London, June 12 : Scientists have long believed that temperature of tree leaves is controlled by the outside environment, but a new University of Pennsylvania study has challenged this belief, by finding that healthy, photosynthesizing tree leaves have an inherent tendency to control their own temperature.
In the study, the researchers surveyed 39 tree species ranging in location from subtropical to boreal climates, and found that the temperature in tree leaves was almost constant.
With these findings, scientists will get new insights in how tree branches and leaves maintain a homeostatic temperature, which is ideal for photosynthesis. It also indicates that plant physiology and ecology should also be considered vital by biologists to tap trees for investigating climate change.
The study said that Tree photosynthesis usually occurs when leaf temperatures touch almost 21 degrees celsius, where latitude or average growing-season temperature play little, if any, role.
Such homeostasis of leaf temperature indicates that in colder climates leaves increase their temperatures and in case of warmer climates tree leaves cool to reach optimal conditions for photosynthesis. Thus, the old belief that leaf temperature is fixed needs a re-thinking.
"It is not surprising to think that a polar bear in northern Canada and a black bear in Florida have the same internal body temperature. They are endothermic mammals like us ,and they generate their own heat. However, to think that a black spruce in Canada and a Caribbean pine in Puerto Rico have the same average leaf temperature is quite astonishing, particularly since trees are most definitely not endothermic," Nature quoted Brent Helliker, professor of biology in the School of Arts and Sciences at Penn, as saying.
"Our research suggests that they use a combination of purely physical phenomena - like the cooling from water evaporation or the warming caused by packing a lot of leaves together - to maintain what looks like leaf-temperature homeostasis," he added.
Now, one can consider leaf temperature, cooled by the physiological and morphological techniques of evaporation, leaf angle or reflection and heated by a decrease in evaporation and an increase in the number of leaves per branch, as adaptations in the run to achieve homeostasis.
Also, the study offers a new hypothesis asking the reason behind certain trees growing specifically in certain climates. It may also lead to a new theory for how and why trees in the north will suffer from global warming, by overheating due to the mechanisms they have evolved for keeping their leaves warm.
Besides, weather-forecasting models are based on precise estimates of surface-water evaporation, which mainly comes from tree leaves. Such knowledge of the temperature of these leaves may help in accurately predicting future climate scenarios.
The study is published online in the latest issue of Nature.