Soil Health and the Importance of
Mycorrhizal Fungi
November 17, 2015
|
Story at-a-glance
−
-
70 percent of the soil microbes are fungi, so they’re a
really critical consideration when you’re trying to
improve soil health
-
Mycorrhizal fungi have microscopic filaments that are
integrated into the plant and branch out into the soil,
giving the plant access to a larger volume of soil and
hence more nutrients
-
The best management practices for mycorrhizal fungi are
cover crops, above-ground diversity, and no-till.
Minimize soil disturbance, as this breaks up the fungal
filaments
By Dr. Mercola
One of the most important strategies for improving your health is
to grow your own food. However, that may not be so easy if you're
unaware of the importance of soil microbes.
Dr. Wendy Taheri is a research microbiologist, to whom I was
introduced via Gabe Brown, a farmer in North Dakota, who is a strong
proponent of regenerative land management.
Dr. Taheri was formerly employed at the United States Department
of Agriculture-Agricultural Research Service (USDA-ARS), and she
recently founded a new company, TerraNimbus, to help farmers enhance
their yields, reduce inputs, and improve nutrient use efficiency
(NUE).
“I got my PhD in ecology and evolutionary biology at
Indiana University,” Dr. Taheri says. ”I was doing
restoration work at old coal mines to make the soil grow plants
again. We were focusing on using microbes for restoration.
During an experiment, I saw that the microbes I used were
able to increase plant biomass by 69 percent. I said to myself,
'Wow, we've got to get this to the farmers.' After I graduated,
I took a job with the USDA to try and do that."
In this interview, she discusses the importance of arbuscular
mycorrhizal fungi (AMF). According to renowned mycologist Paul
Stamets, 70 percent of the soil microbes are fungi, so they’re a
really critical consideration when you’re trying to improve soil
health.
What Are Mycorrhizal Fungi?
While few people have actually seen mycorrhizal fungi, as you
need a microscope to see them, they are a very important foundation
for healthy soils. Their spores are in the soil and their hyphae
(long, branching filamentous structures) are not only in the soil;
they also integrate with the plant via its roots.
The filaments penetrate the roots of the plant and get inside the
cells where they grow an organ called an arbuscule. There are seven
different kinds of mycorrhizal fungi, but arbuscular mycorrhizal
fungi (AMF) are the most important to farmers, as they are
associated with so many different plants.
While the arbuscular kind associates with 90 percent of plant
families, the other six kinds are more specialized for specific
plant groups.
The hyphae, which is integrated into the plant, branch out into
the soil, acting like very fine roots, giving the plant access to a
larger volume of soil and hence more nutrients. These filaments
specialize in uptaking nutrients such as trace minerals,
particularly phosphorous, which is a limited resource.
Mycorrhizal Fungi as an Ecological Solution to Pollution
When phosphorus is applied as fertilizer, only a portion of it is
utilized by the plants. A lot of what is being applied ends up
running off and spilling into waterways, as tilling promotes soil
erosion and hinders water retention.
From various waterways, phosphorous and other agricultural
nutrients and chemicals eventually end up in our oceans, where it
can lead to oxygen depletion (eutrophication).
"We tend to put a lot of phosphorus in our soils and use
it not as wisely as we could, or as conservatively as we
should,' Dr. Taheri says. This is really important
because we're going to run out eventually...
Our soil, our atmosphere, our water, our oceans, our
streams, and our lakes are all interconnected through nutrient
cycles...
It’s my opinion that everyone who eats food or breathes
oxygen should be concerned with how we manage our agricultural
complex because the soil and the organisms in it is the only
system large enough to offset global warming, which affects us
all.
AMF are drawing carbon through plants, via
photosynthesis. The plant is taking carbon out [of the
atmosphere]. It’s feeding carbon in the form of sugars to
mycorrhizal fungi. In fact, they get 100 percent of their carbon
from the plant.
And then they utilize that carbon to build soil
structure, which increases the soil quality. It's the best way
to sequester carbon, and it's the only system big enough to
offset all the oil we burned over the last century. We could
actually do that.
A group of scientists is working on demonstrating that
how we manage our soil can affect how much carbon we can store
in it. And mycorrhizal fungi use that carbon to form soil
aggregates, which is how we build our soil structure. They are
keystone species in the soil; they’re very important.”
Tilling the soil promotes runoff, allowing a lot of phosphorus to
wind up in the ocean. But matters are made even worse by the fact
that we also have so much carbon dioxide in the air. This carbon
dioxide forms carbonic acid when it mixes with water, making the
water acidified.
Few people realize that 50 percent of the oxygen we breathe
actually comes from the algae in the ocean, and acidification may be
affecting the microbes and algae responsible for the production of
this oxygen...
