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Q/A
with Dr. Marx
What are mycorrhizal
fungi?
Dr. Marx:
Mycorrhizal fungi are root-inhabiting, symbiotic fungi
that colonize the fine absorbing roots of more than 95
percent of the land plants in the world. These fungi
colonize trees and other plants to get the simple
carbohydrates or sugars they need. In return, the
fungi extend 'feeding tubes' called mycelia far into
the soil. This increases the surface area of the
roots, improving absorption of water and essential
mineral elements which are shared with their host
plant. Some forms of mycorrhizae can increase the
absorptive surface area of root systems by more than
700 percent when compared to nonmycorrhizal roots.
What are the
benefits of mycorrhizae?
Dr. Marx:
Mycorrhizae, are able to absorb, accumulate and
transfer all of the 15 major and minor mineral
elements and water to plants more rapidly and for
longer periods of time than nonmycorrhizal absorbing
roots. Through this alliance with plants, mycorrhizae
increase the tolerance of their tree hosts to drought,
compaction, high soil temperatures, heavy metals, soil
salinity, organic and inorganic soil toxins and
extremes of soil pH. They also depress many root
diseases caused by pathogenic fungi and nematodes.
Are mycorrhizae a
requirement for plant life?
Dr. Marx: Most
plants cannot survive without mycorrhizae in natural
environments. In other words, plants without
mycorrhizae cannot satisfy their water and mineral
element needs. Here's why. For a plant to produce
enough absorbing roots to generate the same surface
area developed by mycorrhizae, a plant would have to
use 100 times more photosynthate (sugars). Most
plants, especially trees, are simply not able to do
this, thus they evolved a dependency upon mycorrhizae.
Does mycorrhizae
stimulate plant growth?
Dr. Marx: No.
Mycorrhizal fungi help plants eliminate inhibited
growth, which is necessary for survival during periods
of stress. Plants evolved with multiple survival
strategies more than 400 million years ago when they
first emerged on this planet; mycorrhizal fungi being
one of the most important of those strategies. When
plants are healthy, they can fully optimize their
survival techniques to ward off normal natural
stresses. For instance, let's say a sprinkler head has
gotten clogged. The plants within range of that head
will survive longer with minimal water if they were
healthy before the clog appeared. If those plants are
fully colonized with mycorrhizae, the expanded
absorptive areas of their root systems will allow them
to last even longer without water. Does this mean you
can shut your irrigation system off? No. But it does
ensure that the water you give plants is used to
maximum benefit. Because mycorrhizae allows plants to
more efficiently and completely gather their water
needs, it provides them with drought tolerance, but it
does not eliminate their need for water.
When do you apply
mycorrhizal fungi?
Dr. Marx: New
installations of virtually any plantings, particularly
transplanted plants, benefit from inoculation with
specific mycorrhizal fungi. There are a number of
reasons:
- Newly transplanted
trees and plants must rejuvenate their root
systems as quickly as possible, so they can begin
to protect themselves from the normal stresses
found in their new environment. Mycorrhizal fungi
form a secondary root system for the plant,
allowing it to become established in its new
setting more quickly.
- Natural soil
populations of mycorrhizal fungi are typically of
the type that benefit only native plant species.
Different types of mycorrhizal fungi attach
themselves to different species of plants. In the
southwest, as well as the rest of the country,
most species of planting materials originated from
outside the area. For example, eucalyptus is from
Australia, Mexican fan palm from Mexico and
Podocarpus from Africa. Application of vesicular
arbuscular mycorrhizal (VAM) fungi and other
specially selected fungal species ensures that
appropriate fungi is available in the planting
soil.
- Mycorrhizal fungi
are not mobile in the soil; plant roots must
contact the fungi before colonization can occur.
Therefore, higher numbers of mycorrhizal fungi
need to be present in the soil at
planting/transplantation.
How are the fungi
applied?
Dr. Marx: I
predict that within 10 years most plant stock with be
inoculated with mycorrhizal fungi and their roots will
be fully colonized with mycorrhizae upon delivery. If
there is time to work with your nursery, you can
specify that mycorrhizal fungi inoculants be used.
Otherwise, application on site has become extremely
easy and can be made by spray, drench, injection or
mixed into the backfill.
Keep in mind that any
above-ground condition that affects root growth will
also affect mycorrhizal development. High light
intensity and low-to-moderate soil fertility encourage
colonization. Check the product labels for specific
instructions about the application of fungicides,
insecticides and herbicides.
In general, plants only
need to be inoculated with mycorrhizal fungi once in
their lifetime. If the plants should undergo periods
of extreme or unusual stress and/or shows symptoms of
decline, re-inoculation would be beneficial.
How should products
be selected?
Dr. Marx: Read
product labels or other manufacturer literature before
you select a mycorrhizal fungal product. The label
should clearly list the type of mycorrhizal fungi used
in the formulation and what plant species the fungi
will benefit. Select products that supply the
mycorrhizal fungi as dormant spores, not fungal
propagules in root fragments. Dormant spores remain
viable for longer periods. The product also should be
guaranteed to be free of pathogenic fungi and
nematodes.
Some manufacturers
package mycorrhizal fungi along with materials and
other microorganisms that stimulate root growth. These
may include soil-enriching bacteria, organic
biostimulants and nutrients, and natural surfactants.
Avoid products that contain high amounts of
fertilizer, which can actually impede fungal
colonization. Also, avoid products that have a putrid
odor; the smell comes from the wrong microorganisms;
mycorrhizal fungi don't do this.
What about mature
trees?
Dr. Marx:
Recent studies have shown that mycorrhizal fungal
inoculation of mature trees is beneficial and can
double the tree's root density. If a mature tree is
undergoing decline, inoculation may be beneficial.
Inoculants can be injected or applied as a vertimulch
into the soil/root zone of the mature tree.
Is there a
mycorrhizal fungi for palms?
Dr. Marx:
Typically there are few tree care products available
for palm trees. But there is a mycorrhizal fungal
product called Mycor Palm Saver on the market. It
contains a blend of endomycorrhizal fungi adapted for
palm and sandy soils; it also benefits other tropical
species.
What else should I
know about these fungi?
Dr. Marx: Learn
everything you possibly can about mycorrhizae. I
believe these microorganisms will be universally
specified and used within the next decade. It is
important to remember that the application of
mycorrhizal fungi goes beyond the simple use of a
product. By acknowledging the importance of the plant
root system, and by designing management programs that
nurture and protect that system, we become better,
more successful plant and landscape managers in the
long run.
Click
Here to download the
FREE Acrobat 4.05 Reader
PHC Cultivating Comparison
Natures
Tree Protection Advertorial
PDF File, 167kb.
Urban
Trees Need Mycorrhizae
Endo
or Ecto Species Finder
Q/A
with Dr. Marx
Fungicide
Effects on VAM
Fungicide
Effects on Ectomycorrhizae
©
2000 PHC Royalty Corp.
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