Fungi That Form Symbiotic Relationships With Plants
Presentation by Dennis Burk as part of
Native Plant Appreciation Week Event, 5/1/10
There are many thousands of varieties of fungi. Some are bad for your health, some taste good, some smell bad in your house, some decompose plant litter in your garden, but some form extraordinary symbiotic relationships with plants – both plant and fungus benefit from the relationship. It is this latter group I want to talk about today.
Fungi that form symbiotic relationships with plant roots are referred to as “MYCORRHIZAL” fungi. I will diverge for a moment and try to demystify the word. First, you have to have a PhD to spell like that.
Mycorrhizae is a composite of “myco” referring to fungi and rrhizae” referring to roots. In plain English, we are talking about “root fungus”. (English differs from many, if not most, languages on the planet by placing adjectives ahead of nouns instead of after.)
Three common forms of the word are:
- MYCORRHIZAE – plural noun
- MYCORRHIZA – singular noun
- MYCORRHIZAL – adjective
People who write or talk about this topic frequently and incorrectly use these three forms interchangeably. (Just smile and make the mental translation for them.)
There are similar irregularities in pronunciation. Since mycorrhizae is a composite of myco and rrhizae one might reasonable expect it to be pronounced “my-co-rye-zee”, but there seems to be a preference for “my-cor-rye-zee”.
It then follows that:
- MYCORRHIZAE – plural noun, is pronounced “my-cor-rye-zee”
- MYCORRHIZA – singular noun, is pronounced “my-cor-rye-za”
- MYCORRHIZAL – adjective, is pronounced “my-cor-rye-zal”
- (or any other variations you can pull off with a straight face.)
Microscopic filaments, hyphae (hy-fee), of mycorrhizal fungi attach to the fine roots of most plants. This was an evolutionary development that occurred over 400 million years ago. Hyphae are astonishing in that a sugar cube volume of soil can contain a couple miles of filaments that increase the absorption area of roots by many fold. Mycorrhizae provide nutrients to plants and plants provide carbon in the form of glucose to mycorrhizae. (glucose = C6H12O6. Plants take Carbon from the atmosphere and through the process of photosynthesis produce glucose)
Another term used for a mass of hyphae is Mycelium (my-see-lee-em). Essentially it is a collective noun like a school of fish, a flock of sheep, a gaggle of geese, a pride of lions, a pod of orca, a mycelium of hyphae, etc.
Latin has been adopted to define the biological sciences because Latin is a “dead” language and is no longer evolving. Also Latin is the same the world around. Many of the “Latin” names used by modern science were not around in ancient Rome, but the names follow the structure of Latin. (Luckily Latin did not take hold in the technology sciences. “Computer Chipae”, “Mother Boarda”, “USB Portae” and “Microsoftae” are not part of the Lexicon. When you travel to a country whose mother language is not English, you can hear “bla, bla, bla Mother Board” and “bla, bla, bla Hard Drive”. Computer technology has adopted English terms the world around.) It should be noted that biological components have been around for millions of years and will still be around for many millions more. Technology components, on the other hand, hang around for only a few decades.
Mycorrhizae come in two ‘flavors’:
- “ENDO” which attach inside roots, will hook-up with about 90% of plants. There are only a couple hundred known endo species.
- “ECTO” which attach to the surface of roots, are typically host-specific to about 5% of plants. Ecto species number in the thousands and are inexpensive to produce commercially.
Most plants hook-up with a potpourri of mycorrhizal species – the mix varies by plant type, soil type and availability of nutrients, minerals and moisture. Only about a dozen most common species are available as commercial inoculants. Wholesale quantities can be ordered in custom mixes, but retail quantities usually include a set mix of 6 to 8 species that are most beneficial to a broad spectrum of landscape plants.
Inoculants are available in a number of forms: granular, tablet, powdered, soluble, liquid and gel. The choice of form is based upon method of application. For small-scale landscape projects, granular is the most popular and inexpensive choice.
Earlier I used the term, “INOCULANT”. I could have also used the term “INFECTANT”. Both terms would work equally well, but “inoculant” has a more positive connotation. What we are doing is infecting or inoculating plant roots with beneficial fungi. So our intent is to get the inoculants into close contact with plant’s fine roots. This is quite different from amending soil by mixing-in sand or humus or fertilizer. We are not baking a cake; we are infecting roots.
The resulting fungal hyphae will supplant the need of a “cake mix.” It is still ok to add humus to loosen and aerate clay soils or to add humus to help hold moisture in the root zone of sandy soils, but the hyphae will do that too. The difference is that when
the host plant dies- back or goes dormant in winter, the hyphae also die-back and go dormant and the soil returns to its original state. When the plant comes back to life in spring, like magic, the hyphae come back to life and repeat their conditioning of the soil. The hyphae can glean far more nutrients from the existing soil than roots can by themselves, but it is also ok to add slow release organic fertilizer to the soil. Strong, fast acting, chemical fertilizer will kill the hyphae and should not be used. Hyphae will also improve plants’ resistance to disease organisms and stimulate root growth.
