Leaves have been found to regulate temperature to “around 21.4° Celsius plus or minus 2.2 degrees,” during photosynthesis. That appears to me to be a design to increase or optimize photosynthesis.
ID Hypothesis: Trees, and other biotic systems regulate leaf temperature to increase or optimize photosynthesis. There will be temperature and/or humidity sensors and transpiration regulation systems to achieve this temperature control.
Corollary: Net primary productivity would be substantially lower without such temperature regulation.
Global Warming Impact: This finding may invalidate tree ring temperature proxies in extrapolating to past temperatures to evaluate climate change.
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Goldilocks tree leaves
by Susan Milius, June 11th, 2008,
Sweating in the heat or huddling in the cold keeps temperatures favorable
JUST RIGHTTree leaves can do plenty to keep their temperatures just right for photosynthesis.Tree leaves do a pretty good job of achieving temperatures that are just right for photosynthesis, even if it’s too hot or too cold where they live, a new study shows.
From roughly the top to the bottom of North America, across some 50 degrees of latitude, trees all do their photosynthesizing at leaf temperatures around 21.4° Celsius plus or minus 2.2 degrees, says physiological ecologist Brent Helliker of the University of Pennsylvania in Philadelphia. That conclusion was based on a broad survey of the ratios of two forms of oxygen that vary depending on the temperature and humidity of leaves. Those properties control evaporation and make a signature in the cellulose of the tree rings, Helliker and colleague Suzanna Richter report in an upcoming Nature.
Such temperature control undermines the assumption that the insides of leaves have the same temperature as the air, Helliker says. That’s an assumption underlying studies that check oxygen ratios in old tree tissue to reconstruct past climates, he says.
. . .Trees release water, and during hot times, that botanical sweat cools them down. And trees that grow in cold places tend to cluster their leaves. These tight formations can affect the rate at which leaves lose heat on cold days, just as fingers pressed together in mittens stay warmer than fingers separated by space in gloves. . . .
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