Clearly there seems to be a great degree of confusion regarding the use
of
CO2, Andy the "dutch researchers" you speak of have most certainley found a
place in thier industry for CO2 supplimentation. As a matter of fact nearly
every large greenhouse on the planet uses CO2 supplimentation. To say that
one would ONLY recieve a benefit if one were to activley measure
concetraions in the air at any given time is an inherently false statement.
Does the tree make a sound if no one is there to hear it?
Here IS some published information by ACTUAL scientists, not some
mysterious group of national "Researchers".
So now Ill take this opertunity to quote Joe J. Hanan from Greenhouses
Advanced Technology for Protected Horticulture, c 1998, CRC Press LLC. ISBN
0-8493-1698-7
"Plants produced in greenhouses consist mostly of water- on the average
around 90% of thier fresh weight. Of the remaining 10%, about half that 10%
is carbon [Levanon et al., 1986]. This carbon is derived from the CO2 in the
air, which has a very low concentration of about 340 ppm or 34 Pa (0.034%).
The principle purpose of photosythesis is to combine water and carbon in the
presence of a suitable energy supply (solar radiation) to form the basic
building blocks of life. The converse of photosynthesis, of course, is
respiration, occurring in all organisms always. Carbon compounds within
plants are broken down, releasing CO2 so that the organism can grow and
replicate.
Many authors, such as Beer [1986], have pointed out that for a plant to
grow, a positve carbon balance must be maintained. The photosynthetic rate
must exceed the respiratory rate sufficiently so that total respiration
during the night and day doe not cause a negative balance. Such a situation
can occur under northern European conditions of long nights and low solar
radiation."[(You can include northern American in this sentance as
well)]."As Shown by Challa [1976], cucumbers, when subjected to the usual
constant night temperatures, can enter a "starvation" phase under Dutch
conditions after 12 hours of dark. A high net photosynthesis, therefore, for
a short period in a single leaf is not always indicative a profitable crop.
If, however, net photosynthesis is expressed by net CO2 uptake per plant or
per unit ground area, then a much better idea of potential productivity can
be suggested [Bravdo,1986]. Most of the basic information on the processes
involved deal with single leaves for obvious reasons of simplicity in the
experimental process. However, there is considerable information on plant
performance where either CO2 uptake by a whole plant, or several plants in a
growth chamber or small green house have been examined. Typical examples
include work by Hand and Bowman [1969], Enoch et al. [1973], Krizek et al.
[1974], Challa [1976], Bierhuizen et al. [1984], plus several others.
One can appreciate that if CO2 is absent, growth cannot occur. Even if
some
CO2 is present in the air around the plant, it may not be at a high enough
concentration to result in a positve carbon balance. If the atmospheric
concentration of CO2 can be increased during the day, the photosynthetic
rate may be increased - provided no other factors limit the process (i.e.,
low temperature, low solar radiation, lack of water supply, or inadequate
nutrition). CO2 enrichment in greenhouses is particularly subject to the
requirements of the species being grown, and to the restrictions imposed by
climatic conditions of the locality."
Well I hope that clears things up a little bit, I could certainly continue
further in this chapter if any of you should desire.
Andy, if you would like thourogh explanation of flower induction in
Phalaenopsis I would suggest you read, Phalaenopsis orchid light
requirement during induction of spiking. Wang, Y.T. 1995. HortScience
30:59-61
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Sent: Friday, November 17, 2006 3:52 AM
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Subject: Orchids Digest, Vol 8, Issue 388
------------------------------
Message: 9
Date: Thu, 16 Nov 2006 19:24:56 -0500
From: "Andrew Easton" <[EMAIL PROTECTED]>
Subject: [OGD] Addition of CO2
To: <[email protected]>
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I'm afraid this discussion has not really addressed any substantive issues.
To get benefit from adding CO2, you would have to be measuring the
concentration in the growing area at the critical time of day (or night) and
be able to show that either it dropped to a level which was rate limiting
for photosynthesis or that increased levels produced some measurable
improvement in some useful physiological process.
The Dutch researchers, always searching for a competive edge, have looked at
CO2 addition and found no benefits and indeed never were greenhouse levels
low enough to limit photosynthesis. Published? Probably not but widely
circulated in grower newsletters.
We used to believe that adding CO2 to the air conditioned houses used to
initiate Phalaenopsis flowers in Florida was useful. Some scientists even
explained that the higher CO2 levels were reducing respiration in the heat
of the afternoon and thereby assisting growth indirectly by this reduction.
I was sceptical and we ceased use of CO2, saving many thousands of dollars
over a summer-fall period and there was absolutely no change in the speed of
initiation or the number of spikes initiated per plant.
Andy Easton
------------------------------
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