Plant-Microorganism Interactions: Effects on the Tolerance of Plants to Biotic and Abiotic Stresses - Crop Improvement: New Approaches and Modern Techniques - page 218

whether intraspecific variation could account for the differences observed between
isolates of the same species.
Hart and Klironomos ( 2002 ) showed that variation in plant growth was greater
among plants inoculated with different AMF species than among those inoculated
with different isolates of the same species. However, this finding does not prove
that the variability within isolates is not ecologically important. More recently,
considerable variability has been observed within AMF species. Munkvold et al.
( 2004 ) demonstrated that large differences in plant growth and P absorption were
observed within AMF species, showing the importance of the ecological potential
of variability within AMF species. Hart and Reader ( 2002 ), tested the effect of 21
AMF isolates on plant growth, and showed that AMF families also differ in the ben-
efits conferred to host plants, although there is great variability within and between
AMF species and genera. These studies show that there is considerable functional
diversity in AMF and that variability within an AMF species can be greater than
between different AMF species or genera. This functional diversity is important for
individual plant growth and the composition of plant communities. Thus, it is clear
that there is great functional diversity in AMF and that the increase in the diversity
of these fungi in soil (Rillig 2004 ) influences the diversity and productivity of the
plant community.
It is unclear whether plants utilise this diversity to select efficient AMF or AMF
combinations that are more beneficial in terms of the stimulation of their growth
(Heijden et al. 2004 ). Thus, it is important to determine whether increasing the
AMF diversity in soil influences plants and which plant-fungus combinations oc-
cur preferentially and effectively. Moreover, it would be important to determine
whether the inoculation of plants with a mixture of AMF reconstitutes the AMF
community observed in nature. Studies like these can be used to monitor plant per-
formance and reveal whether the diversity of the AMF species in plant roots is
linked to functional diversity.
Almost all data on the variability of the functions or functional diversity of AMF
were obtained from experiments in which plants have been inoculated with an AMF
isolate and the plant growth or total P absorption was measured. Such experiments
are not entirely relevant to field situations when more than one AMF species is gen-
erally present in a single root system (Jansa et al. 2003 ). Currently, the challenge
is to establish mixed communities using different AMF species to assess whether
plants are able to select efficient AMF or AMF combinations that are complemen-
tary in their functions. However, such studies are complex because of the difficulty
to identify the AMF that are colonising the roots, which becomes a limiting factor
for understanding the control of these relationships. The consequences of the si-
multaneous colonisation of a plant by functionally different AMF have been little
explored.
If a plant is colonised by AMF species that are complementary in their func-
tions, for example the absorption of nutrients from different soil “pools”, they can
be more beneficial to the plant as a mixture than any one species separately (Alkan
et al. 2006 ; Gustafson and Casper 2006 ). Johnson et al. ( 2004 ) showed that the di-
versity of AMF in the roots of Plantago lanceolata was positively correlated with