Decomposers and Decomposition

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Chapter 7

• Decomposers and Decomposition

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Decomposition?

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Decomposition

• Decompositionbreakdown of chemical bonds formed
  during the construction of plant and animal
  tissue.
• Organisms that feed on dead organic matter or
  detritus
• Microbial decomposersbacteria and fungi
• Detritivoresanimals that feed on dead material

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Carbon

• Carbon sequestration
• CO2 vs. organic matter
• Forests vs. barren land
• Atmosphere vs. biomass

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Stages of decomposition

• Leachingloss of soluble sugars/dissolved
  compounds
• Fragmentationreduction into smaller
  particles physical/chemical fragmentation

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Energy processing

• Energy and nutrients from organic compounds
• oxidation of carbohydratesrespiration
• Mineralizationorganic ? inorganic
• Immobilizationinorganic ? organic

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Decomposers

• Groups based on size
• Microfloramost common decomposers
• bacteriaanimal material
• fungiplant material
• Aerobicrespiration
• Anaerobicfacultative/obligate anaerobes
• Fermentationsugars? organic acids/alcohol

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Decomposers

• Microfauna/microflora lt1 mm ? 100 mm
• Mesofauna 100 mm ? 2mm
• Macrofauna 2mm ? 20 mm
• Megafauna 20 mm ? 64 mm
• Microbivores feed on bacteria and fungi

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Food Quality

• Energy and nutrient source
• Litterdead plant material
• Quality related to chemical bonds/structure
• simple sugars vs. complex carbohydrates
• Lignincomplex class of carbohydrates
• little net gain of energy for decomposers

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Rate of decomposition

• Inverse relationship between rate and lignin
  content
• Quality influences feeding of large detritivores

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Aquatic environments

• Phytoplanktonlow lignin content
• Vascular plantshigh lignin content
• O2 dependent
• Low O2 absence of fungi

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Animal matter

• Chemical breakdown easier than plants
• Flesh consumed by scavengers
• 70 decomposed by bacteria and arthropods
  (maggots)
• Temperature dependent

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Fecal matter

• Mostly decomposed
• Herbivorespartially digested organic matter
• Specialized detririvores larvae incubate and
  feed
• Tumblebugsincubate larvae

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Physical influence

• Temperature and moisture
• Influence rate of decomposition
• Decomposition highest in warm/wet climates
• Temperature parallels CO2 release

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Nutrients

• Nitrogen ? nutrient value
• Organisms require N for growth during
  mineralization
• Mineralization and immobilization taking place
  simultaneously
• Net mineralization rate

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Stages of nutrient concentration

• Water soluble compounds leached
• Dependent upon soil moisture
• N increasesimmobilization from other sources
• As C quality declinesnet release of N
• Dependent upon original nutrient content

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Aquatic decomposition

• Similar to terrestrial ecosystems
• Influenced by abundance of water
• More stable environment favors decomposition
• More accessibility to detritivores

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Aquatic systems

• Particulate organic matter (POM)
• Coarse particulate organic matter (CPOM)
• Fine particulate organic matter (FPOM)
• Water depth determines organic makeup
• Benthic organic matter bacteria
• Aerobic vs. anaerobic
• Dissolved organic matter (DOM)

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Aquatic sources

• DOM readily available
• Sourcesalgae, zooplankton
• Death of phyto/zooplankton
• Bacteria concentrate DOM
• Mineralization and immobilization of nutrients
• Excretion of exudates and feces

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Organic matter processing

• Physical mechanism
• Water soaked leaves sink
• 5 30 organic matter leached
• Biological mechanism
• Covered withbacteria fungi
• CPOM FPOM
• Degrade celluloseand metabolize lignin

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Flowing water

• Shredders attack CPOM
• Feed also on attached microbes
• Becomes FPOM
• Filterers / collectors gather FPOM
• Feed also on attached microbes
• Grazers feed on algal coatings
• leftovers enter stream as FPOM
• Gougers feed on woody debris
• Predators feed on all the above

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• Nutrient passes from water column? plants ?
  consumer ? another consumer ? poop nutrient
  cycling
• Downstream flow new dimension
• Physical retention
• Storage in wood detritus
• Leaf sediments
• Beds of macrophytes
• Biological retention
• Uptake and storage in plant/animal tissue

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Recycling, retention downstream displacement

• Downstream transport nutrient cycling
  nutrient spiraling
• One cycle
• Uptake of an atom from DOM
• Passage through food chain
• Return to water for reuse
• Spiraling distance of one cycle
• shorter cycle tighter spiral
• longer cycle more open spiral

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River Continuum Concept

• From headwaters to mouth ? continuum of
  changes in conditions
• Headwater streams (1-3)
• Swift, cold, forested
• Strongly heterotrophic
• Dominant organisms
• Shredders CPOM
• Collectors FPOM

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• Midorder streams (4-6)
• Riparian vegetation important
• Canopy opens ? primary production
• Temperature increases / current slows
• Primary production gt community respiration
• Dominant organisms
• Collectors FPOM
• Grazers algae macrophytes

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• Higher order streams (6 10)
• Channel wider deeper
• Volume of flow increases
• Autotrophic production decreases
• Shift back to heterotrophy
• Energy from FPOM
• Utilized by bottom dwellers
• Phytoplankton zooplankton population minimal