When buying a plant at a nursery, we are all thoroughly conditioned to bring it home, remove the root ball from the container, fluff-up any roots that reached the container wall, dig a hole twice the diameter of the root ball, plop the root ball in the hole, back fill with chemical fertilizer and nicely conditioned topsoil, tamp it down and soak with water, then repeat the fertilizer and water seasonally for life.
We need a new paradigm. After fluffing-up the roots, we inoculate with mycorrhizae, dig a smaller hole, lightly sprinkle a slow acting organic fertilizer around the walls of the hole, plop in the root ball, backfill with native soil, tamp it down and soak with water. Seasonally you may never have to fertilize again and your plant will be far more drought tolerant. You may have to water a little through the dry season while the new roots and mycorrhizae get established.
Perhaps the most important part of your new paradigm is to realize that the above ground part of your landscape plants is not the only crop you are cultivating. Your second crop is the below ground colony of mycorrhizal hyphae and spores. When you plant inoculated trees, shrubs, perennials and grasses, mycorrhizae grow with the roots year after year. Mycorrhizae will go dormant in winter as the plant roots do, but when plant roots start their spring growth, mycorrhizae will follow. Mycorrhizae can spread from an inoculated plant to adjoining plants as their roots come into close proximity.
When you cut back dead stalks of annuals, it is important to leave their fine root mass in the soil. The roots are full of mycorrhizal hyphae and spores that will attach to your new annuals in the spring. Hyphal fragments are also capable of inoculating plants, but fragments are not as viable or potent as spores.
I slid by a topic I want to revisit in detail. LAWNS. Environmentalists have long been harping on the negative ecological impacts of lawns – and justifiably so. The negative impacts are too much water consumption, and run-off of chemical fertilizers, and herbicides.
To seed in a new lawn, prepare the bed as usual, broadcast granular Mycorrhizae, rake in lightly, broadcast grass seed, roll, cover with a thin layer of peat moss, and sprinkle with water. To lay sod, prepare bed, broadcast Mycorrhizae, lay sod (green side up), and sprinkle with water. The sod roots are laid directly on the Mycorrhizae.
For existing lawns, if you have not added chemical fertilizer to your lawn yet this spring, don’t. Instead cut your grass very short, thatch as needed, plug aerate, broadcast granular mycorrhizal then water to wash the granules down to the ground and perhaps into the plug-holes. Exposure to direct sun can damage mycorrhizal spores. Your lawn will green-up nicely, it will be much more drought tolerant and need less water. A vigorously growing lawn chokes out weeds so you can get rid of your weed-n-feed forever. Although, you may have to occasionally spot-spray a vigorous dandelion and annually apply a light application of slow release organic fertilizer. What’s not to like?
Today almost all plants propagated and sold in nurseries are in sterilized soil – which is a good thing because otherwise weeds and all manner of bad organisms could be transplanted to your yard. Unfortunately mycorrhizae are also killed. How do you inoculate those roots with mycorrhizae? Let me recount the ways: first, if you purchase a fir seedling from a nursery, read the label carefully. Some nursery wholesalers inoculate their trees and shrubs. Most don’t. (Why spend the money and charge a higher price if the customer is not demanding it?) If your fir seedling was not inoculated by the nursery and you intend to plant it in a healthy fir forest, not to worry, the inoculants are already in the forest top soil. If you are digging a fir seedling from a fir forest and transplanting to your yard, its roots have already been inoculated. The same goes for other native plants.
If you are planting a native plant propagated in sterile soil, you can harvest your own mycorrhizae by finding a natural, healthy grove or cluster of your native species and digging a plug of soil from the drip zone. Brush aside dry leaf litter and cut a 6” plug that includes decomposing leaf litter and the soil below to a depth of 4 to 6 inches. Cut additional broadly separated plugs depending upon the number of plantings. About a cup of plug material will inoculate one plant. Put your plugs in a bucket or plastic bag and take home for processing. Scrub your plug material through a ½” screen to separate out rocks and chunks of wood and to finely shred fine roots and decomposing leaf litter.
Thoroughly mix the screened material.
It is best to harvest plug material as needed even though spores may remain viable for a year. Hyphal fragments are fragile and may only be viable for a couple months. Don’t store your plug material in direct sun and keep it damp not soaked.
If you are planting native annuals in either seed or seedling form, find last season’s stalks of the same, but naturally growing, species. Cut away the dry stock, dig up the fine root-ball that contains mycorrhizal hyphae and spores, finely shred the roots and sprinkle the shreds among the seeds or on the seedling root balls. Once your annual beds are inoculated, they should remain inoculated from year to year.
In this area some houses were carefully shoe-horned into absolutely beautiful natural forests. All of the natural topsoil, brimming with natural mycorrhizae, remained intact (except for under the house, patio, walks and driveway). Any native plant, you want to add to this ideal slice of nature, will have its mycorrhizae waiting for it.
