The Instant Expert Guide to Mycorrhiza

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The Instant Expert Guide to
Mycorrhiza
The Connection for Functional Ecosystems
Ted St. John, Ph.D.
Find it Fast
Myco-what? 1
The Terms: Let’s Get It Right! 2
Why become an expert on mycorrhiza? 3
Learn the terms 4
The questions that clients always ask 6
Learn the benefits of mycorrhiza 7
Where is the proof? 12
What your clients can reasonably expect 13
Why not just fertilize instead of inoculate? 14
Learn why some sites require inoculation 15
Topsoil as inoculum for restoration 15
Determine whether your plants need to be mycorrhizal 16
Determine the best fungal species 18
Consider a mixture of mycorrhizal fungi 19
Consider local native fungi 19
Are there fungal “weeds”? 20
Determine whether your site requires inoculation 20
Determine whether your soil is toxic to mycorrhizal fungi 22
Use mycorrhizal inoculum correctly 22
Choose the best way to place inoculum 23
The cost of mycorrhizal inoculum 26
Mycorrhizal status of some California plant species 26
Form a strategy for building the mycorrhizal network 27
Detect the scent of sales tactics 29
Spacing of mycorrhizal propagules 29
How mycorrhizal inoculum is produced 31
Conduct a field trial 32
Judge the success of an inoculation trial 33
Inoculate in a production nursery 34
Inoculate for erosion control 35
Inoculate agricultural crops 35
Learn more about mycorrhiza 38
Look at the scientific literature 39
Modify the standard specifications 45
Site
Evaluation Background
Inoculation
Process
Evaluating
Inoculum
Re-sources Non-
Restoration


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Myco-What?
Most plant species form a symbiosis (mutually advantageous living
arrangement) with beneficial fungi. The roots are colonized by the
fungus, which also ramifies through the soil. The combination of root
and fungus is called mycorrhiza. Mycorrhiza is considered such a
fundamental part of the plant that most species could not survive in
nature without it. The few plants that do not need mycorrhiza (mostly
weeds) are considered to be departures from the normal state of the
plant kingdom.
The mycorrhizal symbiosis appeared in the fossil record along with
the earliest land plants, and may have made possible the transition
from the aquatic to the terrestrial environment. Mycorrhizal fungi
constitute the dominant microorganisms in most undisturbed soilsestimated
at about 70% of microbial biomass. They make plant
growth possible, link the roots of different species, control the mix of
plant species on the site, and dominate the microflora, selecting a soil
full of “good bugs” when the site might otherwise fill up with pathogens.
Is it any wonder that Dr. R. M. Miller has called restoration
without mycorrhiza “lipstick on a corpse?”
Mycorrhizas are fundamental to ecosystem function: the sum of energy
flow and mineral cycling processes that characterize a natural
community and allocate the resources that maintain it. It hardly states
the case to say that mycorrhizas are important to ecosystem function.
It is much more accurate to say that mycorrhizas are ecosystem function.
It is important to understand what mycorrhizal fungi are not. These
are not the organisms that fix nitrogen (make atmospheric nitrogen
available to plants) in association with legumes (those are bacteria of
the genus Rhizobium) or with alders and Ceanothus (those are certain




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The Terms: Lets Get It Right!
The first job is to learn the language of this discipline. Misuse
of these terms is a giveaway that you are operating on the
edges of your expertise.
Noun: The word mycorrhiza comes from Greek origins: myco
for fungus and rhiza for root. The extra “r” is free. The most
common way to make this into a plural in North America has
been the Latinized mycorrhizae (say my-co-RIZ-ee), a mixture
of Latin and Greek in the same word. The British have no patience
with this unsuitable mixture of languages and pluralize
the word by simply adding an s, a mixture of Greek and English
instead. The British practice is somewhat more defensible,
since the earliest uses of the word was by a German in the late
1800s who pluralized the term in accordance with his own language.
Adjective: The adjectival form is mycorrhizal. Speak of a mycorrhizal
plant, but please do not speak of a mycorrhizae plant.
The fungus: The term mycorrhiza refers to a combined structure.
The mycorrhiza is not the fungus - the mycorrhiza is
the symbiotic combination of plant and fungus. This subtlety
is elusive enough that even specialists have lapses from
time to time, and say mycorrhiza when they really mean the
fungus. Even if you occasionally slip, be sure you grasp the
central idea that a mycorrhiza is the combination, which includes
the mycorrhizal fungus and the mycorrhizal host plant.
specialized actinomycetes). Mycorrhizal fungi do not fix nitrogen at
all; in most cases what they do for the individual plant is aid in uptake
of phosphorus.
Native mycorrhizal fungi are present in healthy ecosystems, but are
often destroyed by disturbance. They are always missing from freshly
graded sites, the most common situation for commercial restoration
projects. The lack of mycorrhizal fungi on disturbed sites is the
Background


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Possible Outcomes of a Restoration Project
basis for inoculation.
Numerous successful trials show that we now have the means to not
just make individual plants mycorrhizal, but to quickly fill the soil
with mycorrhizal roots and the network of mycelium (the mass of fungal
filaments) that mediates ecosystem function. By putting the network
in place on a restoration job, we can realize the same benefits
that the network extends to natural ecosystems.
Why Become an Expert on Mycorrhiza?
The purpose of this booklet is to bring restoration and revegetation
consultants up to speed on the symbiosis, its importance in ecosystem
function, and its use in habitat restoration. The level of expertise we
are hoping to achieve is an ability to understand the symbiosis and its
role in a particular project, and an ability to make the procedures ap-



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propriate for each project.
The most important reason for you to know about mycorrhiza is that
its use in restoration is here to stay. This is now an established technique
for greatly improving the success of revegetation efforts, and a
method that successful consultants need to know in order to stay current
with the industry.
Learn the Terms
The sidebar indicates the most central, and most often misused terms.
Here are a few more with which you should be comfortable:
Host status: There is potential for confusion when speaking of the
plant and its mycorrhizal status. In this booklet a plant that is incapable
of becoming mycorrhizal is a non-host. A plant that can become
mycorrhizal but just happens to be without symbiotic fungi is called a
non-mycorrhizal plant.
Mycotrophy: Host plant species differ in the degree to which they
depend on the symbiosis. That is, some (mostly weedy) species benefit
little, even though they are capable of becoming mycorrhizal.
Other species are mycotrophic: they depend upon the symbiosis and
make little growth without it unless heavily fertilized.
Some particularly mycotrophic plants are trees and shrubs with roots
that are sparsely branched and have few root hairs (cellular extensions
that help roots take up nutrients). Perennial grasses are often strongly
mycotrophic. Most weedy plants are either non-mycotrophic (i.e. annual
grasses and weedy composites) or non-hosts (e.g. the families
Amaranthaceae, Chenopodiaceae, Brassicaceae, Aizoaceae, Cyperaceae,
and others).
Colonization: Until the 1970s, mycorrhizal plants were said to be infected
by mycorrhizal fungi. Since infection sounded too pathological,
we began saying colonization instead. Today, hard looks will befall
those who speak of mycorrhizal infection.
Types: Mycorrhiza come in about seven types, which differ by kind


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of fungus, kind of host plant, and morphology of the interface. The
fungi of these several kinds of symbiosis may differ so completely
that they cannot be related to each other. In other words, mycorrhiza
was so successful that evolution produced it several times in several
different versions.
These various types of mycorrhiza share certain characteristics. Mycorrhizal
fungi plug into the cortex (a layer of cells found only on
relatively young roots), and at the same time pass into the soil, forming
a bridge to the plant. They all provide soil nutrients to the plant
and draw energy compounds from the host.
Ectomycorrhizal fungi enter the roots, where the hyphae (fungal filaments)
pass between root cells. They do not enter the root cells, as do
endomycorrhizal fungi. There is often a mantle (covering) of interwoven
fungal mycelium (mass of fungal filaments) on the surface of
the finest roots, and an internal network, the Hartig net, that weaves
between the cells in the root. The mantle is often visible to the unaided
eye or by use of a hand lens. Ectomycorrhiza is found on many
dominant forest trees and involves a “higher” (often mushroomforming)
fungus. The term is abbreviated ECM or EM.
Endomycorrhiza is not really a natural group; it simply refers to the
fact that fungal hyphae enter the root cells. Under this name are the
very dissimilar mycorrhizas of orchids, Ericaceae and relatives, and
the largest group, the arbuscular (AM), or vesicular-arbuscular
(VAM) type of mycorrhiza. This last group is so dominant in the
plant kingdom that we might simplify the whole discussion by giving
AM primary rights to the term endomycorrhiza. The less common
types would then go by their own separate names. This book is almost
entirely directed toward endomycorrhiza (AM).
The arbuscules and vesicles, for which AM/VAM were named, are
structures found in the roots of mycorrhizal plants. AM fungal species
form arbuscules (branched structures inside the root cells) at
some point in the colonization cycle, but not all form vesicles (oil
storage organs in the roots). Thus, the current trend to drop the V part
of VAM. Among mycorrhizal specialists, those who still say VAM
are thought to be badly out of date, and there has been a stampede to
the more current term. Say VAM at your peril.


