Transcript Prairie Ridge Soil Profile

Biogeochemical Investigation at Prairie Ridge, NC
Prairie Ridge Soil Profile
Amy Keyworth
Jovi Saquing
November 2006
Prairie Ridge Soil Profile
Outline
• What we expect to see… and why?
• What we do see… and how come?
• What can we conclude?
Prairie Ridge Soil Profile
Soil Profile Description
Litter (undecomposed)
Organic layer, fermented
Organic layer, humified
Mineral layer with organic
carbon and leached
minerals
Mineral layer with
precipitation of
oxides/hydroxides and/or
carbon
Unaltered parent substrate
Source: Gleixner, G. 2005. Stable isotope composition
of soil organic matter. In Stable isotopes and
biosphere-atmosphere interactions. ed. Flanagan,
L.B., E.J. Ehleringer and D.E. Patake.
Prairie Ridge Soil Profile
Organic Compounds
Cellulose
Lipid
Monosaccharide
(e.g. glucose)
Lignin
Lignin
monomers
Intermediates
Protein
Amino acid
Ammonium
(e.g. acetic acid)
Alkanes
Nitrites/Nitrates
CO2
Humic
Substances
Source: Gleixner, G. 2005. Stable isotope composition of
soil organic matter. In Stable isotopes and biosphereatmosphere interactions. ed. Flanagan, L.B., E.J. Ehleringer
and D.E. Patake.
N2, N2O
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Organic Compounds
Cellulose
Lignin
Lignin
Monomers
Alkanes
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What we expect to see..
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13C – increase with depth
C/N – decrease with depth
% C – decrease with depth
% N – increase/decrease with depth
Carboxylic and aromatic groups –
present in organic layers, increasing
aromaticity with depth
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What we expect to see - 13C
Valley
Lower Slope
Upper Slope
Ridge Top
Carbon isotopic composition profiles.
Undisturbed site
Disturbed (agricultural) site
(Fig 2 middle, J.G. Wynn, et al., 2006)
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What we expect to see – [C]
Carbon concentration profiles.
Undisturbed site
Disturbed (agricultural) site
“Kink” in the C(z) curve reflects root depth or productivity zone
(Fig 2. Top, J.G. Wynn, et al., 2006)
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What we expect to see – C/N
Source: C/N of soil organic matter from different depth intervals
(Gleixner, 2005)
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Why do we expect to see it ?
1.
2.
3.
4.
Suess effect
Soil carbon mixing
Preferential microbial decomposition
Kinetic fractionation
Prairie Ridge Soil Profile
Why we expect to see it ?
1.
2.
3.
4.
Suess effect
Soil carbon mixing
Preferential microbial decomposition
Kinetic fractionation
Prairie Ridge Soil Profile
1.
Suess effect
– Older, deeper SOM originated when
atmospheric 13C was more positive (CO2
was heavier)
– From 1744 to 1993, difference in 13C app 1.3 ‰
– Typical soil profile differences = 3 ‰
Prairie Ridge Soil Profile
1. Suess effect
Mixing of SOC derived from the modern atmosphere versus
that derived from a pre-Industrial Revolution
atmosphere. (Fig. 1A, J.G. Wynn, et al., 2006)
Prairie Ridge Soil Profile
Why we expect to see it ?
1.
2.
3.
4.
Suess effect
Soil carbon mixing
Preferential microbial decomposition
Kinetic fractionation
Prairie Ridge Soil Profile
2. Soil carbon mixing
a. Surface litter (depleted) vs. root derived (enriched) SOM
Mixing of leaf litter-derived SOC and root-derived SOC.
(Fig. 1B, J.G. Wynn, et al., 2006)
Prairie Ridge Soil Profile
2. Soil carbon mixing
b. Variable biomass inputs (C3 vs. C4 plants)
Mixing of SOC formed under two different vegetation communities,
e.g. C3 vs C4. Slope could vary from positive to negative depending
on direction of shift. (Fig. 1C, J.G. Wynn, et al., 2006)
Prairie Ridge Soil Profile
2. Soil carbon mixing
c. Some of the carbon incorporated into SOM
by these critters has an atmospheric or soil
gas, not SOM, source.
d. Atmospheric C is heavier. Atmospheric CO2
in the soil is 4.4 ‰ heavier than CO2
metabolized by decomposition (Wedin,
1995)
Prairie Ridge Soil Profile
Why we expect to see it ?
1.
2.
3.
4.
Suess effect
Soil carbon mixing
Preferential microbial decomposition
Kinetic fractionation
Prairie Ridge Soil Profile
3. Preferential microbial decomposition
– Lipids, lignin, cellulose - 13C depleted with
respect to whole plant
– Sugars, amino acids, hemi-cellulose, pectin
- 13C enriched
– Lipids and lignin are preferentially
accumulated in early decomposition
– Works against soil depth enrichment
– More C than N are lost from soil as SOM
decomposes due to internal recycling of N.
Prairie Ridge Soil Profile
Why we expect to see it ?
1.
2.
3.
4.
Suess effect
Soil carbon mixing
Preferential microbial decomposition
Kinetic fractionation
Prairie Ridge Soil Profile
4. Kinetic fractionation
– Microbes choose lighter C
– Microbial respiration of CO2 – 12C
preferentially respired
– Frequently use Rayleigh distillation analyses
(Wynn 2006)
– No direct evidence for this (Ehleringer 2000)
– Preferential preservation of 13C enriched
decomposition products of microbial
transformation
Prairie Ridge Soil Profile
4. Kinetic fractionation
13C
distillation during decomposing SOM. The gray lines
show the model with varying fractionation factors from 0.997
to 0.999. (Fig. 1D, J.G. Wynn, et al., 2006)
Prairie Ridge Soil Profile
4. Kinetic fractionation
Rayleigh distillation

