Subject: Tomatoes---reflected light

From: [email-masked] (ALFRED VORNE)
Date: 5 Apr 1995 01:41:41 GMT

I recently read that the USDA found a red plastic mulch increased yield 
20% apparently because reflected light increased photosynthesis by 
reflecting light back up to the plant.

It would follow that tomato flavor will also increase because flavor is 
related to sugars which increase with sun light.

Post your plus and minus comments on the above. I grow tomatoes for 
flavor and would like to know if you think this would be worth the 
effort.

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From: [email-masked] (Polar)
Date: 5 Apr 1995 07:24:31 GMT

In <[email-masked]> [email-masked] (ALFRED 

>flavor and would like to know if you think this would be worth the 
By that logic, wouldn't you get even -more- reflected light by putting 
down aluminum foil?  I, too, would be curious if there's a basis to the 
"red mulch" theory.  And if so, where one gets it.

Polar

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From: [email-masked] (Dick Gilman)
Date: Wed, 05 Apr 1995 15:48:06 GMT

I put aluminum foil around the edge of my seedlings when they are
still inside by the window.  You put the foil around the edge that
is not in the sunlight.  The light is then reflected back onto the
plants.  This helps the plants get enough sun from both sides.  

Has anyone tried this in a garden setting???  Considering that I
have a fence around the edge of my garden I just may try this to
see what happens.  

Martin Kosiak

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From: [email-masked] (Polar)
Date: 5 Apr 1995 07:24:31 GMT

Polar

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From: [email-masked] (Dick Gilman)
Date: Wed, 05 Apr 1995 15:48:06 GMT

Martin Kosiak

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From: [email-masked] (Polar)
Date: 5 Apr 1995 07:24:31 GMT

Polar

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From: [email-masked] (Dick Gilman)
Date: Wed, 05 Apr 1995 15:48:06 GMT

Martin Kosiak

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From: [email-masked]
Date: 7 Apr 95 13:08:41 -0600

In article <[email-masked]>, [email-masked] (Karen Kolling) writes:
> In article <[email-masked]> [email-masked] writes:

>>I'd really like to see this study, and particularly replications
>>of this study... it sounds a little fishy to me (but I'm not
>>a plant physiologist).  I thought most tomatoes, as grown in home
>>gardens, were pretty well "light-saturate", as tomatoes are a C-3
>>species, and adding more light isn't going to help much, if at all.
> 
     Should have been "light-saturated": I'm not typing well this
     week.

> Say what? "light-saturate"? C-3?  Perhaps unrelated to this, I
> recollect being told to line the innards of a plant light fixture with
> red paper to shift the light to a more useful part of the spectrum.

"Light-saturated":  When you put a plant in a small amount of light,
you get a small amount of photosynthesis.  Increase the amount of
light, and you increase the amount of photosynthesis.  This works
up to a point:  at some point, there is so much light reaching the
plants that photosynthesis is cranking along at maximum rates for the
plant, and giving it more light won't do anything.  You've hit the
light saturation point, and it's equivalent to flooring the accelerator
in a car.  Adding more gas to the carburetor isn't going to make the
car go any faster.

C-3 plants are the equivalent of my little Honda... a nice, ordinary
car, quite conventional, and it maxes out at about 85 mph.  C-3
photosynthesis is the ordinary photosynthesis your biology teacher
made you memorize in college... C-3 plants (it's normally written
C-subscript 3) have as the first major product a 3-carbon acid,
phosphoglyceric acid.  Hence the name.

C-4 plants are the turbo-charged racecars of the plant world.  They
make a 4-carbon acid (oxaloacetic, malic, or aspartic acids, for instance)
as their major step in CO2 fixation.  And most of them have the
ability to use more photons (light wave/particles) than C-3
plants.

There's some other things that go on here:  C-4 plants can do C-3
photosynthesis at the same time, but C-3 plants can only do C-3.
In addition, photorespiration, the respiratory loss of CO2 from
utilizing sugar to run photosynthesis and other plant metabolism,
doesn't occur in C-4 species, because C-4 plants can scavenge the
respired CO2, and run it back through photosynthesis (CO2 is often
a limiting factor in photosynthesis: that's why some greenhouse
crops are produced in an atmosphere enriched in CO2.

