichment experiment, located at Horsham, Australia. Treatments included CO 2 by water, N and temperature. The location represents a semi‐arid environment with a seasonal VPD of around 0.5 kPa. Over 3 years, the observed mean biomass at anthesis and grain yield ranged from 4200 to 10 200 kg ha−1 and 1600 to 3900 kg ha−1, respectively, over various sowing times and irrigation regimes. The mean observed response to daytime eCO 2 (from 365 to 550 μmol mol−1 CO 2) was relatively consistent for biomass at stem elongation and at anthesis and LAI at anthesis and grain yield with 21%, 23%, 21% and 26%, respectively. Seasonal water use was decreased from 320 to 301 mm (P = 0.10) by eCO 2, increasing water use efficiency for biomass and yield, 36% and 31%, respectively. The performance of six models (APSIM‐Wheat, APSIM‐Nwheat, CAT‐Wheat, CROPSYST, OLEARY‐CONNOR and SALUS) in simulating crop responses to eCO 2 was similar and within or close to the experimental error for accumulated biomass, yield and water use response, despite some variations in early growth and LAI. The primary mechanism of biomass accumulation via radiation use efficiency (RUE) or transpiration efficiency (TE) was not critical to define the overall response to eCO 2. However, under irrigation, the effect of late sowing on response to eCO 2 to biomass accumulation at DC65 was substantial in the observed data (~40%), but the simulated response was smaller, ranging from 17% to 28%. Simulated response from all six models under no water or nitrogen stress showed similar response to eCO 2 under irrigation, but the differences compared to the dryland treatment were small. Further experimental work on the interactive effects of eCO 2, water and temperature is required to resolve these model discrepancies.

Elevated field atmospheric CO2 concentrations affect the characteristics of winter wheat (cv. Bologna) grains

“…An average grain-yield increase of 15% in bread wheat grown at elevated CO 2 in FACE experiments has been found through meta-analyses (Ainsworth and Long 2005). Increases of 10% and of 26% have been reported in German and Australian environments, respectively (Högy et al 2010;O'Leary et al 2015). The first conclusion is therefore a confirmation of the 'fertiliser' role of elevated CO 2 even in winter wheat in the Southern European environment considered here.…”

Projected Dryland Cropping System Shifts in the Pacific Northwest in Response to Climate Change

“…These simulations were performed using CropSyst (Stockle et al, 1994;Stöckle et al, 2003), a cropping system model that has been widely used for climate change assessment studies under different climatic conditions around the world (Sommer et al, 2013;Donatelli et al, 2015;Holzkämper et al, 2015;O'Leary et al, 2015). Downscaled gridded daily weather data (4 × 4 km) for the period 1979-2010 (Abatzoglou, 2013) were used for baseline simulations.…”

“…These projections remained unchanged when the variation of downloaded weather from 12 GCMs used in this study was considered or when yields with a probability of exceedance of 70% were used to classify AECs. One weakness of the study is the use of a single crop model for yield projections, although the CropSyst model has been used extensively in wheat studies in the IPNW (Pannkuk et al, 1998;Peralta and Stöckle, 2002;Stöckle et al, 2010; and around the world, Pala et al, 1996;Sommer et al, 2013;Donatelli et al, 2015;Holzkämper et al, 2015;O'Leary et al, 2015). Previous studies conducted with other models have also shown positive impacts of climate change in the region (Thomson et al, 2002;Rosenzweig and Tubiello, 2007).…”

Challenges and Responses to Ongoing and Projected Climate Change for Dryland Cereal Production Systems throughout the World

“…Inclusion of CO 2 fertilization in crop models leads to projected increases in wheat yields for the Pacific Northwest of the USA well into the 21st century despite the negative effects of warming [66,96]. The yield gain measured in the Free-Air CO 2 Enrichment (FACE) experiment at 550 ppm (representing expected concentrations for 2050) at Horsham, Australia, was 25% and so exceeds the national projected losses to that date in the absence of fertilization (12%) [97]. However, FACE experiments also have limitations because they measure response to CO 2 without the temperature, precipitation, and vapour pressure differences of future climates.…”