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. 2015 Jun 10:5:11214.
doi: 10.1038/srep11214.

Selective stabilization of aliphatic organic carbon by iron oxide

Dinesh Adhikari  1 , Yu Yang  1
Affiliations

Selective stabilization of aliphatic organic carbon by iron oxide

Dinesh Adhikari et al. Sci Rep. .

Abstract

Stabilization of organic matter in soil is important for natural ecosystem to sequestrate carbon and mitigate greenhouse gas emission. It is largely unknown what factors govern the preservation of organic carbon in soil, casting shadow on predicting the response of soil to climate change. Iron oxide was suggested as an important mineral preserving soil organic carbon. However, ferric minerals are subject to reduction, potentially releasing iron and decreasing the stability of iron-bound organic carbon. Information about the stability of iron-bound organic carbon in the redox reaction is limited. Herein, we investigated the sorptive interactions of organic matter with hematite and reductive release of hematite-bound organic matter. Impacts of organic matter composition and conformation on its sorption by hematite and release during the reduction reaction were analyzed. We found that hematite-bound aliphatic carbon was more resistant to reduction release, although hematite preferred to sorb more aromatic carbon. Resistance to reductive release represents a new mechanism that aliphatic soil organic matter was stabilized by association with iron oxide. Selective stabilization of aliphatic over aromatic carbon can greatly contribute to the widely observed accumulation of aliphatic carbon in soil, which cannot be explained by sorptive interactions between minerals and organic matter.

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Figures

Figure 1
Figure 1. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) for original organic matter (HA1ck, HA2ck and HA3ck) and hematite-bound samples (HA1s, HA2s and HA3s) with the highest organic carbon content.
Figure 2
Figure 2
(A–C) Surface chemical compositional analysis for hematite-organic matter complex, determined by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). (D) Comparison of surface carbon composition for samples with highest and lowest bulky carbon content, based on EDS analysis. HA1-H, HA2-H, and HA3-H represent samples with highest carbon content, and HA1-L, HA2-L, and HA3-L stand for those with lowest carbon content. (E–F) Transmission electron microscope (TEM) observations for particles of HA3-hematite complex (E) and the EDS-based elemental distribution (F), with blue for iron, green for oxygen, and red for carbon.
Figure 3
Figure 3. δ13C for hematite-bound organic carbon and the residual fractions after reduction-release experiments.
See this image and copyright information in PMC

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