By Glenn Fitzgerald
Climate change and extreme weather events are already impacting our food, from meat and vegetables, right through, till wine. In our series on the Climate and Food, were looking at what this means for the food chain.
The concentration of carbon dioxide in the atmosphere is increasing.
Everything else being equal, higher CO? levels will increase the yields of major crops such as wheat, barley and pulses but the trade-off is a hit to the quality and nutritional content of some of our favourite foods.
In our research at the Australian Grains Free Air CO? Enrichment (AGFACE) facility, we at Agriculture Victoria and The University of Melbourne are mimicking the CO? levels likely to be found in the year 2050. CO? levels currently stand at 406 parts per million (ppm) and are expected to rise to 550 ppm by 2050. We have found that elevated levels of CO? will reduce the concentration of grain protein and micronutrients like zinc and iron, in cereals (pulses are less affected).
[su_pullquote align=”right”]The degree to which protein is affected by CO? depends on the temperature and available water.[/su_pullquote]
The degree to which protein is affected by CO? depends on the temperature and available water. In the wet years, there will be a smaller impact than in drier years. But over nine years of research we have shown that the average decrease in grain protein content is 6% when there is elevated CO?.
Since a decrease in protein content due to elevated CO2 levels can be more severe in dry conditions, Australia could be particularly affected. Unless methods are found to ameliorate the decrease in protein through plant breeding and agronomy, Australias dry conditions may put it at a competitive disadvantage, since grain quality is likely to decrease more than in other parts of the world with more favourable growing conditions.
Food quality
There are several different classes of wheat some are good for making bread, others for noodles etc. The amount of protein content is one of the factors that sets some wheat apart from others.
Although a 6% average decrease in grain protein content may not seem large, it could result in a lot of Australian wheat being downgraded. Some regions may be completely unable to grow wheat of high enough quality to make bread.
The protein reduction in wheat will be manifested in a number of ways. As many farmers are paid premiums for high protein concentrations, their incomes could suffer. Our exports will also take a hit, as markets prefer high-protein wheat. For consumers, we could see the reduction in bread quality (the best bread flours are high-protein) and nutrition. Loaf volume and texture may be different but it is unclear whether the taste will be affected.
The main measure of this is loaf volume and texture, but the degree of decrease is affected by crop variety. A decrease in grain protein concentration is one factor affecting loaf volume, but dough characteristics (such as elasticity) are also degraded by changes in the protein make-up of grains. This alters the composition of glutenin and gliadin proteins which are the predominant proteins in gluten. To maintain bread quality when lower quality flour is used, bakers can add gluten, but if gluten characteristics are changed, this may not achieve the desired dough characteristics for high quality bread. Even if adding extra gluten remedies poor loaf quality, it adds extra expense to the baking process.
[su_pullquote align=”right”]If grain protein concentration decreases, people with less access to food may need to consume more (at more cost) in order to meet their basic nutritional needs.[/su_pullquote]
Nutrition will also be affected by reduced grain protein, particularly in developing areas with more limited access to food. This is a major food security concern. If grain protein concentration decreases, people with less access to food may need to consume more (at more cost) in order to meet their basic nutritional needs. Reduced micronutrients, notably zinc and iron, could affect health, particularly in Africa. This is being addressed by international efforts like biofortification and selection of iron and zinc rich varieties, but it is unknown whether such efforts will be successful as CO? levels increase.
The extreme climate changes are gradually burning away the vast wheat fields thus reducing the yield drastically. | Photo Courtesy: PasselWhat can we do about it?
Farmers have always been adaptive and responsive to changes and it is possible that the management of nitrogen fertilisers could minimise the reduction in grain protein. The research we are conducting shows, however, that adding additional fertiliser has less effect under elevated CO? conditions than under current CO? levels. There may be fundamental physiological changes and bottlenecks under elevated CO? levels that are not yet well understood.
If management through nitrogen-based fertilisation cannot, or can only partly, increase grain protein, then we must question whether plant breeding can keep up with the rapid increase in CO?. Are there traits that are not being considered but that could optimise the positives and reduce the negative impacts?
Selection of high protein wheat varieties often results in a decrease in yield. This relationship is referred to as the yield-protein conundrum. A lot of effort has gone into finding varieties that increase protein while maintaining yields. We have yet to find real success down this path.
Will the new, genetically modified varieties of wheat be able to withstand the elevated carbon dioxide levels? | Photo Courtesy: PasselA combination of management, adaptation and breeding may be able to maintain grain protein while still increasing yields. But, there are unknowns under elevated CO? levels like whether protein make-up is altered, and whether there are limitations in the plant to how protein is manufactured under such conditions. We may require active selection and more extensive testing of traits and management practices to understand whether varieties selected now will still respond as expected under future CO? conditions.
Finally, to maintain bread quality we should rethink our intentions. Not all kinds of wheat need to be destined for bread. But, for Australia to remain competitive in international markets, plant breeders may need to select varieties with higher grain protein concentrations under elevated CO2 conditions, focusing on varieties that contain the specific gluten protein combinations necessary for a delicious loaf.