Land, then, is not merely soil; it is a foundation of energy
flowing through a circuit of soils, plants and animals. Aldo
Leopold
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Soil is the hidden, secret friend, which is the root domain of
lively darkness and silence Francis Hole Soil by parts: 5% organic,
50% space, 45% mineral
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Living, dead, decomposing, decomposed
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85% 5% 10%
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What is special about Organic compounds? They have ENERGY Food
chain passes energy along through photosynthesis and
respiration
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Photosynthesis: CO 2 + H 2 O + solar energy C 6 H 12 O 6 + O 2
organic !
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Respiration: C 6 H 12 O 6 + O 2 ENERGY + CO 2 + H 2 O
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Energy is passed from one trophic level to the next.
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What is an organic compound? Bank of energy
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More living biomass below ground than above! Beneath 1 acre:
equivalent to 12 horses 1 cubic meter of soil: 50,000 earthworms
50,000 insects and mites 12 million roundworms 1 pea-size bit of
soil: 30,000 protozoa 50,000 algae 400,000 fungi Billions of
bacteria
Arthropods Invertebrates with external skeleton Spring or hop
Detrivores 100,000 / m 3 topsoil
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Arthropods; order Coleoptera 400,000 species (40% of all known
insect species) Some omnivores, some eat plants, fungi, some are
carnivores Larvae (grubs)
Annelids Some 2700 different types 3 categories: Epigeic (leaf
litter/compost dwelling ) Endogeic (topsoil or subsoil dwelling )
Anecic (deep burrow drillers)
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Giant Giant Benefits to soil Move air in and out of soil
Castings are rich in available nutrients Produce 10 lbs / yr
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Roundworms Occupy many positions in soil food web > 28,000
species Most microscopic Can be predatory or parasitic
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arachnids
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Extracted from one ft 2 of top two inches of forest litter and
soil
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Abundant; most important decomposers Adaptable Specialized:
Non-photosynthetic Photosynthetic Oxidize ammonium, nitrite, iron,
manganese Oxidize sulfur Nitrogen-fixing Aerobic, anaerobic
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1 ton / acre
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Bacteria and fungal hyphae
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Break down OM, esp important where bacteria are less active
branched hyphae form mycelium: bears spores attack any organic
residue
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Mycorrhizae: s Symbiotic ; infecting plant roots, formed by
some fungi normal feature of root systems, esp. trees increase
nutrient availability in return for energy supply plants native to
an area have well-developed relationship with mycorrhizal
fungi
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Higher fungi have basidium : club-shaped structure, bearing
fruiting body toadstools, mushrooms, puffballs, bracket fungi
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Filamentous morphology varies adaptable to drought neutral pH
usually aerobic heterotrophs break down wide range of organic
compounds
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A respiration process: Organic matter + O2
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Energy for decomposers CO2 + H2O Nutrients, that were in the
original organic tissue, for plants Carbon, nitrogen, etc. for the
decomposers HUMUS !
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Ultimate decay product of decomposition Amorphous, colloidal
mixture of complex organic substances, not identifiable as
tissue.
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< 0.00001 mm in diameter Nutrients and water attach to
surface area of soil particles Smaller the particle, the greater
the surface area per unit volume