ABSTRACT
Soil is the habitat of an array of organisms in all three taxonomic domains (sensu Woese et al, 1990) and many phyla. The taxonomic classification of living organisms is still controversial (e.g. Margulis and Schwartz, 1998; Cavalier-Smith, 1998, 2004), especially regarding the taxa to be created at higher levels, and the numbers of such higher categories (such as kingdom) to be considered, in addition to domain. However, whatever classification system is used, the diversity of soil biota is high at all levels of analysis (for reviews, see Swift et al, 1979; Lavelle, 1996; Brussaard et al, 1997; Wall, 2004, Bardgett, 2005; Moreira et al, 2006). Table 1.1 lists the main phyla of eukaryotic organisms and prokaryotes that are or can be represented in the soil community, with more than 1.5 million species for the eukaryotes and an estimated species richness far beyond 10,000 for the prokaryotes.
