Ever wonder?

[Rick]

I may be remembering this incorrectly, but I understand that plants actually have "pumps" that selectively grab up K, even if they don't need it at the moment, socking it away in the vacuoles for a "rainy day" when they might.

If that's true, then lowering it in the fertilizer might result in a slower accumulation, but won't stop it.

I think you are close to my understanding too Ray. Except I'm leaning towards the notion that many orchids don't have control of when to stop those pumps, and/or the storage vacuoles are inadequate to keep up with the high concentration offered in fertilizers leading to K toxicity (which actually causes deficiencies of N, Ca, Mg). If there is plenty of Ca and Mg then I think the situation in the plant is reversible. Also there is potential for the plant to grow out of this stockpile if conditions are right.

This is similar to the freshwater mussel situation I was talking about earlier too.

In the wild freshwater mussels never see more than a few ppm of K in the water. They still need it for metabolic and muscular activity, so they use selective cell pumps to grab up as much as they can (since there's virtually none to get in the first place). But if you put them in a solution high in K, the pumps still work like crazy and overload the mussel tissue (causing paralysis). I think that as more K gets into the mussel tissue it kicks out Ca. The mussels seem to be able to control the system partially if there is more sodium than K so when you put them back into low K water they regain muscle control. If sodium is low, then generally there is no recovery of movement after going back into low K water. Most other aquatic organisms(like fish and crustaceans) seem to have more controllable pumps or means of getting the K back out of their tissues.