Use Of Mycorrhizal Inoculum 81 When is it Appropriate

Over the past three decades, there has been increasing interest in using mycorrhizal inoculation in large-scale plant production situations, including manipulating and managing the effectiveness of plant-fungus relationships (Miller et al. 1994). Before the selection and culture of fungi begins, it should be determined that inoculation is more appropriate as a management option than manipulation of the native mycorrhizal population. Identifying whether a disturbed site would respond favorably to AM or EM inoculation is the first step. This involves knowing the limitations to plant growth or establishment in a particular soil, and determining whether mycorrhizal fungi can alleviate those restrictions (Dodd and

Thomson 1994). Large-scale disturbances always change soil characteristics, alter plant communities, and reduce mycor-rhizal abundance and diversity. Where native fungi have low colonization capacity, but provide benefits to host plants, managing to increase the abundance of fungal populations may be more appropriate than augmenting with nonnative fungi (Dodd and Thomson 1994). Most areas to be restored vary greatly from their predisturbance state. Native ecotypes may or may not be better adapted to the prevailing site conditions (Azcon-Aguilar and Barea 1997). Consequently, using nonnative mycorrhizae better adapted to the current environmental conditions is an important consideration. For instance, management for native populations of mycorrhizal fungi may not be appropriate where exotic trees are planted on disturbed sites. Dunstan et al. (1998) noted that the first attempts to establish pine plantations, especially Pinus radiata, in Western Australia were large-scale failures, and it was not until inoculation with compatible EM fungi that pines were successfully introduced. Nevertheless, after 100 years of successive inoculation with exotic EM, the diversity of fungi colonizing roots of pines in plantations remains low, attributed to the host-specific nature of some EM fungi. Another important consideration for inoculating with mycorrhizal fungi is the ability of the symbiosis to reduce the use of fertilizers and pesticides. The use of fungi to reduce fertilizer and pesticide application has been achieved in plant production systems for agriculture, horticulture, and recently, ecosystem restoration (Azcon-Aguilar and Barea 1997). Maximum benefits will only be obtained from careful selection and inoculation of compatible host-fungus-soil combinations (Azcon-Aguilar and Barea 1997).

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