Root Death

[Ray]

This is a new thread, started at Keith's good recommendation, as separate from the one on probiotics.

Originally Posted by K-Sci

But Ray, how much oxygen do you think there is in stagnant water in an gas-impermeable glass container? My inclination is to conclude that the success of S/H and H proves that suffocation is not the mechanism that causes root death in broken down media. This was the genesis of my post months ago speculating on a variety of other possible factors that could cause orchid root death in old media. I'm not saying you're wrong, but only that it appears to me that the evidence suggests that you are wrong.

Is it possible to measure the O2 in a beaker without changing the result when getting a sample?


-Keith

Below is my chain of thought that led me to the "suffocation" suspicion.

Many years ago, when I was developing the S/H technique for orchids, Rod Venger (Venger's Orchids in Colorado Springs) began playing with what is now called "water culture". He had some contacts with (I think) Texas A&M and a PhD candidate there pointed out that orchids roots modify their cell structure to function optimally in the environment into which they are growing, and that, once grown, they cannot change, which explains quite well the need for a plant to basically grow a whole new root system when there is a big change in the medium conditions.

As part of both of our experiments, we noted that existing roots from "dry" media, when submerged in water, would die. That seemed to follow from the "they cannot change" concept, and our best guess was "drowning", AKA "suffocation". That was further supported when we noted that roots that grew into the water on their own were perfectly fine and did not drown.

It is also well-established that if too fine of a potting medium is used and the pot is overwatered, the roots can fail, even if the potting medium if fresh and not decomposing.

All of those scenarios combine to point to suffocation, in my mind.

Consider the case in which a plant is moved from one potting medium into another - for example, from a bark-based medium into sphagnum, as an attempt to not have to water so often. The sphagnum, likely being more moisture-retentive, becomes an inhospitable, possibly suffocating, environment for the existing roots, but not so extreme to cause rapid failure, giving the roots time to grow viable "optimized" roots within the moss. (See the attached photo.)

However, there is another scenario that may-, or may not absolutely point to suffocation, but certainly supports that possibility, if you so choose: Looking at that same image, what if that were a case in which the roots grew well in fresh medium. Over time, however, the medium began to decompose, becoming finer and finer, suffocating those roots. But wait! The new root growth, with the upper parts having been given a "stay of execution" by the slowly decomposing medium, were able to successfully grow in it.

It seems to me that the second scenario is a lot like roots growing into the reservoir in a S/H pot, and the two scenarios combined suggests that it's not a pathogen or "toxic chemistry" situation that's the issue.

Might it be something other than suffocation? Sure, and if that's the case, I'd love to understand the mechanism, but it sure looks that way to me.