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C3 V C4

Carbon dioxide has a bearing on food supply. For example, some cereals are specifically adapted to low concentrations of carbon dioxide. Pascal-Antoine Christin and colleagues from the University of Lausanne, Switzerland, used a model to show that particular kinds of cereal emerged around 30 million years ago when carbon dioxide levels dropped significantly.

Cereals like corn, sugarcane, sorghum and millets belong to C4 group of plants. They are so called because of the number of carbon atoms in the compounds produced during photosynthesis. C4 plants are specially equipped to reduce the energy needed by the plant during respiration in special conditions like high temperature, drought, high salinity and low carbon dioxide levels. C4 photosynthesis is considered as an evolution over the simpler and older C3 process. C3 cereals include rice, wheat and barley.

"Increased carbon dioxide concentrations could trigger important ecological changes in ecosystems by affecting the distribution of C4 plants and related flora and fauna,' the study notes. Given that low carbon dioxide concentrations favour the growth of C4 plants, would a rise in carbon dioxide levels, as is currently happening, stymie their growth? Christin says that the predicted rise of carbon dioxide will not affect the growth of C4 plants, but instead, will favour the growth of the C3 group. Such an ecological change would probably have repercussions. However, Christin adds that human action may prevent C3 crops from competing with C4 plants.

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