Thirunavukkarasu, Aswin
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
Doctoral thesis2025Open access
Lignin degradation dynamics in boreal forest soils : influence of chemical composition and nitrogen on lignin degradation
Thirunavukkarasu, Aswin
Abstract
Soil organic matter (SOM) is a critical component of the global carbon cycle, storing more organic carbon than the atmosphere and global vegetation combined. Plant-derived organic inputs are the primary carbon source for SOM formation, which arises through the microbial decomposition processes. Among these inputs, lignin, a complex biopolymer abundant in plant biomass, is often considered a key contributor to SOM due to its resistance to degradation. However, the influence of lignin’s moieties on SOM stability remains poorly understood. In this thesis, I have investigated the lignin decomposition and its contribution to SOM formation using Aspen wood (Populus tremula) genotypes with varying lignin content and composition as model substrates. Laboratory incubations (Paper I-II) and field experiments (Paper III), coupled with advanced two-dimensional Nuclear Magnetic Resonance (2D NMR) spectroscopy, were systematically employed to characterize the degradation of lignin moieties. In Paper I, lignin content did not affect overall decomposition, with approximately 60% mass loss across substrates. While the lignin decomposed at a similar rate to carbohydrates, oxidized syringyl units exhibited resistance to degradation compared to other lignin monomers. Paper II demonstrated that nitrogen addition altered fungal community structure, suppressing the ligninolytic fungus Renatobasidium notabile and increasing fungal diversity. This shift enhanced the degradation of more resistant lignin moieties, such as guaiacyl units and their linkages. Paper III demonstrated that lignin composition, rather than content, is crucial in early-stage decomposition across pine and spruce forest stands. Long-term nitrogen fertilization enhanced mass loss but selectively degraded syringyl units and their linkages. These findings highlight that lignin composition and microbial community dynamics regulate decomposition rather than lignin content alone. This emphasizes the need to focus on microbial and compositional factors to better understand SOM dynamics and carbon cycling.
Keywords
SOM; Lignin degradation; 2D NMR; Early-stage decomposition
Published in
Acta Universitatis Agriculturae Sueciae
2025, number: 2025:3
Publisher: Swedish University of Agricultural Sciences
SLU Authors
UKÄ Subject classification
Forest Science
Soil Science
Publication identifier
- DOI: https://doi.org/10.54612/a.3fhgnfah04
- ISBN: 978-91-8046-438-3
- eISBN: 978-91-8046-488-8
Permanent link to this page (URI)
https://res.slu.se/id/publ/132943