What's the difference in productivity between C-3 and C-4
species?

Plant type                           maximum photosynthesis rate*
------------------------             -------------------------------
                  ------C-3 plants------
slow growing perennials                      1-10
  (orchids, desert species)             
evergreen woody species                      5-15
deciduous woody species                     15-30
rapidly maturing annuals                    20-50
  (wheat, soybeans, tomato, sunflower...)

                      ----C-4 plants----
tropical grasses (esp. Andropogonoids)     50-100
  (sugar cane, corn, pigweed, saltbush) 
__________________________________________________________________
*mg CO2 fixed per square decimeter of leaf per hour

There are a lot of other things that contribute to the efficiency
of photosynthetic plants, like the fact that photorespiration
rates increase at a faster rate with increased temperature than does
increases in photosynthesis.  At temps of 25-35oC (80-95oF) C-3
plants have no net photosynthesis.  They quit growing because it's
just too hot for them.   C-4 plants are just getting going then..

Most plants have C-3 photosynthesis.   I'm sure, as veggie or
flower gardeners, we've observed that peas are cool climate or
cool season crops, but corn does best in the middle of the summer.
That's the C-3 vs. C-4 photosynthesis kicking in.  

If a farmer wants good pasture in the summer for his grazing animals,
he'd be advised to plant "warm season grasses", like big and little
bluestem, instead of "cool season grasses" like kentucky bluegrass,
fescues, etc.  C-4 vs. C-3.

_______________________________________

As to lining a growth chamber with red paper, it's not going to 
"shift" the light to a more usable part of the spectrum (photosynthetic
pigments absorb strongly in the red region, with a secondary
peak in the blue region).  Red paper is going to reflect red light
back onto the plants, but it's also going to absorb blue photons.
Maybe that's what you want: white lining paper would reflect all
wavelengths equally (assuming perfect reflectance), and there are
some processes that are regulated by red light, and others by blue
light.  Still, the overall effect should be a net reduction in 
photosynthesis in a red-lined box, compared to a white-lined box
if you're putting the same amount of light into each box.

If you're interested in how plants grow, and why they grow, Malcolm
Wilkins has written an excellent and quite readable book called
_Plant Watching_.  It's not very technical, and certainly assumes
no technical knowledge... gorgeous pictures and interesting examples.
First plant physiology book that didn't put me to sleep in 5 milliseconds!

Kay Klier  [email-masked]

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From: [email-masked] (Mcdevlin)
Date: 6 Apr 1995 21:37:10 -0400

I read about putting tin foil around the bottom of plants, because it
helps them get sun below the leaves.  You just have to be cause of to much
sun, so it doesn't burn the leaves.

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From: [email-masked] (Mcdevlin)
Date: 6 Apr 1995 21:37:10 -0400

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From: [email-masked] (Mcdevlin)
Date: 6 Apr 1995 21:37:10 -0400

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From: [email-masked] (Mcdevlin)
Date: 6 Apr 1995 21:37:10 -0400

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From: [email-masked]
Date: 6 Apr 95 13:28:49 -0600

BTW, the flavor components of ripe tomatoes are not all due to
sugars, but to a wide variety of esters and glycosides, and all
sorts of things.  Some of the flavor chemicals don't even develop
until the tomato is sliced and cells are ruptured (part of the
reason sliced-tomato-on-plate tastes different from tomato-eaten-
out-of-hand-in-garden.

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From: [email-masked]
Date: 6 Apr 95 13:28:49 -0600

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From: [email-masked] (Gerald Sacks)
Date: 6 APR 95 11:14:52

There was an article in the Winter 1993/1994 issue of The Growing EDGE
that mentioned this research.  Since mulch isn't available in red, the
researchers painted the mulch.

Gerald Sacks			[email-masked]

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From: [email-masked] (Karen Kolling)
Date: Fri, 7 Apr 1995 10:55:47 GMT