References

Interactions Between Microorganisms and Soil Micro- and Mesofauna 261
The soil mesofauna comprises microarthropods, the mites and springtails,
and enchytraeids. The latter are assumed to be 80% microbivorous
(bacteria and fungi) and 20% saprophagous (Didden et al. 1997). Mites
feed either on soil microflora or on dead plant material (Luxton 1972) and
springtails particularly feed on fungi, but also on bacteria or algae (Rusek
1998). As for the soil microfauna, grazing by the mesofauna may enhance
mineralization of nutrients (Verhoef and Brussaard 1990; Beare et al. 1992).
Moreover, microarthropods and enchytraeids affect decomposition processes
largely by comminution, channeling and mixing of litter and soil.
Comminution of uningested organic matter increases the surface area for
microbial colonization. By fragmentation or mastication of plant debris,
previously unexploited areas become available as a resource, which stimulates
microbial activity and thereby enhances organic matter decomposition
(Seastedt 1984; Visser 1985). Comminution followed by consumption
and defecation results in a substrate with changed chemical quality and
microstructure (pore volume, moisture retention, aeration) and these animal
pellets can act as enrichment sites supporting microbial development
(Parkinson 1988). The channeling and mixing of organic material by the
mesofaunaarelargelydonebytheburrowingactivityofenchytraeids.Their
microtunnels in the soil system provide changed environmental conditions
for microbial growth and sporulation (van Vliet et al. 1995). In addition, the
mesofauna is mobile and migrates through different soil layers, passively
transporting bacteria, fungi and their propagules in the gut or on the body
surface to new microsites and substrates. Despite being miniscular compared
to macrofauna species like earthworms and millipedes, which are
the main bioturbators, the soil mesofauna may significantly contribute to
forming the microbial habitat. As documented by Babel and Vogel (1989),
humus material (H layer) of forest ecosystems on acid soils may almost
entirelyconsistoffecalpelletsofcollembolansandenchytraeids.
Micro- and mesofauna do not affect their food source solely by harvesting;
selective grazing on certain microbial species may also change the
community structure of the microflora. This alters abundance and activity
of bacteria and fungi and modifies the pattern of organic matter decay
(Hanlon 1981; Moore et al. 1987; Klironomos et al. 1992). Feeding preferences
are well known for the fungivore fauna, e.g., nematodes (Ruess et
al. 2000), mites (Kaneko 1995; Maraun et al. 1998) and springtails (Visser
and Whittaker 1977; Shaw 1985; Sadaka-Laulan et al. 1998). Fungivorous
microarthropods with specific preferences may apply high grazing pressure
on a favored species and alter the outcome of competition between
fungi (Newell 1984; Klironomos et al. 1992). On the other hand, many microarthropods
are general grazers and switch food sources (Chen et al.
1995; Maraun et al. 2003). Their grazing activity probably increases fungal
species diversity as more species can coexist when the biomass of single in-