In farming lore of times past it was a practice of French (and other) farmers to "bless" a new field by sprinkling it with earth from an older field known to be productive. Modern research has now shown that such a ceremony may have more than spiritual value.
It has been found that many species of fungi, beyond just breaking down and feeding on dead plants and animals, associate themselves with the roots of living plants, establishing a symbiotic relationship. These mycorrhizal fungi produce fungal threads that coat the plant roots, even penetrating the cells in many cases, getting nutrients from the plant while providing benefits for it's host at the same time. Indeed, a large number of plants require this "invasion" for good health, and many others are much better off with than without the fungi. Orchids and pines, for example, can't even grow normally without the presence of the right species of fungi on their roots. Another plant requiring fungi on it's roots is the temperate fruit,the pawpaw (Asimina triloba)
Foresters have been aware that plants need fungi for some years. In the Pacific Northwest, the seedlings in Douglas fir nurseries did better when the soil they were growing in was given an inoculation of soil from an old stand of the same species. Inoculating the soil of the nursery with fungi from old trees helped the young trees get off to a much better start.
Home growers and farmers knew composting helped plants, but probably thought it was simply the nutrients, when it fact the compost also helped by introducing more fungi into the soil, and providing improved conditions for them to grow, so that they might form associations with the plant roots. Since then, the study of fungi and how they associate with the roots of plants has moved into many new areas.
There are four classifications of mycorrhizal fungi, based largely on how they associate with the plant roots.
The first are the "ectomycorrhizal fungi". "Ecto" is a prefix meaning"outside,", so ectomycorrizahal fungi are ones that wrap themselves around the outside of the roots, without actually penetrating the cells, though they may insert themselves between the cells, even if they don't actually penetrate the cell walls. Because they tend to form a sheath around the roots of the plant, these mycorrhizas can actually be seen with the naked eye, or under a lens. They tend to suppress the formation of root hairs, but stimulate the growth of many more short roots than normal, so the plant has much more root growth overall. Root tips can be seen to be covered with a white layer, and fungal threads, or strands, are visible on and around the root.
Second are the "endomycorrhizal fungi." "Endo" = "into," thus endomycorrhizal fungi actually invade the cells, sending their hyphae, or fungal threads, into the cells of the roots themselves. They are not always obviously visible to the naked eye, though their effects may be seen in many ways, however, as we'll see farther on. They are also known as Vesicular Arbuscular Mycorrhizal (or VAM) fungi.
The third group are an "in between" group, the "ectendomycorrhizal"types, which has characteristics of the other two groups. Some researchers now put these types into one or the other of the first two classifications.
The fourth group, mentioned only in passing because of it's oddity, is something of a maverick, the "ericoid" mycorrhizas. One plant family, the Ericaceae, which contains blueberries, cranberries, rhododendrons, heather and heath, manzanitas, and a few others, only form mycorrhizal associations with a certain few fungi that haven't been found to associate with other plants.
Many species of fungi form mycorrhizal relationships with plants, including a lot of the common forest mushrooms in the Basidiomycetes, and the Ascomycetes. A classic example of a mycorrhizal fungi is the exalted truffle, which has to associate with the roots of oak and hazelnut trees to produce it's gourmet delicacy. Many of the species most people think of as"toadstools" are mycorrhizal types, so having mushrooms pop up in your yard might actually be a sign of healthy plants.
What exactly do mycorrhizal fungi do for the plants they associate with?
Increase the number of roots. As noted with the ectomycorrhizas, many of the mycorrhizal fungi stimulate root growth in plants. Dr. Robert Linderman of Oregon State University is a leader in mycorrhizal fungi research, and some of his work shows that the right strain of fungi can actually double the number of roots in potted nursery stock, making the plants more resistant to dryness, and allowing them to establish themselves faster in their new location when they are planted out. This applies to both annual and perennial plants.
Further, the fungi allow plants to take up phosphorus and other nutrients more efficiently. Indeed, Dr. Linderman's work showed that plants in phosphorus-poor soil with mycorrhizal fungi did better than fungi-less plants with adequate phosphorus.
Protect plants from disease. All the exact mechanisms aren't established, but plants with mycorrhizal fungi are less susceptible to diseases, both of the roots and the rest of the plant. Some of the effects must be due to improved nutrition of the plant, while others may be related to substances given off by the fungi, natural antibiotics which keep disease organisms at bay. The physical presence of the fungi may form a natural barrier to disease, as well.
Improve the soil. Dr. Linderman's work describes how many of the mycorrhizal fungi actually penetrate the cells of the roots, creating a sort of "leakage" or exuding of substances from the roots. These substances had various effects on the soil, one of the most important of which was causing soil particles to clump together into aggregates. This clumping effect opened up the soil structure to allow better movement of water and oxygen into the soil.
