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BENEFICIAL
FUNGI - SCIENCE |
The soil in the picture above has formed aggregates and adheres to the roots largely through the activity of mycorrhizal fungi. The soil in the photo below, from only a few feet away, had no mycorrhizal roots and quickly turned to mud when shaken in water. USDA researchers have shown that a soil binding agent called glomalin, produced by mycorrhizal fungi, is the primary cement for soil aggregates. Photos courtesy of Ted St. John.
Earth-kind Gardening: Mycorrhizae
by Dr. Lakshmi Sridharan, TRN Science Editor
"Don’t bite the hand that feeds" is not a new concept in gardening. Gardeners of yesteryear paid homage to Mother Earth by enriching the trillions and trillions of microorganisms (bacteria, fungi, and protozoa) and other beneficial organisms such as earthworms. Sustaining the living organisms in the soil is the best way to maintain soil fertility and a healthy garden. Green revolution in the mid-20th century changed the approach to farming and gardening. Gardeners have drifted away from older wiser methods of gardening. Pesticides, fungicides and chemical fertilizers have replaced ancient ways of handling problems in a garden. A bountiful harvest at any cost is the goal of most gardeners. Gardeners fill coffers of manufacturers of harmful chemicals. Air pollution by aerosols from toxic spray materials and water pollution by poisonous effluents, proliferation of pesticide-resistant pests and fungicide-resistant fungal pathogens, and depletion of beneficial organisms in the rhizosphere (the root zone) from unhealthy gardening practices. Bioremediation is the only solution. We need to focus on earth-kind gardening.
How do we focus on earth-kind gardening? One can easily have a healthy productive garden by enriching soil microorganisms. Microorganisms work diligently in an organically rich soil converting the yard waste into nutrients, recycling nutrients, and solubilizing nutrients for an easy root uptake of soil nutrients. One such group of microorganisms is mycorrhizae that can convert an impoverished soil into a soil rich in nutrients.
Mycorrhizae are symbiotic fungi associated with plant roots. In Greek, mycos means fungus and rhizae means roots. In symbiosis, two living organisms mutually benefit. The plant provides carbon to the fungi and the fungi help in the movement of soil nutrients into the plant root system. Mycorrhizae bridge the soil to plant roots providing a two-way traffic. By doing so, it enhances plant growth and reproduction.
Mycorrhizae handle the two-traffic with its extensive network of mycelia. (mycelium--singular; mycelia--plural). Just as the shoot and root systems constitute the vegetative body of a plant, the mycelia constitute the vegetative body of the fungus. Mycelium is an extensive network of microscopic branched filamentous structures known as hyphae. This extensive network of hyphae associated with the root system of a plant extends the roots beyond their zone of absorption. This helps in a better absorption of nutrients and water beyond the roots' reach. Plants associated with mycorrhizae, therefore, can handle stress imposed by less water and nutrient supplies.
The two types of mycorrhizae associated with plant species are ecto and endomycorrhizae. Ectomycorrhizae are visible to the naked eye, for example, in red pine, they are visible as light-colored, bifurcated short roots along a lateral root. They may look like stubby short root sheathed in a light- or dark-colored fungal mantle. Profusely branched hyphae that extend from the root into the rhizosphere increase the effective surface area of the root system. The hyphae penetrate the root cortex, working their way between the walls of cortical cells. The resulting matrix of hyphae in the cortex is called the Hartig net. The hyphae are intercellular (in between the cortical cells, not inside the cortical cells). Ectomycorrhizae are found on most tree species in temperate forests, such as pines, spruces, firs, larch, birch, aspen, oak, or hickory. What appear to be mushrooms in forests are mostly the fruiting bodies of ectomycorrhizae. In an organically rich soil that is untouched by pesticides, fungicides or chemical fertilizers, there is mycorrhizal association with a number of plant species.
The endomycorrhizae do not form a fungal sheath around the root, hence, invisible to the naked eye. Unlike the ectomycorrhizae, the endomycorrhizae penetrate the walls of root cortical cells, where they form vesicles and arbuscules, hence, is the name vesicular-arbuscular mycorrhizae--VAM.
The endomycorrhizae produce huge spores. The spores on germination, give rise to profusely branched microscopic filamentous hyphae, which form the fungal body, the mycelium . Hyphae penetrate roots and form vesicles and finger-like projections, the arbuscules in the cortical cells. The arbuscules store and deliver nutrients inside the plant cells. Soil nutrients travel through the fungal hyphae and enter the arbuscules. The arbuscules break down the nutrients and release the nutrients to plant cells.
Mycorrhizae function as root hairs, extending the surface area through which plants can absorb nutrients, especially phosphorus that is not easily mobile in the soil. The friendly fungi increase absorptive sites, the rate of inflow, and the translocation of phosphorus. When roses have small legumes as companion plants, the mycorrhizae , in addition to increasing the nitrogen fixation in the legumes, act as channels for the transfer of nitrogen containing compounds from the legumes to the roses. In addition to delivering nutrients to a plant, the mycorrhizae eliminate the pathogen population in the soil by secreting antibiotics and creating a favorable environment for the beneficial microbes.
Roses need plenty of water and nutrients for a spectacular show. Roses are highly susceptible to a host of fungal diseases. Most rose gardeners rely heavily on chemical fertilizers and fungicides to get their roses on trophy tables. The soil in such rose gardens is not favorable for the growth and reproduction of mycorrhizae. Excessive uses of chemical fertilizers have been shown to burn the fungal hyphae. When high concentrations of fertilizers containing phosphorus are in the soil, the roots go towards the phosphorus away from the mycorrhizae. Therefore, avoid high levels of chemical fertilizers, especially phosphorus to promote a more vigorous feeding through the mycorrhizae.
Mycorrhizae are plant specific; hence use a cocktail of more than one type of mycorrhizae. Roses when grown with their roots inoculated with two different mycorrhizae showed an increase in weight compared to the weight of the same varieties grown without mycorrhizae. The inoculation was done by dusting the rose roots with spores of Glomus deserticola and G. intraradices at the time of planting. The inoculated roses showed significant increases in weight. Roses showed variable responses to the type of mycorrhizae used. Some of the roses did better with G. deserticola while others did better with G. intraradices . Roses raised by tissue culturing are able to handle transplant stress better when transferred from the culture medium to the soil. Inoculate the mycorrhizal cocktail for better results at the time of transplanting. Make sure that the soil contains plenty of composted material. Do not fumigate or use chemical fertilizers, pesticides or fungicides. Do not till the soil. Initial investment on mycorrhizae may appear to be a little expensive. Inoculations with mycorrhizae will save tons of money on water bill, chemical fertilizers, pesticides, or fungicides for earth-kind gardeners.
Sources:
Mycorrhizal inoculums are commercially available. Follow manufacturer's instructions for applications.
Bio-Organics
MYCORRHIZAE INOCULANTS
53606 Bridge Drive
La Pine, Oregon 97739
1-888-332-7676
Horticultural Alliance, Inc.
Sarasota International Trade Center
172 Sarasota Center Boulevard
Sarasota, Florida 34240
Tel: 800-628-6373, 941-917-0670
Fax: 888-483-4478, 941-917-0671
Rootgrow, inc.
79 Gazza Blvd.
Farmingdale, NY 11735
1-866-ROOT-GRO
fax 631-249-4910
For more info:
http://www.ars.usda.gov/is/AR/archive/oct97/glomalin1097.htm
http://www.waite.adelaide.edu.au/Soil_Water/mycor.html
http://www.mycorrhiza.org/downloads.htm
BENEFICIAL
FUNGI - SCIENCE |