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The Questions that Clients Always Ask
Mycorrhiza is invisible to anyone but a specialist, and this leads newcomers
to dismiss the symbiosis as non-existent, insignificant, or selfmaintaining.
The claims made for its effectiveness resemble the
claims made for a large number of amendments, solutions, vitamins,
and other "miracle" products. Mycorrhiza is distinguished from the
other plant growth enhancers by a large body of scientific work, extending
over more than a century. Nevertheless, clients and customers
always have a certain sense of skepticism, and almost always ask
one or more of the questions in the following list:
• What beneficial effects can I expect on my project?
• Why is inoculation better than fertilization?
• Μicrobes are everywhere, especially in soil. Why do I need
to add them?
• Can I get the same effects by replacing the topsoil?
• Do my plant species need to be mycorrhizal?
• Does it take a separate kind of mycorrhizal fungus for each
species of plant?
• Is a mixture of fungi better than a single species of fungus?
• Are native fungi better than the generic fungi in commercial
inoculum?
• Will the non-native fungi in commercial inoculum become
microbial weeds at the project site?
• How much will inoculation cost?
• How do I know I do not already have mycorrhizal fungi?


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The remainder of this booklet addresses the questions and ways to
explain the underlying principles to your clients.
Learn the Benefits of Mycorrhiza
Growth response: The best known mycorrhizal effect is that mycorrhizal
plants take up more soil phosphorus and grow faster than
corresponding non-mycorrhizal control plants. Hundreds of photographs
of this growth response have been published. The pictures of
big plants and little plants are largely responsible for the common perception
that mycorrhizal inoculation ought to bring on a "Jack and the
Beanstalk" response.
The growth response is probably the least important and indeed, the
least likely of the effects of inoculating a restoration project. The
growth response may be duplicated, and usually exceeded, by adding
phosphorus fertilizer. The difference in growth rate is simply a meas-


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ure of what one might have gained by spending pennies on fertilizer
instead of dollars on inoculum. By dwelling on the relatively unimportant
growth response instead of the enormously important ecosystem
effects, you will set your client up for disappointment. You and
your client may then miss out on a chance to make a real ecosystem
instead of a fertilized garden.
Greenhouse trials: The growth response is common in greenhouse
trials, and many hundreds of these experiments have been published.
Specialists are rather tired of them, as the point was well established
by the early 1970s. Nevertheless, people want to see it work with
their plant, in their conditions, in their greenhouse. It is unlikely that
these experiments will end any time soon.
In the field, growth responses are considerably less evident than in
the greenhouse. This does not mean that mycorrhiza is less important;
it is probably more so. Non-mycorrhizal plants in the field can extend
their root systems to find new nutrient sources, one of the reasons the
growth response may be much less than in containers. If you compare


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only growth rates between inoculated and uninoculated plots, you
may overlook the fact that many more plant species appeared from the
same seed mix on the inoculated plot, or that many more individuals
of some species survived on the inoculated plot.
If the plot was designed as an experiment to test the effects of inoculation,
you may have used only the few plant species known to perform
well on disturbed sites. If so, you have pre-selected species that
will show little or no growth response. The major reason that informal
field trials are considered failures is that people look only for
a growth response in plant species that have been pre-selected for
non-mycotrophy.
A more useful measure of success would be survival from a seed mix
of many plant species. Many native plants fail if they are unable to
become mycorrhizal soon after germination. This failure rate is differential:
the most mycotrophic species are the least likely to survive.
Many species are badly underrepresented on the uninoculated plot,
and others do not appear at all (zero survival). Any difference in average
plant size is accidental and largely beside the point. This important
improvement in plant species diversity would be very unlikely
from fertilization.
Seedlings become mycorrhizal very quickly if the soil is full of mycorrhizal
hyphae, but more slowly if the soil contains only dormant


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spores (fungal reproductive structures). The living mycelial network
favors the diverse native species that must become mycorrhizal
quickly. Soil with little inoculum selects against most natives and
favors the plant species that do not need to become mycorrhizal early
in life. These plants are better known as weeds.
Links: The effects of the fungus on the soil are even more significant
than its effects on the plants. As more and more plants become mycorrhizal,
the fungus links one root system to the next. This is possible
because the fungus can colonize almost any plant species. Experiments
have shown movement of soil nutrients and even photosynthate
between plants of different species, as the mycorrhizal fungi pass materials
back and forth. The early ecologists who spoke of the community
as a “super-organism” were not entirely wrong. Below ground,
the community is to some extent a super-organism with a single nutrient
uptake system. The active hyphae that make up the network are
by far the biggest component of the soil microbiota, and make the essential
difference between living soil and inert “dirt.”
The structure of the network is much more complex than this simple
picture. It includes not only a mixture of plant species, but a mixture
of mycorrhizal fungal species. Different fungi are most active in different
parts of the soil, they change seasonally, and to some extent
associate with preferred plant species.
Structure: Fungal hyphae, and the bacteria they encourage, are the
primary agents that bind soil particles into soil aggregates. These
fungi control aggregates in the visible size range; ionic and other
processes operate in the smallest aggregates. The hierarchy of soil
aggregates, and the voids, pores, and cracks that form between aggregates
constitute the structure of the soil. Soil structure allows water
and air to infiltrate the soil and keeps soil particles from washing or
blowing away. Root growth and animal movement generally follow
the cracks between aggregates (the macropore space of the soil). In
this way, the life of the soil and the structure of the soil are heavily
interdependent. New research is showing that the fungi that best form
soil structure are the ones that produce the most Glomalin, a biological
glue that helps hold the soil together.
Soil structure is poorly developed or non-existent on badly disturbed


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sites, and very well-developed in native ecosystems. Successful creation
of soil structure should be a primary objective of habitat restoration,
and is only possible after the mycorrhizal network is in place.
Soil microbiology: Because mycorrhizal fungi are so pervasive, they
exert a large effect on other soil organisms. Research by the USDA
has shown that beneficial soil bacteria are more abundant in soils permeated
by mycorrhizal fungi, and pathogenic organisms less abundant.
Protection by AM against pathogens probably depends primarily
on independent pathogen antagonists. ECM appear to protect by
other mechanisms, including physical shielding of the root by the fungal
mantle, and perhaps by production of antibiotics.
Function: As the first organ of nutrient uptake, the mycorrhizal network
mediates nutrient cycling. As the instrument of rapid root colonization,
it determines the plant species composition of the community.
As the medium of soil structure, it determines the flow of water,
nutrients, and air, directs the pathways of root growth, and opens
channels for the movement of soil animals. As the moderator of the
microbial community, it determines the metabolic processes of the
soil. In other words, the mycorrhizal network is practically synonymous
with ecosystem function.
Seedlings that germinate on soil with an existing mycorrhizal
network can very quickly become mycorrhizal.
Seedlings that germinate on soil without a mycorrhizal
network become colonized much more slowly.


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Where is the Proof?
Mycorrhiza is probably the best studied of all plant-microbial relationships.
There are thousands of publications in the technical literature
that demonstrate the importance of mycorrhiza in plant growth
and ecosystem function, but you will have to represent this base of
knowledge to your client. At the end are lists of books and articles
that can take you to the next step.
Since the scientific literature is difficult to read without a solid background
in biology, you may want to show and interpret some examples
for your client. You might try showing your client graphs and
tables from scientific papers, documenting the growth response, seedling
survival, species diversity, or effects on soil structure. Suitable
papers might be the review by Brundrett, or that by Frances and Read
in the bibliography. These papers are available in the technical libraries
of universities that have good agricultural or biological programs.
I have written for both scientific and semi-popular audiences, and
have included some of those in the bibliography.
Using energy gained from previously colonized roots, the mycorrhizal
mycelium connects to additional roots of this and
nearby plants. Roots of many species may be linked by the
same network. The mycelium intensively exploits
the soil, supporting key parts of the soil
microflora, binding soil aggregates, and
extracting nutrients for use by the plants.


