Adapting crops to increasing atmospheric carbon dioxide

Australian Grain Free Air CO₂ Enrichment (AGFACE) program scientists are studying the responses of field grown crops to elevated carbon dioxide (CO₂). The aim of this study is to lay the foundations for crop production and agro-ecosystem management practices that are well adapted to future climates.

By 2050, CO₂ levels are predicted to rise by almost 50 per cent and according to scientists this will have both positive and negative effects on grain production. Faced with this prospect, the impact of rising atmospheric CO₂ levels on grain yield and quality is being closely examined.

Researchers involved in the AGFACE program – a joint initiative of the Department of Primary Industries and the University of Melbourne – have revealed that because CO₂ acts as a fertiliser for many crops, raised levels may increase water use efficiency, growth and yield, but grain quality could be compromised.

International research has shown that current cultivars do not take advantage of increasing levels of CO₂ to maximise yields and maintain quality. To address this, AGFACE was established in 2007 to investigate how the grains industry might realise the potential of the ‘CO₂ fertilisation effect’ while maintaining grain quality, and under which conditions it will be beneficial.

If the Australian grains industry is to adapt to and profit from rising levels of CO₂, information must become available about how to alter crop management and about which traits need to be selected to maintain productivity.

What is Carbon Dioxide (CO₂)?

Carbon dioxide (CO₂) is a colourless, odourless, non-flammable gas that is emitted naturally through the carbon cycle and through human activities. It is the most prominent greenhouse gas in the earth’s atmosphere and is responsible for global warming.

A large portion of CO₂ in the atmosphere is absorbed by the oceans and other water bodies and some is used by forests and other vegetation for growth. In the past, this process kept a balance of CO₂ concentration in the atmosphere, however the global atmospheric concentrations of CO₂ began to increase at the beginning of the industrial revolution and are now rising faster than ever before. By 2050 scientists predict CO₂ levels will rise by 45 per cent, from the current level of 380 parts per million (ppm) to 550 ppm.

While there has been much public discussion about the secondary effects of elevated CO₂ levels which can lead to changes in climate, such a large change in the prime source of plant growth will also have impacts on crop production by, and in, itself. In other words, regardless of associated climate change, elevated CO₂ will impact plant growth on its own and growers will need to adapt.

The AGFACE program

The AGFACE program seeks to gain knowledge about cultivar traits and cropping systems capable of performing under elevated atmospheric CO₂ and to provide tools and information to the grains industry, policy makers and pre-breeders that will enable yield and grain quality to be maintained or increased despite changes in climate. BCG is involved in an extension capacity – charged with the task of raising awareness about the AGFACE program and the work being done to address issues that will emerge as a consequence of rising CO₂ levels.

Through the AGFACE program researchers are addressing a range of issues with six separate projects currently being conducted. These include:

• Cultivars for the future – Researchers are aiming to identify plant traits responsive to elevated CO₂ so that wheat cultivars better adapted to future conditions can be developed;
• Grain quality – Changes in grain nutritional qualities and grain chemical composition which may also impact bread and noodle making traits are being actively studied.
• Pulse-wheat rotations – Researchers are assessing crop physiology, grain quality, plant nutrition and pest and disease dynamics in a long-term field pea-wheat rotation system under rain-fed and irrigated regimes.
• Pest and diseases – Researchers are studying crown rot, barley yellow dwarf virus and insect pests in wheat and ascochyta blight in field peas to determine whether there are direct changes in pest pathogen behaviours or their interactions with the crop.
• Simulation modelling – To ensure AGFACE research is relevant to all Australian grain growing regions, crop simulation models are being used to help ascertain the future effects of elevated CO₂ on crop production across Australia.
• Below-ground processes – A complimentary project, SoilFACE, is looking at the effect of three soil types on a field pea-wheat rotation with intact soil cores under field conditions. Researchers are aiming to identify any direct elevated CO₂ effects on the rhizosphere and agronomic carry-over effects on soil nitrogen from the pea crop to wheat.

AGFACE Research Method

AGFACE research involves fully replicated wheat and pea trial plots grown under elevated CO₂ levels (550ppm) and compared with plots grown under the current CO₂ concentration (370ppm).

