And it does make a lot of sense. Plants need Light, CO2, and
nutrients. If the light level is very low, plants need to work
harder to utilize that light. If the CO2 level is very low, plants
need to work harder to utilize that CO2. If the plant is spending its
energy to utilize CO2 and light, then that energy can't be used for
growth. So, if you supply more of light or CO2, then the plant
doesn't have to work quite as hard, and so it has a little more energy
left for growth.


There are few other good ideas that spin off this concept.
One is algae. Algae growth is reduced, herbivores don't need to work
as hard(slower algal growth). The aquarist spends less time pruning
and scrubbing algae.

In a similar way, very low NO3 for example will reduce PO4 and NH4
uptake, basically stunting a plant through starvation. It won't
necessarily kill the plant, but it's not doing much(and becomes a good
place for algae to grow) it just stops growing until the nutrients are
available again.
Only severe nutrient deficiencies will result in death of the plant.

The more pieces of the nutrient/CO2 equation that are put together,
the more flexibilty one has with other factors and parameters.

To gauge things like light, a tank is set at an optimum, then
manipulate one paratmeter at a time to see how the system responds.
Adding High CO2 and nutrients allows the light to be the limiting
factor.

Adding high nutrients and light allows the CO2 to be the limiting
factor.

Adding high CO2 and light allows the nutreints to be the limiting
factor.

Adding high light, CO2, PO4, K and NO3 allows the Traces to be the
limiting factor.

And so on..........

Most of the issue for folks is knowning what these optimum ranges are
and being able to maintain them long enough to consider the parameter
they are wanting to manipulate. This is/has been confounded with poor
testing and test kits, no standards to test these kits against etc.

Regards,
Tom Barr