One particularly interesting aspect was Dr. Linderman's revelation that fungal threads or hyphae from one plant could actually reach out into the soil and connect with threads of other fungal species on other plants. In effect, this meant that as the network of hyphae becomes well established,all the plants in an area would be tied together into one giant community,presumably able to exchange substances and nutrition with each other. This could be at least one aspect of why mixed plant communities often seem to function better than stands of single species. With all plants tied together, different species might exchange with each other, balancing nutrition and moisture amongst the community.
While mycorrhizal fungi were first studied in trees, research now encompasses all types of plants, both annual and perennial. Many strains of mycorrhizal fungi have been isolated, many of which are adapted to specific plant species. More importantly for the consumer, much work is being done by commercial companies, who are culturing mycorrhizal fungi and making them available to growers. This eliminates the variable results of using compost, which didn't always contain the best strains for the plants it was used on. However there are also species of fungi that work with many species of plants.
Different companies have taken different approaches in working with mycorrhizal fungi. Buckman Laboratories sells the species Glomus intraradix as a treatment for turf and nursery plants. Plant Health Care, Inc. uses a second approach by selling mixtures of three Glomus species and a species from the Entrephospora family. They feel that such a mix insures that at least some of these VAM fungi will adapt to a wide range of soil conditions and pH. Bio-Organics is testing strains of many fungi specific for different species of plants, but also have mixes of strains and general purpose types for use on crops for which no specific types have been identified. Thus far, it appears that VAM types are the most useful commercially, with about 90% of the types in use being VAM.
Mycorrhizal fungi don't just affect the plant roots, either. The health of the entire plant is boosted when the right fungi associate with it. Don Chapman at Bio-Organics, one of the companies studying Mycorrhizal fungi, reported results at one grower's grounds in which all pots of test plants with mycorrhizae, accompanied with trace minerals and organic fertilizer, had little or no damage from insects. Plants treated with conventional chemical fertilizers, and lacking mycorrhizal fungi, had considerable insect damage to the leaves. One theory says that insects lack amino acids to digest plant matter and that only sick plants develop high levels of certain amino acids, which stimulates the insects to feed on them. If a leaf is healthy, it will lack the amino acids that stimulate insect feeding behavior and they leave after taking only a taste. Apparently even though the plants without fungi had all the correct nutrients supplied to them chemically, they weren't able to make good use of them without the presence of fungi on their roots.
One of Mr. Chapman's customers, a Master Gardener, reported the yield of his tomatoes doubled with fungi, while ripening time was as much as a week earlier. He also said the tomatoes tasted much better. Similar results have been reported with other crops elsewhere. One grower reported an increase of 6,000 pounds per acre on his sweet potatoes using mycorrhizal fungi.
In my own garden, I applied mycorrhizal fungi and minerals to part of a potato patch, and minerals without fungi to the rest of the patch. All the area with fungi came up faster, bloomed sooner, and there were fewer blanks in the rows. At this writing, the crop has yet to be harvested, so the overall yield isn't known, but the difference in the performance of the plants was striking enough that I'll be very surprised if there isn't some difference in yield.
In the case of perennial plants, one application of the fungi should probably treat the plant for life. With annuals, it's advisable to reapply it every year, to be sure there is enough in the soil to properly inoculate the plants.
The naturally known species of fungi occur in many different soil types and pH ranges, making it highly probable that the commercially available types should also work well in many conditions.
Dr. Linderman also mentioned that some mycorrhizal fungi are even effective in hydroponic situations.
The commercial products can be either liquid or powder, for various means of application, from soil drench to root dips. Bio-Organics has formulations that combine minerals, organic (usually fish) fertilizer and fungi all in one to give the plant an extra boost. The other companies deal mainly with commercial growers, but Dr. Mike Kern at Plant Health Labs says their flower bed drench should work well for home growers as well.
Not only growers, but the environment itself can benefit from using mycorrhizal fungi. With the fungi, much less fertilizer is needed, reducing the sort of over-fertilization that leads to runoff and contamination of ground water. In fact, extra fertilizers may not even have any added effect with the fungi on the job.
While mycorrhizal fungi may not be the absolute cure-all for agriculture, it is certainly the most promising tool to be developed in a very long time, promising to improve the health and yield of plants, reduce the need for fertilizer, improve the soil, and reduce the need for pesticides.
In cell biology, many of the "organelles" (literally, "little organs")of cells are thought to have originally been simple, small cellular organisms that took up residence inside larger ones. Perhaps they were parasites at first, but at some point the relationship became symbiotic, beneficial to both parties. When the large ones replicated, the small ones followed suit, so each new large cell had some of the small ones.
Eventually, they became so interdependent the small ones had become an integral part of the larger cells. An instance considered proof of this is the presence in some species of amoebae of a pair of rod-shaped organelles near the nucleus which look very much like bacteria. Treat the amoeba with a specific substance that kills only bacteria and the amoeba isn't hurt, but the two rod-shaped organelles disintegrate. Only after those organelles are gone does the amoeba die. This suggests the organelles were originally a bacteria-like life form that adapted themselves to living inside the amoeba, until they eventually took over production of a substance, or some other function the amoeba had previously been doing for itself.
