Lifetime Charter Member
Lifetime Member
Jan 24, 2005
A few days ago Tom patiently explained, again, how the enzyme rubisco is used by plants in order to make use of CO2 in their metabolic processes. Plants in low CO2 environments need more of that substance than do plants in high CO2 environments.

When plants move from low CO2 to high CO2 environments, their level of rubisco declines. When they move to lower CO2 environments they have to produce more rubisco, and if the difference in CO2 levels is too great, the plants would not do well until the rubisco levels have increased.

So, given the ability of plants to increase their levels of rubisco as required to utilize the available CO2, it would seem that CO2 levels were not terribly important in the cultivation of most aquatic plants. Only those that couldn't readily increase their rubisco levels would actually need additional CO2.

Now, additional CO2 is beneficial to all plants, but this is not because they need it to live and grow. Rather, it is akin to feeding animals more food than they need, to make them grow faster and larger.

Is this right?



Tom Barr

Staff member
Jan 23, 2005
Yes, pretty much that is the main thesis.

It takes time for them to produce more, that lag period allows algae to grow in their place and use up the higher light/NH4 available as well as an inactive surface to grow on(the plant's leaves).

Rubsico represents more enzyme protein than any other in a plant, and for that's the most prevalent enzyme in the entire world.

Given it's role, it's wise to adapt and change the levels as needed.
It also gives a nice model to why stable, vs merely high or low levels of CO2 allow plants to grow well.

With less CO2, you will have less growth, just like with terrestrial plants, they will grow faster with added CO2 as well, if you have enough water etc, not an issue for us, but in limiting soils, or where water is an issue, adding more CO2 to the air is a bad thing for plants, then by proxy, animals and then by proxy, us.

Amplification of growth has it's trade offs.

Tom Barr
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