Soil biodiversity and food webs

Although it is not apparent to the naked eye, soil is one of the most complex habitats on earth, containing one of the most diverse assemblages of living organisms (Lavelle and Spain, 2002). Over 1000 species of invertebrates were identified in 1 m2 of soil in temperate forests in Germany (Schaefer and Schauermann, 1990). The diversity of the microbial component of soil may be even greater than that of the invertebrate component. However, this is only just beginning to be realized, as a result of phylogeneüc and ecological studies using molecular methods (Torsvik et al., 1996). A single gram of soil is estimated to contain several thousand species of bacteria (Giler et ai, 1997a). Of the 1.5 million species of fungi estimated to exist worldwide, remarkably little is known about soil fungi, apart from common fungal pathogens and mycorrhlzal species. Some 100,000 species of protozoa, 500,000 species of nematodes and 7000 species of earth worms are estimated to exist (Reynolds, 1994), not to mention the other invertebrate groups of the mesofauna (e.g. sprLngtails, mites and potworms) and macrofa una (e.g. ants, termites, beetles and spiders) (Brussaard et al., 1997). Few data are available from tropical regions, where it is suspected that the highest levels of diversity may be found. Consequently, although the biological diversity of the community of organisms below the ground is probably higher in most cases than that above ground, it has generally been ignored in surveys of ecosystem biodiversity.

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