Initially trials were conducted at Walpeup and Horsham but now all the research takes place at a purpose-built facility at Horsham and crop modelling is used to apply the findings to cropping zones outside of the Wimmera.

The AGFACE field lab achieves elevated CO₂ levels with a cleverly engineered system that sees CO₂ injected into the atmosphere from pipes circling the research plots. The CO₂ is injected into the atmosphere on the upwind side, through 0.30 mm laser drilled holes (on stainless steel tubes) at supply line pressures of up to 500kPa. The CO₂ is then quickly mixed with air and transported across the ring by the prevailing wind. The concentration and direction of the gas is regulated by an infrared gas analyser (IRGA) in the centre of the trial plots, which turns individual outlets on and off to retain a set 550 ppm of CO₂.

The Horsham facility is one of only six such sites operating in agro-ecosystems internationally and the only one in the southern hemisphere. It is also the only FACE site in the world representing low rainfall, rain-fed grain production.

Plant sampling is carried out during vegetative growth, at flowering and at maturity. Soil water and nitrogen are measured at the beginning and end of the season and non-destructive measurements taken between these dates allow scientists to quantify growth, development, stress response and soil status.

Pest and disease dynamics are studied in the AGFACE facility and in growth chambers. Grain quality factors are also analysed.

Results and Impacts of the AGFACE Research Project

AGFACE project leader Glenn Fitzgerald said that according to data collected so far, wheat and pea yields grown under raised CO₂ conditions at Horsham are consistently yielding on average 25 per cent higher than their counterparts grown in ambient CO₂ conditions.

However, Dr Fitzgerald pointed out that these results were being achieved under current temperatures. As reported in BCG’s 2011 Research Results handbook (‘Adapting crops to increasing atmospheric carbon dioxide, pp41-44), whether future yields increase will depend largely on rainfall and temperature changes.

Dr Fitzgerald said crop modelling shows that due to predicted higher temperatures and changing rainfall patters, by 2050 wheat yields could decrease by about 10 per cent in low-rainfall zones such as the Mallee and increase by about 10 to 20 per cent in higher rainfall zones such as the south west.

In terms of quality, early AGFACE trial results saw wheat protein decrease by four to 14 per cent meaning more food may be required to maintain protein intake. Nutrients important to humans such as zinc and iron also decreased under elevated CO₂. This would particularly affect consumers in poorer regions who have insufficient micronutrients in their diets. Results have also shown that bread and noodle making characteristics will be negatively impacted under higher CO₂ levels, potentially affecting the classification of premium wheat grades.

Other early findings have pointed to a possible increase in fertiliser demand in the future with heavier crops taking up between 25 and 60 per cent more nitrogen. Also, researchers are seeing crown rot fungus in wheat producing higher fungal biomass under elevated CO₂ which could lead to a greater prevalence of this disease at a greater cost to the industry.

Where to from here?

Maintaining productivity in the future will require new crop cultivars that can maintain yield and grain quality under elevated CO₂ in conjunction with changes in rainfall patterns and increasing temperatures. Because it can take up to 20 years for new cultivars to become available commercially, growers can accelerate this process by engaging with pre-breeders and funding bodies to ensure that they are available when needed.

In those regions in which biomass is predicted to increase, greater application of nitrogen fertiliser may be required to take advantage of increased yield potential; legumes in rotation might be able to supply at least some of this.

As the AGFACE program continues and more data is collected and analysed, knowledge of crop traits that can address the challenges of the future will be delivered. Early results with crop modelling indicate that growers in the future may be able to take advantage of different temperatures and rainfall patters by adapting crop management, altering sowing times and choosing longer season cultivars.

If nothing is done now Australian agricultural productivity may continue to decline.

The AGFACE program is a collaborative venture between the Victorian Department of Primary Industries and the University of Melbourne, with crucial additional funding from the Grains Research Development Corporation and the Australian Commonwealth Department of Agriculture, Fisheries and Forestry. For more information visit the Primary Industries Climate Challenges Centre website at: www.piccc.org.au/AGFACE.