killing microorganisms

I will give some arguments to Jim's side.

Thanks, but changing well-entrenched minds here is as productive as spitting into the wind.

It's like dispelling the myth of Superthrive.

Let's not get too personal, or they might lock the thread.
Here is the reference to the article about pomegranates. http://cat.inist.fr/?aModele=afficheN&cpsidt=14431663
I agree it is difficult to tell how much any of this research applies to bonsai, but since Micro Plus is not that terribly expensive and not harmful, I will continue to use it. There is another question here. As generally sold, Micro Plus contains both mycorrhiza (note spelling) and MicroMax, a mixture of trace elements. If it is beneficial, how do we know which component is providing the benefit?
Unfortunately, bonsai is too small a component of the horticulture industry to make it financially feasible to support bonsai-specific research. Even worse, there is no research at all that I know of on growing bonsai, or even any woody plants, under artificial light. All of that research has been done on herbaceous plants, mostly flower crops. I would like to see the largest bonsai sellers and the bonsai product manufacturers, like Joshua Roth and Masakuni, provide some funds for bonsai research. It might be bread cast upon the waters for them.
Iris

And it says :

A pot culture experiment using sterile, P-deficient soil was conducted to study the symbiotic relationship of pomegranate

so we are very much in the case I described : "improvements are shown when at least one element (usually phosphorus) is restricted."

It is not significant for correctly grown bonsai.

Alain Bertrand wrote:I wil give some arguments to Jim's side.

First, granted that mycorrhiza is without doubt beneficial to plant in soil, in a word because they vastly increase the root sphere that is the volume of soil from which a tree can retrieve water and mineral elements.

Interesting term root sphere. The papers previously posted mentioned that mycorrhizae increases the surface area of the roots. It is really irrelevant how large or small the pot is until a plants roots have totally colonized the pot. Prior to achieving a root bound status having increased root absorption efficiency will enhance the growth of the plant. Good bonsai practice does not allow a plant to become totally root bound, so for a significant portion of a plant's life the mycorrhizae will be accelerating its growth. (Even with a root bound plant, having mycorrhizae is probably still going to help in that it increases root access to what it needs. ) Since bonsai is about imposing a human's design onto a plant, fast growth is conducive to good bonsai development. How much the benefit is needs to be proven by test. For pines, I have observed that the benefit is significant. It should be used.

You assume that mycelium in the pot wil grow faster than the roots. Why ? And even if it where the case, for the plant to gain something it is needed that energetical efficiency of the mycelium is better that those of the roots. Again, this is far different of the situation in a real soil, where the mycelium is already there and the plant has just to connect itself to this " supply network ".

For pines, I have observed that the benefit is significant. It should be used.

So you saw that pines with lot of mycorrizha grow faster or are healthier ?

Alain Bertrand wrote:You assume that mycelium in the pot wil grow faster than the roots. Why ? And even if it where the case, for the plant to gain something it is needed that energetical efficiency of the mycelium is better that those of the roots. Again, this is far different of the situation in a real soil, where the mycelium is already there and the plant has just to connect itself to this " supply network ".

The relative rate of growth of the roots versus the mycorrizha is not the driving factor. As long as the mycorrizha grows with the roots it will increase root efficiency - its akin to growing roots faster. However, since it is a symbiotic relationship, both organisms benefit from the relationship. The tree gets more nutrients and the mycorrizha uses the carbon provided by the plant for its physiological functions, growth and development. So both grow faster. Your concept of the supply network is throwing you off. It is the symbiotic relationship that adds the benefit to both organism. The tree doesn't just tap into a feed line. The relationship will form its own "supply network" in the pot. The actual chemical transfer does not happen over a large distance (we are talking microscopic distances). Its the increase in the root surface area that helps the tree.

By the way, root pruning and rough handling of roots will hurt the relationship. This is one reason to go easy on pine roots vice say pruning a ficus roots.

Alain Bertrand wrote:

So you saw that pines with lot of mycorrizha grow faster or are healthier ?

Yes, every time I repot. Frankly I have never seen a full mycorrizha colony on a sick pine and my healthy pines always have a full colony when I repot.

Iris quoted:

I am very hesitant about making suggestions to you, because I know how I feel when experts from the tropics try to tell me what to pot my bonsai in, having no understanding of my growing conditions.

And she keeps going!!! I guess that I'll have to live with the sarcastic rhetoric. By the way, I lived in upstate New York and was succesful growing maples, pines, junipers and other temperate trees. I detracted from growing tropicals because the conditions were NEVER optimal and the results were frustrating. Achieving world class quality was next to impossible.

Rob Kempinski wrote:

The relative rate of growth of the roots versus the mycorrizha is not the driving factor. As long as the mycorrizha grows with the roots it will increase root efficiency - its akin to growing roots faster.

You are missing a very important point : building roots or mycelium is energetically expensive. The required energy is furnished by the plant so any sugar given by the tree to the fungus will result in less root being built by the plant. This is called "energetical allocation" and this is a very important concept in ecology.

However, since it is a symbiotic relationship, both organisms benefit from the relationship. The tree gets more nutrients and the mycorrizha uses the carbon provided by the plant for its physiological functions, growth and development. So both grow faster.

You are in fact saying that because it is a symbiosis, it has to be always beneficial to both. This is a mistake. Usually, symbiosis is more like balanced parasitism and any decent presentation of what is symbiosis will explain that depending of circumstances, a symbiosis may start to be unbalanced. I suggest you read [url= http://mycorrhiza.ag.utk.edu/reviews/brundrett_mycorrhizal_terms.pdf this article, especially page 479 to have a more accurate view of the problem. It is explicitly stated that in high fertility soils the association becomes detrimental to the plant.

Your concept of the supply network is throwing you off. It is the symbiotic relationship that adds the benefit to both organism. The tree doesn't just tap into a feed line. The relationship will form its own "supply network" in the pot. The actual chemical transfer does not happen over a large distance (we are talking microscopic distances).

You don't understand the situation in a decently established soil. In that kind of soil, there is a full network of mycelium some of them degrading the organic matter, some of them capable of mycorrhizal associations, some of them (few) capable of doing both. When a seedling grows, its roots will reach the network of mycelium, connect to it and start to benefit from it without having to build it first though of course it will have to pay with sugar (mostly) to maintain and develop the association. It don't know why you are stating that transfer is done only on microscopic distances because to my knowledge it is false. See

Mycelial network connects plants
within and across species for nutrient
exchange “Wood-wide web"

from http://alrlab.pdx.edu/courses/mycosphere.pdf or this book extract

Frankly I have never seen a full mycorrizha colony on a sick pine and my healthy pines always have a full colony when I repot.

I observe exactly the same but this is a mistake to think that it supports the idea that mycorrhize in a pot with good fertilization is beneficial to plants because it is as well compatible with the idea that healthy trees also make more sugar that sick trees and thus are able to sustain more fungus.

So, like Jim, I will stick to what controlled experiments usually show : in a well fertilized pot, mycorrhizal association has little if any nutritional benefit, the most interesting part of the association being the exclusion of potential pathogens by installed mycelium.

Regards,

So, like Jim, I will stick to what controlled experiments usually show : in a well fertilized pot, mycorrhizal association has little if any nutritional benefit, the most interesting part of the association being the exclusion of potential pathogens by installed mycelium.

Maybe we can end this discussion by saying that if you have 'em, OK. If you don't have 'em, OK too.