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Nutrient Cycles. Nutrient requirements Biogeochemical cycles Rates of decomposition Plant adaptations in low nutrient conditions. Nutrient Requirements for Plant Growth. Taken up in gaseous form, Oxygen (O 2 ), Carbon CO 2 , and from roots - Water (H 2 O).

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PowerPoint Slideshow about 'Nutrient Cycles' - Jims


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Nutrient Cycles

  • Nutrient requirements

  • Biogeochemical cycles

  • Rates of decomposition

  • Plant adaptations in low nutrient conditions


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Nutrient Requirements for Plant Growth

  • Taken up in gaseous form, Oxygen (O2), Carbon CO2, and from roots - Water (H2O).

    • Derived from water and carbon dioxide

  • Rest are taken up from soil solutions

    • Macro-nutrients –Nitrogen (N), Phosphorous (P), Potassium (K),

    • Calcium (Ca), Magnesium (Mg), Sulfur (S)

    • Micro-nutrients – Boron (B), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Zinc (Zn)


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Nutrient Cycles

  • Nutrient requirements

  • Biogeochemical cycles

  • Rates of decomposition

  • Plant adaptations in low nutrient conditions


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Biogeochemical Cycling

The cycling of nutrients through ecosystems via food chains and food webs, including the exchange of nutrients between the biosphere and the hydrosphere, atmosphere and geosphere (e.g., soils and sediments)


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  • Ecosystems produce and process energy primarily through the production and exchange of carbohydrates which depends on the carbon cycle.

  • Once energy is used, it is lost to the ecosystem through generation of heat

  • Carbon is passed through the food chain through herbivory, predation, and decomposition, it is eventually lost to the atmosphere through decomposition in the form of CO2 and CH4 . It is then re-introduced into the ecosystem via photosynthesis.

  • However, the amount of carbon present in a system is not only related to the amount of primary production, as well herbivory and predation (e.g., secondary production), it is also driven by the rates of decomposition by micro-organisms

  • Atmospheric carbon is rarely limiting to plant growth


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  • When we look at other nutrients, a somewhat different picture emerges than with the energy cycle – e.g., phosphorous in a food chain within a small pond.

  • Algae remove dissolved phosphorous from the water

  • The phosphorous is then passed through different trophic levels through herbivory and predation.

  • At each level there is some mortality, and then the phosphorous is passed to decomposers

  • These organisms release phosphorous into the water where it is again taken up by primary producers and the whole cycle starts up again


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Key Elements of Biogeochemical Cycles picture emerges than with the energy cycle – e.g., phosphorous in a food chain within a small pond.

  • Where do the nutrients that ecosystems use come from?

  • What happens to the nutrients within the ecosystem itself?

  • What happens to the nutrients once they leave the ecosystem?

  • Once nutrients are cycled through an ecosystem, how do they get back?

  • What are the rates of exchange of nutrients between the different pools?


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Nutrient Pools and Nutrient Flux picture emerges than with the energy cycle – e.g., phosphorous in a food chain within a small pond.

  • Nutrient pool – a specific component or compartment where a nutrient resides

    • Can be a single organism, a population, a community, a trophic level, and an abiotic feature (e.g., lake, soil, atmosphere, etc.)

  • Nutrient flux – the rate of exchange (e.g., unit of material per unit time) of nutrients between pools


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  • Example of changes in the amounts of tracer phosphorous being exchanged within an aquatic food web

  • The values themselves represent changes in the pool levels, where each one of the lines represents a different pool

  • Understanding the feeding relationship allows us to build a nutrient cycle model for this ecosystem


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  • Model of phosphorous cycle for an aquatic ecosystem – flux rates per day shown.

  • This system is not closed – inputs, probably from run-off from land.

  • Exports include  herbivores moving outside of system and dead plant/animal material moving out of system, probably through sedimentation.

  • Rate of uptake by plants is directly proportional to net primary production.

  • Exchange of nutrients by higher trophic levels is controlled by processes regulating secondary production.

  • Rates of inputs and outputs of nutrients from an ecosystem are driven by both biotic and abiotic factors.


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Types of Biogeochemical Cycles rates per day shown.

Three major categories of biogeochemical cycles based on slowest-changing pool(=reservoir):

  • Gaseous cycles of C, O, H20

  • Gaseous cycle of N, (S)

  • Sedimentary cycles of the remaining nutrients

Global scale

Local scale


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Sedimentary Cycles rates per day shown.

Gaseous Cycles



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Biological Nitrogen Fixers rates per day shown.

