Potassium requirements in plants:
A HYPOTHESIS RELATING CRITICAL POTASSIUM CONCENTRATIONS FOR GROWTH TO THE DISTRIBUTION AND FUNCTIONS OF THIS ION IN THE PLANT CELL - LEIGH - 2006 - New Phytologist - Wiley Online Library

Plants do not have pumps for all nutrient ions, only certain ones.

That linked study pertained to terrestrial plants, not epiphytes, and there are huge differences between the two.

Most nutritional studies have been done on dicots, not monocots.

In a chart presented in Marschner's Mineral Nutrition in Higher Plants, he shows the content of maize (a monocot) roots after 4 days of exposure to a fertilizer solution. To try to make a table, I'll list the ion, the millimoles in the solution, and the millimoles found in the roots, then in parenthes, the multiplier:

Potassium 2.00 160 (80)
Calcium 1.00 3 (3)
Sodium 0.32 0.6 (1.875)
Phosphate 0.25 6 (24)
Nitrate 2.00 38 (19)
Sulfate 0.67 14 (20.9)

I'll add that you might want to go over to the Slippertalk forum - there are several detailed threads on this subject

They do have potassium pumps.

Hmm, I would have thought that slipper orchids would be classified as terrestrial but then I know very little about slipper orchids which is why I don't post on SlipperTalk.

Wow, that moncot is working really hard to pump potassium inside. That would leave me to think that large amounts of potassium are pretty important.

I have read one or two of the threads but I don't know anything about slipper orchids. Perhaps they have some highly unusual nutritional requirements that other orchids and other plants don't so that is why I don't post there.

I think that's where our opinions differ.

The amount of a mineral found in the tissues does not necessarily mean the plant needs that much. Those measurements were in the roots, so might simply be related to the activity of the ion itself, and not the need of the plant (it's likely a combination, actually).

As a materials scientist, I know that potassium has a huge affinity for anions, tying them up preferentially over other cations in glass/ceramic systems. The possibility that the same occurs in biological systems does not seem so far-fetched to me.

I don't know what you mean by "simply related to the activity of the ion". Roots have potassium selective pumps that work to extract potassium from the environment.

The Ionic Environment Controls the Contribution of the Barley HvHAK1 Transporter to Potassium Acquisition

Barley is an orchid?

Is maize an orchid? Why did you post that table if only data about orchids is relevant?

So, do you have _any_ data to justify this belief that orchids have these very special nutritonal requirements wrt potassium? It seems unlikely since by your own arguments only studies on orchids are relevant. If a study was on epiphytic orchids would it then have any applicability on terrestrial orchids? How about CAM vs C3? What if the orchids are in different genera?

So when plant physiologists study Arabidopsis is it your opinion that these studies can only apply to Arabidopsis? You should tell the plant physiology community about this so that they can stop wasting their time.

Fascinating, I have 3 phals. in contact of a top dressing of 5-1-1 composted chicken manure for a different culture and never had such luxuriant growth and spike productions, I was wondering about it.

Thank you