It was energy efficient for the amoeba to stop duplicating the the symbiote's efforts, so the amoeba became dependent on the "bacteria," while the "bacteria" lost the ability to live outside the amoeba. Thus, the two organisms became parts of one new form.
It's a truism that patterns repeat in Nature, and this kind of interaction of life, where a species involves itself with another so closely that the two eventually become one, can be seen to repeat at other levels. In this case, we are considering the interaction of soil microflora with plants, and how it fits this pattern.
In the previous articles of this series, about mycorrhizal fungi, we saw that the fungi not only attach themselves to the plant roots, even to the extent of penetrating the cells, they can also send threads out into the soil and interconnect with other fungi attached to the roots of other plants. In essence, they combine entire plant communities into one big super-organism. As they do this, they both use substances from the plants, and provide others to the plants in return. They also translocate photosynthates between plants, as in the case where young trees in a mixed, established forest were found to be receiving a large percentage of their photosynthates from older trees, through the fungal connections. Obviously, this is a very intimately interconnected system, almost resembling the way blood vessels joint different parts of a body. If the fungi are indeed acting as "blood vessels", then it might follow that there would have to be "blood cells" of some sort.
I spent several hours with Dr. Robert Linderman (USDA, attached to Oregon State University) discussing this and related ideas. He pointed out that while the fungi are indeed important to the system, other microflora, such as bacteria, may have a greater role. First, while the fungi provide the connections, it now appears that bacteria travel on and even in the fungal threads, often moving into and out of the plants, both producing and acquiring substances and carrying them into the plants as they go.
But the bacteria almost certainly have a much more important role. Bacteria are commonly thought of as "simple" organisms, yet anyone who has studied them can tell you they are anything but simple. For instance, bacteria can ingest pieces of genetic material directly and incorporate it into their own genetic makeup. That is, they aren't just digesting it and using the amino acids to construct new RNA or DNA, they are taking in whole genes, intact, and incorporating them directly into their own makeup. One proof is in disease-causing bacteria, in which types with a cell wall not resistant to certain antibiotics could be mixed with genetic material from dead cells that had cell walls resistant to the antibiotic, and in short order they had picked up the genetic material and had developed the resistant type of cell wall. Bacteria have also been shown able to metabolize an incredible range of substances, including asphalt, crude oil, even metals. Bacteria can produce chemical compounds that human laboratories cannot, or could only do with great expense and labor.
Bacteria may be uncomplicated in appearance, but they are great metabolizers. Is it any wonder, then, that other life forms would find ways to make use of that ability to metabolize?
Dr. Linderman discussed the role of bacteria and other single celled organisms and concluded that they were as important, if not more so, to the plants than mycorrhizal fungi. Some types we recognize already, such as the rhizobium that colonize the roots of legumes and fix nitrogen. But the full range of what bacteria can do in connection with plants hasn't been worked out yet. In addition to fixing nitrogen, it is likely that they help make other elemental plant nutrients, such as phosphorus, potassium, etc., more readily available to plants, much as the mycorrhizal fungi do. But why couldn't they work with more complex substances?
Suppose you were told to build a house within a certain length of time and were given a choice of piles of materials to work from. The first pile contains only raw logs. You would have to cut them into lumber, finish the lumber and cut it to the needed lengths to be able to build the house.
The second pile, however, contains prefabricated sections of walls, pre-built ceiling joists, etc. A few extra pieces might need to be added or removed here and there, but mostly they can simply be put into their proper positions and be nailed together.
Unless you just like to do things the hard way, you would choose the second pile. With the first pile, you would probably exhaust yourself and might be able to build anything more than basic shelter. With the second pile, you could probably construct a much larger, more elaborate house with less effort.
Why should a plant be any different? Nature is conservative in the extreme, always choosing the route that uses the least energy, whenever possible. If a plant had a way to ingest pre-formed materials into itself, saving it the energy needed to assemble the compounds, why shouldn't it do that? We think of plants as natural synthesizers, taking in water, minerals and carbon dioxide and converting them into sugars, proteins, vitamins, etc...
That life is interconnected has been a common philosophical and spiritual theme down through the ages, but the study of mycorrhizal fungi has greatly strengthened it as a biological one as well.
Work on mycorrhizal fungi has been carried out more extensively and for a longer time in forestry than in other branches of horticulture, as was briefly noted in part one of this article. Work on the ecological niches of the fungi have shown that they may be far more vital to plant growth and the ecology in general than ever considered before. Indeed, their relationships to plants may actually be necessary for some species to be able grow at all.
Article used on this website with permission of the author. If you wish to use the information other than for your personal use, please contact Lon Rombough:
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A condensed version of this article is also included in my upcoming book
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