Soil Carbon:
Fractions and Compounds
Michael Zimmermann
Drummond Street
suspension < 0.45 µm
bulk
soil
DOC
light
fraction
POM
heavy
fraction
S+A
fraction > 63 µm
fraction < 63 µm
s+c
rSOC
200
150
100
50
0
chemical shift (ppm)
Stabilization mechanisms
CO2
plant
residues
unprotected
microbial
attack
CO2
physically
protected
CO2
mineral
associated
aggregation
CO2
biochemically
protected
chemical
resistant
modified after Six et al. 2002
1
Fractionation
suspension < 0.45 µm
bulk soil < 2 mm, then
dispersion with 22 J ml-1,
wet sieving to 63 µm
DOC
light
fraction
POM
heavy
fraction
S+A
fraction > 63 µm,
afterwards densityseparation at 1.8 g cm-3
s+c
fraction < 63 µm
6% NaOCl
rSOC
soil fractions
carbon fractions
e.g. Zimmermann et al., EJSS 2007
Fractionation
suspension < 0.45 µm
bulk soil < 2 mm, then
dispersion with 22 J ml-1,
wet sieving to 63 µm
DOC
light
fraction
POM
heavy
fraction
S+A
fraction > 63 µm,
afterwards densityseparation at 1.8 g cm-3
fraction < 63 µm
s+c
6% NaOCl
rSOC
soil fractions
carbon fractions
e.g. Zimmermann et al., EJSS 2007
2
DRIFT
(Diffuse Reflectance Infra-red Fourier Transformed spectroscopy)
Molecul vibrations
stretching
bending
symmetric
asymmetric
scissering
wagging
rocking
twisting
DRIFT
(Diffuse Reflectance Infra-red Fourier Transformed spectroscopy)
100.0
95
90
85
80
Reflectance (%)
75
70
65
C=C
60
55
C=O
C-H
50
%R
45
C-H
40
35
30
O-H
25
20
C-O
15
10
5
0.0
4000.0
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400.0
cm-1
Wavenumber (cm-1)
3
DRIFT
(Diffuse Reflectance Infra-red Fourier Transformed spectroscopy)
Pros:
• Simple to use
• Fast
• Cheap
Cons:
• Qualitative
• Interferences with minerals
DSC
(Differential Scanning Calorimetry)
25
700
20
600
500
10
5
400
0
300
-5
200
Temperature
Heat flow
15
-10
100
-15
-20
0
0
10
20
30
Time
Heat flow
Heating rate
4
DSC
(Differential Scanning Calorimetry)
70
-1
Heat flow (mW mgC )
60
50
40
30
20
10
0
200
Ti
300
T1
400
T2
500
600
Temperature (C)
Horizon
Oh
A
B1
B2
First
Second 50% burn
Soil depth Energy
-1
(cm)
(kJ gC ) peak (°C) peak (°C) off (°C)
0-17
17-27
27-37
37-47
19.5
19.1
23.4
22.3
358.9
308.8
330.1
326.9
456.2
361.4
369.6
450.9
423.7
352.9
354.9
370.2
DSC
(Differential Scanning Calorimetry)
Pros:
• Auto-sampler
• Track changes over time
• Energy contents
• Some quantitative values
Cons:
• Qualitative
• Not common instrument
5
CP/MAS 13C NMR
(Cross Polarization Magic Angel Spinning Nuclear Magnetic Resonance)
•
Use the spin property (S) of nucleus (protons and neutrons), works only for
odd numbers, therefore 13C
•
Polarization of nucleus within magnetic field (CP)
•
Application of electro-magnetic impulse at various settings, Spinning (MAS)
•
Resonance frequencies are proportional to compound composition
For detailed information:
http://www.dur.ac.uk/solid.service/information/
CP/MAS 13C NMR
(Cross Polarization Magic Angel Spinning Nuclear Magnetic Resonance)
48.8%
25.6%
10.0%
3.3% 12.3%
11.6%
44.5%
12.1%
41.1%
12.5%
34.6%
20.4%
4.0% 19.5%
3.5%
Esters
Amides
Lignin Sugars Cellulose
Tannin
Proteins
Charcoal
Lipids
Suberin
Cutin
Fatty acids
2.8%
25.6%
34.3%
stable
200
150
labile
100
17.7%
15.8%
stable
50
0
chemical shift (ppm)
6
CP/MAS 13C NMR
(Cross Polarization Magic Angel Spinning Nuclear Magnetic Resonance)
Pros:
• Non-destructive
• Quantitative C groups
• Well established
Cons:
• Expensive
• Interferences with minerals
7