From Canada to the Caribbean: Tree leaves control their own temperature, Penn stu...( PHILADELPHIA - The temperature insi...)

PHILADELPHIA - The temperature inside a healthy, photosynthesizing tree leaf is affected less by outside environmental temperature than originally believed, according to new research from biologists at the University of Pennsylvania.

Surveying 39 tree species ranging in location from subtropical to boreal climates, researchers found a nearly constant temperature in tree leaves. These findings provide new understanding of how tree branches and leaves maintain a homeostatic temperature considered ideal for photosynthesis and suggests that plant physiology and ecology are important factors to consider as biologists tap trees to investigate climate change.

Tree photosynthesis, according to the study, most likely occurs when leaf temperatures are about 21C, with latitude or average growing-season temperature playing little, if any, role. This homeostasis of leaf temperature means that in colder climates leaf temperatures are elevated and in warmer climates tree leaves cool to reach optimal conditions for photosynthesis. Therefore, methods that assume leaf temperature is fixed to ambient air require new consideration.

"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," Brent Helliker, professor of biology in the School of Arts and Sciences at Penn, said. "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. 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."

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