FNR-104
forestry & natural resources
MARKETING AND UTILIZATION 
Some Soil Fungi Are Beneficial to Tree Seedling Growth
by
P. E. Pope, Assistant Professor of Forestry
Infection of tree seedling roots with certain types of soil fungi can increase seedling growth as much as 400 percent. In fact, some tree species must have fungi on their root systems to develop “normally.” These types of fungi are called mycorrhizal fungi and are credited with improving a seedling’s ability to withstand extremely droughty soil conditions and low soil nutrient levels. In fact, hardwoods and conifers which have mycorrhizal fungi on their root systems survive and grow under soil moisture conditions where non-mycorrhizal seedlings die. Research on several hardwood seedling species indicates that mycorrhizal seedlings are capable of growing as large as non-mycorrhizal seedlings but at one-half the level of soil nutrients.
Forest scientists are working to increase yields of fuel and fiber which are essential to human needs and which must be produced on a diminishing quantity of forest land. Largely as a result of research on forest trees, a new technology that attempts to use mycorrhizal fungi for mankind’s benefit is emerging. Plant scientists have learned to think of a continuum system—the soil, the plant, and the atmosphere. This thinking should be expanded to include another component—the mycorrhizal fungi.
Mycorrhizae are specialized, root-like organs formed as a result of the symbiotic (mutually beneficial) association of certain fungi with the roots of higher plants. Specific fungi grow upon and vigorously invade portions of the root in that area of the root system that is primarily responsible for nutrient absorption. The term “mycorrhiza” literally means “fungus-root”and is used to denote these particular associations of roots and fungi.
The vast majority of economically important plants form mycorrhizae. Without mycorrhizae, most of our important tree species could not long survive in the dynamic, fiercely competitive biological communities that inhabit forest soils. Furthermore, the mycorrhizal condition is the rule, not the exception, in nature. The physical appearance or morphology of mycorrhizae varies among plant species, and each plant species tends to have characteristic groups of fungi capable of producing mycorrhizae. On the basis of their morphology, these associations are currently divided into two major groups: ectomycorrhizae and endomycorrhizae. Of the two, endomycorrhizae are by far the most common, but ectomycorrhizae are formed on some very important families of forest trees.
Types of Mycorrhizal Fungi
Ectomycorrhizae
Ectomycorrhizae are formed by fungi belonging to the higher Basidiomycetes (mushrooms and puffballs), Ascomycetes (cup fungi and truffles), and Phycomycetes in the family Endogona-ceae. The host plants of these fungi are predominantly trees such as pine, hemlock, spruce, fir, oak, birch, beech, eucalyptus, willow, and poplar. Many species of fungi may be involved in the ectomycorrhizal association of a forest, a single tree species, an individual tree seedling, or even a small segment of lateral root. As many as three species of fungi have been isolated from an individual ectomycorrhizal root cluster.
Ectomycorrhizal infection is initiated from spores (reproductive structures) or hyphae
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