Re: Abridged summary of lifeinthesoil@googlegroups.com - 2 Messages in 1 Topic

[Elsa Higby]

Dr. Elaine,

As I way of starting the conversation and perhaps bringing up more questions, would you explain the relationship of functions between saprophytic fungi and mycorrhizal fungi as they pertain to nutrient cycling?  Are there any interdependencies?  Can you have one functioning without the other?

Thanks,

Elsa

[Ingham, Elaine]

Saprophytic fungi: Decomposer fungi.....they consume, digest, use dead organic matter. They do not attack living tissue. They immobilize nutrients in their bodies (their C:N, P, S, Ca, K, etc concentrations are much higher than most of the things they consume), build structure (macroaggregates), and protect root systems, leaves, bark, stems, etc from disease organisms if the habitat stays aerobic. A wide diversity of species is required to make certain that beneficial species can be active in all the weather and habitat conditions that may occur through a year. There are beneficial species that help plants grow (make grow hormones, build soil structure, suppress diseases) that generally require aerobic conditions to do their jobs. There are disease-causing organisms that require reduced oxygen conditions in order to flourish (drop below 6 ppm as a general rule).

Pathogenic fungi: Attack living tissue. Generally require reduced oxygen conditions to be able to outcompete other organisms. These are pathogens like Rhizoctonia, Pythium, blight, mildew, most often in the group of Oomycetes, and quite soon to not be called fungi at all, but a whole new kingdom. Which will brighten up our feelings about fungi!

Parasitic fungi (as opposed to pathogenic fungi): Endophytic fungi, generally make spores in the seed, and generally give some benefit to the plant (e.g., decrease water use, improve phosphorus uptake, makes plant un-desirable to grazing animals), but then make the seed deadly for mammals. Ergot poisoning is the classic example.

Mycorrhizal fungi: Several types of mycorrhizal fungi based on the plants they colonize: Endo-mycorrhizal usually colonize plants that can be perennial which includes most vegies (just because you grow and harvest it does not mean they can't grow for several years when they are on their own), herbs, grasses, shrubs, and deciduous trees. Ecto-mycorrhizal means they colonize evergreen plants like conifers. Ericoid means they colonize ericoid plants like blueberry. IR means fungi that orchids require.

With mycorrhizal fungi, the plant initiates the colonization process by releasing an exudate of a particular kind of sugar. Evidence suggests it could be any one of a number of sugars, so the plant selects for the association it wants based on the sugar it makes. This isn't my area of expertise, so talk with Tom Bruns or people who work at the root scale to understand colonization processes to get deep into this.

The spore of the mycorrhizal fungus germinates, grows into the root zone. with endo-mycorrhizal fungi, the hyphae grows between the root cells until it finds an infection site, and then grows between the cell membrane and the cell wall. Again, lots of detail available there, but google info on this if you want that detail. The plant "tells" the fungus what it wants, the fungus retrieves it, in exchange for more sugars from the root. As long as the fungus delivers the nutrients the plant need to continue photosynthesing, life is wonderful for both plant and fungus.

There is no evidence of a pathogenic interaction EXCEPT if human beings muck this up and drown the seed or seedling in monstrous levels of spores. You guessed it, the only report of negative effects by mycorrhizal fungi is if people get carried away ...... the a little is good, more is better approach? Not wise in the world of growing plants.

So, IF THE PLANT NEEDS mycorrhizal colonization, there is quite a bit of evidence in the scientific literature that if you match up what the plant needs, positive effects occur. BUT REMEMBER, mycorrhizal fungi do not work alone.... they require the rest of the organisms in the food web to get ALL the benefits possible.

All the benefits? Prevent disease, prevent pest problems, reduce water use, nutrient cycling occurs normally so no need for toxic chemicals, no weeds because we set the stage to grow the plant you want instead of weeds, etc.

So, to have mycorrhizal fungi do all the things they can do to help plants, the whole food web that the plant requires needs to be present and functioning.

If you apply mycorrhizal fungi, but the rest of the food web is not present, soil structure can't be built, compaction will happen and can't be gotten rid of, roots won't go to the depths they should be able to go, the plant can't get to water in the summer, diseases and pests will predominate in the soil. These can't be fixed by mycorrhizal fungi alone.

It takes a village, with all the different "professionals" doing their jobs, on every single root hair of your plant, on every single sixteenth of an inch on your leaf surfaces, stems, bark, crown, blossom, seed surface, etc to grow a healthy plant. The villages are unique for different leaves, different roots. And they have to be different for different plants, in different soils, in different seasons. How do we learn all this, what is needed at which times, under which conditions, for which plants? Luckily, we don't really need to know that level of detail. Let the plant work its magic, where the plant puts out the exact food that the exact beneficial organism needs so it will grow and do its job.

Humans just need to make sure the balances of ALL the beneficials are present. OK?

Questions?

Elaine R. Ingham
Chief Scientist
Rodale Institute

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