Diversity Of Other Components Of The Soil Food

FIGURE 7.2. Steps in the hypothesis that increased heterogeneity of carbon (C) substrates from aboveground organisms will positively influence belowground diversity. This mechanism postulates strong bottom-up control of diversity in belowground communities; it should be tested in the context of other potential (e.g., top-down) controls (Hunter and Price, 1992). Step 1. Diversity of primary producers leads to diversity of C inputs belowground. Step 2. Carbon resource heterogeneity leads to diversity of herbivores and detri-tivores. (Alternative Step 2. Carbon resource quality, rather than heterogeneity, leads to diversity of detritivores.) Step 3. Diversity of detritivores or belowground herbivores leads to diversity of organisms at higher trophic levels in belowground food webs. (From Hooper et al., 2000; see paper for more details of the complex interactions involved in aboveground and belowground diversity.)

bacterial feeder, one microbial feeder, and one omnivore-predator that are present in very low numbers (2-5per kg-1 soil) (Wall and Virginia, 1999). These systems have very low precipitation (the equivalent of about 10 centimeters of rainfall per year), and make the usually harsh climate of the Chihuahuan desert of New Mexico seem like an oasis, with 7 plant parasites, 10 genera of microbivores, 2 omnivore genera,

TABLE 7.3. Main Biological Features of the Three Main Humus Forms

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