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Generation and properties of organic colloids extracted by water from the organic horizon of a boreal forest soil

Andersson, Erika LU ; Meklesh, Viktoriia LU ; Gentile, Luigi LU ; Bhattacharya, Abhishek LU ; Stålbrand, Henrik LU ; Tunlid, Anders LU ; Persson, Per LU and Olsson, Ulf LU (2023) In Geoderma 432.
Abstract

Organic colloids are an important part of dissolved organic matter (DOM) yet many of their properties remain elusive. The main aims of this study were to assess how the colloidal properties of DOM extracted with water from an organic boreal soil horizon varied with the extraction protocol, and thereby provide insight into the nature of the DOM colloids and develop a mechanistic understanding of how the colloids were generated from the parent soil aggregates. This was accomplished by systematic variations of extraction temperature (4 °C–100 °C), time, mechanical agitation, and pH, together with a combination of chemical analyses, and light and X-ray scattering. Our results agreed with the previous identification of two main colloidal DOM... (More)

Organic colloids are an important part of dissolved organic matter (DOM) yet many of their properties remain elusive. The main aims of this study were to assess how the colloidal properties of DOM extracted with water from an organic boreal soil horizon varied with the extraction protocol, and thereby provide insight into the nature of the DOM colloids and develop a mechanistic understanding of how the colloids were generated from the parent soil aggregates. This was accomplished by systematic variations of extraction temperature (4 °C–100 °C), time, mechanical agitation, and pH, together with a combination of chemical analyses, and light and X-ray scattering. Our results agreed with the previous identification of two main colloidal DOM species, one fractal cluster and a second, smaller colloidal DOM species described as chains or coils. Fractal clusters completely dominated the colloidal DOM in extracts from our soil at room temperature and below. Colloidal coils only existed in DOM extracted above room temperature, and their amount increased significantly between 50 °C–100 °C. Moreover, the temperature variation indicated that the fractal clusters partly dissolved into colloidal coils at elevated temperatures. Mechanical agitation at 4 °C significantly increased the amount of DOM extracted, increasing the concentrations of both fractal clusters and low-molecular weight organic compounds. While the clusters were extracted from agitated and non-agitated soil suspensions, the low molecular weight organics were mainly released by agitation. Based on the experimental observations, we propose a conceptual model where parent soil aggregates contain the fractal clusters in mobile and occluded forms, and that the occluded clusters co-exist with occluded low molecular weight organics. These occluded forms may be released by mechanical forces, increasing pH and temperature. At higher temperatures, the soil aggregates and the fractal clusters start to break up, and subsequently individual colloidal coils, presumably carbohydrates, disperse in the water phase. The model explains the origin and properties of the fractal clusters that completely dominate the colloidal DOM extracted from our soil at room temperature and below.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
H NMR, Dissolved organic matter, Organic colloids, Small-angle X-ray scattering, Soil aggregates, Water-extractable organic matter
in
Geoderma
volume
432
article number
116386
publisher
Elsevier
external identifiers
  • scopus:85148546853
ISSN
0016-7061
DOI
10.1016/j.geoderma.2023.116386
language
English
LU publication?
yes
id
6c53e883-c98d-41ad-8173-858676f83af6
date added to LUP
2023-03-03 12:50:35
date last changed
2024-05-16 22:48:01
@article{6c53e883-c98d-41ad-8173-858676f83af6,
  abstract     = {{<p>Organic colloids are an important part of dissolved organic matter (DOM) yet many of their properties remain elusive. The main aims of this study were to assess how the colloidal properties of DOM extracted with water from an organic boreal soil horizon varied with the extraction protocol, and thereby provide insight into the nature of the DOM colloids and develop a mechanistic understanding of how the colloids were generated from the parent soil aggregates. This was accomplished by systematic variations of extraction temperature (4 °C–100 °C), time, mechanical agitation, and pH, together with a combination of chemical analyses, and light and X-ray scattering. Our results agreed with the previous identification of two main colloidal DOM species, one fractal cluster and a second, smaller colloidal DOM species described as chains or coils. Fractal clusters completely dominated the colloidal DOM in extracts from our soil at room temperature and below. Colloidal coils only existed in DOM extracted above room temperature, and their amount increased significantly between 50 °C–100 °C. Moreover, the temperature variation indicated that the fractal clusters partly dissolved into colloidal coils at elevated temperatures. Mechanical agitation at 4 °C significantly increased the amount of DOM extracted, increasing the concentrations of both fractal clusters and low-molecular weight organic compounds. While the clusters were extracted from agitated and non-agitated soil suspensions, the low molecular weight organics were mainly released by agitation. Based on the experimental observations, we propose a conceptual model where parent soil aggregates contain the fractal clusters in mobile and occluded forms, and that the occluded clusters co-exist with occluded low molecular weight organics. These occluded forms may be released by mechanical forces, increasing pH and temperature. At higher temperatures, the soil aggregates and the fractal clusters start to break up, and subsequently individual colloidal coils, presumably carbohydrates, disperse in the water phase. The model explains the origin and properties of the fractal clusters that completely dominate the colloidal DOM extracted from our soil at room temperature and below.</p>}},
  author       = {{Andersson, Erika and Meklesh, Viktoriia and Gentile, Luigi and Bhattacharya, Abhishek and Stålbrand, Henrik and Tunlid, Anders and Persson, Per and Olsson, Ulf}},
  issn         = {{0016-7061}},
  keywords     = {{H NMR; Dissolved organic matter; Organic colloids; Small-angle X-ray scattering; Soil aggregates; Water-extractable organic matter}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Geoderma}},
  title        = {{Generation and properties of organic colloids extracted by water from the organic horizon of a boreal forest soil}},
  url          = {{http://dx.doi.org/10.1016/j.geoderma.2023.116386}},
  doi          = {{10.1016/j.geoderma.2023.116386}},
  volume       = {{432}},
  year         = {{2023}},
}