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Friday, May 14, 2010

Rising atmospheric Carbon Dioxide levels threaten crop yields and food security

Crop yields are under threat from rising carbon dioxide emissions with climate change, according to new scientific research. In a new study published in Science on wheat and the mustard plant Arabidopsis at the University of California at Davis, scientists found that increasing atmospheric carbon dioxide interferes with plants' ability to convert nitrate into protein resulting in lower nutritional yield.

Related: Koalas face starvation, extinction due to climate change

This has implications for global food production, food nutritional quality and food security. It effects not only humans but the animal ecosystems dependant on current plant physiologies.

"Our findings suggest that scientists cannot examine the response of crops to global climate change simply in terms of rising carbon dioxide levels or higher temperatures," said lead author Arnold Bloom, a professor in UC Davis' Department of Plant Sciences.

"Instead, we must consider shifts in plant nitrogen use that will alter food quality and even pest control, as lower protein levels in plants will force both people and pests to consume more plant material to meet their nutritional requirements," Bloom said.

As climate change intensifies, careful management of nitrogen fertilization by farmers will become critical to reduce losses in crop productivity and quality, according to the research.

The concentration of carbon dioxide in Earth's atmosphere has increased by 39 percent since 1800, and on current projections will increase by an additional 40 to 140 percent by the end of the century.

Plants require nitrogen, mostly in the form of nitrates in the soil, to survive and grow. Research has shown that when atmospheric carbon dioxide concentrations increase by 50 percent, the nitrogen status of plants declines significantly.

"This indicates that as atmospheric carbon dioxide concentrations rise and nitrate assimilation in plant tissues diminishes, crops will become depleted in organic nitrogen compounds, including protein, and food quality will suffer," Bloom said. "Increasing nitrogen fertilization might compensate for slower nitrate assimilation rates, but this might not be economically or environmentally feasible."

"One fear is insect outbreaks will become more extensive, because the insects will have to eat more to meet nutritional needs." Arnold Bloom told the ABC. (Listen to a popdcast interview with Arnold Bloom)

A study at the University of Illinois found that in a soybean field subjected to higher concentrations of carbon dioxide, the plant leaves were more prone to attack from beetles.

As plants absorb more carbon dioxide, levels of plant nutrition will go down and for some toxin levels will go up. So crops will have less nutritional yield which will mean humans or other animals will need to eat more to get the same level of nutrition. Plants will put more energy into defensive systems such as phenols or cyanide compounds.

Dr Ros Gleadow told a recent ABC Catalyst program "Leaves of plants grown at elevated carbon dioxide have a lot less protein. Wheat, barley, rice, all of those in probably only 50 to 60 years time will have 15 to 20% less protein in them than they do now." she said, "In about 50 years time or even 100 years time eucalyptus leaves will have trouble supporting arboreal herbivores like koalas because the phenolic concentration will be too high and the protein level too low."

Bad news for the Koala, one of Australia's iconic creatures, facing extinction from climate change.

Cassava is one of the world's staple food crops because of the plant's drought tolerance. However increased CO2 will stimulate more cyanogen compounds in the plant. Dr Ros Gleadow told Catalyst "We grew cassava at three different concentrations of carbon dioxide. Today's air, one and a half times the amount of carbon dioxide and twice the carbon dioxide of today. And we found that cyanogen concentration in the leaves increased."

Cyanide poisoning from Cassava produces a serious paralytic disease known as Konza, which was first diagnosed in 1981 in Mozambique. Simple methods have been devised to treat the cassava root to allow enzymes to eliminate some of the cyanide as hydrogen cyanide gas, making the tuber relatively safe to eat after processing.

Dr Ros Gleadow outlined that in high carbon dioxide environment the yield from the tuber is also reduced, "The plants actually made less tubers when we grew them at elevated carbon dioxide." she said, "It is all very highly balanced in plants, the ratio of the proteins and the toxins. When you grow plants at elevated carbon dioxide the plants are more efficient so they can grow really well. And at the same time allocate more of their resources to defence."

You can watch the whole segment from Catalyst - Toxic Crops - on the ABC website or download for later viewing.

While carbon dioxide is increasing, there will also be effects from changes in rainfall and water, changes in temperature, which will effect crops. Corn, soybeans and cotton are the largest three crops by production value in the US which will be affected by extreme heat. Above a certain threhold - 29 degrees - crop yields decline rapidly with the effects being described as 'damaging large' by a report by Agricultural Economists published in August in the Proceedings of the National Academy of Sciences.

We appear to be in for a period of declining crop yield as well as nutritional yield due to climate change which will challenge feeding the world's still growing population.



Takver is a citizen journalist from Melbourne who has been writing on Climate Change issues and protests including Rising Sea Level, Ocean acidification, Environmental and social Impacts since 2004.