Well there are a lot of aquatic plants but when folks generalize, they often lump in other terrestrial plants that have recently come into the hobby that are not submersed for long periods ...if at all.
If a plant has to transport something from the root or the leaf, first it has to take the nutrient in across a membrane. There's an energetic cost associated with that. There's also transport issues.
It takes energy to get a nutrient from one place to the other and to change it's form for transport and unloading in some cases such as iron.
Iron is one nutrient I have to argue for is best in BOTH places, rather than just the water column. I think overall, most people if they are critical with their rotuines will find they can grow Amano quality with fish food/water column dosing and some iron in the gravel.
I'm not too sure about the impacts of the others besides Fe but it seems less important overall than any others. I've added jobes and other macros to substrates and when the nutrients are fine in the water column, no improvenment in growth was noted, this was also supported by a number of other folks who kept good water column dosing at the time of the macro substrate additions.
The old method of putting everything in the substrate and nothing/little in the water column _also_ works and there's no reason why it should not.
Some seem to assume that this in direct conflict with water column dosing of macros and it is not.
But it still has the same nutrients available to the plants and provides perhaps for a little slower growth(not a bad thing in some cases).
Past issues(algae) with that method were often from using urea and NH4 based ferts.
But poor growth was often seen regardless of base ferts vs a water column dosing routine if you apply a pure system which is never the case in anyone's tank test I've ever seen in the hobby.
Folks calim nothing added but then you find out they have a substantial fish load, traces are dosed, K+ etc.
You can try various combo's of macros in various ratios in both sinks(water column or substrate), but ultimately the nutrients wneed to come from somewhere, providing some in both places is not a bad idea it seems.
Some claim less algae when they add more to the substrate but these are not critical test by any means.
I've worked with the water column extensively and extremely nutrient poor substrates(which is how I got to know a good deal about water column interactions).
This makes for a good base to approach what works well in a substrate vs the water column.
Many aquatic plants do not have stomates BTW, eg Hydrilla, Egeria, etc.
They are only 2 cells thick.
But back to your approach, both is best IMO. You gain little by having a pure water column with few nutrients.
But pure systerms are exceedingly rare in both nature and in the hobby.
So when folks talk about their "new" system, little has changed in the last 50 years, they use both the substrate and the water column.
I did this same nutrient poor substrate approach with Flourite some 7-8 years ago. It really did much better with many plants with a number of routines vs sand or sand+ laterite.
Iron did play a significant role and there was slower, perhaps one could argue, more managable, growth with sand/laterite mixes.
But I think a good goal: Have some NO3/PO4/Fe in the substrate, accreation of organic matter in the substrate, dose some NKP and traces to the water column also, you might be able to lean the water column more to get the desired effect but I think anyone can have Amano quality tanks by adding a little more or less to each sink of nutrients without any issues.
Having a back up in both areas will prevent any nutrients from running out.
I will say switch the nutrientr levels back and forth in either region is not good for the plant, it needs to have a steady supply no matter what, but still, having some in another sink is better than none at all.
Regards,
Tom Barr