Quantifying quality under elevated CO2

The impact of rising atmospheric carbon dioxide (CO²) levels on Australia’s grains industry is being closely examined by scientists involved in the Australian Grain Free Air CO₂ Enrichment (AGFACE) program at Horsham in the Victorian Wimmera.

With CO₂ levels predicted to rise by about 40 per cent over the next 40 years, the AGFACE program – a joint initiative of the Department of Primary Industries, the University of Melbourne and the GRDC  – was set up in 2007. The objective was to provide tools and information that will enable the grains industry, through policy makers and pre-breeders, to remain productive and competitive despite changes in climate.

According to researchers, increases in atmospheric CO₂ will bring with it both benefits and challenges. Because CO₂ acts as a fertiliser, it promotes improved water use efficiency, plant growth and yield, but under elevated levels grain quality is reduced. AGFACE scientists are investigating how the grains industry might realise the potential of this ‘CO₂ fertilisation effect’ while maintaining grain quality, and under which conditions it will be beneficial.

The aim is to identify the combination of management techniques and germplasm that will ensure sustainable production in the Australian grains industry under future environments.  

The program

The AGFACE program seeks to gain knowledge of cultivar traits and cropping systems capable of performing under elevated atmospheric CO₂. BCG (Birchip Cropping Group) 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.

As well as looking at traits future varieties will need, AGFACE researchers are working on projects focusing on grain quality (including the impact on bread and noodle making), increased nitrogen uptake and how pulse and wheat rotations can address this, the behaviour of pests and diseases in an elevated CO₂ environment and below-ground processes.

A laboratory without walls

AGFACE research involves fully replicated wheat trial plots grown under CO₂ levels expected in 2050 (550 parts per million) and compared with plots grown under the current CO₂ concentration (370ppm).

The research takes place at a purpose-built facility at Horsham which achieves elevated CO₂ levels by means of a cleverly engineered system that sees CO₂ injected into the atmosphere from pipes circling the research plots. 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.

In 2010, 2011 and 2012 wheat cultivars grown at the Horsham facility included Janz, Silverstar, Yitpi and H45. Large scale quality analyses were completed on the machine harvested wheat samples.

Grain quality

According to data collected so far, elevated CO₂ has been found to adversely affect important grain traits such as protein content, mixing properties and baking properties, as well as the micronutrients in wheat.

However, different wheat cultivars interact differently when grown under elevated CO₂ conditions which will allow breeders to select for adaptations.

For the past three years, the wheat quality research team at DEPI Horsham have examined how elevated CO₂ effects grain protein, grain weight and screenings, endosperm hardness and test weights.

But the program goes a step further, with the wheat milled and the flour’s baking and milling qualities examined. Elements such as dough rheology, flour colour, milling yield, dough mixing properties, water uptake, mixing stability, dough strength and extensibility are all tested.

Protein is a major determinant for processing quality and there have been significant decreases in grain protein under elevated CO₂ levels.

Research scientist Cassandra Walker said depending on variety, wheat grown under elevated CO₂ was generally one to 1.5 per cent lower in grain protein content than its equivalent grown under ambient conditions.

Additionally, dough rheology properties were adversely affected by elevated CO₂ which is significant from a baking perspective.

“Potential, grain now classified as AH could become ASW,” Ms Walker said.

“But some varieties aren’t as affected as others.”

The impact of elevated CO₂ is especially evident after baking with loaves made from wheat grown under elevated CO₂ smaller and denser (up to a 10 per cent reduction in volume).

“A likely consequence of this reduction in baking quality is increased baking costs and a demand for higher quality wheat,” Ms Walker said.

“This would flow on to the farmer with increased input costs, particularly in terms of fertilisers and nutrients.”

Nutritional changes

AGFACE research also indicates that in the future wheat micronutrients could be reduced as a consequence of higher CO₂ levels.

AGFACE project leader Glenn Fitzgerald said while this effect is less well documented, it is critical to future human and animal nutrition and food security.

“Changes in grain nutritional qualities would impact people most severely in developing nations where much of the food consumed is plant based,” he said.

“These aspects are being actively studied in AGFACE.”

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.

So far the research has found the quality premium grade wheats such as Yitpi and Janz suffer greater effects of elevated CO₂ than H45 or Silverstar.

The AGFACE facility is helping researchers to provide vital information on benchmarking cultivars such as Janz and Yitpi and monitor potential new cultivars.

Data from this research will help ensure key quality parametres such as protein content, dough rheology and loaf volume, are not compromised as CO₂ increases in the future.