Other houses were not so fortunate if their land was scraped to bare dirt and graded like a gravel pit. By the time the house was built and ready for landscaping, all the natural mycorrhizae were dead. It needs to be re-inoculated.
If you are looking to purchase retail quantities of mycorrhizal products, keep in mind that all products are not created equal. For general landscaping, you want material that includes endo and ecto spores. The spore counts, for endo and ecto, should be stated separately and not include Hyphal fragments in the count.
The material should be produced in the USA by major wholesalers to the Forestry, Agriculture or Horticulture industries. You want to find a retail supplier who buys wholesale material from the big boys and re-packages it into small quantities. A fair question to ask is “Who is your wholesale producer?” Then look them up on the web.
As mentioned earlier, 90% of plants respond to ENDO-mycorrhizae, 5% respond to ECTO-mycorrhizae and 5% do not respond to either endo or ecto. The following are partial lists of common Northwest landscape and garden plants that fall into those categories:
Alder*, Apple, Apricot, Asparagus, Aspen*.
Bamboo, Basil, Beans, Begonia, Blackberry, Boxwood, Bulbs.
Cactus, Camellia, Carrot, Cassava, Cedar, Celery, Cherry, Chrysanthemum,
Coral tree, Corn, Cucumber, Currant, Cypress.
Dogwood, Eggplant, Euonymus.
Fern, Fescue, Fig, Flowers, Forsythia, Fuchsia.
Garlic, Geranium, Grapes, Grasses-perennial.
Hawthorn, Herbs, Hibiscus, Hostas.
Impatiens, Juniper, Leek, Lettuce, Lily.
Magnolia, Mahonia, Maples, Marigold, Nasturtium, Onion.
Pacific Yew, Peas, Peach, Pear, Peppers, Plum, Poplar, Potato, Pumpkin.
Raspberry, Rose, Ryegrass.
Serviceberry, Shallot, Snapdragon, Squash, Strawberry, Succulents, Sudan Grass, Sunflower, Sweet gum, Sweet potato, Tomato, Violets, Yam, Willow*.
Alder*, Aspen*, Birch, Douglas Fir, Filbert, Fir, Hazelnut, Hemlock, Madrone,
Oak, Pine, Spruce, Willows*,
DO NOT respond to common ENDO or ECTO
Broccoli, Brussels sprouts, Cabbage, Cauliflower, Collards, Kale.
Azalea, Blueberry, Cranberry, Huckleberry, Lingonberry, Rhododendron.
Beet, Carnation, Mustard, Orchids, Sedge, Spinach
* Some trees are known to respond to both endo and ecto.
Inoculating with granular mycorrhizae:
Transplant root-balls: Make sure soil in the pot is thoroughly wet. Remove the pot from the root-ball and trim away excess roots. Using thumb and forefinger, sprinkle pinches of mycorrhizae on exposed roots.
New bulbs: Dig hole to depth specified for bulb, sprinkle one pinch mycorrhizae per bulb in bottom of hole, mix into soil ¼ to ½ inch, set bulbs, backfill to top of bulb, water, and then complete backfill.
Seeds: Scratch trench to depth specified for seeds, sprinkle mycorrhizae in trench bottom two pinches per running foot, mix into soil ¼ to ½ inch, distribute seed at specified rate, backfill, and water.
Existing perennials: With edge of trowel, scrape away a patch of mulch and topsoil, at the drip-line, until fine roots begin to show. Sprinkle a pinch of mycorrhizae onto roots, backfill patch, and water. For small plants fewer small patches will suffice, for trees and large shrubs apply inoculations in greater numbers of larger patches. One of the primary objectives is to disturb existing roots a little as possible. Mycorrhizae will spread from the roots you inoculated to all the other roots of the plant.
Material Safety Considerations:
Endo/ecto mycorrhizal products contain no environmental hazards and should be handled much as you would for garden soil.
- Sweep or vacuum spilled product and dispose as soil.
- Product is non-toxic, non-allergenic and non-pathogenic to mammals
- Wear rubber or plastic gloves for prolonged contact.
- Avoid exposing eyes or lungs to dust.
- Flush eyes with water and wash skin with soap & water.
- For small ingested amounts, drink water; for more than a mouthful, induce vomiting and drink water.
- Keep containers tightly closed, avoid storage in damp areas.
- Product has slight ammonia odor.
- Ammonia fumes may be released by charring or by contact with strong oxidizers/alkalis.
- May char or smolder >400 F, but will not burn.
- Use water or CO2 to smother.
For more information about mycorrhizae:
Mycorrhizal Applications, Inc., Oregon
Major producer and wholesale supplier of mycorrhizal products (MycoApply)
Mycorrhizal Products, Florida
Retail supplier of mycorrhizal products
(associated with Mycorrhizal Applications)
Search On-line for:
Mycorrhizae, Mycorrhiza, Mycorrhizal
Mycorrhizal hyphae, Hyphae
Other On-line Info Sites:
http://www.mycolog.com/chapter17.htm <= Photos