So I'm trying to find an academic article, but it's not just the substrate. They blew right past it in the article but there is electric potential applied, and the substrate is slightly conductive which is what allows it. They seem to imply that leads to better root growth but like I said the article barley mentioned the actual e of the e soil lol.

But bioelectrochemistry is a thing. I work on the other end, where microbes are depositing electrons, but I am aware of different technologies where the bugs use a potential as an energy source for specific reactions, usually around remidiating some nasty stuff in the ground.

Im less aware of it affecting a plant directly (I'd assume it changed the soil bugs or something) but it's not hard to picture. Good be something as simple as the potential changing the osmotic pressure and making it easier for the plants to take up nutrients or something.

But yeah, pretty far from a rod in the ground, although in some cases that is basically all you'd need. The bioelectrochemistry field always had junk science to contend with.