"Balancing global warming, carbon dioxide through
management of agricultural systems can solve a lot of problems
for humanity," Dr. Taheri says.
The Importance of Soil Carbon for Water Retention
About 20 years ago, scientists discovered a glycoprotein called
glomalin, which adds to soil aggregates. It is produced by
arbuscular mycorrhizal fungi.
"If you don't have aggregates, you have dust and
everything goes away. That's not a good soil for farming.
Aggregates are little glued-together particles that don't fit
together and compact. This is how we alleviate compaction,"
Dr. Taheri explains.
“And the pore space is what allows drainage and air to
get into our soil because plant roots need air and many of the
microbes that are important to plants do too.”
Those pore spaces are also what determine, to a great extent, the
water-holding capacity of the soil. It’s actually the carbon in the
soil that permits water to be retained. Much of that carbon occurs
as what we call soil organic matter (SOM). As the carbon content in
the soil declines along with SOM, so does its ability to hold water,
making us more subject to problems from both droughts and floods.
When there's flooding, the soil cannot absorb the water and hold
it for when there's a drought later. Instead, all the water runs off
the top, taking the topsoil with it, and the topsoil is the most
biologically active, most nutritious, and most valuable part of the
soil profile.
As discussed in a previous
interview with Gabe Brown, in North Dakota he gets about 16
inches of rain each year, most of which falls in a day or two.
Because of his no-till farming practices and the improved soil
structure he's achieved with his regenerative land management, he's
actually able to retain almost all of that water, whereas his
neighbors struggle with runoff and topsoil depletion.
That's also why cover crops, and diversification of crops, are so
important in protecting and improving the quality of soils. We also
need to limit our use of chemicals in agriculture, as they tend to
destroy important soil fungi.
"Individual families of mycorrhizal fungi are more
sensitive to some chemicals than others," Dr. Taheri says.
"We tend to put a lot of different chemicals into our
[mono]cropping systems. What I have seen is a decline in
numbers, a decline in diversity, and a dominance by certain
species [of fungi] in our agricultural complex, which means
we're not getting all the benefits we could out of it."
Growing Organic Foods Is Part of the Small- and Large-Scale Solution
One of the steps nearly everyone can do to help increase the
fungal growth in the soil is to buy and consume organically-grown
foods. Those who are willing can take it a step further, because the
fact that something is organically produced does not mean that
no-till strategies or cover crops were used. The next step is to
either grow it yourself, or find a farmer who is integrating these
important land regeneration practices.
“Randy Anderson, a weed scientist for the USDA at ARS has
done a lot of research on cover crops that can be used to
suppress weeds. If you go cool season-cool season followed by
warm season-warm season, he told me that over the course of a
few years, you’ll deplete that weed seed bank and won’t have a
weed problem anymore.” But it’s hard to get farmers to switch
over from what they know works and try something new, although
Gabe Brown, myself, and many others are trying to help them make
that switch,” Dr. Taheri says.
Modern Crop Breeds are Losing Mycorrhizal Association, Which May
Prevent Us From Becoming Sustainable
Aside from using no-till practices and cover crops, we need to
reduce the amount of phosphorus used, because too much phosphorus
suppresses the plants association with mycorrhizal fungi. One of the
problems Dr. Taheri is seeing is that modern crops, probably bred
under high-input breeding systems, has led to plant species that are
no longer sensitive to mycorrhizal association.
This means the ability of the plants to form the association with
mycorrhizal fungi is being bred out of them. In March of this year,
Dr. Taheri is starting a seed certification program for commercial
growers that will score whether or not, and how well associated with
mycorrhizal fungi various seed varieties are.
“Any commercial growers can send me seeds and say, “I
want to know how well these guys respond. If we lose that
symbiosis—because of the nutrient use efficiency that is created
by these microbes, and their important position in the soil—and
they start to die out in our soils, I don’t think we will ever
become sustainable, which means our residence here as a species
on the planet will be numbered, as far as how many years we have
left. We have to be able to grow enough food and we can’t really
afford to lose this association.”
Some people counter such arguments by saying that we can shift to
alternative growing methods, such as hydroponics. However, shifting
all agriculture to hydroponics is unlikely to work on a large scale.
And you still have problems like runoff to deal with. It's not
entirely ecologically sound.
Also, that's not the way food was historically grown. That's not to
say you can't produce some descent food using hydroponics, if done
properly. But without this association with mycorrhizal fungi and
other soil microbes, it's difficult to imagine optimally healthy and
nutritious plants being produced, because there's such a dynamic,
complex symbiosis that occurs to improve the health of the soil and
nutrients that it provides us.
