Hi,
Well, comparing a CO2 enriched tank to a non-enriched tank is like comparing a Formula 1 race car to a Metro Bus. Although the processes are the same, the rates of chemical reactions within the plant are vastly different.
The addition of CO2 fundamentally changes not only the structure and chemical makeup of the plant, but it also radically alters the metabolic functions that occur.
If you imagine that a plant is like a factory complete with a moving assembly line this will help to visualize the how and why things go wrong. The whole point of light, CO2 and nutrients is to build a final product which is a sugar. The plant then eats the sugar to gain energy and to grow, and any excess sugar is stored in silos for future hard times.
CO2 is THE most important ingredient for making the sugar. Without CO2, shining a light on a plant is about as effective as boiling it in a soup. Plants produce what is probably the single most important enzyme called
Ribulose-1,5-bisphosphate carboxylase oxygenase, normally abbreviated to "RuBisCO". All carbohydrates on the planet are made possible by the action of this very complicated enzyme. Here is a typical image:
The areas in dark grey and light grey are the areas on the enzyme where individual CO2 molecules are attracted and held. They are then transported to an area where the Carbon portion of CO2 is combined with other molecules to create a form of glucose.
Despite its huge importance in life, RuBisCO is, by enzyme standards, rather slow, with a turnover rate of between 3 and 10 CO2 molecules per second. Typical enzyme reaction rates are somewhere around 1/2 million molecules per second. So the first two severe limitations to this enzyme are:
1. Complicated and energy expensive molecule for a plant to manufacture, which may require a few weeks to adjust the levels.
2. Very slow reaction rate.
The central role of RuBisCO in the process of photosynthesis means that it must be tightly regulated, to ensure that it is active only where and when it should be. One important layer of this regulation is the activation of RuBisCO at the beginning of the day. During the night, the RuBisCO active sites are blocked by inhibitors. So, at the beginning of the photoperiod, the plant then has to re-activate the binding sites by removing the inhibitors from the CO2 binding sites. This means that there is another set of proteins which are sensitive to light. There are additional regulators to ensure that RuBisCO only operates at daytime. Magnesium typically increases as the chlorophyl molecules become active so the sensors monitor the movement of Mg++. So here is a third limitation:
3. Activation of the enzyme is very slow at the beginning of the photoperiod. The RuBisCO in algae is more efficient because algae have a mechanism which concentrates CO2 and holds it, so they respond very quickly to the daylight. This is why siestas are a very bad idea.
Competing with CO2 for RuBisCO binding sites are O2 molecules. As both CO2 and O2 are small gaseous molecules, and moreover as RuBisCO evolved at a time when atmospheric oxygen concentrations were negligible, RuBisCO does not have perfect specificity for CO2 over O2,, i.e, it cannot tell that Oxygen has bonded instead of CO2. This is a problem for plants and algae because the Oxygen activity reduces the sugar yield. So there is a fourth and fifth limitation:
4. Oxygen availability reduces the efficiency and sugar yield of RuBisCO.
5. When RuBisCO reacts with Oxygen this results in a product called Phosphoglycollate, which cannot be converted into sugar and instead, the plant performs a function called photo-respiration which results in dangerous radical formation such as Hydrogen Peroxide, which is highly toxic to the plant.
In a low tech, non-CO2 enriched environment, because the CO2 levels are low and constant, and because the metabolic rates are also very low, the plant has time to slowly increase the RuBisCO content of the leaves.
In a high tech CO2 enriched environment, plant actually
reduces the concentration of RuBisCO, because there is less need for this expensive and high maintenance protein if CO2 availability is high. However our total incompetence at maintaining a steady state high CO2 concentration means that the the plants are forever seeing changes in the level of CO2 which commands a production rate changes and confuses the plant. Have you ever tried steering a large boat or lorry? When you turn the wheel the vehicle dose not respond right away so you turn it some more, then suddenly the rate at which it turns accelerates so you correct in the opposite direction and you suddenly find that vehicle becomes a yo-yo. That is what the plants try to deal with in our tanks.
When you add CO2 the assembly line in that factory speeds up. Sugar production rate increases and so this requires that the nutrients accumulation also speeds up. More CO2 results in a higher demand for Nitrogen. More Nitrogen creates a higher demand for Phosphorous. More Phosphorous creates a higher demand for Potassium and so on and so forth.
Likewise, adding more Phosphorous drives a higher demand for Nitrogen and adding more Nitrogen creates a higher demand for CO2. So when you start adding more of one thing you yourself create a shortage for something else. So that's why there are so many problems in a CO2 enriched tank and that's another reason why ratios can have such a profound negative effect, because no one can monitor any ratio and no one knows, under any given condition, how much of what is needed at any one time.
People always seem to assume that adding CO2 to a tank will automatically solve their problems but they are wrong. Adding CO2 only changes the type and speed of your problems. The concept of EI is to add more than the plants will ever need and so if you see a deficiency then you have to fix the deficiency of that nutrient, not play with ratios or balances.
Because people have not yet learned how to identify nutritional deficiencies, they often add the wrong things, or worse, they actually stop adding the right things, which makes their problems more acute. There are almost an infinite number of ways to screw up a CO2 tank and that's because CO2 has so many far ranging effects. Therefore, if you have a problem in a CO2 enriched tank, there is a 95% probability that it's due to incompetent CO2 administration.
Cheers,
