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Interaction modification in the Lolium perenne-Rhinanthus minor
host-parasite association: the role of mycorrhizas
Talk Session 2: Ecology
DAVIES, DEBORAH & JONATHAN GRAVES
Department of Biology, PO BOX 373, University of York, York YO1 5YW
ICOM1 Abstract
Arbuscular mycorrhizal (AM) fungi are ubiquitous components of the
natural grasslands that the annual hemiparasitic angiosperm
Rhinanthus minor colonizes. As such, there is a high probability of
simultaneous infection of a host by these two symbionts. Given that
both angiosperm parasites and mycorrhizas act as sinks for host
carbon, dual infection could result in competition for photosynthate
and hence the occurrence of higher order interactions. This paper
describes the results of a glasshouse experiment which investigated
the outcome of simultaneous infection of Lolium perenne by R.minor
and AM, at two phosphorus levels (0.13mM and 0.65mM P). Host
biomass accumulation was markedly reduced by R.minor; a response
which appeared to be related to not only sequestration of carbon by
the parasite, but also morphological changes in the host. AM
colonization did not affect host performance either in the presence or
absence of the parasite. The most startling findings were the
occurrence of very strong and conflicting parasite responses to AM
and phosphorus. Parasite growth, fecundity and attachment rates were
significantly higher in the presence of AM, yet were markedly reduced
by increasing phosphorus supply. Given that angiosperm parasites are
known to be non-mycorrhizal, the AM response must have been
mediated via the host.