The establishment of mycorrhizal associations depends largely on two facets: the characteristics of the host plant and the spatial pattern of planting. Plants exhibit different degrees of mycotrophy, primarily based on their capacity for nutrient uptake and their growth response to fungal colonization. In early work by Stahl (1900), plants were divided into nonmycotrophic, facultatively mycotrophic, and obligately mycotrophic categories, forming a continuum from the least to most responsive mycorrhizal fungi (Allen and Allen 1990). Studies conducted along successional sequences have demonstrated that early-seral plant species are often nonmycorrhizal, followed by facultative and late-seral obligate species (Janos 1980). Interestingly, many pioneer species in the Chenopodiaceae, Brassicaceae, and Amaranthaceae (Gerdemann 1968) are nonmycotrophic and persist on disturbed soils where mycorrhizal inoculum densities are low (Allen and Allen 1980). For most restoration projects, the goal is to establish late-seral plant species in early-seral soils. The appropriate mycorrhizal association must be considered. Because mycorrhizae are generally adapted to local plant populations (Weinbaum et al. 1996), using locally adapted seeds for the revegetation of a particular species could facilitate mycorrhiza formation. Transplanting mycorrhizal seedlings onto disturbed sites can quickly increase AM infectivity because fungal hyphae expand into open habitats and along roots, slowly spreading the association to adjacent plants (Warner and Mosse 1980).
Manipulating the spatial arrangement of transplants to concentrate resources and create resource islands may provide greater benefits than less intensive treatments over a large area (Allen 1988; Allen and MacMahon 1985). These resource islands can provide seed and inoculum for surrounding areas. Replanting multiple shrubs in a clumped pattern enhances mycorrhizal recovery by trapping more wind-carried propagules between plants than would be deposited around individually spaced plants (Allen et al. 1997).
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