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What Your Clients Can Reasonably Expect
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
Natural soils are organized into a hierarchy of aggregates, with
both chemical and biological factors maintaining the aggregation.
This organization is called soil structure. The pore spaces
between the aggregates allow movement of water and air, and
growth of roots. Mycorrhizal fungi play a key role in formation
and maintenance of soil structure.


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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.
Why not Just Fertilize Instead of Inoculate?
Fertilization can produce large plants, but it often suppresses mycorrhiza
formation. Fertilization lacks or even suppresses the other
important benefits of mycorrhiza. Fertilization cannot increase plant
species diversity; it tends to favor large individuals of the few most
vigorous species. Fertilization cannot improve plant survival, but
rather tends to favor a few large plants rather than many smaller ones.
Fertilization does not make the site unfit for weeds, but instead gives
them a nearly insurmountable competitive edge against native plants.
Fertilization does nothing to decrease root disease, favor beneficial
bacteria, or improve soil structure, perhaps the most important effects
of mycorrhiza in natural systems. In a revegetation project, fertilization
is often a serious mistake.


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Learn Why Some Sites Require Inoculation
If mycorrhizal fungi are in all soils, why do we have to worry about
them? Actually, the correct statement is that mycorrhizal fungi are in
all natural soils. Any serious disturbance takes a heavy toll on the
soil microbes, and such activities as grading, erosion, or overgrazing
can destroy the fungi completely. The fungi do not disperse with the
wind like mold fungi, but instead move by growing from root to root,
or by moving with quantities of soil. Unless your site is within a few
feet of healthy native vegetation, mycorrhizal fungi are very unlikely
to show up fast enough to benefit your plants in the critical early
stages. There are confirmed cases of native plants that sat three years
(surviving only with artificial maintenance) before native mycorrhizal
fungi moved to the site.
Topsoil as Inoculum For Restoration
For restoration of native vegetation, the ideal way to inoculate is to
salvage and re-apply quality native topsoil. It is very important that
the soil be as free of weeds as possible, and that it previously supported
diverse, healthy native vegetation. Topsoil contains a range of
valuable organisms and chemical properties, and often contains seeds
of native plants.
Topsoil salvage is expensive and destroys the donor site; thus it
should be considered only if the site to be graded can furnish the topsoil.
Topsoil should be collected during a dormant season: the dry
part of the year in warm climates, or the cold part of the year if there
is no distinct dry season. The stockpile should be close to the restoration
site; ideally, the soil is moved immediately from donor to receiving
site. If it must be stockpiled, do not pile more than 30 cm deep for
clay soils or two meters deep for sandy soils. While viable mycorrhizal
propagules have been documented in stockpiles as much as twelve
years of age, in general two to three years is the longest that stored
soil should be considered reliable mycorrhizal inoculum. Salvaged
topsoil may be spread over about twice the area from which it was
collected.
Background
16 Site Evaluation
Determine Whether Your Plants Need to Be Mycorrhizal
Most plant species- probably 70 to 80%- are normally mycorrhizal in
nature, and most of those are AM rather than some other kind. If in
doubt, assume that your plants need to be AM. If your plant list contains
few AM hosts, you should in most cases add some to the species
list to be sure you gain the benefits of soil structure and favorable microbiology.
ECM hosts include members of the Pinaceae (most timber species),
the oak and beech family, some tropical legume trees, and scattered
members of other families from the arctic to the tropics. ECMAs
a lateral root grows into new
soil, a propagule of a mycorrhizal
fungus may be present nearby. In
this case, the propagules is a hypha
attached to a clay granule.
The encounter between the two
symbionts is more likely to result
from root rather than hyphal
growth. It is important in
inoculum placement that fungal
propagules be within reach of the
new seedlings.
Figure 9
Mycorrhizal colonization of roots
17
Site Evaluation
dominated forests tend to be low in species diversity compared to AM
forests, and may have a thick layer of organic debris on the forest
floor.
Among ECM hosts are some species that can be simultaneously ECM
and AM. These include willows, cottonwoods, alders, Eucalyptus,
and some of the tropical legumes. There is a tendency for these doubly
symbiotic plant species to be AM as seedlings and both AM and
ECM as mature trees.
Ericads: The family Ericaceae, found worldwide on impoverished,
acid soils, has two mycorrhiza types of its own. Arbutoid mycorrhizas,
found in Arbutus and Arctostaphylos, look like and are related to
ECM, except that the fungi penetrate the cells of the cortex. Ericoid
mycorrhizas, found in most ericads, are quite different, and involve
At very close range, the hypha is
attracted to the root surface.
There it forms an appressorium
and penetrates the epidermis
between adjacent cells. Once
inside the root, the hypha
branches and forms arbuscules
within the cells of the cortex.
Once the connections have formed inside
the root, the external portion of the fungus
begins to grow and branch more rapidly. At
this point it forms runner hyphae along the
root, from which it produces multiple entry
points. The external mycelium also
grows into surrounding soil to
contact new roots and
absorb nutrients.
18
fine, specialized roots. Some of the non-photosynthesizing plant species
of families related to Ericaceae share the ectomycorrhizal fungus
with a nearby ECM tree, and extract sugars from the tree by way of
the mycorrhizal fungus. Their roots look much like arbutoid mycorrhizas.
AM hosts include almost everything else: grasses, shrubs, trees including
redwoods and cedars, most domesticated plant species, and
many members of the forest understory. You cannot distinguish AM
roots from those without mycorrhiza except by a laboratory clearing
and staining procedure.
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.
Site Evaluation
19
Consider a Mixture of Mycorrhizal Fungi
Several scientific studies have concluded that growth responses were
improved with mixtures of fungi rather than single species. However,
none of these studies has included a "wonder fungus" of the type
sometimes isolated in large-scale screening projects. G. intraradices
has turned up as a "wonder fungus" in several surveys, and field experience
so far has shown it to be equal or superior to mixtures of
other fungi. There is a concern that less effective fungi could dilute
the propagules of the fungus that works best, perhaps decreasing its
effectiveness. Even so, many researchers believe that mixtures of
fungal species are preferable.
Plant diversity depends to some extent upon fungal species diversity.
There may be a benefit to some rare plant species of having particular
fungi that grow at the right time of year or produce some other specific
effect. Until we know exactly how the effects are produced, the
only way to include such fungi would be in quality topsoil from the
native habitat of the rare plant species. What is very clear, from every
study that has done the tests, is that inoculation is greatly superior to
no inoculation, with differences between fungal species forming a
secondary effect.
The pattern has been that high quality commercial inoculum allows a
diversity of plant species to become established, and a diversity of
fungi from nearby undisturbed land moves onto the site in subsequent
months. Neither scientific nor commercial experience has sufficiently
precise information to know which fungi provide the widest range of
benefits, or may be required for particular rare plant species. If native
topsoil is not available, the best strategy at this point is make sure a
diversity of plant species succeed and are available to propagate more
fungal species as they find their way onto the site.
Consider Local Native Fungi
Genetics of the organisms used in restoration is always a concern.
Since mycorrhizal fungi are not strongly specific to hosts, there is
usually no need to culture fungi from the same plant species. However,
the fungi must be suitable for the soil and the climate of the res-
Site Evaluation
20
toration site.
In some cases introduced fungi meet these tests better than the natives.
This is likely to be the case if the soil has been so modified by
disturbance that its properties no longer resemble the original native
topsoil. Subsoil, which usually differs in many ways from topsoil, is
the material into which most restoration projects are planted. There is
no assurance, or even likelihood, that the native fungi that came from
the topsoil are better suited to the subsoil than exotic fungi.
Mixtures of local native fungi are available on contract from BioNet
LLC. Their production requires appropriate material from the field
site and takes several months. Because restoration projects often run
on a compressed or unpredictable schedule, there will be times when
neither topsoil nor native fungi are available and "generic" commercial
inoculum will be the only realistic alternative to no inoculation at
all.
Are There Fungal "Weeds"?
