Formation Mechanisms of Humic Substances in the Environment

Huang, P. M.; Hardie, Ailsa G.

doi:10.1002/9780470494950.ch2

Cited by 28 publications

(22 citation statements)

References 228 publications

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“…[79] This assumption has led to the Humic Polymer Model of soil organic matter, [80] in which the component molecules are depicted as large, covalently bonded ('humic') polymers with unique chemical structures that are different from those of the starting materials. Consequently, the Humic Polymer Model implies inherent resistance of so-called humic substances to decomposition.…”

Section: Complexity and Recalcitrance As The Results Of Humificationmentioning

confidence: 99%

“…Consequently, the Humic Polymer Model implies inherent resistance of so-called humic substances to decomposition. [81] This model forms the basis of a huge literature (see reviews by Haider et al, [82] Stott and Martin, [51] Huang and Hardie [79] ) on methods to synthesise model humic substances like the ones that Haider and Martin [65] used to demonstrate how carbon in polymers decomposes more slowly than carbon in monomers (Fig. 1).…”

Section: Complexity and Recalcitrance As The Results Of Humificationmentioning

confidence: 99%

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What is recalcitrant soil organic matter?

Kleber¹

2010

Environ. Chem.

341

206

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Environmental context. On a global scale, soils store more carbon than plants or the atmosphere. The cycling of this vast reservoir of reduced carbon is closely tied to variations in environmental conditions, but robust predictions of climate-carbon cycle feedbacks are hampered by a lack of mechanistic knowledge regarding the sensitivity of organic matter decomposition to rising temperatures. This text provides a critical discussion of the practice to conceptualise parts of soil organic matter as intrinsically resistant to decomposition or 'recalcitrant'.Abstract. The understanding that some natural organic molecules can resist microbial decomposition because of certain molecular properties forms the basis of the biogeochemical paradigm of 'intrinsic recalcitrance'. In this concept paper I argue that recalcitrance is an indeterminate abstraction whose semantic vagueness encumbers research on terrestrial carbon cycling. Consequently, it appears to be advantageous to view the perceived 'inherent resistance' to decomposition of some forms of organic matter not as a material property, but as a logistical problem constrained by (i) microbial ecology; (ii) enzyme kinetics; (iii) environmental drivers; and (iv) matrix protection. A consequence of this view would be that the frequently observed temperature sensitivity of the decomposition of organic matter must result from factors other than intrinsic molecular recalcitrance.

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Section: Complexity and Recalcitrance As The Results Of Humificationmentioning

confidence: 99%

Section: Complexity and Recalcitrance As The Results Of Humificationmentioning

confidence: 99%

What is recalcitrant soil organic matter?

Kleber¹

2010

Environ. Chem.

341

206

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“…Pyrolysis products were reported for lysine (pyridine) (Sorge 1995), hydroxyproline, proline (1H-pyrrole, 1-methyl-) (Nguyen et al 2003), hydroxyproline (1H-pyrrole, 2,5-dimethyl-) (Chiavari and Galletti 1992), alanine, tyrosine (pyridine) (Chiavari and Galletti 1992;Nguyen et al 2003), threonine (pyridine, 5-ethenyl-2-methyl-) (Sorge et al 1993), and phenylalanine (quinoline) (Patterson et al 1973) (pyrolysis product in parenthesis). However, such a formation of N-heterocyclic compounds as pyrolysis products does not necessarily exclude their genuine occurrence in soils (Leinweber and Schulten 1998), especially if we consider recently described abiotic pathways for the formation of heterocyclic N (Jokic et al 2004a;Huang and Hardie 2009) and the impact of vegetation fires on soils (Knicker 2009).…”

Section: Resultsmentioning

confidence: 99%

Nitrogen speciation in fine and coarse clay fractions of a Cryoboroll - new evidence from pyrolysis-mass spectrometry and nitrogen K-edge XANES

Leinweber

Jandl²,

Eckhardt³

et al. 2010

Can. J. Soil. Sci.

