Abstracts |
The community composition of arbuscular mycorrhizal fungi (AMF) was investigated
in roots of four different plant species (Inula salicina, Medicago sativa, Origanum vulgare, and
Bromus erectus) sampled in (1) a plant species-rich calcareous grassland, (2) a bait plant
bioassay conducted directly in that grassland, and (3) a greenhouse trap experiment using soil
and a transplanted whole plant from that grassland as inoculum. Roots were analyzed by
AMF-specific nested polymerase chain reaction, restriction fragment length polymorphism
screening, and sequence analyses of rDNA small subunit and internal transcribed spacer regions.
The AMF sequences were analyzed phylogenetically and used to define monophyletic phylotypes.
Overall, 16 phylotypes from several lineages of AMF were detected. The community composition was
strongly influenced by the experimental approach, with additional influence of cultivation
duration, substrate, and host plant species in some experiments. Some fungal phylotypes, e.g.,
GLOM-A3 (Glomus mosseae) and several members of Glomus group B, appeared predominantly in the
greenhouse experiment or in bait plants. Thus, these phylotypes can be considered r strategists,
rapidly colonizing uncolonized ruderal habitats in early successional stages of the fungal
community. In the greenhouse experiment, for instance, G. Mosseae was abundant after 3 months,
but could not be detected anymore after 10 months. In contrast, other phylotypes as GLOM-A17 (G.
Badium) and GLOM-A16 were detected almost exclusively in roots sampled from plants naturally
growing in the grassland or from bait plants exposed in the field, indicating that they
preferentially occur in late successional stages of fungal communities and thus represent the K
strategy. The only phylotype found with high frequency in all three experimental approaches was
GLOM A-1 (G. Intraradices), which is known to be a generalist. These results indicate that, in
greenhouse trap experiments, it is difficult to establish a root-colonizing AMF community
reflecting the diversity of these fungi in the field roots because fungal succession in such
artificial systems may bias the results. However, the field bait plant approach might be a
convenient way to study the influence of different environmental factors on AMF community
composition directly under the field conditions. For a better understanding of the dynamics of
AMF communities, it will be necessary to classify AMF phylotypes and species according to their
life history strategies.
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