Another question is the possibility of introducing a “weedy” mycorrhizal
fungus, which might displace native fungi. This appears
unlikely, since attempts to do so in agriculture have consistently met
with failure. In every documented case that I have found, natives replaced
the introduced species between one and three years after introduction.
As commercial inoculation increases, we must be alert for
any evidence that there can be "weedy" mycorrhizal fungi.
Determine Whether Your Site Requires Inoculation
Laboratory tests can indicate whether the soil contains spores or
whether the roots of existing plants are already mycorrhizal. However,
in most cases you can make a very good guess without laboratory
work, just by considering the condition of the site.
Mycorrhizal fungi are removed entirely by grading, and newly graded
land always requires inoculation if the objective is a functional terres-
Site Evaluation
21
trial ecosystem. Eroded land is in nearly the same condition. Overgrazed
land usually has greatly reduced amounts of native inoculum,
and may have none at all. Agricultural sites that have been fumigated
or disked several times a year may have a low concentration of native
inoculum.
A good first look at your site should consider the existing vegetation.
If there is none at all, or if it is occupied by weeds of the mustard,
Chenopod, and Amaranthus families, you may assume that inoculation
is mandatory. If it is occupied by weedy annual grasses and composites,
or exotic perennials known to be highly invasive (brooms,
Arundo, salt cedar), there may be some inoculum but the site would
probably benefit from inoculation. If the site includes natives in a
degraded state, say scattered early-successional native shrubs with
weeds in between, inoculation is also likely to help, but the problem
might be solved by overseeding or imprinting with aggressive natives
that are good mycorrhizal hosts. These natives will propagate the
fungi and if not overwhelmed by weeds, will build a continuous network
that should favor improvement of the native community.
Sites that receive carefully stored topsoil, less than a year or two in
age, should not require inoculation.
Some scientists believe that in humid climates native fungi invade so
rapidly that inoculation is unnecessary. This requires more research,
since the most mycotrophic species must become mycorrhizal very
early in life, perhaps too early for even the fastest natural recolonization.
You can examine the soil directly for mycorrhizal spores during the
season of plant dormancy. Combine ten or more soil samples from
the upper soil and have a specialized laboratory look for spores, or
find the methods for wet-sieving and spore identification to try it
yourself. It is also possible to clear and stain field-collected roots or
carry out a bioassay with the soil. There are very few laboratories
prepared to provide these services. One good one is Soil Foodweb
Incorporated of Corvallis, Oregon (541/752-5066).
Site Evaluation
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.
Use Mycorrhizal Inoculum Correctly
Root zone: One of the most important points is that endomycorrhizal
inoculum must be placed in the soil, where new roots will grow
through it. Colonization will succeed only if the fungi are properly
placed and if the roots are healthy and growing. ECM spores are better
able to penetrate the soil due to their small size.; even so surface
application is not the best use even of ECM inoculum.
The Inoculation Process
23
Propagules: In a soil with an established mycorrhizal network, the
most active kind of propagule (structure that can produce new fungus)
is fungal mycelium. Most new seedlings in healthy native vegetation
are colonized in this way. Commercial inoculum contains several
kinds of propagules, including spores, mycorrhizal root fragments,
and living mycelium.
Most species of AM fungi form resting spores, either in the soil or in
the root. Spores are more resistant to environmental stress than other
propagules, but do not produce mycorrhiza as quickly as live mycelium
or fragments of mycorrhizal roots. Spores can be separated from
inoculum or the soil, and form the basis for classification for these
fungi.
Fragments of roots may contain live fungi, and these fragments are
often good propagules. In some cases the root fragments contain
spores, and in other cases only fungal mycelium. Hyphae deteriorate
once separated from the host plant, but continue for weeks or months
as active propagules in whole inoculum.
As a living material, mycorrhizal inoculum is susceptible to environmental
stress. It is important not to allow the inoculum to sit in the
sun or expose it to freezing temperatures. Temperatures over about
50º C (122º F) may be lethal for many temperate zone isolates. The
life span of mycorrhizal spores as given in the scientific literature is in
the neighborhood of 6 months to a year. Certain kinds of carriers appear
to provide protection, and in good storage conditions, with the
original production vessel kept intact, inoculum in calcined clay has
retained its viability for two or more years.
Choose the Best Way to Place Inoculum
The best options are mechanized and can be carried out at the same
time as something else already being done on the project. For example,
a compacted site may have to be ripped before planting. It works
out well to rip, broadcast the inoculum, then finish with a process that
incorporates the inoculum into the cracks and openings created by
ripping. This might be another pass with the ripping equipment, disking,
or dragging with a heavy timber. Some land imprinters are
The Inoculation Process
24
equipped to drop inoculum from a fertilizer box, such as those sold
under the brand names Clampco or Gandy. From the fertilizer box it
falls through delivery tubes behind short ripping shanks. On agricultural
land, where compaction and large rocks are not a problem, the
inoculum can be delivered below ground with a fertilizer box and
chisel type shanks, designed for placing fertilizer in the root zone.
Land imprinters and some other land preparation machinery moves
the soil around during operation, and somewhat “accidentally” incorporate
a significant portion of the inoculum. Imprinter operators are
increasingly deciding that this somewhat inefficient means of incorporating
inoculum is preferable to the problems caused by shanks, which
tend to rake up weeds, bend during turns, and otherwise require continuous
attention.
If the inoculum is laid down in lines, as by a fertilizer box, the lines
should be about a foot apart. This is difficult on sites with vegetative
debris, which becomes tangled in the shanks. Eighteen-inch spacing
gives less trouble, and has given good colonization in most cases.
When growing from root to root, the fungi spread between ½ and 1
meter per year. Soil animals may move it somewhat faster. Most often,
the roots grow to the inoculum rather than the reverse, so the real
requirement is to be sure that there is some inoculum close enough to
each new seedling that its roots can find the fungi quickly. With wide
spacing, there are probably a fair number of seedling deaths, but
enough survive to give good representation of the seed mix.
Broadcast: It is possible to broadcast the inoculum (this has even
been done by air), followed by disking or chaining. In one case a contractor
with his own hydroseeding equipment blew it on, then disked
to incorporate the inoculum.
Hydroseeding: a California consultant and landscaping company
established some careful trials of EndoNet inoculation with hydraulic
seeding equipment. There was a surprising degree of success, especially
when seeds and inoculum were applied in the first pass, then
mulch and other components in a second pass. The California Department
of Transportation (Caltrans) has prepared some specifications
The Inoculation Process
25
for mycorrhizal inoculation by hydroseeding.
Hand labor is less efficient but may be the only option on small inaccessible
or rough sites. Mycorrhizal container plants or salvaged wild
plants can be used to introduce inoculum. This is not generally a satisfactory
way to introduce inoculum for plants that follow from seed,
since the spacing of containers is generally too wide for access by any
but the closest seedlings. Container plants may be inoculated at the
time of planting, either by adding a small amount of bulk inoculum to
the root zone, or by dropping in a biodegradable “teabag” package.
It is possible to put inoculum, rather than container plants, in the
ground at intervals. A worker can make a slit in the soil with the
blade of a shovel, drop a few inoculum granules into the slit, and
press the hole shut. Seed can be placed by hand in the loose soil
above the slit and pressed into the soil as the hole is firmed shut.
These spot applications should be spaced as closely as possible to
quickly fill the soil with mycorrhizal roots and mycelium. Again, one
foot spacing is better, although much more labor-intensive, than eighteen
inch spacing. At one foot spacing, there are 43,560 applications
per acre. Even if it takes only 30 seconds to do each application, this
process may cost thousands per acre in labor.
For very small jobs, you can collect topsoil from the root zone of a
known mycorrhizal host. For AM inoculum, try a late-successional
native shrub or tree, or a perennial grass. For ECM or arbutoid hosts,
use the duff or upper soil from under the target plant species. In any
of these cases, look for soil that is free of weeds, contains roots of the
wild host plant, and has good structure. The disturbance caused by
removing topsoil may negate any expediency of using wild-collected
inoculum.