  13Cf



1
 1000

1

F 
 13Ci    1  e t  1  

 1  
 1 


 1000
   e  1t  1  t  
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fraction of remaining soil organic matter (SOC) – approximated by the
calculated value of fSOC
13Cf isotopic composition of SOC when sampled
13Ci isotopic composition of input from biomass
α
fractionation factor between SOC and respired CO2
e
efficiency of microbial assimilation
t
fraction of assimilated carbon retained by a stabilized pool of SOM
F
Assumptions by Wynn etal
•
Open system
– All components decompose
– Contribute to soil-respired CO2 at same rate with depth
•
FSOC  fSOC
Prairie Ridge Soil Profile
Anthropogenic mixing (agriculture)
Various reasons that disturbed land might
not conform to nice regression curve in
Fig 1D (Wynn fig 9 )
A – natural
B – introduce C4 plants, enriched
in 13C
C – Cropping – removes new, low
13C material, leading to
surface enrichment
D – Erosion – removes upper layer,
moving the whole curve up
E – Reintroduce soil organic carbon
(better management practices)
– reverses the trends in B, C,
and D
Prairie Ridge Soil Profile
What we do see - results
δ13C
%C
%N
Mean
C:N
Mole
O- horizon
PRS-5 Bulk
-19.6
4.2
0.4
13.5
O- horizon
PRS-7 Bulk
-19.8
4.0
0.4
12.7
O- horizon
PRS-15 Bulk
-19.1
1.5
0.1
14.4
A- horizon (0-6 cm)
PRS-16 Bulk
-19.0
2.0
0.2
13.4
AP horizon (6-11 cm)
PRS-17 Bulk
-15.9
0.8
0.1
17.3
B horizon (11+ cm)
PRS-18 Bulk
-22.8
0.7
0.1
16.0
O- horizon
PRS-15 Plant Fragment
-21.3
36.8
1.4
31.4
A- horizon (0-6 cm)
PRS-16 Plant Fragment
-29.6
39.1
1.9
23.7
AP horizon (6-11 cm)
PRS-17 Plant Fragment
-27.0
18.7
0.6
34.1
B horizon (11+ cm)
PRS-18 Plant Fragment
O- horizon
PRS-15 Heavy Fraction
-19.0
1.5
0.1
15.4
A- horizon (0-6 cm)
PRS-16 Heavy Fraction
-18.7
1.2
0.1
14.7
AP horizon (6-11 cm)
PRS-17 Heavy Fraction
-15.6
0.7
0.0
17.7
B horizon (11+ cm)
PRS-18 Heavy Fraction
Prairie Ridge Soil Profile
What we do see - results
• 13C – increase 3‰ from surface to 8 cm
• C/N – increases to 8 cm, then decreases
• % C – decrease with depth
• % N – decrease with depth
Prairie Ridge Soil Profile
What we do see - 13C
Depth vs δ13C
δ13C
-26
-24
-22
-20
-18
-16
-14
Depth (cm)
0
5
10
15
20
Increase of 3‰ from surface to 8 cm (PRS 18 = anomaly)
Prairie Ridge Soil Profile
What we do see – C/N
Depth vs C/N
C/N
0
5
10
15
20
Depth (cm)
0
5
10
15
20
Increase of from surface to 8 cm then decreases
Prairie Ridge Soil Profile
What we do see – C%
Depth vs %C
%C
0
1
Depth (cm)
0
5
10
15
20
Decrease with depth
2
3
4
5
Prairie Ridge Soil Profile
What we do see – N%
Depth vs %N
%N
0
0.1
Depth (cm)
0
5
10
15
20
Decrease with depth
0.2
0.3
0.4
0.5
Prairie Ridge Soil Profile
Soil FTIR - Normalized
15
16
17
18
7
1
0.9
0.7
0.6
0.5
