Ill tell you about the day I first saw this with my own eyes.
I was in a plant store called Holland Gardens here in Lubbock. Was looking for terrestrial plants for the terrarium bowls, then I came across this outdoor pond that had large pots of dwarf saggitaria--a better aquatic plant specimen than id ever seen in a LFS, who has mainly small plant cuttings or rubber banded groups for sale.
These were dense little pots of saggitaria, three being enough to fill a ten gallon twice over. they had been in this pond for two years and not been sold or fertilized. This was not a fish pond, the water was not circulated or changed in two years, it just held seasonal plants to keep them moist outside (it was moved in during winter) Other plant shipments were continually stacked on top of them or in front of them, but they still managed to grow root masses so thick it was about to split the side of the heavy plastic pots---thickest root matrix I have ever seen on an aquatic bundle. And, the soil was pure dark clay mud 9 inches deep. Black as night, but did not smell foul in the least. If any aquarist had substrate like this they'd panic, but I think mother nature is telling us that an extremely organic, fine-particle substrate is not detrimental in the presence of strong root matrix. Without the root growth, anaerobic rot would prevail underwater due to the abundance of nutrients and the lack of higher fixation. I think it may be vital in sustaining such a matrix over the long haul