Machine application is generally much less expensive than hand application.
There is need for some kind of hand-operated machinery
that can reduce this high labor cost on inaccessible sites. Some kinds
of antique corn planting tools might be modified to release inoculum
from a backpack, and might reduce the time for each application to a
few seconds. Other possibilities include a modified walk-behind tiller
or lawn edger that would drop a line of inoculum into a narrow slit in
the soil.
The Inoculation Process
26 The Inoculation Process
Mycorrhizal status of some California
plant species
Facultative mycotrophs
Lotus scoparius California broom
Baccharis pilularis Coyote brush
Eriogonum fasciculatum California buckwheat
Nassella pulchra Purple needlegrass
Artemisia californica California sagebrush
May be facultative mycotrophs
Salvia mellifera Black sage
Salvia apiana White sage
Encelia californica Brittlebush
Net-builders
Iva hayesiana Poverty weed
Epilobium canum California fuchsia
Eriophyllum confertiflorum Golden yarrow
Ericameria spp. Goldenbush
Hazardia squarrosa Goldenbush
Isocoma menziesii Goldenbush
Bromus carinatus California brome
Hemizonia fasciculata Tarweed
Obligate mycotrophs
Most long-lived perennials, including
Nassella lepida Foothill needlegrass
Nassella cernua Nodding needlegrass
Rhus ovata Sugar bush
Rhus integrifolia Lemonade berry
May be non-hosts
Atriplex spp. Saltbush
Sambucus mexicana Mexican elderberry
27
The Cost of Mycorrhizal Inoculum
The direct components of this cost are materials and application. The
cost of materials depends upon bulk cost, propagule count, and desired
number of propagules per unit land area. The bulk inoculum
itself varies in cost depending on supplier and quantity purchased.
Commercial inoculum costs from near $100 to thousands per acre at
the time of this writing, with the trend in cost downward over time.
Since mycorrhizal inoculum must go into the root zone, there is a cost
associated with placing the material below ground. If the site is already
being imprinted, ripped, or tilled, inoculum incorporation adds
little to the existing costs. If inoculum application must be a separate
step, the cost depends on the method. See the section on getting inoculum
into the root zone, and the model specifications for details on
some of the available methods.
Form a Strategy for Building the Mycorrhizal Network
Distance: The shorter the distance the root must grow before encountering
a propagule, the more quickly the plant will become mycorrhizal
and the more quickly the mycelial network will form. It is important
to minimizze the average distance between propagules.
An important consideration is how much inoculum to use. Suppliers
may make recommendations based on their own economic ambitions
rather than the best interests of the customer. You may have to satisfy
yourself that their recommendations are appropriate for your project.
All inocula registered in the state of California have to guarantee the
number of propagules. You can determine this yourself with a bioassay,
but for now accept the figure given by the supplier. Most suppliers
determine their number of propagules with a bioassay method that
takes into account all means of forming new colonization. If the supplier
offers no propagule count, look for a better product.
The Inoculation Process
28
Carrier: Commercial inocula usually come in the carrier that was
used to grow the host plants. If so, dispersal is essentially a matter of
distributing the carrier. EndoNet comes in a carrier that consists of
porous clay granules. A granule of the carrier material with attached
fungal structures may be considered a single propagule in practice,
even if several fungal structures are attached to each granule.
Calculations: You can use some general guidelines to help decide
how much inoculum to apply. In native soils with an active mycelial
network, new roots need grow only a few millimeters before encountering
propagules. In stored topsoil most surviving propagules are
probably spores. With 10 to 1000 spores per liter of soil, a root needs
to grow from one-fourth to four inches before encountering a spore.
The Caltrans recommendation of 3.6 million propagules per acre
would be diluted in a six-inch layer of soil to give an average spacing
of 2.2 inches between propagules. To calculate the distance for some
other amount of inoculum, find the number of propagules to be applied
to an acre, then interpolate from the table. The table is based on
the simplifying assumption that propagules are distributed evenly
through the top six inches of soil, and that they sit at the intersections
of a cubic grid.
To give another example, a commercial inoculum supplied as a liquid
suspension claims 2 propagules per ml (2000 per liter). They recommend
15 gallons (57 liters) per acre. Using the above calculation, this
application would give 6.9 inches between propagules.
How close is close enough? This is a fair question, and one without a
firm answer. Greater spacing means slower colonization, and a
greater chance that the natives will lose the race to the weeds. The
figure given above for top soil (one-fourth to four inches) would be
about the right range. A guideline might be that the wider spacing
should make use of fast growing native plants that are very active mycorrhizal
hosts. Closer propagule spacing should be used when
slower-growing natives are the dominant plant species. If host plants
were in rows, as with some agricultural crops, a line of inoculum
would give a predictable distance of propagules from seedling roots.
Careful use of this principle might make possible very low rates of
inoculum application, but would not result in a uniform mycorrhizal
The Inoculation Process
29
network between the rows.
Choice of host plants: it is important to choose host plants that will
become mycorrhizal quickly, propagate the network aggressively, and
grow quickly enough to help suppress weeds. Every local flora includes
such plants. Many turn out to be short-live perennials from the
grass and composite families. The decision of which host plants to
use is a matter of seed availability, cost, and suitability of the site for
the potential choices. Be sure to include several candidate plant species,
not just one or two.
Detect the Scent of Sales Tactics
Unfortunately, the relatively immature inoculum industry has made
use of a time-honored sales technique: BS. BS has been applied liberally
by newcomers to the industry, many of whom are veterans of
Evaluating Inoculum
Spacing of Mycorrhizal Propagules
Number of Separation
propagules Distance,
per acre inches
Pure EndoNet 60,000,000,000 0.086
Best native topsoil 6,000,000,000 0.19
3,000,000,000 0.23
Average topsoil 600,000,000 0.40
300,000,000 0.50
60,000,000 0.86
30,000,000 1.1
6,000,000 1.8
Subsoil with EndoNet 3,600,000 2.2
Poorest topsoil 600,000 4.0
300,000 5.0
Subsoil with very 60,000 8.6
low inoculation rate 30,000 10.8
30 Evaluating Inoculum
miracle plant growth formulas and potions of all kinds. These people
give an unfortunate flavor to the whole concept, and have no doubt
convinced many that mycorrhiza is just one more form of snake oil.
Mycorrhiza is a natural part of the soil and a part of plant nutrient uptake.
The fungi are the dominant soil microorganisms, and soil biology
depends heavily upon the presence, density, and types of mycorrhizal
fungi. However, mycorrhizal fungi cannot make it rain, cannot
decompact a fill slope, cannot compensate for planting out of season,
and cannot make up for methods that are otherwise very poor.
Here are some of the claims that should raise a red flag:
Plants show dramatic growth increases within a few days: Mycorrhizal
growth responses are slow to develop; a rapid response
would have come from fertilizer in the inoculum.
Growth response in spinach, broccoli, or other non-host: plants
known to be non-hosts are good tests of fertilizer or other nonmycorrhizal
factor in the inoculum.
No guarantee of propagule count on label: California and several
other states require guarantees of propagule or spore counts. Even so,
a number of inoculum products are being sold with no indication of
propagule density. On close examination, these have usually proven
to have no detectable propagules, or at best a very low count. Others
claim multiple fungal species but offer only a total propagule count.
Very low propagule counts: propagule and spore counts vary from
as low as two to several hundred per cubic centimeter of inoculum.
Be aware that the cost of the material should reflect the propagule
density.
Inoculum offered in liquid or powder form: ECM fungal spores are
fine enough to be incorporated in a powder form, but AM fungal
spores are relatively large and are destroyed by grinding. The small-
BS: that in which we try not to step while crossing a pasture;
that which is not so.
31
est viable root fragments are about 1/10 mm in length, and the spores
themselves are also in that size range.
Mycorrhizal propagules settle out quickly in water and must be continuously
agitated to remain in suspension. Inoculum suspensions
have been recommended for application through drip irrigation systems
with hundreds of yards of pipe and tubing. AM inoculum is singularly
unsuited for such use; see the earlier section on BS.
How Mycorrhizal Inoculum is Produced
ECM fungi are generally grown in laboratory media by methods of
industrial microbiology. Some fungal species cannot be easily cultured
in laboratory conditions, and those are either unavailable as
commercial inocula, or are collected from the wild. Certain fungi that
fruit belowground, including truffle-like species of the genus
Rhizopogon, lend themselves to wild collection. The fruiting structures
