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Title: Organic Matter Stabilization in Soil Microaggregates: Implications from Spatial Heterogeneity of Organic Carbon Contents and Carbon Forms

Abstract

This study investigates the spatial distribution of organic carbon (C) in free stable microaggregates (20-250 {mu}m; not encapsulated within macroaggregates) from one Inceptisol and two Oxisols in relation to current theories of the mechanisms of their formation. Two-dimensional micro- and nano-scale observations using synchrotron-based Fourier-transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy yielded maps of the distribution of C amounts and chemical forms. Carbon deposits were unevenly distributed within microaggregates and did not show any discernable gradients between interior and exterior of aggregates. Rather, C deposits appeared to be patchy within the microaggregates. In contrast to the random location of C, there were micron-scale patterns in the spatial distribution of aliphatic C-H (2922 cm-1), aromatic C=C and N-H (1589 cm-1) and polysaccharide C-O (1035 cm-1). Aliphatic C forms and the ratio of aliphatic C/aromatic C were positively correlated (r 2 of 0.66-0.75 and 0.27-0.59, respectively) to the amount of O-H on kaolinite surfaces (3695 cm-1), pointing at a strong role for organo-mineral interactions in C stabilization within microaggregates and at a possible role for molecules containing aliphatic C-H groups in such interactions. This empirical relationship was supported by nanometer-scale observations using NEXAFS which showed that the organicmore » matter in coatings on mineral surfaces had more aliphatic and carboxylic C with spectral characteristics resembling microbial metabolites than the organic matter of the entire microaggregate. Our observations thus support models of C stabilization in which the initially dominant process is adsorption of organics on mineral surfaces rather than occlusion of organic debris by adhering clay particles.« less

Authors:
; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
959639
Report Number(s):
BNL-82625-2009-JA
TRN: US201016%%783
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biogeochemistry; Journal Volume: 85
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; ABSORPTION; ADSORPTION; AROMATICS; CARBON; CLAYS; COATINGS; DISTRIBUTION; FINE STRUCTURE; KAOLINITE; METABOLITES; ORGANIC MATTER; POLYSACCHARIDES; SOILS; SPATIAL DISTRIBUTION; SPECTROSCOPY; STABILIZATION; national synchrotron light source

Citation Formats

Lehmann,J., Kinyangi, J., and Solomon, D.. Organic Matter Stabilization in Soil Microaggregates: Implications from Spatial Heterogeneity of Organic Carbon Contents and Carbon Forms. United States: N. p., 2007. Web. doi:10.1007/s10533-007-9105-3.
Lehmann,J., Kinyangi, J., & Solomon, D.. Organic Matter Stabilization in Soil Microaggregates: Implications from Spatial Heterogeneity of Organic Carbon Contents and Carbon Forms. United States. doi:10.1007/s10533-007-9105-3.
Lehmann,J., Kinyangi, J., and Solomon, D.. Mon . "Organic Matter Stabilization in Soil Microaggregates: Implications from Spatial Heterogeneity of Organic Carbon Contents and Carbon Forms". United States. doi:10.1007/s10533-007-9105-3.
@article{osti_959639,
title = {Organic Matter Stabilization in Soil Microaggregates: Implications from Spatial Heterogeneity of Organic Carbon Contents and Carbon Forms},
author = {Lehmann,J. and Kinyangi, J. and Solomon, D.},
abstractNote = {This study investigates the spatial distribution of organic carbon (C) in free stable microaggregates (20-250 {mu}m; not encapsulated within macroaggregates) from one Inceptisol and two Oxisols in relation to current theories of the mechanisms of their formation. Two-dimensional micro- and nano-scale observations using synchrotron-based Fourier-transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy yielded maps of the distribution of C amounts and chemical forms. Carbon deposits were unevenly distributed within microaggregates and did not show any discernable gradients between interior and exterior of aggregates. Rather, C deposits appeared to be patchy within the microaggregates. In contrast to the random location of C, there were micron-scale patterns in the spatial distribution of aliphatic C-H (2922 cm-1), aromatic C=C and N-H (1589 cm-1) and polysaccharide C-O (1035 cm-1). Aliphatic C forms and the ratio of aliphatic C/aromatic C were positively correlated (r 2 of 0.66-0.75 and 0.27-0.59, respectively) to the amount of O-H on kaolinite surfaces (3695 cm-1), pointing at a strong role for organo-mineral interactions in C stabilization within microaggregates and at a possible role for molecules containing aliphatic C-H groups in such interactions. This empirical relationship was supported by nanometer-scale observations using NEXAFS which showed that the organic matter in coatings on mineral surfaces had more aliphatic and carboxylic C with spectral characteristics resembling microbial metabolites than the organic matter of the entire microaggregate. Our observations thus support models of C stabilization in which the initially dominant process is adsorption of organics on mineral surfaces rather than occlusion of organic debris by adhering clay particles.},
doi = {10.1007/s10533-007-9105-3},
journal = {Biogeochemistry},
number = ,
volume = 85,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}