Microarthropods and larger fauna, especially earthworms, increase the rate and amount of mineralization by comminution of organic matter and by redistribution of "hot spots" of activity through movements. However, mineralization and return of nutrients to plants occur in the water films covering soil aggregates and filling their pores. Here, bacteria and fungi decompose organic matter and immobilize the extracted nutrients into their bodies, but grazing by the microfauna, protozoa, and nematodes regulates and modifies the size and composition of the microbial community and enhances microbial growth through microfaunal excretions. Nematodes also graze fungi (Chapter 1), but protozoa, especially amoebae, can graze bacteria in tiny pore spaces unavailable to nematodes. The degree of nutrient recycling is influenced by external factors of climate and soil management (e.g., inputs of fertilizers and biocides, compaction by farm machinery) and internally by the community of protozoa and nematodes, reflected in their biodiversity.
Most of the microfauna are located in small hot spots scattered through the soil mosaic, which is soil aggregates of 1 mm or smaller, containing bits of organic matter, detritus and the overlying litter, rhizosphere, and the "drillosphere" parts of the soil influenced by earthworm secretions and castings. The microbial-feeding microfauna constitute an essential component of the soil ecosystem; therefore, changes in their community structure can influence mineralization and soil fertility.
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