Mycorrhizal Fungi and Plant Nutrition

The term “mycorrhiza ” was coined by A. B.Frank, a scientist in Germany, more than 100 years ago. It literally means fungus-root, and describes the mutualistic association existing between a group of soil fungi and higher plants. The association is based on the plant component providing carbohydrates and other essential organic compounds to the fungi. In return, the fungal component, which colonizes both the root and the adjacent soil, helps the plant take up nutrients by extending the reach of its root system. Although mycorrhizal associations were discovered over 100 years ago, their role in plant productivity did not receive the attention it should until the past 30 years. Today, hundreds of scientists all over the world are engaged in the study of mycorrhizal associations, and any discussion of plant productivity that does not in-clude mycorrhizal associations can hardly be consid-ered complete. Mycorrhizal types Of the many types of mycorrhizal association (see Harley and Smith 1983), two are of major economic and ecological importance: ectomycorrhizal associa-tions, and the endomycorrhizal association of the ve-sicular-arbuscular (VA) type. In ectomycorrhizal associations, the fungi invade the cortical region of the host root without penetrating cortical cells. The main diagnostic features of this type of mycorrhiza are (1) the formation within the root of a hyphal network known as the Hartig net around corti-