0.4
Absorbance
0.8
0.3
0.2
0.1
0
4000
3500
3000
2500
2000
1500
1000
500
0
Wavelength (cm-1)
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PRS 7 and PRS 15, both surface soils, have similar absorbencies
All soils have peak at wavelength 1032
All 5 spectra have similar peaks, though not necessarily similar absorbencies
In our bulk and heavy samples, are the mineral spectra masking the organics,
as in Poirier’s M-SOM?
Prairie Ridge Soil Profile
Soil FTIR - Normalized
16
17
18
7
1
Si-O
O-H
0.9
0.8
Aliphatic
C-H
0.7
C=C,C=O,
N-H
0.6
0.5
0.4
0.3
0.2
0.1
0
4000
3500
3000
2500
2000
1500
Wavelength (cm-1)
1000
500
0
Absorbance
15
Wave
number
Description
Possible functional groups
3700
sharp peak
O-H stretching region (3800-3400 for clay mineral)
3622
sharp peak
O-H stretching region (3800-3400 for clay mineral)
Bands due to Si-O-O-OH vibration.
3464
broad, strong intensity
O-H , N-H
Since it's broad and strong intensity, this
is due to O-H bond rather than NH bond.
2935
tiny broad
C-H (3150-2850)
The peak is below 3000, so it is an
aliphatic C-H vibration. Medium
intensity absortions at 1450 and
1375 cm-1 will indicate -CH3
bend. strectching.
1655
medium intensity
C=C (1680-1600 for aromatic and alkenes); C=O
vibrations (1680-1630 for amide), C=N (1690-1630)
and also of N-H bend (1650-1475)
Some soil literature assigned this to
C=O vibratios of carboxylates and
aromatic. Vibrations involving
most polar bonds, such as C=O
and O-H have the most intense IR
absorptions. This peak has
medium intensity and most likely
due to N-H bending.
1450 & 1400
weak
C-H, alkanes, -CH3 (bend, 1450 and 1375), -CH2 (bend, at
1465),
Most likely CH3 bending.
1099-1034
sharp & strongest peak
Si-O vibration of clay minerals
Consistent with FTIR spectra of soil in
the literarture
800
medium intensity, saw tooth
NH2 wagging and twisting, =C-H bend, alkenes
696
medium intensity, sharp
540
medium intensity, sharp
N-C=O bend for secondary amides
Intense absorption at 460-475
-2
corresponds to SiO3 vibration. In
the literarture, bands at
800,780,650,590,530 and 470 are
attributed to inorganic materials,
such as clay and quartz minerals.
472
strong intensity, sharp
C-C=O bend for secondary amides, SiO3
cm
Comments
-1
-2
Prairie Ridge Soil Profile
Problems with Methods
• Haphazard protocol on soil sampling at the
site (i.e. depth interval, mass of soil)
• Inconsistent sample preparation procedure
(i.e. different mass, subjective sorting)
• Poor implementation of IRMS protocols
(i.e. sample size, standard calibration)
• Insufficient samples for statistical accuracy
Prairie Ridge Soil Profile
Conclusions
• 13C – increase 3‰ to 8 cm as expected
• C/N – decreases in lower portion of profile
as expected
