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Autumn Leaf Color Questions

Tue Sep 10 09:03:39 EST 1996

Dear Plant Eder's:
I am teaching a plant physiol class this fall and need to clarify a few
"points" concerning leaf color changes which occur in the autumn.

Here are some of the "facts" as I know them:

1. Light Intensity Requirement. Color changes are enhanced by high photon
flux densities. Presumably this "slows" the senescence process and allows for
more cyanidin biosynthesis (any other ideas??).

2. Ambient Temperature. It seems that high daytime temperatures during leaf
senescence also enhances the intensity of color.

3. Growing Season Conditions. This is a fairly encompassing category and
includes things like water-deficit stress, air pollutants, biotic pathogens,
mineral deficiencies. It appears that "stressed" trees undergo leaf
senescence early and with less vibrant color produrction. This is particularly
true for tree species such as poplar exposed to ozone.

What I am unsure about is effect of rainfall accumulation. Does a "wet" fall
assure better color production vs. a "dry" fall? Also, what is the normal
order of species which "turn" in the autumn? 

Any other info would also be helpful!!

Thanks in advance. I'll post a compiliation of all responses in a week's

Alex Enyedi

Dr. Alexander J. Enyedi
Dept of Biological Sciences
Western Michigan University
Kalamazoo, Michigan 49008
(616) 387-5627

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