SOIL ORGANISMS - Soil Ecology - page 354

Micro- and meso-fauna dominate the soils of ecosystems in which climatic limitations
strongly constrain biological activity. These invertebrates have highly-developed
abilities to survive such harsh environmental conditions as low temperatures and
drought. Under such conditions, the macrofauna is poorly represented (if at all) and does
not compete for soil and litter resources with the micro- and meso-fauna. In the
semi-arid grassland soils of North America (Hunt et al., I987) or in desert ecosystems
(Freckman and Mankau, 1986), micro- and meso-faunal activity play key roles in
determining microbial activity. Their selective removal may result in significant changes
to decomposition and nutrient dynamics ( e.g., Ingham et al., 1986a). In these ecosystems,
micropredator food-webs ( i.e., food-webs based on predation of micro-organisms by
microfauna) and mesofauna, or mutualistic relationships between mesofauna and micro-
organisms (as defined, e.g., by Moore, 1988) are the major interactive systems that control
decomposition processes. They regulate decomposition and channel nutrients from
decomposing resources to micro-organisms which are in turn consumed by protists,
nematodes and microarthropods or Enchytraeidae. These animals release nutrients ( e.g., N
as ammonium) as products of their metabolism or during the decomposition of their dead
bodies (see also Chapter IV. 1.5.3).