MadSci Network: Botany

Re: Why can pine needles carry on photosynthesis during the winter ?

Date: Thu Dec 17 15:40:30 1998
Posted By: Paul Odgren, Instructor, Cell Biology, University of Massachusetts Medical School (Dept. of Cell Biology)
Area of science: Botany
ID: 901632564.Bt

Hello, I just noticed your long-standing question in the unanswered list, 
and I thought you deserved a response.

The answer is that the difference between evergreen and deciduous trees in 
latitudes where there is winter is NOT in the chlorophyll. The 
chlorophylls are nearly identical. The difference is that pines and other 
conifers that bear needles all winter actually protect the cells in the 
needles from frost damage by making their version of antifreeze. Some of 
the delightful aromatic smells of pines, spruces, and balsams are due to 
the mixture of organic compounds that are constituents of the sap that 
helps protect the photosynthetic machinery from sub-freezing temperatures.

The problem for deciduous trees is not that the light level gets too low in 
winter for their chlorophyll to function. They respond to shortening hours 
of daylight by shedding their leaves and shutting down for the winter as an 
evolutionary adaptation to the coming COLD, not the lack of light per se. 

I hope you find this answer, that you didn't give up on ever getting one. 
And I hope it answers your question.

Paul Odgren, Ph.D.
Dept. of Cell Biology
Univesity of Massachusetts Medical School
Worcester MA

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