This seems a good description of how one unique property of Akadama might make it especially useful as a potting soil media. I had seen this process as primarily a negative, a beginning toward its ultimate downfall, so I am putting it out here to see what others think…
Evan LaBrant, a Cellular Biologist and new Bonsai practitioner in the midwest describes this concept well: "Here’s my theory on Akadama and why it’s so preferred by many bonsai enthusiasts: immediately after repotting, the soil needs to drain quickly to allow mass flow of air for oxygenation. Before the tree’s roots completely colonize the available rooting volume, you rely on soil physics to drain and prevent stagnation. Once the tree’s roots have completely filled the pot, the removal of water (and subsequent exchange of air/oxygen) shifts from drainage to evapotranspiration. At that point, you would want the soil to shift from free draining to water-retaining to support the tree’s evapotranspiration, which is facilitated in situ by Akadama breaking down and forming a more agglomerated soil structure. A grower can’t really change the soil’s properties in situ like that very easily unless something in the mix does so automatically.
I’m sure there are other things going on, like root development/ramification. But I think the dominant feature of Akadama is the transition from free-draining to water-retaining."
There are other qualities of Akadama that are beneficial in terms of mineral content, CEC, etc., but this does seem to be a unique aspect that might not be well described.
What does the rest of the forum think? Does this strike you as something that is unique to Akadama? Does it explain why there seems to be a sweet spot in terms of “weathering in the pot” where the development of the root system into broken down Akadama seems to reduce watering needs and make more of water applied available to the tree? How long have you seen mixes of Akadama (or straight) stay within the “broken down” stage before needing to be repotted due to water passage/use problems?
In some ways, might this developed state of breakdown essentially create a shin of the entire potted soil mass?