Info

mesofauna, microfauna

(rich), microfauna

(poor)

Faunal group dominant in biomass

Earthworms

Enchytraeids

None

Microbial group dominant in biomass

Bacteria

Fungi

None

Affinites with polluted condition

Low

Medium

Abbreviations: OF, fermentation layer; OH, humifaction layer; OL, litter layer, OM, matted organic matter just above the mineral soil, VA, vesicular-arbuscular (endo)mycorrhizae.

From Ponge, 2003.

Abbreviations: OF, fermentation layer; OH, humifaction layer; OL, litter layer, OM, matted organic matter just above the mineral soil, VA, vesicular-arbuscular (endo)mycorrhizae.

and 3 genera of predators (Fig. 7.3) (Wall and Virginia, 1999). The latter system contains numerous vascular plants, with considerable organic inputs both above- and belowground. In the McMurdo Dry Valleys, the sources of organic matter are restricted to allochthonous inputs from algae in nearby lakes or streams, or small amounts of indigenous soil algae and cyanobacteria. Although depauperate in species, their distributions spatially are markedly different, and highly correlated with differences in tolerances to desiccation and salinity, with the omnivore-predator and bacterivore being more water-requiring, concentrating in stream beds, and the microbivorous (bacteria and yeast spp.) endemic species Scottnema lindsayae restricted to the drier uplands (Treonis et al., 1999). Although complicated in terms of life-history details, the fact that the number of species is so small makes it seem likely that a

Plant Roots

Organic Matter

Plant Roots

Organic Matter

FIGURE 7.3. Complexity of soil nematode food webs in a hot desert (Chihuahuan, Jornada Long-Term Ecological Research [LTER], New Mexico) with 22 nematode genera, and a cold desert (Taylor Valley, McMurdo LTER in Antarctica) with three genera. For the nematodes, the height of the boxes illustrates the number of genera. The Antarctic Dry Valley has one species of a microbivore, Scottnema lindsayae, that feeds on bacteria and yeast; one bacterivore, Plectus antarcticus, that feeds on bacteria; and an omnivore-predator, Eudorylaimus antarcticus, that probably feeds on algal cells, bacteria, yeast, fungi, nematodes, and other small fauna (from Wall and Virginia, 1999).

FIGURE 7.3. Complexity of soil nematode food webs in a hot desert (Chihuahuan, Jornada Long-Term Ecological Research [LTER], New Mexico) with 22 nematode genera, and a cold desert (Taylor Valley, McMurdo LTER in Antarctica) with three genera. For the nematodes, the height of the boxes illustrates the number of genera. The Antarctic Dry Valley has one species of a microbivore, Scottnema lindsayae, that feeds on bacteria and yeast; one bacterivore, Plectus antarcticus, that feeds on bacteria; and an omnivore-predator, Eudorylaimus antarcticus, that probably feeds on algal cells, bacteria, yeast, fungi, nematodes, and other small fauna (from Wall and Virginia, 1999).

fuller understanding of microbial and faunal interactions related to diversities is possible.

The role of redundant species and the functional roles played by them are crucial to understanding the interplays between biodiversity and ecosystem function. Without detailed knowledge of the biology of species involved, it can be difficult to decide how many functional types are present in a system or determine the functional roles of individual species (Bolger, 2001). Pathogen protection benefits of arbuscular mycorrhizas may be as significant as the nutritional benefits to many plants growing in temperate ecosystems (Newsham et al., 1995, cited in Bolger, 2001).

MODELS, MICROCOSMS, AND SOIL BIODIVERSITY

Hunt and Wall (2002) modeled the effects of loss of soil biodiversity, viewed from a functional group perspective, on ecosystem function. They constructed a model for carbon and nitrogen transfers among plants, functional groups of microbes, and fauna. They used 15 functional groups of microbes and soil fauna: bacteria; saprophytic and mycorrhizal fungi; root-feeding, bacteria-feeding, fungal-feeding, omnivorous, and predaceous nematodes; flagellates and amoebae; collembola; r- and k-selected fungal-feeding mites; and nematophagous and predaceous mites (see Fig. 6.2) (Hunt et al., 1987). The 15 functional groups were deleted one at a time and the model was run to steady state. Only 6 of the 15 deletions led to as much as a 15% change in abundance of a remaining group, and only deletions of bacteria and saprophytic fungi led to extinctions of other groups. By this analysis, no single faunal group had a significant effect on subsequent ecosystem behavior. However, the authors caution that, despite numerous compensatory mechanisms that occurred, it is premature to assume that the system is inherently stable even with the loss of several faunal groups. In fact, earlier analyses of similar food webs by Moore et al. (1993) and Moore and De Ruiter (2000) showed that loss of top predators had much greater impacts on lower trophic levels than their low biomasses might indicate.

Another approach to biodiversity and its linkages to soil processes is by use of experimental microcosms. Building on results of earlier studies of Setala et al. (1997), Liiri et al. (2002) established microcosms with litter, humus, and mineral layers, and controlled access from the outside soil allowed by using either 45-micrometer or 1-millimeter mesh screens on the side of the microcosms. The microcosms were then half-buried to the top of the mesh in the side of the funnel, and then the upper portion left open to provide light for the pine seedling in the microcosm (Fig. 7.4) (Liiri et al., 2002). Microcosms were watered at regular

448 mm

Transparent plastic cover 45 Mm mesh 45 Mm or 1 mm mesh

448 mm

Pine seedling

Hose for collecting leachate water

Pine seedling

Litter layer Humus layer Mineral layer Root mat

0 0

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