"Now, humans are doing the work of nature. Instead of
looking at nature and saying, 'How can I get nature to do this
as part of the balance of how I'm growing my plants?',
instead... we've been doing nature's job with chemicals. Well,
we inevitably have discovered we're not as good as Mother Nature
and there are side effects to what we've done. We have to be
careful, because look at the size of our agricultural complex;
it's a third of the terrestrial surface of the world. It is the
largest ecosystem on the planet. We have to take a real serious
look at the impact of that system on our water and air quality.
We can't ignore it, it's too big."
Benefits of Mycorrhizal Fungi
Most of commercial agriculture is focused on increasing yield,
but according to Dr. Taheri, we really need to be looking at
improving the mycorrhizal association, and breeding our microbes and
our plants together to work as a team. Doing so can produce
tremendous benefits, including but not limited to the following:
Increased soil fertility |
Increased essential oil production |
Increased water-holding capacity |
Protection from both fungal and bacterial diseases |
Reduced soil compaction |
Drought tolerance |
Heavy metal tolerance |
Salinity resistance |
Higher nutrient content |
Increased biomass |
Reduced inputs, meaning decreased need for harmful
chemicals |
Earlier flowering; increased flowering, and more fruits |
Reduction or elimination of runoff and leaching |
Carbon sequestration, which will reduce atmospheric
carbon dioxide |
How to Encourage Mycorrhizal Growth in Your Garden
Arbuscular mycorrhizal fungi, which are the focus of this
article, are primarily associated with vascular plants, this
includes the vast majority of everything we eat. (Notable exceptions
are the Brassicas and Amaranth families.) The mycorrhizal fungi that
associate with trees are from other groups of mycorrhizal fungi. For
example, pine trees associate with a group we collectively call
ectomycorrhizae, while the arbuscular mycorrhizal fungi are often
referred to generically as endos or endomycorrhizae.
AMF, or endos cannot live without host plants, which is why cover
crops are so important. There should always be living roots
in the ground to support your microbes. There are mycorrhizal fungi
inoculants that you can buy for your home garden, but according to
Dr. Taheri, you need to be aware that when using soil inoculants,
they’re competing with all the microbes already in your soil that
have adapted to your current soil conditions. The scales of success
are already tipped against them because they’re not pre-adapted.
As noted by Dr. Taheri:
“Most of the inoculants that I have seen are the same
group of 12 species that are being recirculated. One of the
species, for instance, is deserticola. It’s from the desert; the
name tells you that. If Glomus deserticola is put in some place
very different from the desert, what are the odds it’s going to
survive? It’s kind of like putting a polar bear into the desert
and expecting it to do well.”
That said, if you get a good association between plant
and mycorrhizal fungi, you can potentially double plant growth. But
most of the inoculants currently on the market are not the most
appropriate species. Dr. Taheri has a very large assortment of fungi
in her own collection, and has started working on a commercially
viable formula. However, it may still be years before it’s
perfected. Compost teas are also ineffective for promoting
mycorrhizal fungi. So what can you do to improve the fungal
composition of your soil?
"The best management practices for mycorrhizal fungi are
cover crops, above-ground diversity, and no-till," Dr.
Taheri says. "Minimize your soil disturbance, because you're
breaking up your hyphae—which is not so good for your plants—as
soon you start digging around."
As far as inoculants go, most of them are, to a large degree, one
species called Rhizophagus intraradices. If you use fertilizer, you
will typically already have plenty of Rhizophagus. It is well
adapted to agricultural conditions. So why pay a lot of money for
it? Dr. Taheri recommends avoiding inoculants containing primarily
Rhizophagus for this reason. Inoculants can be helpful if you’re
buying pottings.
However, as these have typically undergone a process that makes the
soil fairly sterile. If you already have healthy soil, then you can
further propagate mycorrhizal fungi simply by increasing the
diversity of plants in your garden. Earthworms are a very good
indicator of healthy soil. Also check your garden for insect
predators, such as lizards and spiders. They too are an indication
of a healthy soil balance.
"When you have diversity, you have homes for a lot of
different kinds of organisms, and that's when your predators
start to come in. That keeps everything in balance," she
explains. "It doesn't matter that you have insects that are
eating a leaf here and there. What matters is whether or not it
gets out of hand. Most of the time, pathogens and things that
grow on your plants are always present. Most of the time, they
don't have much impact because things are in balance. You want
to make sure that your management practices are not favoring
things that are eating your plants while disfavoring the things
that hunt those things that eat your plants."
© Copyright 1997-2015 Dr. Joseph Mercola. All Rights Reserved.
http://articles.mercola.com/sites/articles/archive/2015/11/17/mycorrhizal-fungi-soil-health.aspx
|