Leaves have internal thermostats

Whether in Canada or the Caribbean, leaves don't have to worry about outside temperatures - they have built-in weather controllers for the purpose of keeping them comfortable.

The long-term concept of plant biologists is that the temperature of a photosynthetic leaf will be similar to the temperature of the surrounding air.

But in a 39-plant study that spreads across 50 latitudes along North America (between Puerto Rico and Canada), biologists at the University of Pennsylvania found that leaves still retain near-stable temperatures while they move. Turn sunlight and carbon dioxide into food.

This work, published in the June 12 issue of Nature, found that photosynthesis occurs when the temperature of the leaves is about 21.4 degrees Celsius, the latitude and average growing season play a very important role Small, if any, in the temperature of the leaves.

Instead, leaves can have physiological and structural adaptations that help them stabilize the internal system (we humans do this when we sweat or shudder in response to hot temperatures or cold to maintain body temperature). This discovery surprised biologists.

(Photo: www.pdphoto.org )

According to a member of the Brent Helliker team, Penn, 'It's no surprise that a polar bear in northern Canada and a black bear in Florida have the same body temperature. They are isothermal animals like us and give birth to temperature for themselves. However, thinking that a black spruce in Canada and a Caribbean pine in Puerto Rico have the same average leaf temperature is exceptional, especially when the absolute tree is not isothermal. '

Helliker and his colleagues suggest that the evaporation and leaf angle (which affect the amount of light they reflect) helps to cool down in warm weather while the reduction evaporates and concentrates more leaves on a branch to help them Keep warm in colder regions.

The results of the project, funded by the University of Pennsylvania Department of Biology and the Andrew W. Mellon Foundation, mean how the northern weather plants will respond to global warming: They can overheating due to the mechanism by which they evolved to 'keep warm'.

The result is also significant for scientists studying past weather changes by measuring the ratio of different oxygen isotopes (number of different neutrons) in tree-ring cellulose. The number of special isotopes present in the cellulose is affected by the temperature of the leaves, and scientists have assumed that the temperature of the leaves is similar to the surrounding temperature. This new work proves that it is not accurate.