Examples of microbes at work could fill hundreds of pages: the miracle of
bread and cheese and beer; the leather top for a pair of shoes; even the white
cliffs of Dover. Without the microbes, starch rich grains would remain
unappetizing and hard to digest. We can understand how yeast is a requirement
for bread and beer, but we seem to forget that food crop harvests wouldn’t
arrive in the first place without the intervention of microbes – microbes in
the soil, microbes called chloroplasts in leaf cells, all harnessed to the work
of trapping solar energy.
Oh yes, those white cliffs of Dover! These are the skeletal remains of
microbes that flourished some 100 million years ago. The seas were just right
for great proliferation of life, one million tons of these microbes dividing to
become 16 million tons in just 240 minutes. As a matter of fact, most
sedimentary rocks are what’s left of microbes.
When we think of microbes, we think of disease, and yet most microbes are
beneficial in nature. Most of the fungi help, not hinder, the farmer. A good
example – more typical than we pause to admit at times – is the predacious
fungus.
In obeying the laws of life and death, it seeks to live and multiply. As a
rotifer or eel-worm goes about its handy work in the soil, it might encounter
the lasso of the predacious fungi. Like a microscopic snake, this fungus holds
its death grip, in time absorbing the body contents of its victim.
The term
mycorrhiza was first used about 90 years ago. It refers to
the many fungi that are found in close contact with – and entering into – the
plant roots growing in virgin soil, or in soil with plenty of organic matter.
Organic gardeners have long considered the mycorrhiza a friend. Not a few
scientists interested in farm technology have considered them a foe.
Just as there are more kinds of plants that grow underground than there are
on the soil’s surface, so too are there more kinds and numbers of livestock
hidden away in the shallows and depths of a soil system than ever walk the
surface of the earth. These tiny underground plants and the little critters
that live on them make possible the growth of higher plant life. This
underground living complex decomposes dead organic materials, making soils
fertile so that higher plants can grow. Reserve mineral elements are made
available by life in the soil. Most important, these life systems enter into
symbiotic relationships with roots of higher plants and supply them with
critically needed compounds.
S.C. Hood of Hood Laboratory, Tampa, Florida once caused these lines to be
printed in a company brochure, and so far we have found little in the
scientific literature to equal them. “It is probable,” wrote Hood, “that this
symbiotic relation began when the first primitive plant forms left the
primordial sea and took to the land. There were primitive forms of fungi and
algae, both of which had developed in water. When cast on dry land, as
separates, both were helpless. The fungi could not make carbohydrates. The
algae could not secure mineral nutrients from the rocks. But united in a
partnership, both could survive. The algae made carbohydrates for both, and the
fungi extracted from the rocks the mineral elements needed by both of them.”
There is nothing to suggest that this relationship does not persist to the
present, especially in the lichens, the first builders of soil. In their
development of complicated structures, higher plants kept a part of this early
relationship. “They are still dependent on their associated fungi for
development, especially chemically,” is the way Hood put it.
These filamentous, underground plants form a cobweb-like growth throughout
the soil and over roots. They are so slender that should we twist together 500
of the larger ones, we would have a rope no longer than a human hair...This is
the study of them which has been neglected and why their importance has only
been recently recognized.
Further, once these are recognized, the fantastic quantities of mycelial
fiber and surface area of the fungus in a limited amount of soil around even
one plant, the importance of mycorrhiza in symbiosis with higher plants comes
clear.
Some hint at this complexity can be found in the scientific literature…in
A
Quantitative Study of the Roots and Roots Hairs of Winter Rye Plants
(American Journal of Botany in 1937 and 1938), H. Dittmer reported on a single
rye plant. He found a root length of 377 miles. Fully 80% or 275 miles of these
roots were feeders. The root hairs on that single plant numbered 14.5 billion,
having a fibrous length of 6,214 miles. The surface area alone was calculated
at more than a tenth of an acre. Combined, the roots and roots hairs had a
length of 6,990 miles with a combined surface area of 63,784 square feet –
close to 1.5 acres. And this was just one plant.
It is true, winter rye has a massive root system and very fine root hairs.
And it may be that Dittmer had a very robust plant on his hands. But the point
is that all plants have fantastic figures involved when these measurements are
taken. In a single acre of winter rye or meadow grass, the area of roots and
root hairs may exceed 30,000 acres. At least one-third of this is covered by a
net of fungus mycelium, and this provides additional area for soil contact.
Mycorrhiza in association with root systems isn’t a one-way street. Let us
refer to a scientific paper translated in 1961 from the Russian under the
auspices of Israel. In
Soil Microorganisms and Higher Plants, N.A.
Krasilnikov put together the findings of some 20 investigators and served up
some breath-taking data on exudates from plant roots. The Russians found
growing roots to exude inorganic elements, sugars, many amino acids, a host of
organic ones, vitamins, biotics, antibiotics and a number of organic compounds.
A man named Denidenko was cited as having found a single corn plant which –
during the vegetative period – exuded 436 milligrams of organic substances when
the nutrient solution remained unchanged. When it was changed seven times
during the growth period, 2.3 times more – or 1,136 milligrams – of organic
substances were exuded. Fantastic. Certainly. But this has been known and
ignored for a long time.
What does this mean? Apparently the root surfaces of higher plants are used
by fungi as feeding ground. Are these fungi friend or foe?
Apparently Fusarium, Trichoderma, Gliocladium and Basidiomycetes are the
important fungi in this fungus-plant symbiosis, the mycorrhiza complex. Moving
from richer virgin soil, where fungus is ever-present in both species and
number, to soils with less organic matter, fungus growth is greatly reduced in
both amount and kind. The Basidiomycetes are the first to disappear. As
conditions worsen, one group after another vanishes. Finally, when the corpse
of a soil is all that is left, only an occasional Fusarium remains in evidence.
When the soil has been reduced to a barren waste, plant species of a weed
nature take over...
Without a full complement of mycorrhiza, lowered quality and yield result.
Lowered quality is the chief reason salt fertilizers are not entirely
satisfactory. Still, inferior quality – lowered protein, less vitamins, poor
mineral content – finds acceptance in the market simply because the naked eye
can’t see the difference as long as bins and bushels remain. It is only when
yields falter that the farmer recognizes the problem.
...the Fusarium genus can provide us with the key for much needed
understanding.
Fusarium oxysparum, for instance, is very versatile.
Whenever investigators look for fungi, they invariably find
Fusarium
oxysparum or other groups of that genus – F.
salani, F.
rodeum,
and so on. Generally this genus is a peaceful homesteader in the soil and a
beneficial symbiont on plant roots.
Yet when this fungus finds a root that
is poorly nourished, a plant with low resistance, it quickly becomes
pathogenic. If the farmer permits plant malnutrition to continue,
pathogenic potential really comes into its own, and the fungus rates attention
as an active parasite.
This is why the biochemistry of immunity is seated in fertility management,
and not in...more lethal molecules of poisons to combat fungus attack. This is
what William A. Albrecht was talking about when he charged that “We are
exhausting the quality of our soils. As we do so the quality of our plants goes
down.”
- Excerpted from Eco-Farm - Lesson 7 - by Charles Walters
