Conclusion

Mycorrhizal fungi are virtually ubiquitous in their evolutionary associations with plants. All trees used for fuel, fiber, and food form mycorrhizae with a diverse array of fungi. All crops, excepting a small number of annuals, and all horticultural plants that decorate our homes and gardens form mycorrhizae. Known benefits range from soil stabili-za?show $132#>tion, to fertilizer and pesticide reduction, to enhanced tolerance of pollutants. These fungi also sequester toxins and could be extremely important in land rehabilitation as well as restoration of lands for grazing or conservation.

Disturbance to plant communities and soil systems can reduce the density, infectivity, and function of mycorrhizae. Without the appropriate fungi present, the natural re-establishment of this beneficial symbiosis may take decades or may never occur. Because of the influential role mycorrhizae play in facilitating plant succession, it is important to understand the factors that regulate mycorrhizal recovery, and to determine how to effectively manage those factors to enhance existing or inoculated fungal populations. For instance, if a disturbance can be anticipated, topsoil preservation could minimize adverse effects to mycorrhizal fungi. If topsoil is lost, or if soil structure is severely altered, soil organic amendments could potentially enhance mycor-rhizal development. The ability of mycorrhizal propagules to colonize disturbed sites from across relatively long distances supports the need to maintain source areas with diverse and abundant mycorrhizal populations. In natural disturbances, mycorrhizal propagules disperse by wind and animals. Evaluating host plant characteristics or manipulating the spatial pattern of planting with respect to these two factors can enhance the rate of mycorrhizal recovery (Allen et al. 1997).

Managing a site to facilitate native fungal reinvasion may be less effective if the area varies greatly from its predisturbance state. Native ecotypes may or may not be better adapted to the prevailing site conditions. For instance, in soils polluted by heavy metals, the survival of mycorrhizal fungi could make them important bioindicators. Their ability to function in heavy metal polluted soils may also confer some degree of tolerance in host plants. In contrast, if native ecotypes are particularly sensitive to changes in the soil environment, inoculating with nonnative mycorrhizae better adapted to the current soil conditions is an important consideration. It should, however, first be determined whether the disturbed site would respond favorably to AM or EM inoculation. This involves knowing the limitations of plants and mycorrhizae in particular soils. Actively restoring the mycorrhizal fungal community is an essential component to the success of any restoration program.

The value of mycorrhizal symbioses has been documented for over a century. However, application of mycorrhizae in current biotechnology techniques remain as ignorant as agronomic and horticultural enterprises that developed practices that reduced or eliminated mycorrhizal benefits in an oversimplified view of the dynamics of soil systems. Mycorrhizal fungi are being studied at the molecular to biochemical level. However, tapping the vast diversity of fungi and alternative mechanisms for increasing yield efficiencies, decreasing pest loss, or rendering polluted landscapes usable has not been studied or extensively utilized. More applied research, especially in developing areas of the world without the financial resources to purchase energy, pesticides, or fertilizers, would pay large dividends.

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