  • Cyanobacteria – blue-green algae

  • Free living soil bacteria

  • Mycorrhizae

    • Symbiotic bacteria living in root nodules


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Root nodules on ? rates per day shown.Cassia fasciculata


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NO from lightning rates per day shown.

Lightning + N2 + O2 NO + O2  Nitrate (NO3)


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Phosphorous Cycle rates per day shown.

Phosphate – PO4-3


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Potassium rates per day shown.


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Sources of Nutrients rates per day shown.

Atmosphere

Parent

Material

Run-off,

Ground water

Floods


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Nutrient Cycles rates per day shown.

  • Nutrient requirements

  • Biogeochemical cycles

  • Rates of decomposition

  • Plant adaptations in low nutrient conditions


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Simple Model of Soil Decomposition/ microbial respiration rates per day shown.

H2O, O2

CO2 or CH4

Litter

Energy

Microbial

Population

Organic Soil

Nutrients

Dissolved

Nutrients


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Factors Controlling Microbial Respiration rates per day shown.

  • Availability of oxygen

    CO2 versus CH4 production

  • Temperature

  • Moisture

  • Quality of material comprising dead organic matter


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Simple Model of Simple Model of Soil Decomposition/ microbial respiration

H2O, O2

CO2 or CH4

Litter

Energy

Microbial

Population

Organic Soil

Nutrients

Dissolved

Nutrients


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k is the microbial respirationfraction of

a material that decomposes

in a given year

Decomposition as a Function of Lignin Content


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Residence Time microbial respiration

  • Residence time is the length of time it takes for biomass or a nutrient to be completely decomposed or recycled from the forest floor


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Residence times microbial respiration

Coniferous forests have longer residence times than deciduous

 C/N control

Boreal forests have longer residence times than temperate forests

 temperature control


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Nutrient Cycles microbial respiration

  • Nutrient requirements

  • Biogeochemical cycles

  • Rates of decomposition

  • Plant adaptations in low nutrient conditions


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Tree Nutrient Content microbial respiration


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Translocation of Nutrients microbial respiration

  • Prior to shedding leaves in the fall, translocation of nutrients often takes place in trees

  • This allows tree to retain essential nutrients that are hard to come by

  • Spruce trees remove more nutrients than other coniferous trees

  • An adaptation to poor nutrient sites


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Question – do plants growing on sites with low soil nutrients have low nutrient contents as well?

The answer is no –

  • Plants on sites with low nutrients tend to have higher nutrient contents

  • They have a higher nutrient use efficiency


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Nutrient Use Efficiency (NUE) nutrients have low nutrient contents as well?

  • Some plants are more efficient at using nutrients because it gives them selective advantages in low nutrient conditions

    NUE = A / L

    A – the nutrient productivity (dry matter production per unit nutrient in the plant)

    L – nutrient requirements per unit of plant biomass


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A common pattern found in ecosystem productivity is saturation curve.

Productivity increases linearly with N availability, up to a certain point, when other resources become limiting (e.g., light, water, temperature, other nutrients)


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Factors Influencing nutrients:Nutrient Availability

  • Presence of nitrogen fixers

  • Microbial activity

  • Fire

  • Precipitation patterns

  • Soil drainage

  • Soil temperature, moisture


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H nutrients:2O - Precipitation

CO2

Fire

GHG

Photosynthesis

Aeolian,

Atmospheric

Deposition

Internal

translocation

N2, O2

Litterfall

nutrients

N fixers

CH4, CO2

Organic soil

Dissolved

nutrients

Through-fall

nutrients

Nutrients

Energy,

Nutrients

Upper mineral soil

Microbes

Lower mineral soil

Leaching, run off


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Forest Type nutrients:

Living

Biomass Pool

Primary

Production Rates

Soil Carbon/

Nutrient Pool

Decomposition

Rates

Tropical

Highest

Highest

Lowest

Highest

Temperate

Middle

Middle

Middle

Middle

Boreal

Lowest

Lowest

Highest

Lowest

Boreal forest has the largest available nutrient pool in soil, but lowest rates of production, where as tropical forest has lowest soil pool, and highest production.


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Role of Disturbances in Nutrient Cycling nutrients:

  • Type of disturbance important

    • Fire versus logging versus large-scale mortality

  • Disturbances directly alter biotic and abiotic controls on nutrient cycling

    • Rates of primary production

    • Controls on evapotranspiration

    • Influences on surface runoff

    • Soil temperature/moisture  decomposition rates

  • Linkages between terrestrial/aquatic systems



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Nutrient Cycles nutrients:

  • Nutrient requirements

  • Biogeochemical cycles

  • Rates of decomposition

  • Plant adaptations in low nutrient conditions




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