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Global Carbon Model. petagrams Pg = 1x10 15 g. 1. 2. Soil Ecology. the process whereby organic material is broken down into its smaller molecules

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Global Carbon Model

petagrams

Pg = 1x1015g

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2


Soil ecology

Soil Ecology

  • the process whereby organic material is broken down into its smaller molecules

  • biological, physical, and chemical breakdown of organic matter resulting in humus formation, release of CO2, H2O, and nutrients

Decomposition

Methods ??

3


Soil organic matter som methods
Soil Organic Matter (SOM) Methods

  • LOI– loss on ignition

  • Wet Oxidation–eg, Walkley-Black (determining C by titration of unreduced dichromate)

  • Dry Combustion– eg, LECO (Infrared & OC&Inorg C)

  • Fractionation

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Decomposition methods
Decomposition Methods comparisons?????

  • Litterbags --- weight loss (g)

  • Density change (g/cm3)

  • Calculation of k values (year-1) (input/accumulation)

  • CO2 evolution (g m-2)

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Decomposition
Decomposition comparisons?????

  • Litterbags

http://www.geog.uu.nl/fg/gapsize/thesis-ovd/Deel10%20Hfd07.pdf

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Decomposition1
Decomposition comparisons?????

  • Litterbags

    • Different mesh sizes

    • Different times

    • Different substrates (pure/mix)

    • Standards?

http://www.geog.uu.nl/fg/gapsize/thesis-ovd/Deel10%20Hfd07.pdf

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Needle/Leaf Litterbags comparisons?????

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Grass Litterbags comparisons?????

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Log Decomposition comparisons?????

(HJ Andrews)

Litterbags???

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Root decomposition comparisons?????

Litterbags

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Wood Decomposition comparisons?????

density changes

g/cm3

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Decay Constant (k) comparisons?????

X = X0 e-kt

100

50

0

%

mass

remaining

Time

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Olsen 1963


Decay constant k
Decay Constant (k) comparisons?????

  • k = (-ln(wt remaining fraction))/yrs decomp

    k yr-1 = (-ln(Xt/X0 )) / t yr

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Examples involving Negative Exponential Decay Curves comparisons?????

(Jenny et al 1949, Olson 1963)

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Decomposition time
Decomposition Time comparisons?????

  • Mean Residence Time (MRT) steady state

    Forest Floor Biomass/Annual Litterfall = ? Year

  • Half-Life (50% remaining)

    k = (-ln(Xt/X0 )) / t years

    t(1/2) = -ln 0.5/k = 0.693/k

  • 1% remaining (~MRT)

    t(.01 ) = -ln 0.01/k = 4.605/k

kg / kg year-1 = year

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Examples involving Negative Exponential Decay Curves comparisons?????

(Jenny et al 1949, Olson 1963)

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20 comparisons?????


(C g/m comparisons?????2 yr)

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22 comparisons?????


So multiple 1 comparisons?????st order decay curves may present different k values thru time!!

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24 comparisons?????


25 comparisons?????


The carbon balance

Net Ecosystem comparisons?????

Carbon Exchange

Gross Photosynthesis

Dark and

Photo

Respiration

CO2 Storage

bole respiration

litter

respiration

microbial

respiration

root respiration

The Carbon Balance

http://www.vaisala.com/DynaGen_Attachments/Att32668/GMP343%20Introduction.pps#6

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Decomposition using comparisons?????CO2 Evolution

Gilson respirometer

Warburg Apparatus

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http://history.nih.gov/exhibits/stadtman/lab.htm


Decomposition using comparisons?????CO2 Evolution

  • Soda lime - Ca(OH)2 (about 75%)  

    • Weight change

  • KOH traps

    • Titration

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Soil respiration system pp system
Soil Respiration System ( comparisons?????PP System)

http://www.ppsystems.com/soil.html

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Infra-Red Gas Analysis Systems (PP Systems)


Century model variables predicting som accumulation
Century Model - variables predicting SOM accumulation comparisons?????

  • Amount above- & belowground plant material to decay

  • Chemical quality of material added to detritus (e.g. lignin, N)

  • Soil texture

  • Climate

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