 Upper layer of soil (rooting zone) is where ENERGY is present in soil  This is the LIVING SYSTEM of soil  Incredible diversity Soil quality is dependent on species diversity

 The means for energy to flow from sun to all organisms.

Fourth-order consumer Primary Producer green plants; photosynthetic bacteria and algae Primary consumer Secondary consumer Tertiary consumer heterotrophs autotrophs

AUTOTROPHS : manufacture living (organic) tissue from non-living (inorganic) chemicals HETEROTROPHS : rely on autotrophs

Green plants, photosynthetic bacteria, algae contain CHLOROPHYLL reflects green; absorbs all other colors  absorption of light = absorption of energy PHOTOSYNTHESIS: CO 2 + H 2 O + energy  C 6 H 12 O 6 + Oxygen (sun) Glucose: carbohydrate Only autotrophs can do this!

RESPIRATION Plants and animals derive energy C 6 H 12 O 6 +Oxygen  CO 2 + H 2 O + energy Heterotrophs do this. Animals, roots, microorganisms in soil

Decomposition is a respiration process.

 Gross primary productivity: rate at which energy is stored in organic chemicals by primary producers in photosynthesis.  In respiration, carbohydrates are broken down and energy is released; remaining carbohydrates can become plant tissue.  Net primary productivity: rate at which energy is stored in plant tissue.  Gross P.P. = Respiration + Net P.P.

 Far more important for energy flow  Study of yellow poplar forest: Of total energy fixed by forest:  50% maintenance and respiration  13% new tissue  2% eaten by herbivores  35% to detrital food chain

 Study of grassland ecosystem: Energy stored:  2/3 – ¾ returned to soil as dead plant material  <1/4 consumed by herbivores  ½ of that returned to soil as feces

 Eukaryotes have cell membranes and nuclei All species of large complex organisms are eukaryotes, including animals, plants and fungi, although most species of eukaryotic protists are microorganisms.speciesanimalsplantsfungiprotists microorganisms  Prokaryotes lack nucleus bacteria

 bacteria  actinomycetes

 Abundant; most important decomposers with fungi  Adaptable  Specialized: Non-photosynthetic Photosynthetic Oxidize ammonium, nitrite, iron, manganese Oxidize sulfur Nitrogen-fixing Aerobic, anaerobic

 Single cell division In lab: 1 can produce 5 billion in 12 hours In real world limited by predators, not enough water, not enough food  Abundant in rhizosphere zone surrounding root  dead root cells and exudate stimulates microbial growth

1/10 inch Exudates: carbohydrates and proteins secreted by roots attracts bacteria, fungi, nematodes, protozoa Bacteria and fungi are like little fertilizer bags Nematodes and protozoa eat and excrete the fertilizer

 Organic chemicals in big complex chains and rings Bacteria break bonds using enzymes they produce  Create simpler, smaller chains

 Filamentous  morphology varies  adaptable to drought  neutral pH  usually aerobic heterotrophs  break down wide range of organic compounds

Protozoa Algae Fungi

 Unicellular  Amoeba, ciliates, flagellates  Heterotrophic Eat bacteria, fungi Form symbiotic relationships e.g., flagellates in termite guts; digest fibers  Require water Go dormant within cyst in dry conditions

 Filamentous, colonial, unicellular  Photosynthetic Most in blue-green group, but also yellow- green, diatoms, green algae Need diffuse light in surface horizons; important in early stages of succession Form carbonic acid (weathering) Add OM to soil; bind particles Aeration Some fix nitrogen

 Break down OM, esp important where bacteria are less active  Most are aerobic heterotrophs  chemosynthetic: adsorb dissolved nutrients for energy  branched hyphae form mycelium: bears spores  attack any organic residue

 Mycorrhizae: symbiotic absorbing organisms 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

 Higher fungi have basidium : club-shaped structure, bearing fruiting body toadstools, mushrooms, puffballs, bracket fungi

(Macrofauna: > 1 cm long) ANNELIDS several types

CHORDATES (vertebrates) mammals, amphibians, reptiles PLATYHELMINTHES (flatworms) ASCHELMINTHES (roundworms, nematodes) MOLLUSKS (snails, slugs) ARTHROPODS : (insects, crustaceans, arachnids, myriapoda)

 Squirrels, mice, groundhogs, rabbits, chipmunks, voles, moles, prairie dogs, gophers, snakes, lizards, etc.  Contribute dung and carcasses  Taxicabs for microbes

