Sources of nutrients to terrestrial systems
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Sources of nutrients to terrestrial systems. 1. Wet deposition. Inputs 2. Recycling Organic Inorganic Rates influenced by: Climate Quality of detritus. 1. Dry deposition. 1. N-fixation. 2*. Recycling. Soil. 1. Weathering. Parent material.

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Sources of nutrients to terrestrial systems
Sources of nutrients to terrestrial systems

1

Wet deposition

  • Inputs

  • 2. Recycling

  • OrganicInorganic

  • Rates influenced by:

    • Climate

    • Quality of detritus

1

Dry deposition

1

N-fixation

2*

Recycling

Soil

1

Weathering

Parent material



Breakdown of organic material through decomposition

occurs in several different ways

Leaching

Physical

Fragmentation

Decomposition

Mineralization

(e.g., ammonification)

Chemical

Fungi

bacteria


Leaching

Physical

Fragmentation

Decomposition


Physical decomposition leaching
Physical Decomposition: Leaching

  • Rainwater falling on leaf litter and other detritus dissolves inorganic nutrients from surfaces and washes them into the soil

  • Compounds are not changed during this process (NH4+ on leaf surface becomes NH4+ dissolved in soil water)

  • These inorganic nutrients (ammonia, nitrate, phosphate, etc.) are immediately available for uptake by plant roots.


Physical decomposition fragmentation
Physical Decomposition: Fragmentation

  • Freeze/thaw cycles and animal activities (munching by insects, slugs, nematodes, etc.) break up detritus into smaller pieces

  • Resulting smaller pieces of detritus have a high surface area to volume ratio, increasing the rate of decomposition


Chemical decomposition mineralization
Chemical Decomposition: Mineralization

  • Conversion of organic matter to inorganic compounds (CO2, H2O, NH4+, NO3+, etc.)

  • Fungi break down the woody components of litter into inorganic molecules (lignin, cellulose)

  • Bacteria & other microorganisms break down just about anything else


Mycorrhizae
Mycorrhizae

  • Symbiotic association between plant roots and fungi

  • Endomycorrhizae vs. Ectomycorrhizae

  • Play a role in decomposition by breaking down proteins into amino acids that are transferred to host plant


Decomposition
Decomposition

  • Mechanisms

    • Leaching

    • Fragmentation

    • Chemical Alteration

  • Factors influencing decomposition rate

    • Quality of Detritus

    • Climate (temperate vs. tropical)

    • Soil Animals


Quality of detritus
Quality of Detritus

  • Animal carcasses decompose faster than plants

  • Leaves decompose faster than wood

  • In any given climate, there is a 5 to 10-fold range in decomposition rates that is attributable to detritus composition


Climate: Tropical vs. Temperate

What does this tell you

about which abiotic factors

are most important in terms

of controls over rates of

decomposition?


Soil animals
Soil Animals

  • Soil animals have effects on soil structure, litter fragmentation, transformation of organic compounds, and composition of microbial community

  • Microfauna (<0.1mm; protozoans, nematodes)

  • Mesofauna (0.1mm – 2mm; taxonomically diverse, have the greatest effect on decomposition)

  • Macrofauna (>2mm; earthworms & termites, called ecosystem engineers because they alter resource availability by modifying physical properties of soils and litter


Soils as a compartment

Low clay content of soils in the tropics results in nutrients washing out of the soil unless there is quick uptake by plants

As a result, most nutrients are found in living biomass rather than soils: important implications of tropical deforestation




Productivity in aquatic ecosystems

Global distribution of chlorophyll in oceans

Where is productivity highest?

Shallow seas, proximity to bottom sediments

Strong upwelling zones




3


Nitrogen cycle
Nitrogen Cycle

Atmosphere

N=N

Nitrogen Fixing

Denitrification

Denitrification

Nitrogen Fixing

Soils,

Organisms

Oceans

Marine

cycling

Leaching

Burial

Low levels of NH4+, NO3-2

Sediments

Mineralization

Assimilation

Nitrification


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