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Soils 2017, 1(1), 4; doi:10.3390/soils1010004

Molecular and Microscopic Insights into the Formation of Soil Organic Matter in a Red Pine Rhizosphere

1
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA
2
Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA
3
Department of Soil and Water Systems, University of Idaho, Moscow, ID 83844, USA
4
School of Environment and Energy, South China University of Technology, Guangdong 510006, China
5
USDA-ARS, Wheat Health, Genetics and Quality Research Unit, Washington State University, Pullman, WA 99164, USA
6
Department of Crop & Soil Sciences, Washington State University, Pullman, WA 99164, USA
7
School of the Environment, Washington State University, Pullman, WA 99164, USA
*
Author to whom correspondence should be addressed.
Received: 15 June 2017 / Revised: 23 August 2017 / Accepted: 24 August 2017 / Published: 26 August 2017
(This article belongs to the Special Issue Rhizosphere Processes)
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Abstract

Microbially-derived carbon inputs to soils play an important role in forming soil organic matter (SOM), but detailed knowledge of basic mechanisms of carbon (C) cycling, such as stabilization of organic C compounds originating from rhizodeposition, is scarce. This study aimed to investigate the stability of rhizosphere-produced carbon components in a model laboratory mesocosm of Pinus resinosa grown in a designed mineral soil mix with limited nutrients. We utilized a suite of advanced imaging and molecular techniques to obtain a molecular-level identification of newly-formed SOM compounds, and considered implications regarding their degree of long-term persistence. The microbes in this controlled, nutrient-limited system, without pre-existing organic matter, produced extracellular polymeric substances that formed associations with nutrient-bearing minerals and contributed to the microbial mineral weathering process. Electron microscopy revealed unique ultrastructural residual signatures of biogenic C compounds, and the increased presence of an amorphous organic phase associated with the mineral phase was evidenced by X-ray diffraction. These findings provide insight into the formation of SOM products in ecosystems, and show that the plant- and microbially-derived material associated with mineral matrices may be important components in current soil carbon models. View Full-Text
Keywords: rhizosphere; soil organic matter; soil microbiome; 16S sequencing; mineral weathering; Fourier-transform ion cyclotron resonance mass spectrometry; electron microscopy; mineral-organic associations; carbon cycle rhizosphere; soil organic matter; soil microbiome; 16S sequencing; mineral weathering; Fourier-transform ion cyclotron resonance mass spectrometry; electron microscopy; mineral-organic associations; carbon cycle
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Dohnalkova, A.C.; Tfaily, M.M.; Smith, A.P.; Chu, R.K.; Crump, A.R.; Brislawn, C.J.; Varga, T.; Shi, Z.; Thomashow, L.S.; Harsh, J.B.; Keller, C.K. Molecular and Microscopic Insights into the Formation of Soil Organic Matter in a Red Pine Rhizosphere. Soils 2017, 1, 4.

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