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Nitrogen speciation in fine and coarse clay fractions of a Cryoboroll Á new evidence from pyrolysis-mass spectrometry and nitrogen K-edge XANES. Can. J. Soil Sci. 90: 309Á318. Soil clay fractions are usually enriched in nitrogen (N), but the chemical identity of this N is largely unknown. Therefore, we investigated organic N in fine and coarse clay of a clay-rich Cryoboroll by Curie-point pyrolysis-gas chromatography/mass spectrometry (Cp Py-GC/MS), Pyrolysis-field ionization mass spectroscopy (Py-FIMS) and synchrotron-based nitrogen K-edge X-ray absorption near edge structure (N-XANES) spectroscopy. The Cp Py-GC-MS revealed 30 structurally different N-containing compounds, such as substituted pyridines, pyrroles; pyrazines, pyrazoles, imidazoles, quinolines, side-chain N-containing benzenes, and single compounds of substituted benzotriazole, purine and indole. These accounted for about 10% of peak area in the Py-GC chromatograms. The Py-FIMS and N-XANES spectra indicated interlayer-NH 4 ' and revealed pyridinic and nitrilic N compounds, but disagreed in the proportions of pyrroles. All three complementary methods confirmed to different extents previous wet-chemical data on N-fractions in these samples, and provided new evidence for about 30 to 40% non-proteinaceous N as major constituent of the so-called ''unknown organic N'' in soil.

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“…Soluble phenolic compounds (PCs) comprise a characteristic and highly reactive part of soil organic matter (SOM). Their transformations in soil include complexation with metal ions (Andjelkovic et al, ), adsorption on to clays and oxyhydroxides (Moreau, Colette‐Maatouk, Gareil, & Reiller, ; Zavarzina, Ermolin, Demin, & Fedotov, ) and polymerization in the presence of oxidative catalysts (Huang & Hardie, ; Zavarzina, ). As a result, PCs have a profound effect on soil mineral and organic matrices, participating in element mobilization and mineral weathering and in formation of organic–mineral compounds.…”

Section: Introductionmentioning

confidence: 99%

Water‐soluble phenolic metabolites in lichens and their potential role in soil organic matter formation at the pre‐vascular stage

Заварзина

Nikolaeva

Демин

et al. 2019

European J Soil Science

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Soil organic matter (SOM) is the largest reservoir of organic carbon in the biosphere. However, little is known about the processes of its formation at the pre‐vascular stage. Lichens are among the pioneer colonizers on mineral substrates and are possible early land flora. This study is the first report on the identification and quantification of water‐soluble phenolic compounds (PCs), potential precursors of humic substances, in epigeyic lichens from two systematic groups. Results show (Folin–Denis assay) that cyanobiont‐containing lichens (order Peltigerales) possess three to five times more total soluble PCs than Lecanoralean lichens (Cladonia, Cetraria spp.) and mosses. Soluble PCs in lichens occur in the conjugated form. Alkali‐hydrolysable compounds (esters) predominate over acid‐hydrolysable compounds (glycosides). Phenolic complexes with N‐containing compounds or reducing sugars, or both, have been identified by thin layer chromatography (TLC). Benzoic acid derivatives were most common among PCs, detected in lichens by reversed‐phase high‐pressure liquid chromatography (RP‐HPLC). Phenolic acids occur in the order (μg 100 g−1): p‐hydroxybenzoic acid (327–1,007) > syringic acid (87–361) > salycilic acid (135–210) > vanillic acid (12–19) (Peltigeralean lichens); salicylic acid (53–102) > p‐hydroxybenzoic acid (45–54) > caffeic acid (29) > syringic acid (18) > vanillic acid (9–13) (Lecanoralean lichens). Protocatechuic, caffeic and p‐coumaric acids were rare; ferulic acid was not detected. Syringyl and vanillyl aldehydes and ketones occur in much larger amounts than acids. Methoxy‐substituted and ortho‐substituted phenols, detected in lichens, are known for their high reactivity in soils under lignified vegetation, suggesting their important roles in SOM formation under a cryptogam cover. Highlights Phenolic composition of SOM and humification processes at pre‐vascular stage are largely overlooked Soluble phenolic acids, aldehydes and ketones are quantified in lichens for the first time Lichens are depleted in phenylpropanoids and enriched in syringyl structures and monophenols Lichen‐derived phenolic compounds are potential precursors of humic substances under cryptogam cover

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Formation Mechanisms of Humic Substances in the Environment

Cited by 28 publications

References 228 publications

What is recalcitrant soil organic matter?

What is recalcitrant soil organic matter?

Nitrogen speciation in fine and coarse clay fractions of a Cryoboroll - new evidence from pyrolysis-mass spectrometry and nitrogen K-edge XANES

Water‐soluble phenolic metabolites in lichens and their potential role in soil organic matter formation at the pre‐vascular stage

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