[compost_tea] RE: follow-up on Steve Divers' mycorrhizae links

From: chris reid <reidchris_at_earthlink.net>
Date: Fri, 17 Oct 2003 08:27:53 -0400


I don't think this message ever appeared. Still thought it might be useful.

-----Original Message-----
From: chris reid [mailto:reidchris_at_earthlink.net]
Sent: Monday, October 13, 2003 1:41 PM
To: Compost Tea
Subject: follow-up on Steve Divers' mycorrhizae links


Following up on Steve Divers' leads, and came across a lengthy document by
Ted St. John. It seems to indicate that use of mycorrhizae in a nursery is
not a walk in the park, and also helps clarify what in his
experience/opinion an ecological restoration customer could expect from AM
inoculated nursery stock/site. This document is dated April 5, 2000.

The document is called the Instant Expert Guide to Mycorrhiza, and is 48
pages long.
Here's the link: http://www.mycorrhiza.org/EXPERTflat.PDF

page 13
What Your Clients Can Reasonably Expect (target audience is eco
restorationists)
If your clients have heard of mycorrhiza at all, they will expect
dramatically
larger plants on the inoculated plots. While there may be
some growth response, plants in the field have a habit of expanding
their root systems, taking over resources left behind by plants that did
not survive, and otherwise compensating for the nutrient uptake that
should be provided by symbionts. There are usually fewer plants on
uninoculated sites, so each plant gets a larger share of soil resources.
The main reason for modest growth responses in the field is that
the few species traditionally used on disturbed sites are those that
do not need to be mycorrhizal. Among those species, there will be
little difference between inoculated and uninoculated plots.

Realistic benefits that your client can expect include survival, diversity,
protection from disease, improved soil structure, and resistance
to invasion by exotic plant species. Most of these benefits depend on
development of the mycorrhizal network in the soil. If the weeds win
the race for control of the soil, none of the benefits will develop and
the restoration effort will fail.

That does not mean inoculation is not worthwhile; it means that timing,
choice of host plants, and other details
are critical and must be carried out with a firm commitment.

page 22
Determine Whether Your Soil is Toxic to Mycorrhizal
Fungi
Mine spoils are often toxic because of processing or because of the
sometimes toxic nature of the ores that contain mineral resources. In
most cases toxicity will have been determined as an early step in the
remediation process, and detailed analyses will be available. A bioassay
with radish seedlings (radish is a non-host) grown in representative
soil samples will indicate whether the medium is suitable for
plant growth. If it is suitable for plants, it is possible but less likely
that there are factors that are toxic for spore germination or root
colonization
by mycorrhizal fungi.
In examining a soil analysis, look for high concentrations of Na, Cl,
B, Cd, Zn, and Mn. Any of these have been shown to interfere with
colonization or may reasonably be suspected of doing so. Look also
for extreme pH values. Soils in a more acid range may have toxic
levels of aluminum ions.
If the soil is receiving organic amendments consider their possible
effects on mycorrhizal colonization. Many forms of peat are tolerated
only as a low proportion of the mix. Very raw compost materials can
sometimes be inhibitory, although mature compost and most humic
materials can be neutral or even stimulatory to fungal growth.
It is possible for artificial media to be so low in some nutrient ions
that colonization is inhibited. I know of no example of this in a natural
temperate zone soil, but it happens in subgrade or spoil material.

**
Determine the Best Fungal Species
Specificity to hosts: AM fungi are very non-specific in their ability to
associate with plants. That is, almost any AM fungus can form mycorrhiza
with almost any AM host plant. However, there are preferences,
in that host plant species may select different mycorrhizal partners
from the mix of fungi available in the soil.

Specificity to soils: Mycorrhizal fungi are in general more specific to
soil type than to host plant. Soil pH is the biggest selective factor, but
soil texture and organic matter may also influence the suitability of
the soil for particular fungi. The fungi commonly available as commercial
inocula tend to have wide tolerance ranges. Glomus intraradices,
the most widely available species, is suitable for soils from
about pH 6 to 9. Another widely available fungus, G. etunicatum, is
at its best in the acid range. There are fungi that tolerate cool spring
temperatures and others that remain dormant until the soil warms up.
Some do best in new plantings and others do not appear to take well
in plantings, but may be abundant in mature native vegetation.
There is reason to believe that some fungal species are better than others
at promoting soil structure. Some species appear to produce more
“Glomalin,” the newly-discovered glycoprotein that acts as a glue for
soil structure.

Page 34
Inoculate In a Production Nursery
At least one native plant nursery has been shipping mycorrhizal plants
for over a decade. To make the production process reliable, it was
necessary to re-examine almost every aspect of nursery operation.
Difficulties were at various times traced to shade conditions, watering
methods, fertilizer formulations and application rates, planting media,
and water sources. Certain kinds of plants became vulnerable to root
disease on a seasonal basis, and were unreliable hosts during those
periods. The smallest containers were found much more troublesome
than larger containers. Containers directly on the ground or on weed
control fabric were more likely to become mycorrhizal without intentional
inoculation. Containers kept in full sunlight, or those that had
been in production a year or more, were also more likely to become
mycorrhizal on their own. The nursery was surrounded by native
ectomycorrhizal
hosts, and container-grown plants of those species often
became mycorrhizal spontaneously.
A nursery program for mycorrhizal plant production is a major undertaking.
The full range of considerations is beyond the scope of this
booklet. The grower must be prepared to modify existing procedures,
sometimes to the extent of a complete overhaul. The economic and
public relations value of doing so will in some cases compensate for
the costs, and in other cases will be irrelevant.









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Received on Fri Oct 17 2003 - 10:44:48 EDT

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