Well, here's an interesting bit of info, it's referring only to this species plant, Dave Spencer's done some other work that suggest NO3 limitation can cause red color appearnaces for4 the exact same reason as this reference.
CSA
Influence of Temperature, Light and Nutrient Limitation on Anthocyanin Content of Potamogeton gramineus L
Ksander, GG; Spencer, DF
Aquatic Botany AQBODS, Vol. 38, No. 4, p 357-367, December 1990. 3 fig, 7 tab, 14 ref.
Folks read this and think they can have redder plants unfortunately.
We are talking about 3x as much nearly as a 1000 w MH light over a 20 gallon at 12" distance.
We get up near this range at the 1000w over a 20 gal.
So it is simply not practical vs natural systems.
Explaining the details is what gets folks all mucked up, they see one thing and do not take ino consideration the other factors and just how much or how little they have vs nature.
Other cases are river systems that are replentished continuely at very low concentrations of nutrients.
Another issue: plant species-species differences, some are very easily changed with NO3, some are not. You have to be specific about what species you are talking about.
The nutrients never run out and are maintained at extremely low levels.
The reservior or nutrients is huge, and many orders of maginitude higher than any aquarium.
So folks measure low or near absent nutrients in natural systems, then assume that is what plants prefer.
I spoke to Kasslemeann about this once, she gave lots and lots of data about the water column in her travels to find Echinordorus plants in her talk we heard.
I ask her if she measured the soil/pore water, she said "no". If the plants are not able to get anything from the water, they will try and get it from the substrate.
Seems strange to try and support a contention without looking at a rather obvious source of nutrients. She's smart, but appeared to overlook such assumptions(I've done such assumptions, but could not explain things in other cases and found my hypothesis to false, so I make a new hypothesis) and having gone with whatever is in nature is best. It's basic procedure to do soil analysis for wetland plants. Often there is little in the water column. It does not suggest presence nor absense of plants, there are many lakes with no nutrients measured in the water and no plants, likewise....... the same can be true for lakes/streams etc with plants...........
Humans would never have form cilvilizations is that was the case.
That may ior may not be so great depending on your view, but the fact remains: what we do with aquriums is not in hardly any way related to nature but rather far more related to horticulture.
Regards,
Tom Barr