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Re: light intensities and latitude

In a message dated 97-02-21 19:52:13 EST, you write:

>NPR reported recently that a film student took a light meter reading out of
>doors at noon on a clear, sunny day in New York, NY, and came up with a
>reading of 300-and- some-odd candle feet. The same week, a film student in
>Los Angeles also took a light meter reading outside on a clear sunny day,
>and his clocked 700-and-something candle feet. .... NYC is located at 40
degrees, 43 minutes N; LA  sits at 34 degrees, 4 minutes N.
>This is a monster difference in light intensity......
>Is there literature about the "physics" of iris acclimation to growing
>conditions? Are plants that survive in dimmer, northern climes less
>ambitious and productive, or does something in their foliage respond more
>efficiently to light? Do they adapt by doing more with less or just by
>doing less? Are they more like high-speed photo films or more like
>Does brightness  play a huge role in how well iris hybridized in one locale
>do when transplanted into  another? celia storey USDA Zone 7b Little Rock,

Well, Celia, I dunno.  I did talk to one of my ecophysiologist friends about
the general subject.  He reminded me that daylength is longer in northern
latitudes until it starts getting cold again.  He said that photosynthesis
(food storage) tends to be cumulative up to total light saturation, which
would occur for most plants at light intensities less than those in
California.  The total amount of light available for photosynthesis would be
about the same (combination of longer days makes up for less light) - he says
there are studies that have shown this.  I think.  He did say that for plants
with dense vertical foliage (like irises), higher light intensities could
make a difference, because they can more successfully illuminate (light
saturate) the lower leaves, which would be shading one another.

This may offer an explanation of why some plants that don't tolerate shade in
the north can tolerate some shade in the south - due to the higher light
intensities, they can get enough light even when it is partially filtered
through tree leaves.

Ok, now you real physicists get in here and straighten out what I said wrong.

Linda Mann lmann76543@aol.com east Tennessee USA

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