'-, The Soil Food Web Arthropods Predators Birds Nematodes Fungal- and 1 101 bacterial-feeders Fungi Mycorrhizal fungi Saprophytic fungi Plants Shoots and roots Organic Protozoa Matter Amoebae, flagellates, and ciliates Waste, residue and o metabolites from Animals plants, animals and Bacteria microbes. I First trophic level : Second trophic level : Third trophic level : Fourth trophic level : Fifth and higher Photosynthesizers Decomposers Mutualists Shredders Higher level predators trophic levels : Pathogens, Parasites Predators Higher level predators Root-feeders Grazers Composting is a Seasonal Microbial Activity great way to "see" early Q summer soil organisms in V o \ a late ~ ° summer first action, breaking _ \ frost last ,a 0) down manure on C v frost the farm or leaves d V v M in the yard . S: January Month December FIGURE 2-13 The rhizosphere . The mucigel is a mixture of gelatinous and other plant products, bacterial cells and; their metabolic products, colloidal minerals, and organic matter, which together with other plant exudates, lysates, and secretions form a gradient of carbon that is most concentrated near the root surface and decreases with increasing distance away from the root . Because of this gradient, the rhizosphere is a zone of intense microbial activity. Original drawing by Kim Luoma . FIGURE 1-1 A soil habitat containing mineral soil particles (sand-Sa, silt-Si, and clay-C), organic matter (OM), water (W), plant root with root hairs (R), and soil organisms (bacteria-B, actinomycetes-A, mycorrhizal spores and hyphae-My, hyphae of a saprophytic fungus-H, a nematode-N, ciliate protozoa-CP, flagellate protozoa-FP, and a mite-M .) This soil can be a habitat of enormous complexity and diversity even over small distances . For example, the actual size of the soil in this drawing is < 1 mm in both directions yet may contain habitats that are acid to basic, wet to dry, aerobic to anaerobic, reduced to oxidized, and nutrient-poor to nutrient-rich . Realizing this complexity and diversity rho kpv tr tindarstandina soil microbiology . Original drawing by Kim Luoma . Used with permission . FIGURE 10.8 A depiction of representative groups of soil microorgan- isms, showing their relative sizes . (Drawing courtesy of R . Weil) FIGURE 10 .16 Diagram of ectomycorrhiza and arbuscular mycorrhiza (AM) association with plant roots . (a) The ectomycorrhiza asso- ciation produces short branched rootlets that are covered with a fungal mantle, the hyphae of which extend out into the soil and between the plant cells but do not penetrate the cells . (b) In contrast, the AM fungi penetrate not only between cells but into certain cells as well . Within these cells, the fungi form structures known as arbuscules and vesicles . The former transfer nutrients to the plant, and the latter store these nutrients . In both types of association, the host plant provides sugars and other food for the fungi and receives in return essential mineral nutrients that the fungi absorb from the soil . [Redrawn from Menge (1981) ; Photo courtesy of R . Weil].