The conclusion is based on an optical illusion. I've also grown this plant for years in a CO2 enriched tank and have NEVER experienced loss of leaves or shriveling. In fact, when pruning, I've simply thrown away the tops. It doesn't matter whether the tank is CO2 enriched or not. The cause is the same. Increased growth blocks circulation within the lower plant bed, starving the leaf of CO2, and that's why the plant sacrifices the leaves. This is the same story for every plant, and this is no exception. If you want to test the theory then all you have to do is to place a separate diffuser within the lower bed and pump CO2 inside the bed. Another method is to measure the PAR in the lower bed and set that PAR value for the tank at the level where the upper leaves are. If the theory of loss of light is valid then this will cause the upper leaves to shrivel. If the leaves continue growth at that lowered PAR then this invalidates the theory of loss of light being a causal factor.
The obvious fact that people often do not consider is that when a leaf, or plant as a whole, is shaded by the placement of an object around it, this same object also causes shading of flow and circulation, which is much more difficult for the plant to overcome. It's very easy for the plant to overcome light shading. It simply increases the chlorophyll density of the affected leaves. In a low CO2 environment, such as low tech, the plant increases the density of Rubisco, but there is a limit to the effectiveness of both of these corrective strategies. Management of light is much easier the management of gas exchange for plants. So just because it's growing in a non-CO2 enriched water, this does not mean that it is impervious to poor CO2. CO2 concentration levels within a plant bed is often as much as 10X lower than it's concentration in open water and that's why flow and distribution is so important. Gases are 10,000X less mobile in water than they are in air, while at the same time, photons can bounce around and reflect off of nearby surfaces - and they still move at the speed of light. So it's actually a very rare occurrence to fall below the LCP, but it's very easy to fall below the CO2 Compensation Point.
The best way to use this plant in an aquascape is to not allow it to grow vertically (unless you want to see the flowers as Darrel shows). It can be held down, tied to hardscape similar to the way moss or Riccia is tied or netted to stone or wood horizontally. Then it's just a matter of pruning the individual shoots and aerial roots that pop up.
Cheers,
