Resolving the influence of lignin on soil organic matter decomposition with mechanistic models and continental-scale data

Confidence in model estimates of soil CO flux depends on assumptions regarding fundamental mechanisms that control the decomposition of litter and soil organic carbon (SOC). Multiple hypotheses have been proposed to explain the role of lignin, an abundant and complex biopolymer that may limit decomp...

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Bibliographic Details
Published in:Global change biology 2023-10, Vol.29 (20), p.5968-5980
Main Authors: Yi, Bo, Lu, Chaoqun, Huang, Wenjuan, Yu, Wenjuan, Yang, Jihoon, Howe, Adina, Weintraub-Leff, Samantha R, Hall, Steven J
Format: Article
Language:English
Subjects:
Biopolymers
Carbon dioxide
Community composition
Decomposition
Fungi
Heavy metals
Hypotheses
Lignin
Litter
Manganese
Metabolism
Ordination
Organic carbon
Organic matter
Organic soils
Soil
Soil chemistry
Soil dynamics
Soil organic matter
Soil pH
Soils
Substrates
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Summary:Confidence in model estimates of soil CO flux depends on assumptions regarding fundamental mechanisms that control the decomposition of litter and soil organic carbon (SOC). Multiple hypotheses have been proposed to explain the role of lignin, an abundant and complex biopolymer that may limit decomposition. We tested competing mechanisms using data-model fusion with modified versions of the CN-SIM model and a 571-day laboratory incubation dataset where decomposition of litter, lignin, and SOC was measured across 80 soil samples from the National Ecological Observatory Network. We found that lignin decomposition consistently decreased over time in 65 samples, whereas in the other 15 samples, lignin decomposition subsequently increased. These "lagged-peak" samples can be predicted by low soil pH, high extractable Mn, and fungal community composition as measured by ITS PC2 (the second principal component of an ordination of fungal ITS amplicon sequences). The highest-performing model incorporated soil biogeochemical factors and daily dynamics of substrate availability (labile bulk litter:lignin) that jointly represented two hypotheses (C substrate limitation and co-metabolism) previously thought to influence lignin decomposition. In contrast, models representing either hypothesis alone were biased and underestimated cumulative decomposition. Our findings reconcile competing hypotheses of lignin decomposition and suggest the need to precisely represent the role of lignin and consider soil metal and fungal characteristics to accurately estimate decomposition in Earth-system models.
ISSN:1354-1013
1365-2486
DOI:10.1111/gcb.16875