Biochemical origin and refractory properties of humic acid extracted from maize plants: the contribution of lignin

Abstract

The soil organic carbon (SOC) pool is the largest terrestrial reservoir of carbon and plant residues play an important role in its maintenance. Up to 70-80% of SOC in arable soil is composed of humic substances (HS). In these soils post-harvested residues, left in arable soil after harvesting the crops, are the basic source of humus. Previous research indicated that maize plants residue contain a humic acid (HA) fraction possessing recalcitrant compounds that contributed to soil-HA fraction. This study presents updated results obtained using Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/ MS) to provide an indication of the contribution of the lignin to the soil HA. Results obtained indicated that the HAs from maize plants were mainly composed of lignin-derived moieties that were likely derived from the partial hydrolysis of p-coumaric and ferulic acid that are linked to lignin, polysaccharides or other biopolymers of the cell wall. Lignin composing the HAs derived from plants and incubated in soil was substantially preserved. Nevertheless the modification of the syringyl/guaiacyl ratio and the oxidation of the side-chains of lignin, suggested a turnover of lignin-derived molecules in soil-HA fraction. This fact indicated an involvement of the alkali insoluble fraction of maize plant residue (humin) in the soil-HA formation, up-dating our previous knowledge.

The influence of microbial communities, management, and soil texture on soil organic matter chemistry

“…We used Curie-point pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) to determine the molecular chemistry of SOM in whole soil samples (Hempfling and Schulten, 1990;White et al, 2004;Kaal et al, 2007;Adani et al, 2007) before and after the 232-d incubation using methods described in detail elsewhere (Neff et al, 2005;. Samples were pyrolyzed using a CuriePoint pyrolyzer (Pyromat, Brechbühler Scientific Analytical Solutions, Houston, USA) at 590°C in pyrofoils (Pyrofoil F590, Japan Analytical Company, Tokyo, Japan).…”

Nitrogen deposition effects on soil organic matter chemistry are linked to variation in enzymes, ecosystems and size fractions

“…We used pyrolysis gas chromatography/mass spectrometry to determine the molecular structure of organic matter (Hempfling and Schulten 1990;White et al 2004;Kaal et al 2007;Adani et al 2007) in whole soils and soil fractions using methods described in detail elsewhere (Neff et al 2005;Grandy et al 2007). Samples were pyrolyzed at 590°C in pyrofoils (Pyrofoil F590, Japan Analytical Company, Tokyo, Japan) using a Curie-Point pyrolyzer (Pyromat, Brechbühler Scientific Analytical Solutions, Houston, TX).…”

Humic Acid Formation in Artificial Soils Amended with Compost at Different Stages of Organic Matter Evolution

“…The unhydrolyzable recalcitrant fraction of HA, the U‐HA, is mainly composed of highly polymerized aromatic lignin‐derived molecules (acid‐resistant lignin) (Leary et al, 1986) and carbohydrates (Kniker and Lüdemam, 1995), probably forming an unhydrolyzable cross‐linked network (e.g., alkali soluble part of the cell wall of plant material) (Adani and Ricca, 2004; Adani et al, 2006c; Adani et al, 2007). The U‐HA was not stable during the composting processes.…”