Of Greenhouse Gases and Evolution of Grasses

C4 plants, like grass, maize, sorghum and sugarcane, are equipped with a mechanism that allow them to efficiently fix carbon dioxide from the environment. The mechanism helps them combat photorespiration, an energetically costly process that occurs during conditions of high temperature, salinity, water and carbon dioxide scarcity.

It has previously been theorized that the drop in global carbon dioxide levels 30 million years ago prompted the evolution of C4 plants. Scientists however, have difficulty proving the theory because of the absence of fossil records. A group of international scientists have now presented evidences that link the event millions of years ago with the evolution of C4 plants. The scientists employed Bayesian molecular dating to estimate the ages of different C4 grass lineages. In this technique, the divergence of two lineages from a common ancestor is deduced by applying a time scale to a number of molecular differences, like mutation in the genome.

The scientists have shown that a grass subfamily emerged around 30 million years ago, right around the time when global carbon dioxide levels were dropping. They also provided evidences that the correlation is not a trivial coincidence and instead reflects a causal relationship. The findings may provide understanding of how climate change influenced the ecosystem in the past and insights on how it may affect the future.

The abstract of the paper, including links to the full article is available at http://www.current-biology.com/content/article/abstract?uid=PIIS0960982207023445