The aim of this Chapter is to review and integrate current knowledge of the impact of mycorrhizal symbioses on plant functioning
and adaptation with specific emphasis on P acquisition at various levels of cellular organization, from the molecular, biochemical
and physiological to the whole plant. Accordingly, the available information will be structured as follows: (i) mycorrhizas
as a plant strategy for P acquisition; (ii) fungal-plant integration to establish functional arbuscular mycorrhizal (AM) symbiosis;
(iii) functional biology of Pi uptake by AM plants; (iv) ecological impact of AM symbiosis on plant community structure and
productivity; and (v) mycorrhizosphere interactions and ecosystem P cycling.
"Although arbuscules were not observed, the presence of vesicles and of mostly non-septate hyphae, and the rare traces of colonization in non-inoculated plants, strongly support the idea that these fungal structures derived from artificial pre-inoculation. The lack of arbuscules could be related to the high level of P in the soil (Smith and Read, 1997), or to the plant species or clone, and was previously observed for another P. alba accession inoculated with the same fungal species (Lingua et al., 2008). When quantified, arbuscule abundance is, in fact, usually rather low in poplar (Kaldorf et al., 2002; Todeschini et al., 2007; Lingua et al., 2008); Takàcs et al. (2005) reported a high value of a % (65 %) only in a few poplar clones on both unpolluted and polluted soils. "
"The symbiosis between AMF and plants is considerably more ancient than the rhizobial symbiosis with legumes. The oldest fossil records of AMF date from the Silurian period, more than 400 million years ago (MYA) (Smith and Read, 1997). In the case of rhizobia, analyses of evolutionary changes in highly conserved bacterial genes suggest that they evolved 500 MYA but it is not certain when nodulation capacity was acquired. "
"Numerous researchers have suggested that mycorrhizal fungimutualists with roughly 90% of plant speciesplay key mediative and integrative roles in plant communities (Bowen 1980; Janos 1980, 1983; Malloch et al. 1980; Pirozynski 1981; St. John and Coleman 1983; Harley and Smith 1983; Brownlee et al. 1983; Read et al. 1985; Perry et al. 1987). Mycorrhizal fungi may allow trees to compete successfully with grasses and herbs for resources (Bowen 1980) and perhaps detoxify allelochemicals produced by those competitors (Perry and Choqueue 1987). "
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