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RE: CO2 in Low Light tanks

Please excuse the delayed response - things have been a little intense at
work lately...

> Date: Thu, 14 Feb 2002 04:53:36 -0800 (PST)
> From: Scott Hieber
> If nitrogen is already a limiting factor (throttle),
> wouldn't adding CO2 make the situation even worse?
> That is, unless something else is actually the
> controlling limit in this situation -- e.g., light.

>> Date: Fri, 15 Feb 2002 07:38:09 +0100
>> From: Soren "Disky" Reinke
>> According to research done by Tropica, the impact on
>> growing speed from CO2 is much bigger in a low light
>> tank than in a high light tank.

Well, I guess if I were to try continuing the throttle analogy I might have
to "waffle" a little bit in fitting carbon into the speed game - in most
situations (higher light levels) it acts like a governor, but in low light
I'd have to describe it more as a turbocharger/ramjet.

Making the case for a "governor" is not much of a problem, as such is the
nature of a "limiting factor". This general situation we're all pretty well
familiar with, and I doubt that it needs reiterating in this case - dealing
with problems of deficiency is part of the everyday traffic on the List.

In a low light environment, the plant's metabolism is slowed down by the
reduced amount of energy absorbed and converted from available light. This
puts everything at a speed that facilitates achieving comparative balances.
Remember, too, that once the plant enters the aquatic environment it must
cope with other limitations inherent to aqueous solutions - like solution
and dissipation rates working against timely replenishment, things like
that. Upping the carbon dioxide concentration at this point makes the "sweet
spot" a whole lot easier to hit, and you are far more likely to provide the
excess glucose desired to not only produce full and lush growth but to
provide for storage within the plant's capacity.

That _stored_ energy is what sustains the plant through "crisis" situations
as well. Best example for us would be transplanting and/or shipping.
Transplanting is enough of a shock itself, and coupled with a nutritional
delay during an indeterminate shipping period the two can generate quite a
need for energy reserves. A well fed plant's advantages are pretty clear in
such a case.

As you increase the light levels, you increase the energy input to the
plant. And plants are definitely energy gluttons, always willing to turn
light into growth. Now the race really begins as the gardener fights to keep
pace on all fronts - and _something's_ always bound to be in short supply.

But this is pretty much only an expanded version of Tom's reply in APD V4
#1610 (Wed PM).

Scott also asks:
> Is the situation, and the answer(s) to my original
> question, the same for slow and fast growth plants
> (say anubia on the one hand and hgro on the other)?

The _relative_ differences still pretty much hold - just at a reduced pace.

As an interesting tangent:
One of the other things I've been playing around with is the combination of
CO2 and low *red* light. Warmer colored light tends to promote the
photosynthetic response, and coupled with the added CO2 the _expected_
results were toward really lush and sturdy growth. What I _got_ was more of
a "miniaturization" of the growth - similar to comparing a miniature Collie
to a full-sized one rather than the stunted growth of Bonsai.

So now I'm playing around with "Designer Warm Whites" and "Kitchen and
Bathroom" lamps to see which enhances the effect most. I think it'd be
interesting to try to scale down an entire aquascape to something along the
lines of Pygmy Corys ;-) ...