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Mycorrhiza ("fungal root") is the association of mutual benefit (mutualistic in-teraction) between a fungus and the root of a higher plant (Agerer et al. to 1986; Willenborg 1990; Allen 1991; Schwantes 1996; Smith and Read 1997; Varma and Hock 1999; Egli and Brunner 2002; v.d. Heijden and Sanders 2002; Peterson et al. 2004). About 80 -95% of the higher plants are capable of mycorrhization (e.g., Bothe and Hildebrandt 2003). Mycorrhizas are differently grouped. The grouping according to Hock and Bartunek (1984) in distinguishes three major forms.

"Hartig net (Kottke and Oberwinkler 1986). The colonized roots do no longer possess root hairs; instead hyphae or rhizomorphs radiate into the soil. In the endotrophic mycorrhiza (endomycorrhiza) of the orchids, only a loose hyphal net is formed around the root, and the hyphae settle inside the cells in the root bark area. As an intermediate, the ectendotrophic mycorrhiza is particularly present on roots of 1 to 3-year-old conifers, whereby the hyphae penetrating into the bark cells degenerate with ageing. The most frequent form, the vesicular arbuscular mycorrhiza (VAM) occurs associated with over 200,000 wild and cultivated angiosperms, in addition, with Ginkgo biloba, Maxus baccata and Sequoia gigantea and S. sempervirens (Werner 1987), as well as predominant form in tropical forests. In the VAM, the unseptate hyphae extend inside the root cells bubble-shaped (vesicles) or branch out tree-shaped (arbuscules). The arbuscules develop by hyphal branching and become enclosed by the peri-arbuscular membranes from the plant (Bothe and Hildebrandt 2003). The benefit for the trees is the improved nutrient (amino acids) and min-eral (N, K, Mg, Cu, Zn, Fe) support and the better water supply (Smith and Read 1997) due to the larger absorption area. Soils with frequently occurring ectomycorrhiza are commonly characterized by a lower nutrient content, the trees growing there would not be competitive without mycorrhizas (Schonhar

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