 Nonsegmented, blind roundworms  > 20,000 species  Eat bacteria or fungi or plants (stylet) And protozoa, other nematodes, algae  Specialized mouthparts Can sense temperature and chemical changes

 nematode

 ¾ of all living organisms  Exoskeleton, jointed legs, segmented body  Insects  Crustaceans  Arachnids  Myriapoda

 Shredders  Microbial taxis

Feeding Habits Carnivores : parasites and predators Phytophages: eat above ground green plant parts, roots, woody parts Saprophages: eat dead and decaying OM Microphytic feeders: eat spores, hyphae, lichens, algae, bacteria

Movement existing pore spaces, excavate cavities, transfer material to surface improve drainage, aeration, structure, fertility, granulation

Distribution with depth most active biotic horizons correspond with amount of OM:  Litter (O): has most OM but extremes of climate, therefore only specialists live there  Most animals in litter Roots: Rhizosphere: zone surrounding root  dead root cells and exudate stimulates microbial growth  Most microbiotic population in A and rhizosphere

Soil Organic Matter and Decomposition

Organic cmpd + O 2 CO 2 + H 2 O + energy + inorganic nutrients (or other electron acceptors)  a form of respiration.  an oxidation reaction  aided by microbial enzymes.

 Get carbon from organic compounds  Get energy from aerobic respiration  Use oxygen as electron acceptor in decomposition

1. Anaerobic respiration use nitrate, sulfate (or others) as electron acceptor 2. Fermentation  use organic substrate as electron acceptor (instead of oxygen)  reduced to by-product, such as alcohol or organic acid

 In aerobes, when oxygen accepts electrons, and is reduced, toxic compounds (e.g., hydrogen peroxide) are produced.  Aerobic organisms have adapted mechanisms (2 enzymes) to counteract toxins  ANAEROBES LACK THESE ENZYMES

Nutrients, Carbon, Energy.  Up to 50% of C in decomposed compounds is retained as microbial tissue  Some N,P,S also  If amount of nutrients exceeds amount needed by microbes, released as inorganic ions (NH 4 +, SO 4 -2, HPO 4 -2 )

organic compounds mineralization immobilization inorganic compounds

 In mineralization, nutrients formerly stored in organic form are released for use by living organisms  In immobilization, these nutrients are reabsorbed and assimilated by living organisms

1 rapid to 6 slow

 “Amorphous, colloidal mixture of complex organic substances, not identifiable as tissue”.  C:N:P:S = 100:10:1:1  Composed of humic substances Resistant, complex polymers  10s to 100s of years  and nonhumic substances Less resistant, less complex Friends don’t let friends eat humus.

 Large surface area per unit volume Greater than clay  Negatively charged OH - and COOH - groups High nutrient holding capacity (high CEC) High water-holding capacity

 Zymogenous: opportunists; eat “easy” food; reproduce rapidly  Autochthonous: eat very resistant organic compounds; slowly reproducing

Notice: CO 2 levels Feeding frenzy Priming effect Arrows: C transfers Humus levels (p. 358)

 Decomposing residue is not only a source of energy, but also a source of nutrients for microbial growth.  N is the element most often lacking in soil/residue to point of limiting microbial population growth  Limiting factor

 Carbon usually makes up 45 – 55% of dry weight of tissue  Nitrogen can vary from 6.0% For a residue with: 50% carbon and 0.5% N, C:N ratio would be ? 100:1 (wide/high C:N) 50% carbon and 3.0% N, C:N ratio would be ? 16:1 (narrow/low C:N)

 determines rate at which residue will decay and whether it will release (mineralize) or immobilize N after incorporation into soil.

Soil microbe cells need 8 parts C for 1 part N (C:N = 8:1) only 1/3 of C from food is incorporated into cells therefore, they need food with a C:N of ? 24:1

 If C:N ratio > 24:1, intense competition among microbes for soil N

 Comparatively low N  Microbes suffer a shortage as they begin decomposing, so have to get N from soil at a cost in energy expenditure and decomposition rate  Greater energy expense and release of CO 2  Higher proportion of C in resistant compounds (cellulose, lignin)  slower decomposition

 Sawdust  Newspaper  Wood chips  Straw

 Comparatively high N content  Mineralized N will be released soon after decay starts So microbes won’t suffer a shortage as they begin decomposing  More C from residue can be diverted to microbial growth  Higher proportion of total C in easily decomposable compounds  Faster decomposition

 Manure  Cover crop  Household compost (composted)

(p. 361) 1.Add high/wide C:N residue: microbial activity, CO 2 long nitrate depression final N level 2.low/narrow C:N: microbial activity, CO2 no nitrate depression final N level