are essentially pouches of spores that may be applied at the
user's convenience.
AM fungi must be cultured with a host plant; these fungi remain the
last important holdouts among microorganisms that cannot be grown
on defined culture media. Inoculum typically consists of roots,
spores, fungal hyphae, and growth medium from the “open pot culture”
method of inoculum production.
Carrier materials include soil, sand, calcined clay (the same material
often used for cat litter), and organic mixes. The trade-offs involve
suitability for plant and fungal use, convenience of storage and handling,
and suitability for application by machinery.
An experimental method that may be finding its way into commercial
inoculum production is the use of "transformed roots". These are
roots that can grow on laboratory media without leaves, and can support
mycorrhizal fungi. It is not yet clear whether this relatively slow
and exacting method can produce inoculum that is economically competitive
with more conventional methods. Also potentially useful are
hydroponic and aeroponic methods, which depend upon a nutrient
solution rather than a solid medium. With certain combinations of
Evaluating Inoculum
32
plant and fungus these methods can produce very concentrated inoculum.
Most such material has been short-lived compared to that produced
in solid media, but there are some indications that the life span
can be considerably extended with post-production treatment.
Conduct a Field Trial
There are thousands of experiments in scientific journals that have
documented every aspect of the mycorrhizal symbiosis. These studies
began to appear in the early part of the 20th century. Much of the scientific
work has incorporated careful experimental design and made
use of laboratory equipment, specialized knowledge, and university
facilities that are not available to field practitioners. Even so, it has
turned out that almost every purchaser of mycorrhizal inoculum ignores
decades of good experiments and performs one bad experiment,
his own, before becoming convinced of the efficacy of mycorrhizal
inoculation.
This attitude among users is not entirely unreasonable. Scientific
work is usually designed to eliminate all variables but the one under
study. Scientists are unfamiliar with commercial restoration practice,
just as contractors are unfamiliar with scientific methods. Practical
work must tolerate conditions that change over space and time, with
details of methodology that are often determined on the job. Every
inefficiency results in lost time and high costs. It is very difficult to
imagine that a scientific project could be done by the methods that are
actually used in practice; these complex, variable, and subjective factors
are to a large extent beyond the reach of the scientific method. It
therefore not surprising that practitioners want to do at least an informal
trial in their own conditions, using their routine planting methods.
There can be no illusion that these trials are scientific, or that their
results can be taken as scientific evidence. Every imaginable factor,
from usage history of each spot to position on the slope, influences
the experimental outcome. However, there is considerable value in
seeing the results in practical conditions and gaining an understanding
of the realistic possibilities. Over several such trials, we can begin to
see whether the result is predictable, and to build a basis for confident
decisions in the future. It is thus important to make these trials as ob-
Evaluating Inoculum
33
jective and enlightening as they can be, given the considerable constraints
of time, cost, and facilities.
The most common design is to divide the project area into two portions
and apply inoculum to half. A serious weakness of this procedure
is that the two halves are never equivalent; one side has some
advantage regardless of inoculation. Watch for different amounts of
sunlight, initial weed loads, amounts of native topsoil incorporated
into the slope, proximity of native vegetation, water distribution, and
activity by animals and human visitors.
When locating control and treatment plots, consider factors that may
cross contaminate them. Inoculum may be introduced onto control
plots by re-use of the same equipment for each treatment, slope position
that lets soil and water move from treated to control, and movement
of personnel and equipment. The plots should be at the same
elevation, and controls should be treated before inoculated plots to
avoid residual inoculum in the equipment. There should be no foot or
wheel traffic after inoculation, especially from treated to control plots.
If at all possible, there should be several plots of each treatment,
spread over the entire available area. All plots must be carefully
marked, photographed, and documented in written records. Many of
these trials have proven useless because of poor documentation.
Plan at the beginning for the evaluation of the trial. Growth response
is a less common result than improved plant diversity, greater seedling
survival, improved root systems, greater vegetative cover by natives,
and reduced weed growth. Use a diverse seed mix, including
species that have traditionally been difficult to use in your conditions.
For this purpose, do not include species with difficult germination
requirements, since mycorrhizal fungi generally have no effect on the
germination stage.
Judge the Success of an Inoculation Trial
The effects of inoculation on native ecosystems are so profound and
such a natural part of the vegetation, that the only complete failure is a
lack of colonization. This can be detected by laboratory examination
of root samples, determination of the presence of mycorrhizal spores
Evaluating Inoculum
34
during an appropriate season after planting, or the formation of soil
structure as the vegetation grows. These tests require facilities and
training, or the services of a specialized laboratory.
Plant growth response in itself is not likely to tell the story. If
uninoculated plots have been kept healthy by fertilization, any mycorrhizal
effects will have been masked. Uninoculated plots will
likely have a different set of plant species, dominated by the least mycotrophic,
and least responsive, species in the seed mix. Plant species
diversity and species-by-species determinations of survival rate are
more likely than growth response to clearly indicate successful inoculation.
In order to see an effect with diversity and survival, the seed mix must
contain mycotrophic plant species. That is, it must not consist only of
species known to be “reliable” on disturbed sites. These species almost
always turn out to be non-hosts or weakly mycotrophic species.
If improved diversity and greater dominance by natives are not apparent
by visual examination, use transects or other quantitative measure
to compare inoculated with uninoculated plots. Doing so has turned
up as much as a two-fold difference in native cover on a site where
the difference was not visually apparent.
Habitat restoration on graded land is the situation in which inoculation
is virtually always required. Within other disciplines, there are particular
circumstances in which inoculation is required, or would allow
a departure from established methods that have been in effect compensating
for a lack of the natural soil microflora.
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
Evaluating Inoculum
35
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.
Inoculate for Erosion Control
Mycorrhizal fungi bind the soil in ways that the plants alone cannot
do. In addition, mycorrhizal fungi promote the formation of soil
structure, allowing movement of air and water through the rooting
volume rather than across the surface. These have obvious implications
for erosion control. In addition, erosion control plants introduced
without inoculation may have a difficult time becoming selfreliant.
In that case, non-host weeds may quickly claim the site, reducing
it to an unsightly, easily eroded condition.
Use of inoculation in erosion control requires a suitable means of introducing
both seed and inoculum, and incorporation of a diverse seed
mix that includes several good mycorrhizal hosts. The use of fertilizer
should be limited to the forms and amounts that approximate the
actual needs of the vegetation. Excess fertilization, the rule in erosion
control, will discourage formation of the mycorrhizal network and
will encourage the growth of weeds.
Inoculate Agricultural Crops
This is a complex topic. The value of inoculation will vary from zero
to great, depending on crop and history of the site, among other
Applications other than Restoration
36
things. The value of inoculating must be balanced against both cost
and benefits of established or alternative procedures. A foremost consideration
is cost; a crop that can only produce $100 net income per
acre can scarcely support an inoculation cost of $100 per acre.
The clearest application is in the establishment of orchards or vineyards
on newly fumigated ground. This is now standard practice in
some areas and there have been good results in citrus, grape, stone
fruits, and apples. The benefits may be less from improved nutrient
uptake than from improved soil microbiology. Mycorrhizal roots encourage
greater populations of native bacteria that fight root pathogens,
and that otherwise promote plant growth. In addition, improved
soil structure may be a worthwhile benefit of inoculation. Done at the
planting stage, inoculation is a one-time cost that may be spread over
the lifetime of the crop. The usual procedure is to drop some inoculum
into the planting hole and backfill so that the roots encounter it as
early as possible when they begin to grow.
