upper layer of soil (rooting zone) is where energy is present in soil this is the living system of...

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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 Producergreen plants;photosyntheticbacteria and algae

Primary consumer

Secondary consumer

Tertiary consumer

hete

rotro

ph

sauto

trop

hs

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:CO2 + H2O + energy C6H12O6 + Oxygen

(sun) Glucose: carbohydrate

Only autotrophs can do this!

RESPIRATION• Plants and animals derive energyC6H12O6 +Oxygen CO2 + H2O + 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.

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 inchExudates: carbohydrates and proteins secreted by roots

attracts bacteria, fungi, nematodes, protozoaBacteria and fungi are like little fertilizer bagsNematodes 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

ProtozoaAlgaeFungi

Unicellular Amoeba, ciliates, flagellates Heterotrophic

• Eat bacteria, fungiForm 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)

ANNELIDSseveral 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 surfaceimprove 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 + O2 CO2 + H2O + energy + inorganic nutrients

(or other electron acceptors)

a form of respiration.an oxidation reactionaided by microbial enzymes.

Get carbon from organic compounds

Get energy from aerobic respiration Use oxygen as electron acceptor in

decomposition

1. Anaerobic respirationuse nitrate, sulfate (or others) as electronacceptor

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 (NH4

+, SO4

-2, HPO4-2)

organic compounds

mineralization

immobilization

inorganiccompounds

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 rapidto6 slow 1

23

4

5

66

“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 friendseat 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:

CO2 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 < 0.5% - >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 CO2

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, CO2

long nitrate depressionfinal N level

2. low/narrow C:N: microbial activity, CO2 no nitrate depression final N level