References

268 S. Scheu, L. Ruess and M. Bonkowski
nitrifiers with important implications for nutrient cycling and ecosystem
functioning. Changes in the composition of the bacterial community are
also likely to be responsible for hormone-like effects of protozoa on plant
growth. The effects of fungal grazers on plant performance strongly depend
on whether fungivorous mesofauna feeds on saprophytic, mycorrhizal or
pathogenic species. Since decomposition of litter materials often is limited
by nutrients such as nitrogen and phosphorus, saprophytic fungi probably
compete with mycorrhiza for mineral nutrients. An important mechanism
by which fungal grazers modify plant growth is, therefore, selective grazing
on either saprophytic or mycorrhizal fungi. For arbuscular mycorrhizal
plants, there is increasing evidence that beneficial effects of fungal grazers
inpartareduetoselectivegrazingonsaprophyticfungi,therebyfavoring
mycorrhiza. Although it is still difficult to define the explicit effects of the
different faunal groups on decomposition processes, nutrient cycling and
plant growth, our knowledge has advanced considerably. New methodological
developments including molecular and stable isotope techniques
provide the opportunity to analyse the complex interactions between microorganisms
and their micro- and mesofauna grazers in unprecedented
detail, promising fundamental progress in the near future.
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