Abstract

Current predictions indicate that Australia is likely to be particularly challenged by the impacts of rising atmospheric carbon dioxide and the consequent perturbations in climate. The Australian Grains Free Air Carbon dioxide Enrichment (AGFACE) project in Horsham, Victoria was designed to simulate predicted atmospheric carbon dioxide levels in the year 2050. The experiment measures the interacting effects of carbon dioxide (ambient aCO2 ~380 ppm, elevated eCO2 ~550 ppm), irrigation (rainfed, irrigated), higher temperatures during grain fill (time of sowing), nitrogen (0, +), and variety (Yitpi, Janz) on wheat growth and production. Carbon dioxide was injected over the crop in open-air 12 m rings from emergence (July) until maturity (December) in 2007. Crop development was not affected by eCO2. The effect of eCO2 was to increase crop biomass at maturity by 20% (P<0.001) and anthesis root biomass increased by 49% (P=0.004). Harvest index was not affected but mean grain yield across all treatments increased from 2.68 t/ha under aCO2 to 3.23 t/ha under eCO2. Both sowing time and additional water affected growth and yield but there were no significant interactions among these factors and eCO2. The effect of higher carbon dioxide was to slightly increase the number of kernels per spikelet (P=0.055). Water use, the sum of rainfall and change in soil water from sowing to maturity was 387 mm with no differences among the treatments other than irrigation. There were no significant interactions between carbon dioxide and genotype or nitrogen treatment on growth or yield. These data will be used to calibrate crop simulation models to assist with developing strategies to assist the grains industry adapt to the changing climate.

Key Words

Climate change, grain protein, water use, root depths.

Introduction

The 2050 IPCC emissions scenario A1B indicates that atmospheric carbon dioxide will reach 550 ppm (Carter et al. 2007), and current climate models suggest that annual rainfall in the grain production regions of Australia will decline by 50–100 mm and annual mean surface temperatures rise by 1-2°C (Whetton 2001).

The effects of elevated carbon dioxide are to increase photosynthetic rates and decrease transpiration, which should result in higher transpiration efficiency (Gifford 2004). However, the concurrent rise in temperature and decline in water availability with climate change are likely to impact significantly on any gains due to the CO2 fertilisation effect.

Methods

In 2007, a FACE facility was established at Horsham (36°45’S, 142°06’E), in the grain growing region of southeastern Australia. The facility consists of 8 elevated carbon dioxide (eCO2) rings each 12 m in diameter, with equivalent ambient carbon dioxide (aCO2) experimental areas spread over a 5 ha site. Treatments imposed aimed to develop a range of temperature and water regimes during crop growth under aCO2 and eCO2 conditions.

Results and Discussion

The treatments selected provided a range of environments for wheat growth and development. The two sowing times and the two water treatments provided a contrast in both temperature and water supply to test the interaction among these factors on the response to eCO2. Figure 1 shows the grain yields for the two sowing times, two water treatments, and the two carbon dioxide levels.

Conclusions

This experiment has demonstrated the “fertilisation” effect of elevated carbon dioxide. The main yield components affected by eCO2 in this experiment were kernels per spike and kernel weight, however these were at a low level of statistical confidence (P=0.07). The actual growth and yield outcomes from this experiment are in the general range of the meta-analyses reported for eCO2 impacts, and there were few significant interactions among the factors tested here between carbon dioxide concentration, time of sowing, water supply, and cultivar.

Acknowledgements

This project has been supported by the Department of Climate Change and the Grains Research and Development Corporation (UM00027), with additional support from BOC Ltd. The authors acknowledge the technical support of R Argall, J Fitzpatrick, and P Howie.

References

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