plant surface microbiology.pdf

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M. Zakaria Solaiman and Lynette K. Abbott
tions. Demonstrations of morphological and genetic diversity of AM fungi
imply that the mechanism of symbiotic nutrient exchange might be diverse
(Smith and Smith 1996), but the taxonomic diversity found might not necessarily
be linked to the functional role of the AM fungi. Both inter- and intraspecific
variation in the effectiveness of AM fungi has been reported (Franke-
Snyder et al. 2001). Studies are required that show whether fungal diversity
reflects quantitative rather than qualitative differences in functioning. The
current understanding of functional diversity is that plants can respond differently
to different AM fungi, not only at the level of colonisation, nutrient
uptake, growth, but also at the level of gene expression (Burleigh et al. 2002).
4 Functional Diversity of Arbuscular Mycorrhizal Fungi in
Root and Hyphal Interactions
Functional diversity of AM fungi associated with roots of plants in different
ecosystems is not well understood. The dynamics of interactions between
roots and hyphae provide a framework for predicting how diversity of AM
fungi might be related to mycorrhiza function, but it is difficult to measure. It
is almost impossible to predict the functional diversity of AM fungi at an
ecosystem level based simply on what fungi are present in soil. On a theoretical
basis, the functional diversity of AM fungi under field conditions cannot
be assumed to be directly correlated with a measure of diversity of AM fungi,
even if the fungi present differ in P uptake and transfer under controlled conditions.
This is because of differences in processes such as rate of root colonisation,
interactions between fungi during colonisation and other strategies
that include shutting down of hyphal infectivity in association with sporulation,
as can occur for both S. calospora and A. laevis (Jasper et al. 1993; Pearson
and Schweiger 1993).
There is increasing interest in the potential role of AM fungi in influencing
plant community structure (Read 1990; van der Heijden et al. 1998a, b;
Klironomos 2002; Franke-Snyder et al. 2001). However, as yet there is little evidence
to support the hypothesis that the diversity of AM fungi is an important
factor influencing plant community structure under natural field conditions.
This would require extensive quantification of AM fungi within roots for
time-intervals that are of significance to plant and fungal growth cycles following
an appropriate approach (Merryweather and Fitter 1998a, b). On the
contrary, there is considerable potential for the plant communities to influence
the fungal community structure through preferential effects on colonisation
by particular fungi and influences on sporulation (Sanders and Fitter
1992).