There is not likely to be much benefit from inoculating an established
vineyard or orchard. If mature plants are not mycorrhizal, look to inhibitory
conditions to find the cause, not lack of inoculum. Possible
inhibitory conditions include excessive fertilization, frequent disking,
soil compaction, or the presence of root disease.
A second category of crop that may benefit from inoculation is nursery
transplants, whether annual or perennial, especially those that go
into fumigated soil. These tend to be high value crops that can support
the added expense. Further, inoculation at the nursery stage
makes very efficient use of inoculum. Possible candidate crops are
strawberry, hops, and melons. Growth responses may be masked by
heavy fertilization, especially with phosphorus. A program that involves
inoculation should also reduce fertilizer and chemical input. It
will require some research to understand the best balance between
"natural" and chemical methods for each crop and each set of growing
conditions.
Row crops, especially those of relatively low value, will be the lowest
priority for inoculation. Unless the soil has been fumigated it is likely
that native mycorrhizal fungi will meet the needs of the crop. Even
with fumigation, the heavy fertilization typical of modern agriculture
Applications other than Restoration
37
will very likely mask the growth benefits of inoculation.
Any future for mycorrhiza in row crops will depend upon particular
problems that can be solved only by a system that involves inoculation.
Constraints may at some point be imposed upon use of phosphorus
fertilizer, especially near bodies of water. Mycorrhizal inoculation
may permit a shift to less mobile forms of phosphorus, including
rock phosphate. Refinement of application techniques and inoculum
placement may allow dramatic reductions in the amount of inoculum
required for rapid root colonization. When those circumstances are
combined, inoculation of carrots, onions, cotton, and certain other annual
crops may become a reality.
Applications other than Restoration
38
Learn more about mycorrhiza
Further reading
Bethlenfalvay, G. J. and R. G. Linderman (eds.). 1992. Mycorrhizae in sustainable
agriculture. American Society of Agronomy Special Publication Number 54. American
Society of Agronomy, Madison, WI.
Brundrett, M. C. 1991. Mycorrhizas in natural ecosystems. Pages 171-313 in: A.
Macfaydn, M. Begon, and A. H. Fitter, Eds. Advances in Ecological Research. Vol.
21. Academic Press, London.
F. L. Pfleger and R. G. Linderman (eds.). 1994. Mycorrhizae and plant health. APS
Press, St. Paul.
Francis, R., and D. J. Read. 1994. The contributions of mycorrhizal fungi to the determination
of plant community structure. Pp. 11-25 in: A. D. Robson, L. K. Abbott, and
N. Malajczuk (eds.). Management of mycorrhizas in agriculture, horticulture, and forestry.
Kluwer Academic Publishers, The Netherlands.
Riefner, R., D. Pryor, and T. St. John. 1998. Restoration at San Onofre State Beach,
California. Land and Water July/August 1998:15-18.
Smith, S. E., and D. J. Read. 1997. Mycorrhizal symbiosis. Second Edition. Academic
Press, San Diego.
St. John, Ted. 1996. Mycorrhizal inoculation: advice for growers and restorationists.
Hortus West 7(2):10.
St. John, Ted, Bob Dixon, and Mick St. John. 1998. Habitat restoration at Discovery
Park, Arizona. Land and Water March/April 1998:6-11.
St. John, Ted. 1998. Mycorrhizal inoculation in habitat restoration. Land and Water,
September/October, 1998.
Web resources
INVAM: By far the best mycorrhizal web site for fungal identification, you can learn
more about AM fungi and fungal taxonomy from this web site than from any available
book: http:\\Invam.caf.wvu.edu/
Microbe Zoo: http://commtechlab.msu.edu/ctlprojects/dlc-me/zoo/
Mycorrhiza Information Exchange: http://mycorrhiza.ag.utk.edu/
MycoInfo: http://www.mycoinfo.com/
Practical use of mycorrhiza: www.mycorrhiza.org
Dr. David Sylvia: http://www.ifas.ufl.edu/~dmsa/
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Examples of experimental results with mycorrhiza
from the scientific literature
Growth Response and Other Benefits to Plants
1. Kough, J., R. Molina, and R. G. 1985. Mycorrhizal responsiveness of Thuja, Calocedrus,
Sequoia and Sequoiadendron species of western North America. Canadian
Journal of Forest Research 15 (6):1049-1054.
AB: These forest tree species responded dramatically to AM inoculation, especially
Thuja.
2. Sylvia, D. M. 1990. Inoculation of native woody plants with vesicular-arbuscular
mycorrhizal fungi for phosphate mine soil. Agriculture, Ecosystems, and Environment.
31:252-261.
AB: Height and stem growth of swamp dogwood was double controls in the nursery,
but no effect after 18 months if planted into soil with native VAM.
3. Gemma, J. N., R. E. Koske, E. M. Roberts, N. Jackson, and K. De Antonis. 1997.
Mycorrhizal fungi improve drought resistance in creeping bentgrass. Journal of
Turfgrass Science 73: 15-29.
AB: Creeping bentgrass (Agrostis palustris cv. 'Penncross') inoculated with the arbuscular
mycorrhizal fungus Glomus intraradices was able to tolerate drought conditions
significantly longer than nonmycorrhizal turf. Protection against drought was conferred
by G. intraradices when turf was grown under conditions of low phosphorus fertilization
(11 mg l-1), but the benefits disappeared when the P concentration of the fertilizer
was quadrupled to 44 mg l-1. Mycorrhizal turf maintained significantly higher chlorophyll
concentrations (avg. 29% more) than did nonmycorrhizal turf during the 10-daylong
drought in the field.
Need for inoculation
1. Bellgard, S. E. 1993. Soil disturbance and infection of Trifolium repens roots by
vesicular-arbuscular mycorrhizal fungi. Mycorrhiza 3(1):25-29.
AB: Severe experimental disturbance disturbed the external hyphal network and root
fragments (containing hyphae and vesicles), which in turn temporarily reduced the
infective potential of the fungus to zero. An observed delay in the initiation of VAM in
the most disturbed blocks can, therefore, be explained by the time required for hyphae
to grow from other propagules in the soil which survived the disturbance event.
2. Powell, C. L. 1980. Mycorrhizal infectivity of eroded soils. Soil Biology and Biochemistry
12 (3):247-250.
AB: Mature pasture soils in North Island, New Zealand, had 6-19 mycorrhizal
propagules per gram. Of 31 samples of eroded soils, 22 had less than 1 propagule per
gram and 13 less than 0.2. In a pot trial mycorrhizal inoculation of white clover increased
shoot growth in 7 eroded soils 1-12 fold.
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3. Reeves, F. B., D. Wagner, T. Moorman, and J. Kiel. 1979. The role of endomycorrhizae
in revegetation practices in the semi-arid west. I. A comparison of incidence
of mycorrhizae in severely disturbed US natural environments. American Journal of
Botany 66 (1): 6-13.
AB: A comparison of a natural, undisturbed ecosystem, a mid-elevation sage community,
with a severely disturbed old roadbed through this community, revealed that more
than 99% of the plant cover in the natural community was mycorrhizal (vesiculararbuscular),
whereas less than 1% of the plant cover in the disturbed area (roadbed) was
mycorrhizal. Examples of non-mycorrhizal plants as primary successional species in
severely disturbed habitats are discussed. The importance of maintaining or reestablishing
the mycorrhizal fungal component in reclamation programs designed to
produce stable ecosystems is emphasized.
Effects on soil
1. Miller, R. M., and J.. D. Jastrow. 1992. The role of mycorrhizal fungi in soil conservation.
P. 29-43 in: G. J. Bethlenfalvay and R. G. Linderman (eds.). Mycorrhizae in
sustainable agriculture. American Society of Agronomy Special Publication Number
54. American Society of Agronomy, Madison, WI.
2. Simmons, G. L., and P. E. Pope. 1987. Influence of soil compaction and vesiculararbuscular
mycorrhizae on root growth of yellow poplar and sweet gum seedlings. Canadian
Journal of Forest Research 17(8):970-975.
AB: Weight, length and fibrosity of sweetgum seedling root systems decreased with
increase in bulk density. Inoculated yellow poplar seedlings had greater root weight at
each bulk density than uninoculated seedlings, but root length was not influenced by
mycorrhizal treatments at higher bulk densities. Fibrosity of yellow poplar roots varied
with mycorrhizal treatment at each bulk density. Results indicate that compaction effects
may outweigh mycorrhizal benefits for yellow poplar at higher bulk densities. At
each bulk density, sweetgum seedlings inoculated with G. fasciculatum showed the
greatest root growth, suggesting that this fungus may alleviate the effects of soil compaction
for this tree species.
3. Tisdall, J. M.; Oades, J. M. 1979. Stabilization of soil aggregates by the root systems
of ryegrass. Australian Journal of Soil Research 17 (3):429-441.
AB: The root system of perennial ryegrass was more efficient than that of white clover
in stabilizing aggregates of Lemos loam because the ryegrass supported a larger population
of vesicular-arbuscular mycorrhizal hyphae in the soil. Electron micrographs
showed that the hyphae were covered with a layer of amorphous material to which clay
particles were attached.
4. Sustainable Agriculture: http://www.ars-grin.gov/ars/PacWest/Corvallis/hcrl/rps003.
htm
Top soil storage and handling
1. Abdul-Kareem, A. W. and S. G. McRae. 1984. The effects on topsoil of long-term
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storage in stockpiles. Plant and Soil 76 (1/3): 357-363.
AB: A study of 18 topsoil stockpiles of different size, age and soil type has revealed
that biological, chemical and physical changes occur, mainly as a result of anaerobic
