Lecture: Chapter 22 - Decomposition and Nutrient Cycling Flashcards

1
Q

Internal cycling

A

refers to recycling of nutrients within an ecosystem as they are transformed between inorganic and organic forms

internal cycling is driven by primary production and decomposition

Nitrogen will be used as an example for internal cycling

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2
Q

Decomposition

A

Chemical and biological transformations in ecosystems alter the chemical form and supply of nutrients

Foremost among nutrient transformations is the decomposition of organic matter, which releases nutrients back into the ecosystem

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3
Q

Nutrient Transformations

A

Nutrients in detritus are made available by decomposition: the process by which detrivores break down detritus to obtain energy and nutrients

Decopoisiton releases nutrients as simple, soluble, inorganic compounds that can be taken up by other organisms

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4
Q

Decomposition processes:

A

Leaching - soluble compounds may be washed out from organic dead matter

Fragmentation

Chemical alteration (mineralization)

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5
Q

Litter

A

Fresh, undecomposed organic matter on the soil surface is known as litter

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6
Q

Fragmentation

A

Animals such as earthworms, termites and nematodes consume the litter, breaking it up into progressively finer particles. This fragmentation increases surface area, which facilitates chemical breakdown.

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7
Q

Bacteria

A

The main decomposers of dead animal matter

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8
Q

Fungi

A

Dominant decomposers of dead plants

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9
Q

Mineralization

A

The chemical conversion of organic matter into inorganic (mineral) nutrients by decomposers

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10
Q

Immobilization

A

Decomposers also need nutrients for their own metabolic processes, so they need to uptake and assimilate inorganic (mineral) nutrients (e.g. ammonia)

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11
Q

Net mineralization rate (NMR)

A

Mineralization rate - immobilization rate

NMR depends on nutrient content of the litter and the nutrient demand of the microbial population

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12
Q

Factors impacting decomposition rate

A

Litter quality

Environmental factors (e.g. temperature, precipitation - climate)

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13
Q

Litter Quality

A

Depends on types of carbon compounds present

  • High : small molecules with high energy bonds (simple sugars)
  • Moderate: Strucutrally more complex, harder to decmopose (cellulose)
  • Low: Large molecules with much complexity, hardest to decompose (Lignin)
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14
Q

Temperature and decomposition

A

Decomposition and mineralization rates are faster in warm, moist conditions

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15
Q

Requirements for decomposers

A

Decomposers require energy and nutrients for their own growth and maintenance

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16
Q

C:N ratio of detritus

A

How much nutrients are released into soil depends on the C:N ratio of detritus. Decomposition of organic matter with a C:N ratio of

  • > 25:1 all N used by the microorganisms
  • <25: net release of N (Nurtients) into the soil available for plant uptake

Lignin content and secondary compounds also affect decomposition rates

17
Q

Rhizosphere.

A

Decomposition rates are higher in the rhizosphere. It is the region in the soil with high root density and where roots function

Roots alter soil chemistry as they secrete carbohydrates into the soil

18
Q

Immbilization

A

The availability of high-quality carbon favors bacteria growth. Plants enhance decomposition rate

Bacteria still limited by limited nutrient content immobilization during bacteria growth

But protozoa and nematodes eat bacteria and fungi biomass and remobilize nutrients for plant uptake

19
Q

The Nitrogen Cycle: an atmospheric cycle

A

Atmospheric N2 — Ocean
|
Land N2
| |
Plant Biomass N2O
| |
Soils ———–Rivers—- Inorganic N

20
Q

Nitrification

A

NH3 and NH4 are converted to NO3 by chemoautotrophic bacteria in aerobic conditions

21
Q

Denitrification

A

Some bacteria use NO2 as an electron acceptor, converting it into N2 and N20, in anoxic conditions

22
Q

Mineralization (organic to inorganic)

A

When C:N is sufficient to meet microbial requirements

23
Q

Immobilization (inorganic to organic)

A

When C:N in food is insufficient to meet microbial requirements; microorganisms need nutrients for themselves

24
Q

Nutrient cycling in open-water systems

A

In shallow water along the shoreline sediment-rooted vascualar plants dominate.

Away from shores, the epilimnion is home to algae and zooplankton. Here the layers of production and decomposition are disconnected.

25
Q

Nutrient cycling: summer

A

Deep lakes and oceans stratify in presence of sunlight

Surface waters, zone of primary producton, “photic zone”, low nutrient content [top waters]

Benthic zone, zone of decomposition, high nutrient content [water along the bottom]

26
Q

Nutrient cycling: Fall

A

Sun is weaker causing epilimnion to cool off. Thus, water density increases and the heavier water sinks and mixes

Mixing permits Oxygen and nutrients to mix across the whole water column

Fall turnover

27
Q

Nutrient cycling: Winter

A

Ice covers the surface

Water cannot mix in lack of wind under the ice

No Oxygen supply to hypolimnion for decomposers

When Oxygen runs out in the hypimnion, in the anoxic environment organisms die

28
Q

Nutrient cycling: spring

A

Spring turn over: ice melts, wind mixes

Oxygen and nutrients mixed across entire water column

PEAK PRODUCTIVITY

Once surface water becomes warmer, stratification re-establishes

29
Q

Upwelling systems

A

Due to the Coriolis effect, wind-driven surface waters are pushed offshore

This causes the nutrient-rich deeper waters to move vertically to the surface.

Vertical circulation of water is called upwelling

Coastal upwelling of nutrient rich cold deep water support highly productive fisheries

30
Q

Internal cycling

A

re-cycling of nutrients between organic and inorganic forms driven by primary production and decomposition

31
Q

Decomposition - VERY IMPORTANT

A

Decomposers and detrivores break down organic matter into soluble inorganic ocmpounds. They need organic matter for energy + nutrients for themselves