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I've read that efficiency of photosynthesis is only like 5%, and it operates on visible light spectrum, not infrared (which is heat radiation). Which means light should either be absorbed and increase plant temperature, or reflected, and heat what's around the plant. But when you get near or touch plants under sunlight, they are at ambient temperature. In contrast, if you touch a metal plate, ceramic tile, rubber, plastic, asphalt, concrete, sand etc, that's exposed to strong sunlight, they are very hot, either because they reflect heat onto you (sand), or because they absorb heat and their temperature is high (asphalt). But with plants, it seems like neither happens, and it stays cool. How does that work?

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  • $\begingroup$ This seems like more of a physics question than a biological one.. $\endgroup$ – MattDMo Nov 9 '16 at 19:00
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    $\begingroup$ Not really, the physics part is well outlined in the question. Radiation (light) must either be reflected or absorbed, and this will result in a heating of the plant or the surroundings, unless the energy is transformed. My question is, what biological mechanisms do plants use to transform energy and avoid excessive temperatures. $\endgroup$ – Southbob Nov 9 '16 at 19:23
  • $\begingroup$ @MattDMo I disagree, I'm pretty sure plants use specific mechanisms to avoid getting too hot, which would hinder their normal metabolism. $\endgroup$ – Dart Feld Nov 9 '16 at 19:27
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Take a look at the Temperature paragraph from this reference: Ecophysiology

Plants can avoid overheating by minimising the amount of sunlight absorbed and by enhancing the cooling effects of wind and transpiration.

They seem to have several ways to counter the heat as we do with transpiration, wind etc.

This article is more complicated but as really useful informations on the effects of wind on the plant's temperature:

Leaves in the lowest and highest winds: temperature, force and shape

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  • $\begingroup$ that makes sense, the reference linked is also very useful. $\endgroup$ – Southbob Nov 11 '16 at 11:59
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    $\begingroup$ Plants 'transpire' a lot. If you look at false-colour photographs, vegetation lights up as dark-red, and not green, because the radiate a lot of near-infrared light: heat. @Southbob $\endgroup$ – RHA Nov 12 '16 at 12:49
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You mix several things.

  • logic: if the plant converts some of the radiation into energy rather than heat + reflection, then it's normal that it heats less than some other object with same amount of reflection.
  • physics: the feeling of cold/hot object is related to his thermal conductivity more than its temperature. That's why walking on wood/wool doesn't feel the same than on steel.
  • physics+bio: plants are mostly made of water, and thus evaporate, which cool them down. Steel doesn't.
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  • $\begingroup$ You misunderstood the question. I acknowledge that energy has to be transformed, what i asked is what is the mechanism used to convert, and how much is converted. $\endgroup$ – Southbob Nov 25 '16 at 20:03

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