Many plants are dependent on soil fungi
By PAUL G. JANTZEN
Contributing writer
Many prairie plants depend for their success on a close association with certain soil fungi. Such an intimate relationship between a specific fungus and the roots of a specific plant species is termed mycorrhiza (pl. mycorrhizae), a term coined in 1885 to mean "fungus root."
In one type of mycorrhiza, the fungus sends threadlike extensions both into the interior of the root's cells and out into the soil where they help the root hairs absorb nutrients and water. The root-fungus combination absorbs calcium, potassium, and especially phosphorus from the soil more efficiently than do the root hairs alone. The fungus also produces antibiotics and plant growth regulators which dramatically increase the rate of plant growth. In a greenhouse experiment, big bluestem grass inoculated with the appropriate mycorrhizal fungus produced more than 80 times as much tissue as plants grown without the fungus. The root in turn supplies the fungus with habitat and the simple sugars that photosynthesized in the plant's leaves. How do we know this? When radioactive carbon is incorporated in carbon dioxide which is then absorbed by a plant, the radioactive carbon is later detected in the fungus.
This type of mycorrhiza is involved in 90 percent of all land plants, especially non-woody species.
Another type of mycorrhiza is found in many woody plants. These fungi form a sheath around the plant roots and develop extensions that reach out into the soil. They also send threads into the root between (not into) the root's cells. The extensions presumably reach out and digest and absorb organic matter in the soil, actually replacing the plant's root hairs. The fungus threads that enter the spaces between the root's cells then transmit those nutrients and water to the root cells.
Many mushrooms, puffballs and truffles are the reproductive structures that develop from this type of fungus.
Botanists have concluded that the formation of the mycorrhizal condition in nature is "the rule and not the exception." In fact, some plants cannot be established or maintained successfully without them.
One could ask why, if mycorrhizae are so beneficial to many plant species, they are not a part of modern agriculture. The answer is complex: 1. It appears that only certain of several fungi relate to specific plant species, so presumably, the fungus-plant combinations need to be matched before applying the technology to specific field crops; 2. The specific fungus required for a specific desired crop may be absent from local soils; 3. Transferring soil with the desired fungus would require large amounts of soil and might also transfer pathogens and insect pests; 4. Identifying and isolating the desired fungus would require much effort and knowledge of its life cycle before inoculants could be prepared; and 5. The resting stage of the fungus must be kept alive until time for inoculation.
Says one biologist, "Before mycorrhizae technology can be applied on a daily basis, persistent, sterile, easily-handled inoculum with a long shelf-life must be commercially available
A casual walk through the prairie hardly hints at the myriad creatures and the complexity of their interactions hidden from our view.
