Leaves Keep Their Cool to Protect Photosynthesis

A study published in Nature showed that plants protect one of their most important functions – photosynthesis – by maintaining the average leaf temperatures at 21°C, regardless of the weather. The findings could have implications on how scientists use tree rings to model past climates, and how they predict future responses to climate change.

The scientists in the study decided to use the oxygen isotope method, a technique which has been employed to determine a region's climate, to calculate the temperature of modern tree canopies. The data revealed that the average temperature of the leaves hovered around 21°C during photosynthesis.

Plants use several mechanisms to adjust their temperature. In warmer climates, some cool off by changing the angle of their leaves relative to the sun, or using fine hairs as a kind of sunscreen. They can also ‘sweat’, sacrificing water for the cooling effects of evaporation. In colder climates, trees clump their leaves closer together on their branches. The branch can be likened to a mitten, keeping the leaves close so that each is less affected by the weather conditions.  

The complete article is available at http://www.nature.com/news/2008/080611/full/news.2008.884.html.