biogeochemical investigation at prairie ridge, nc

Biogeochemical Investigation at Prairie Ridge, NC

Prairie Ridge Soil Profile

Amy Keyworth

Jovi Saquing

November 2006

Outline

• What we expect to see… and why?

• What we do see… and how come?

• What can we conclude?


Soil Profile DescriptionLitter (undecomposed)

Organic layer, fermented

Organic layer, humified

Mineral layer with organic carbon and leached minerals

Mineral layer with precipitation of oxides/hydroxides and/or carbonUnaltered 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.


Organic CompoundsCellulose

Monosaccharide (e.g. glucose)

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.


Intermediates

(e.g. acetic acid)

CO2

Amino acid

Ammonium

Nitrites/Nitrates

N2, N2O

Lignin monomers

ProteinLigninLipid

Alkanes

Humic Substances

Organic Compounds


Cellulose

Lignin

Lignin Monomers

Alkanes

What we expect to see..

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


Carbon isotopic composition profiles. Undisturbed site Disturbed (agricultural) site (Fig 2 middle, J.G. Wynn, et al., 2006)

What we expect to see - 13C


Valley Lower Slope Upper Slope Ridge Top

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)

What we expect to see – [C]


What we expect to see – C/N

Source: C/N of soil organic matter from different depth intervals (Gleixner, 2005)


Why do we expect to see it ?

1. Suess effect

2. Soil carbon mixing

3. Preferential microbial decomposition

4. Kinetic fractionation


Why we expect to see it ?

1. Suess effect





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 ‰


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)



1. Suess effect






Mixing of leaf litter-derived SOC and root-derived SOC. (Fig. 1B, J.G. Wynn, et al., 2006)


a. Surface litter (depleted) vs. root derived (enriched) SOM


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)


b. Variable biomass inputs (C3 vs. C4 plants)


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)



1. Suess effect






– 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.



1. Suess effect






– 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



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)



Assumptions by Wynn etal• Open system

– All components decompose– Contribute to soil-respired CO2 at same rate with depth

• FSOC fSOC

11111

1

1100013

1100013

tteteCi

Cf

F

• F 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


Rayleigh distillation

Anthropogenic mixing (agriculture)

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


Various reasons that disturbed land might not conform to nice regression curve in Fig 1D (Wynn fig 9 )

What we do see - results


δ13C % C % N C:N

Mean Mole

O- horizon PRS-5 Bulk -19.6 4.2 0.4 13.5



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

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


What we do see - 13C

Increase of 3‰ from surface to 8 cm (PRS 18 = anomaly)


Depth vs δ13C

0

5

10

15

20

-26 -24 -22 -20 -18 -16 -14

δ13C

Dep

th (c

m)

What we do see – C/N

Increase of from surface to 8 cm then decreases


Depth vs C/N

0

5

10

15

20

0 5 10 15 20

C/N

Dep

th (c

m)

What we do see – C%

Decrease with depth


Depth vs %C

0

5

10

15

20

0 1 2 3 4 5

%C

Dep

th (c

m)

What we do see – N%

Decrease with depth


Depth vs %N

0

5

10

15

20

0 0.1 0.2 0.3 0.4 0.5

%N

Dep

th (c

m)


• 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?

Soil FTIR - Normalized

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

05001000150020002500300035004000

Wavelength (cm-1)

Ab

so

rban

ce

15 16 17 18 7


Soil FTIR - Normalized

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

05001000150020002500300035004000

Wavelength (cm-1)

Ab

sorb

ance

15 16 17 18 7

Aliphatic C-H

O-H

C=C,C=O, N-H

Si-O

Wavenumber Description Possible functional groups Comments

cm-1

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 N-H 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 Intense absorption at 460-475 corresponds to SiO3

-2 vibration. In

the literarture, bands at 800,780,650,590,530 and 470 are attributed to inorganic materials, such as clay and quartz minerals.

696 medium intensity, sharp

540 medium intensity, sharp N-C=O bend for secondary amides

472 strong intensity, sharp C-C=O bend for secondary amides, SiO3-2

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


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


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


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.


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


biogeochemical investigation at prairie ridge, nc

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