Subject: I'm totally stummped re: leaf areas

From: [email-masked] (Dennis)
Date: 1 Dec 1995 09:03:53 -0800

Although silence is golden, please forgive me from braking it with
something this has puzzled me and to which I can find no help in the
literature.
 
We have measured leaf areas over several seasons of an evergreen oak
in Arizona.  Before I analysed the data I expected that leaf areas would
increase following bud burst, leaves would expand to their terminal size,
then leaf areas would remain relatively constant over the rest of the
season.  However, my data indicate that this certainly is not the case.
So could I impose on the wisdom of the net to offer an explaination?
 
We had 20 trees (randomly selected out of 200 trees at the study site),
and haphazzardly picked 20 leaves from each tree yeilding 400 leaves for
each sample date.  Leaves were collected at roughly 2-2.5 month intervals
throughout the "tree-year" (a tree-year is from about Mar or Apr when leaves
flush through next Mar or Apr when leaves synchroinously abscise).
Leaf areas were imaged within 24 hrs and areas measured accurately with
an image analysis program.
 
We observed the following trends by calculating mean leaf area (for all 400
leaves for each collection date) and plotting leaf area against time.
We did observe the initial increase in area following bud burst.
 Then a steady decrease in area by up to 25%, then an increase
in area by up to 30% over the tree year.  Remember that the same leaves were
not measured on each date as sampling is destructive. We were careful not to
sample leaves which sometimes flush mid season or leaves which might remain
on the tree from the previous season, i.e., those leaves which did not
abscise when most leaves did at the end of the tree year.
 
Why should we get such differing leaf areas on the trees thoughout the year?
I don't think it is simply sampling error as 400 leaves is a pretty good
sample size and the error bars for each date are very small (around .08).
 
Any suggestions would be appreciated
 
Cheers Dennis Wilson

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From: Lauraine Hawkins <[email-masked]>
Date: Tue, 5 Dec 1995 08:46:00 EST

Hi Dennis & other symbiologists!
I'm not a plant person, so my off the cuff questions may not mean much,
but here goes...
You said you measured leaf area on a computer image. I'm assuming that
means you flattened the leaves out, so a change in area wouldn't have
come from leaves folding into a curved shape... Did you also measure
leaf length in any way? Are your area changes absolute changes or
relative changes? I guess what I'm wondering is whether there were some
real shape changes as the leaves aged -- can leaves 'enlarge' due to
changes in water content of the leaf cells (without adding new cells)??
If it is possible, I would think that changing the water content in the
leaf cells would be fairly plastic & enlarging the leaves during times
when the plants had plenty of moisture might even be adaptive. But maybe
this is off the wall & not even possible??

Wishing my fellow symbiologists the bappiest of holiday seasons-
Lauraine Hawkins