MYCORRHIZAE: The hidden marriage of plants and fungi

Normally when we think of fungi relating to plants, what comes to mind is infection and disease: powdery mildew, blackspot, slime flux and canker; Oh, NO!! However there is a growing awareness of the far more extensive benefits that fungi contribute to our world. Decomposing fungi are primary agents in the composting process which to us recyclers is the magic of turning garbage into gold. Not only do our plants love the rich humus and organic matter, but pesticides and herbicides are also broken down. Much of the body of soil itself is made up of fungi, especially loamy, well-aerated soil. And then there are the symbiotic fungi, the ones forming mutually beneficial relationships with plants. These associations of absorbing roots with fungal mycelium are known as mycorrhizae, from “mycor”- fungus and “rhiza”-root. Even though these beneficial relationships were discovered in 1885, it is not widely known today that 95 % of all plants on earth intermingle their roots with mycorrhizal fungi.

Vera Evenson, local author of Mushrooms of Colorado, has called this interweaving of various species of trees’ roots with various species of fungi “a marriage underground.” She explained that fungi lack the chlorophyll which allows green plants to make their own food out of sunlight, carbon dioxide and water in the process of photosynthesis. Instead they are more like animals in that they must get their nutrition from already-made carbohydrates and amino acids. And so for millions of years, fungi have made relationships with plants: some parasitic which can harm or kill the host plants; some saprophytic, living off the tissues of dead plants; and some symbiotic, like the mycorrhizal fungi which benefit plants. Of these, most enter the cells of absorbing roots forming endomycorrhizae, and some form sheathes on the roots forming ectomycorrhizae.

To think of these mycorrhizal fungi as “infecting” the roots of plants is to underestimate the mutual evolution that derived these specialized relationships. The natural world is a highly competitive environment where few of the seeds that germinate reach maturity and fewer still live long and vigorous lives. One of the primary structures of survival for a plant is an extensive root system, and here is where the mycorrhizal fungi expand the concept of “survival of the fittest.” Usually we think of this Darwinian concept as symbolizing the struggle of the mightiest to the top of the gene pool. However all sorts of alternative strategies have proved successful: the skunk, the turtle, the tapeworm and the human, to name a few. In this case, the successful strategy was non-aggressive mutual aid.

Millions of years ago trees were putting out roots into lean soils and there, beneath the earth, these roots met with the hollow, threadlike mycelium of fungi; and both were looking for food. The fungal mycelium being more branching, fine and extensive are far more efficient than roots in contacting the soil, expanding the surface of a root sometimes by 700%. Therefore in economic terms (which a surviving plant is desperate to consider), an investment of 10-20% of its carbohydrates, vitamins and amino acids in the development of symbiotic fungi will give a return of over 100 times the value of that investment in root-like development. Plus these mycorrhizal fungi are able to mobilize complex nutrients otherwise unavailable to plants. The trees, of course, made the obvious right choice: “Give the little suckers a place at the table.!” Thus began the marriage made in earth.

This marriage continues today to benefit plants. Dr. Donald H. Marx, a leading scientist who founded the Institute for Mycorrhizal Research and Development for the US Forest Service stated that through this alliance with plants:1) the fungi bring water, sometimes from as far as 30′ away, to the roots making the plants more drought-tolerant. 2)the fungi bring minerals essential to plant health to the roots: phosphorus, nitrogen, zinc, manganese and copper. 3) the fungi present physical and sometimes antibiotic barriers to root pathogens, thereby preventing diseases. 4) they increase the tolerance of plants to extremes in soil temperatures and pH. 5) they increase the longevity of absorbing roots. 6) they help plants tolerate stresses like transplant shock, soil compaction, soil toxins and heavy metals.

Dr. Marx points out that even though mycorrhizae are already present in city soils, both the numbers of species and the numbers of fungi present are less than one fourth of what they should be for good plant health. In addition, native mycorrhizae typically only benefit native plant species. For these reasons, and  because of the many stresses on plants in urban settings, why not introduce supportive fungi? He believes this is especially important for newly planted balled-and-burlap trees that are dug in the fields, which reduces their root system by 70%-90%. Here the fungal mycelium can form a “secondary root system” much more quickly than the actual roots, to prevent stress-related diseases and pest problems. The addition of mycorrhizae in a multiple-species cocktail has been the most beneficial reclaiming mine sites, deserts and arid locations, nutrient-poor and depleted soils and subsoils as are found around many new homes. Dr. Marx added that sticking a tree into a barren soil is like trying to raise a polar bear in Florida.

Paul Stamets, another pioneering mycologist and author of Mycelium Running, acknowledges dramatic benefits from these fungi. He has studied how a continuous network of one mushroom can connect many acres of a forest, creating a kind of “web” intelligence where the “mycelium guards the forest’s overall health, budgeting and multi-directionally allocating nutrients.” This is not an airy-fairy idea. Because the fungus is connected to the whole area, it has an interest in the prosperity of the whole forest, upon which it is dependent.

Rob Reinsvold, a mycologist and biologist teaching at the University of Northern Colorado in Greeley, believes that if the mycorrhizae already present in the soil are given more supportive conditions, they will populate in larger numbers. Conditions which support mycorrhizae also support other beneficials like soil bacteria and earthworms. These conditions include: mulching, incorporating composted organic matter, keeping the soil moist but not soggy, fertilization with slow-release organic fertilizers or low doses more frequently, and avoiding habitual use of fungicides and pesticides.

Just in the last 10 years many companies have sprung up selling mycorrhizal fungi products to nurseries and gardeners. However there are many differences of opinion as to their effectiveness. Lakshri Sridharan, who has a PhD in microbiology says, “Initial investment on mycorrhizae may appear to be a little expensive, but inoculations with mycorrhizae will save money on water bills, chemical fertilizers, pesticides or fungicides.” But Christina Wells at Clemson University said of her research, “In general we found little benefit from mycorrhizal products, as all products purchased through typical consumer channels contained no living inoculum.” One of the problems is that mycorrhizae are living beings that may dry out on the shelf of a garden center or overheat in direct sunlight.

From my own research, there appears to be several atypical sources for mycorrhizae that may have good viability. Some of these are: Organica Biotech, Plant Health Care, Inc., Mycorrhizal Applications, Inc.,  BioLynceus and Eco-Cycle Compost Tea.

But the latest hot tip comes from Tom Selvig, a heartful microbiologist with many years of experience in the field. He says that mycorrhizae can be increased the most rapidly in association with photosynthetic bacteria that can not only fix atmospheric nitrogen, but also change raw materials into sugars that feed the fungi. These bacteria can rapidly adapt to new environment and can dramatically improve conditions for fungi and plants. He emphasizes that it is not just elements like N-P-K that support plant life; it is biological life.

There seems to be a theme already characterizing the 21st Century: nothing stands alone; everything is interconnected. If a boat is sinking, it isn’t “his” boat it is our boat. Likewise the more we learn about how soil life works, the better we can design sustainable systems for plants, and therefore, for us humans who are dependent on plants. Mycorrhizae may indeed be very beneficial for plants, especially in stressful conditions, like much of the West, and especially if temperatures are rising. But we must not forget that fungi are just one of many populations of microorganisms that constitute soil life. These emerging revelations emphasize the old gardening dictum: “Feed the soil, not the plants.”