pp 113-132

Mycorrhiza Helper Bacteria

  • Mika T. TarkkaAffiliated withDepartment of Soil Ecology, UFZ, Helmholtz-Centre for Environmental Research Email author 
  • , Pascale Frey-KlettAffiliated withUMRINRA-UHP 1136 (Interactions Arbres-Microorganismes), Centre INRA de Nancy

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Mycorrhizal symbiosis should not be considered merely as a bipartite plant-fungus interaction, but should instead incorporate the associated organisms. These mycorrhiza-associated organisms are known to influence each other mutually, the outcome of which is described as the “mycorrhizosphere” (Foster and Marks 1966; Meyer and Linderman 1986; Frey-Klett and Garbaye 2005). The mycorrhizosphere comprises mycorrhizas, extramatrical mycelium and the associated microorganisms. In the same way the rhizospheres exert a pressure on microbial populations (Barea et al. 2005), the mycorrhizal roots and hyphae of mycorrhizal fungi (MF) shape the bacterial species composition due to root and hyphal exudation and turnover (Bowen 1993; Morgan et al. 2005). This “mycorrhizosphere effect” may lead to improved plant nutrition, growth and disease resistance (Linderman 1988; Frey-Klett et al. 2005). Determining the functional significance of the mycorrhizosphere organisms for plant productivity presents a major challenge for the future (Artursson et al. 2006).