Upper layer of soil (rooting zone) is where ENERGY is present in soil This is the LIVING SYSTEM of...
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Transcript of Upper layer of soil (rooting zone) is where ENERGY is present in soil This is the LIVING SYSTEM of...
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
Fourth-order consumer
Primary Producergreen plants;photosyntheticbacteria and algae
Primary consumer
Secondary consumer
Tertiary consumer
hete
rotro
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sauto
trop
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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
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
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
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
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
¾ of all living organisms Exoskeleton, jointed legs, segmented
body
Insects Crustaceans Arachnids Myriapoda
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
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)
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
“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
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
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
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