14 DAY TRIAL // According to a new study led by biologists from the University of Pennsylvania, tree leaves maintain a constant temperature during photosynthesis, regardless of the latitude they inhabit. Researchers used to believe that the temperature of a leaf while converting sunlight and carbon dioxide into nutrients would equal that of the surrounding medium.
However, the results of the study clearly show that during photosynthesis the temperature of the leaves average about 21.4 degrees Celsius. The study involved 39 species of trees in the North American continent at a latitude higher than 50 degrees, up to the border between the United States and Canada.
It seems that tree leaves have adapted specifically to do so by triggering physiological and structural responses that closely mimic those of a human being, which regulate their internal temperature by secreting sweat in hot environments or causing shivering when the temperature drops.
"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 [warm-blooded] 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", said Brent Helliker of the University of Pennsylvania, one of the participants in the study.
If their theory is correct then leaves could regulate their temperature by increasing evaporation and the angle sunlight falls at on their surface while in warm climates, whereas in cold environments high numbers of leaves are clustered on a single branch in order to reduce heat loss.
The discovery made by the Penn team of researchers could also have significant impact in other areas of investigation, such as the study of past climate changes, since the technique used to determine such events involves the measuring of oxygen isotope ratios in the ring-like cellulose structures of the trees. The rise and drop in temperature is signaled by the different amounts of oxygen isotopes in the cellulose, but this is only true if the temperature of the leaves is close to that of the surrounding air. The new study shows that this is hardly the case.