Abstract
Thermally assisted Hydrolysis and Methylation (THM), and 2D-heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy were used to monitor the transformation of ramial chipped wood (RCW) from Gmelina arborea and Sarcocephalus latifolius, together with their organosolv lignins, following soil incubation in Benin (West Africa). Mesh litterbags containing RCW were buried in soils (10 cm depth) and were retrieved after 0, 6, 12 and 18 months of field incubation. Chemical analysis showed that total carbohydrate content decreased, while total lignin content increased as RCW decomposition progressed. Ash and mineral content of RCW increased significantly after 18 months of decomposition in soil. Significant N-enrichment of the RCW was determined following 18 months incubation in soils, reaching 2.6 and 1.9 times the initial N-content for G. arborea and S. latifolius. Results of THM showed that the S + G sum, corresponding to lignins, increased with RCW residence time in the soils, in contrast to the response of compounds derived from carbohydrates, the sum of which decreased. Remarkably, lignin interunit linkages, most notably β-O-4′ aryl ethers, β-β′ resinol, β-5′ phenylcoumaran and p-PCA p-coumarate, survived after 18 months in the soil, despite their gradual decrease over the duration of the experiment.
Highlights
Assisted Hydrolysis and Methylation (THM), and 2D-heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy were used to monitor the transformation of ramial chipped wood (RCW) from Gmelina arborea and Sarcocephalus latifolius, together with their organosolv lignins, following soil incubation in Benin (West Africa)
Further refinement of the technique has been achieved through the introduction of tetramethylammonium hydroxide (TMAH)-assisted pyrolysis known as Thermally assisted Hydrolysis and Methylation (THM)[30], which has proven to be useful for studying lignins and various other lignocellulosic materials in soils[31,32]
The important enrichment in nitrogen of the RCW following 18 months incubation in soils, reaching 2.6 and 1.9 times the initial N- content for G. arborea and S. latifolius, respectively, could be linked to microbial activity. This N- enrichment of the RCW indicates that their application could improve the release and availability of N in soils, which is fundamental to maintaining soil fertility and important for plant nutrition
Summary
Assisted Hydrolysis and Methylation (THM), and 2D-heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy were used to monitor the transformation of ramial chipped wood (RCW) from Gmelina arborea and Sarcocephalus latifolius, together with their organosolv lignins, following soil incubation in Benin (West Africa). RCW amendments have been shown to improve physicochemical and microbial properties of s oils[4,7,8], by increasing the organic carbon and nitrogen content, which is promoted by soil b iodiversity[7,9,10]. Félix and collaborators indicated that RCW amendment mitigates degradation of tropical s oils[6] Beyond these beneficial effects that are accrued to crops, detailed characterization and transformation of structural components occurring within RCW in soils and, that of lignins, has remained largely unexplored. The monitoring transformation was conducted at after 6, 12 and 18 months of soil incubation, using THM and 2D HSQC NMR spectroscopy techniques
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