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Do Leaves Get Hotter in Sunlight?

Botanists used to assume that the temperature of a photosynthesizing tree leaf would be the same as that of the surrounding air. But a 2008 study published in the journal Nature showed that tree leaves have a built-in climate control system that keeps them at a constant 69.8 degrees Fahrenheit (21.4 degrees Celsius) while they are in the process of converting sunlight, water, and carbon dioxide into food. This temperature stays about the same, whether they are located in frosty Canada or the toasty Caribbean.

A leaf's inner thermostat:

  • Biologists at the University of Pennsylvania studied 39 tree species that grow within a range of 50 degrees of latitude across North America, between Puerto Rico and Canada.
  • “To think that a black spruce in Canada and a Caribbean pine in Puerto Rico have the same average leaf temperature is quite astonishing,” said researcher Brent Helliker.
  • Plants use several mechanisms to adjust their temperature, from changing the angle of their leaves relative to the sun, clustering leaf growth, or altering evaporation rates.
Discussion Comments
By anon1000076 — On May 22, 2018

There are a multitude of reasons for leaf drop. Unseasonably high temperatures alone is not one of them.

By anon1000065 — On May 19, 2018

I'm surprised because of the way leaves 'dry' up and curl as they fall off of trees even in the spring.Just last week, we had massive leaf drop when it warmed up to no higher than the 80's. And this is NorCal-East Bay area of San Francisco, Sonoma County.

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