Abstract
Enemy release of exotic plants from soil pathogens has been tested by
examining plant¿soil feedback effects in repetitive growth cycles. However, positive soil
feedback may also be due to enhanced benefit from the local arbuscular mycorrhizal fungi
(AMF). Few studies actually have tested pathogen effects, and none of them did so in arid
savannas. In the Kalahari savanna in Botswana, we compared the soil feedback of the exotic
grass Cenchrus biflorus with that of two dominant native grasses, Eragrostis lehmanniana and
Aristida meridionalis. The exotic grass had neutral to positive soil feedback, whereas both
native grasses showed neutral to negative feedback effects.
Isolation and testing of root-inhabiting fungi of E. lehmanniana yielded two host-specific
pathogens that did not influence the exotic C. biflorus or the other native grass, A. meridionalis.
None of the grasses was affected by the fungi that were isolated from the roots of the exotic C.
biflorus. We isolated and compared the AMF community of the native and exotic grasses by
polymerase chain reaction-denaturing gradient gel elecrophoresis (PCR-DGGE), targeting
AMF 18S rRNA. We used roots from monospecific field stands and from plants grown in pots
with mixtures of soils from the monospecific field stands. Three-quarters of the root samples of
the exotic grass had two nearly identical sequences, showing 99% similarity with Glomus
versiforme. The two native grasses were also associated with distinct bands, but each of these
bands occurred in only a fraction of the root samples. The native grasses contained a higher
diversity of AMF bands than the exotic grass. Canonical correspondence analyses of the AMF
band patterns revealed almost as much difference between the native and exotic grasses as
between the native grasses.
In conclusion, our results support the hypothesis that release from soil-borne enemies may
facilitate local abundance of exotic plants, and we provide the first evidence that these
processes may occur in arid savanna ecosystems. Pathogenicity tests implicated the
involvement of soil pathogens in the soil feedback responses, and further studies should
reveal the functional consequences of the observed high infection with a low diversity of AMF
in the roots of exotic plants
Original language | English |
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Pages (from-to) | 978-988 |
Journal | Ecology |
Volume | 88 |
Issue number | 4 |
DOIs | |
Publication status | Published - 2007 |
Keywords
- gradient gel-electrophoresis
- enemy release hypothesis
- plant invasions
- ammophila-arenaria
- lehmann lovegrass
- community composition
- biotic resistance
- fungi
- herbivores
- spread