Microbes at Work

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