Air movement improves orchid nutrition

[K-Sci]

Discussion topic: In an environment with good humidity, strong air movement improves orchid nutrition by increasing the amount of nutrient containing moisture taken in by the orchid's roots.

-Keith

[Ray]

Interesting, but I'm having a hard time wrapping my head around that. Here's some "off-the-top" mental ramblings to add to the conversation:

There is an insignificant amount of nutrition in the humidity, if any. It is evaporated pure water, for the most part, equivalent to the first part of distillation.

Strong air movement tends to evaporate liquid water faster than does the preferred "tumbling, buoyant air". Faster evaporation may mean any contained nutrients will concentrate, but 1) is that a good thing for the plant?, and 2) I would think the solutions will be preferentially absorbed by the potting medium as that happens, simply due to it having a greater wetted surface area, if not also for the physical characteristics of the media used.

If the faster evaporation reduces the water at the roots, the plant will send hormonal cues to the stomata to close, in order to conserve moisture. Closed stomata means slower CO2 capture, slower growth, and less need for nutrients.

[DirtyCoconuts]

i think this is a good general rule up to a point (hurricanes and tornados are not optimum growing areas) and there are some plants that grow in very stagnant areas and they might appreciate the dank and unchanging air- BUT MOST, yes

[Shadeflower]

a too soggy substrate can lock out nutrients. So a more airy substate encourages good nutrient uptake vs too soggy.
I've changed too soggy substate before not because any roots went bad but the orchid wasn't growing as well.
So yes it's about finding the right balance.
We all know that orchid roots have to be able to do gas exchanges. So periodically they have to dry enough for that to happen. Too wet all the time blocks the air exchange.

[K-Sci]

Originally Posted by Ray

Interesting, but I'm having a hard time wrapping my head around that.

The topic was the result of reading an article about orchid calcium deficiencies that identified insufficient air movement as a contributing factor.

Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 + 6H2O
Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + 32 ATP

Noting that both equations have 6H2O on both sides, neither photosythesis nor respiration change the amount of H2O in the orchid. Therefore, unless more water is stored in the plant, doubling the evaporation must double the water uptake at the roots. Unless the roots filter the nutrients out, the nutrients in the water would be transported as well.

-Keith

---------- Post added at 11:13 AM ---------- Previous post was at 11:04 AM ----------

Originally Posted by Shadeflower

a too soggy substrate can lock out nutrients. So a more airy substate encourages good nutrient uptake vs too soggy.

Shadeflower, I knew this topic would interest you.

I think we can assume that the orchid is given water as needed, so the moisture content of the substrate might fall more rapidly but on average be the same.
-Keith

---------- Post added at 11:22 AM ---------- Previous post was at 11:13 AM ----------

Originally Posted by DirtyCoconuts

i think this is a good general rule up to a point (hurricanes and tornados are not optimum growing areas) and there are some plants that grow in very stagnant areas and they might appreciate the dank and unchanging air- BUT MOST, yes

As I mentioned, this topic occurred to me because of the aforementioned article identifying insufficient air movement as contributing to calcium deficiencies. But also the amount of evaporation occured to me because I have a phalaenopsis with flowers being blown about inches by air from a fan. I thought it would reduce the flower longevity, but I've been very surprised that it hasn't. With the large amount of surface area on the large white flowers the moisture uptake by the plant must be significantly increased.

-Keith

[TZ-Someplace]

Throwing some pocket change into the discussion.

Unfortunately, I had to learn all of the transpiration physics (water surface tension angles at cell wall fibers and things like that), plus the biochemistry of photosynthesis a long time ago for some really important mental torture tests, and I seem to remember some of it. Most orchids we grow are not very tall (less than 1 m) and don't transpire very much so osmotic root pressure is generally fine for getting water to the top of the plant. More calcium in the water would probably work better than trying to pull more water up the plant if for no other reason than orchid roots are not made to pull in a lot of water quickly. But that is the big question here; has calcium transport been measured in some/many orchids or are we applying an idea from a different situation? A small epiphytic orchid is very different from a 2m tall tomato plant suffering from blossom end rot (BER) as it tries to grow five or ten pounds of elongate plum-paste tomatoes in water-logged soil during a week of rainy gloomy weather (which is where calcium movement research is going to have funding). BTW, the last time I checked (about ten years ago) they hadn't figured out a way to totally prevent BER in tomatoes even with the scientifically formulated calcium (nitrate?) foliar sprays.

Root growth stage may be a very important factor. Iirc, calcium is also mainly taken in by a short region at the end of a growing root. I forget the reason but it has something to do with it being bad if the whole root can take it in. Probably something to do with competition with potassium. The cell physiology needs potassium to function while calcium is mainly needed to stiffen cellulose fibers in elongating cell walls.

My final though is that adequate air movement (don't know about strong) will definitely benefit growth by boosting carbon fixation by maintaining high CO2 and low O2 inside the leaves. I read a study recently that discussed orchids (Phal/Dend/Catts???) jacking up photosynthesis rate at first light and reducing it starting at mid morning even before light reached the physiological saturation point, and it stayed low until late afternoon, so air movement (high CO2) was very important during low light periods to optimize photosynthetic rate.

[Shadeflower]

Shadeflower, I knew this topic would interest you.

It does and I'm glad I am not the only one browsing the board thinking about orchids when other people are thinking about fireworks...

[Ray]

Originally Posted by K-Sci

Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 + 6H2O
Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + 32 ATP

Noting that both equations have 6H2O on both sides, neither photosythesis nor respiration change the amount of H2O in the orchid. Therefore, unless more water is stored in the plant, doubling the evaporation must double the water uptake at the roots. Unless the roots filter the nutrients out, the nutrients in the water would be transported as well.

OK. Explain that one to me.

Evaporation means there is LESS water available for the plant to uptake...No?

You're also assuming the chemical reactions take place at the same time and rate. Do they?

[TZ-Someplace]

Water must pass through the endodermis layer to get into the root-stem vascular system. The hydrophobic cell wall casperian strip around those cells forces water to go through cell membranes at that point so the plant has control of ions-minerals and such coming into the central vascular system. The rest of the time the water moves through the spaces outside the living cells.

[Keysguy]

Off the top of my head K-Sci I could understand the humid environment contributing because it allows the cells to remain constantly hydrated and open and therefor receptive to available nutrients.
The air flow, I'm not so sure about. What do you think it's adding? It's not blowing nutrients around!
I'm convinced the air flow is critical for a couple reasons but nutrition isn't one of them.
As a matter of fact, one might be able to make an argument that a good breeze (air flow) would negatively impact and perhaps totally negate the benefit of the humidity by drying the roots out.