Media Release - 28 March 2003

NEW LIGHT ON PLANTS AND CARBON DIOXIDE

Changes in the kind of light plants receive might be affecting the regulation of the greenhouse gas carbon dioxide within the atmosphere, according to Australian scientists.

Working for CRC Greenhouse Accounting, Professor Graham Farquhar and Dr Michael Roderick, two researchers at the Australian National University, showed that plants photosynthesise more effectively when sunlight is diffused through cloud or haze rather than when it hits plant canopies directly.

“On clear sunny days light comes directly from the sun causing strong shadows to fall and leaves to shade each other,” Dr Roderick says.

“Under hazy conditions the light comes from all directions, reducing shade – this has a marked effect on plants.”

“The effect might seem subtle, but the Mount Pinatubo eruption in 1991 provided a large-scale test of the importance of diffuse light.”

“At the time of that eruption, growth of carbon dioxide in the atmosphere slowed.

“A couple of years ago we suggested that the cloud from the Mt Pinatubo eruption diffused sunlight, plants responded by growing more, and the rate at which carbon dioxide was accumulating in the atmosphere dropped,” he says.

Scientists in the United States have since re-analysed data collected at the time of the eruption and confirmed this effect.

“Understanding this effect is important because in the northern hemisphere over the past 50 years greater cloudiness and more pollution has increased the amount of diffuse light and we expect that plants should have responded accordingly,” Dr Roderick says.

Writing this week in the prestigious US Journal Science, Professor Farquhar and Dr Roderick point out that visual artists have long known of the importance of light and shade.

“We have used the work of the French impressionist Claude Monet and his 1880 painting ‘View of Vetheuil’ to illustrate the importance of the interplay of light and shade to plants,” he says.

INFORMATION:

Dr Mike Roderick (02 6125 5589) (0427 440 360)

Dr Chris Mitchell, CEO, CRC for Greenhouse Accounting (Mobile: 0419 992 914)

Prof Graham Farquhar (Mobile: 0404 048 960)