• % C – decrease with depth as expected
• % N – decrease with depth
Prairie Ridge Soil Profile
Conclusions
• Don’t have enough samples or rigorous
sampling method
– Many studies examine only the organic layer
– 5 cm only
• Minerals swamp the organics in our FTIR
results
– Look at methods to extract organics
Prairie Ridge Soil Profile
References
•
Antil, R.J., Gerzabek, M.H., Haberhauer, G. and Eder, G. 2005. Long-term
effects of cropped vs. fallow and fertilizer amendments on soil organic matter I.
Organic carbon. J.Plant Nutr.Soil Sci., 168, 108-116.
•
Ehleringer, James R., Buchmann, N., Flanagan, L.B., 2000 Carbon Isotope
Ratios in Belowground Carbon Cycle Processes, Ecological Applications, vol.
10, no. 2, p. 412-422
•
Gerzabek, M.H., Antil, R.S., Kogel-Knabner, I., Knicker, H., Kirchmann, H., and
G. Haberhauer. 2006. How are soil use and management reflected by soil
organic matter characteristics: a spectroscopic approach. European Journal of
Soil Science, 57, 485-494.
•
Gleixner, G. 2005. Stable isotope composition of soil organic matter. In Stable
isotopes and biosphere-atmosphere interactions. ed. Flanagan, L.B., E.J.
Ehleringer and D.E. Patake.
•
Haberhauer, G., Rafferty, B., Strebl, F. and Gerzabek, M.H. 1998. Comparison of
the composition of forest soil litter derived from three different sites at various
decompositional stages using FTIR spectroscopy. Geoderma 83, 331-342.
•
Johnson, M.D., Huang, W. and Weber Jr., W.J. 2001. A distributed reactivity
model for sorption by soils and sediments. 13. Simulated diagenesis of natural
sediment organic matter and its impact on sorption/desorption equilibria.
Environ. Sci. Technol. 35, 1680-1687.
Prairie Ridge Soil Profile
References
•
Melillo, Jerry M., Aber, J.D., Linkins, A.E., Ricca, A., Fry, B.,
Nadelhoffer, K.J., 1989, Carbon and nitrogen dynamics along the
decay continuum: Plant litter to soil organic matter, Plant and Soil, vol.
115, p. 189-198
•
Poirier, N., Sohi, S.P., Gaunt, J.L., Mahieu, N., Randall, E.W., Powlson,
D.S., Evershed, R.P., 2005, The chemical composition of measurable
soil organic matter pools, Organic Geochemistry, vol. 36, p. 1174-1189
•
Still, C.J., Berry, J.A., Ribas-Carbo, M. and Helliker, B.R. 2003, The
contribution of C3 and C4 plants to the carbon cycle of a tallgrass
prairie: an isotopic approach. Ocecologia 136:347-359.
•
Wedin, David A., Tieszen, L.L., Dewey, B., Pastor, J., 1995, Carbon
Isotope Dynamics During Grass Decomposition and Soil Organic
Matter Formation, Ecology, vol. 76, no. 5, p. 1383-1392
•
Wynn, J.G., Harden, J.W., Fries, T.L., 2006, Stable carbon isotope
depth profiles and soil organic carbon dynamics in the lower Mississippi
Basin, Geoderma, vol. 131, p. 89-109