conditions within the heaps, but also as a result of mechanized handling during the
stripping and stockpiling. Visible changes occur within 0.3 m of the surface of stockpiles
of clayey textured soils, but only below about 2m depth for sandy textures. These
visible changes are accompanied by chemical changes, particularly in the forms of nitrogen,
manganese and iron present but also in the content of available nutrients, pH
and organic matter levels. Biological changes include reductions in potential for mycorrhizal
infection, soil biomass and especially earthworm population. The soil atmosphere
contains high levels of carbon dioxide, methane, ethane and ethylene. Physical
changes include reduction in aggregate stability and resistance to compaction, increase
in bulk density and changes in pore size distribution and micro-structure, asrevealed by
scanning electron microscopy. Limited evidence suggests that many of the adverse
effects quickly disappear when the soil is re-spread.
2. Gould, A. B., and A. B. Liberta. 1981. Effects of topsoil storage during surface
mining on the viability of vesicular-arbuscular mycorrhiza. Mycologia 73(5):914-922.
AB: Population levels of viable VA mycorrhizal inocula were lower in stored topsoil
than in undisturbed soil, and decreased with increasing periods of storage. The populations
of viable VA mycorrhizal inocula decreased after topsoil storage for 4 years compared
with storage for 3 years.
Plant survival
1. St. John, T. V. 1996. Specially-modified land imprinter inoculates soil with mycorrhizal
fungi (California). Restoration and Management Notes 14:84-85.
AB: The land imprinter was an effective and economical way to add mycorrhizal inoculum
on a California restoration site. Mycorrhizal inoculation led to a five-fold increase
in plant survival and doubling of plant species richness.
2. Sylvia, D. M. 1986. Effect of vesicular-arbuscular mycorrhizal fungi and phosphorus
on the survival and growth of flowering dogwood (Cornus florida). Canadian Journal
of Botany 64 (5): 950-954
AB: Mycorrhizal development and growth of Cornus florida seedlings were investigated
in a field nursery and greenhouse. After 12 weeks., seedlings inoculated with G.
etunicatum had greater survival, shoot dry mass and root fresh mass than seedlings
inoculated with G. intraradices or the control. However, G. etunicatum did not affect
the concentration or total uptake of P into shoots. This fungus can apparently enhance
the survival and growth of dogwood seedlings without improving P nutrition.
Species diversity
1. Doerr, T. B., E. F. Redente, and F. B. Reeves. 1984. Effects of soil disturbance on
plant succession and levels of mycorrhizal fungi in a sagebrush-grassland community.
Journal of Range Management 37(2):135-139.
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2. Gange, A. C., V. K. Brown, and L. M. Farmer. 1990. A test of mycorrhizal benefit
in an early successional plant community. New-Phytologist 115(1):85-91.
AB: The fungicide Rovral (iprodione) was applied in granular form in an attempt to
reduce VA mycorrhizal infection of plants during the early stages of secondary plant
succession, namely the first year of colonization of bare ground. In 7 out of 11 plant
species examined, infection levels were reduced by the fungicide. Four of these also
showed reduced cover abundance as a result of fungicide application. Since 3 were
annual forbs, which as a plant life-history grouping comprised 73% of the community,
total cover of the vegetation (as measured by point quadrats) was significantly reduced
by the fungicide. In 3 species, reduced infection levels did not appear to result in reduced
vegetation cover. The reasons for this are discussed in relation to the dependency
of plants on mycorrhizal infection. It was found that fewer plant species recruited
into communities where iprodione was applied. The implications of these results, in
terms of the role that mycorrhizas play in the structuring of early successionl plant communities,
are discussed.
3. Grime, J.P., J. L. M. Mackey, S. H. Hillier, and D. J. Read. 1987. Floristic diversity
in a model system using experimental microcosms. NATURE; 328(6129):420-421.
AB: Most investigations of floristic diversity have involved studies of natural vegetation.
Progress using these approaches has been limited because some potentially important
factors are not amenable to precise field measurement or manipulation. Here
the authors describe an alternative research strategy in which communities were allowed
to develop in turf microcosms providing factorial combinations of soil heterogeneity,
grazing and mycorrhizal infection, all of which are capable in theory of promoting
diversity. The effect of grazing is shown to be due to the differential sensitivity of
the canopy dominant to defoliation.
Resistance to weeds
1. Allen, M. F., E. B. Allen, and C. F. Friese. 1989. Responses of the nonmycotrophic
plant Salsola kali to invasion by VA mycorrhizal fungi. New Phytologist
111:45-49.
AB: S. kali reacted to VAM fungi as to a pathogen.
2. Francis, R., and D. J. Read. 1994. The contributions of mycorrhizal fungi to the
determination of plant community structure. P. 11-25 in: A. D. Robson, L. K. Abbott,
and N. Malajczuk (eds.). Management of mycorrhizas in agriculture, horticulture, and
forestry. Kluwer Academic Publishers, The Netherlands.
AB: Ruderal species that have been tested are suppressed in undefined ways by proximity
of the hyphal network to their root systems (Francis and Read 1992). This suppression
is very likely a major component of the resistance to invasion of functional
ecosystems.
Pathogen resistance
1. Graham, J. H., and D. S. Egel. 1988. Phytophthora root rot development on mycorrhizal
and phosphorus-fertilized nonmycorrhizal sweet orange seedlings. Plant Dis-
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Resources
ease 72(7):611-614.
AB: Root dry weight and leaf P content of noninfested VAM sweet orange seedlings
were greater than those of nonmycorrhizal plants, which were nearly deficient in phosphorus.
P. parasitica reduced leaf P status of VAM and non-mycorrhizal seedlings
alike but reduced dry weight of only VAM plants. There were significantly fewer rotted
root tips on VAM seedlings. P. parasitica reduced VAM colonization as a result of
the loss of root tips.
2. Linderman, R. G. 1994. Role of VAM fungi in biocontrol. P. 1-26 in: F. L. Pfleger
and R. G. Linderman (eds.). Mycorrhizae and plant health. APS Press, St. Paul.
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Specifications for inoculation by
hydroseeding equipment
Endo (arbuscular) mycorrhizal inoculum shall consist of spores, mycelium,
and mycorrhizal root fragments in a solid carrier suitable for handling by hydro-seeding
equipment. The carrier shall be the material in which the inoculum was originally produced,
and may include organic materials, vermiculite, perlite, calcined clay, or other
approved materials consistent with mechanical application and with good plant growth.
Each endomycorrhizal inoculum shall carry a supplier's guarantee of number
of propagules per unit weight or volume of bulk material. If more than one fungal species
is claimed by the supplier, the label shall include a guarantee for each species of
mycorrhizal fungus claimed. Endomycorrhizal fungal species shall be suitable for the
pH of the soil at the planting site. If the inoculum consists of a mixture of species, no
more than 20% of the claimed propagule count shall consist of fungal species known to
be unsuitable for the pH of the soil at the planting site.
Endomycorrhizal inoculum shall be applied at the rate of 8,900,000 live
propagules per hectare (3,600,000 live propagules per acre), based on the guarantee of
the supplier or the analysis returned by an independent laboratory.
Endomycorrhizal inoculum shall be applied in the same application as the
seeds. In no case shall endomycorrhizal inoculum be applied after the seeds. Inoculum
must be applied within one hour of addition to the mixing tank. The inoculum shall be
applied with hydro-seeding equipment within 60 minutes after the seed has been added
to the mixture.
Endomycorrhizal inoculum is a live material. It shall be stored, transported
and applied at temperatures of less than 32º C (90º F). If temperatures exceed 32º C
(90º F), remaining erosion control applications must be applied within three hours of
the application of the inoculum.
A sample of approximately 28 grams (one ounce) of inoculum will be taken
from each inoculum container by the Engineer. The number of propagules will be determined
by laboratory testing. Propagules shall include live spores, mycelial fragments,
and viable mycorrhizal root fragments.
Acknowledgements
I thank Dr. Jim Bever, Dr. Margot Griswold, Mr. Peter
Nebb, and Ms. Maria Anderson for constructive comments
on an earlier version of this publication.
© 2000 by Ted St. John, Ph.D.
April 5 2000​

 

[eggmansky]

HFS!...and I thought I knew a little...

 

[eggmansky]

Suggested sources of Myco using Coco?

Dude,
THAT was some heavy reading! My biology 202 books simply 'touch' on the bennies of myco. Which, if any, commercial sources of myco would you suggest/recommend? Thanx in advance!

 

[A4]

I use Great White because of the diversity of species it contains. It is probably the most expensive of the entire bunch but the cost is really negligible when you factor everything in. You use very minute amounts per plant so $30 worth of mychos lasts well over a year. I have never broken it down but for sure less than a dollar per plant.

It has 15 different species of mycho, 11 different species of beneficial bacteria and 2 species of trichoderma.

 

[eggmansky]

Thanx A4
Noted

Can't wait til my NEXT grow!