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Abstract Fine root litter is a primary source of soil organic matter (SOM), which is a globally important pool of C that is responsive to climate change. We previously established that ~20 years of experimental nitrogen (N) deposition has slowed fine root decay and increased the storage of soil carbon (C; +18%) across a widespread northern hardwood forest ecosystem. However, the microbial mechanisms that have directly slowed fine root decay are unknown. Here, we show that experimental N deposition has decreased the relative abundance of Agaricales fungi (−31%) and increased that of partially ligninolytic Actinobacteria (+24%) on decaying fine roots. Moreover, experimental N deposition has increased the relative abundance of lignin‐derived compounds residing in SOM (+53%), and this biochemical response is significantly related to shifts in both fungal and bacterial community composition. Specifically, the accumulation of lignin‐derived compounds in SOM is negatively related to the relative abundance of ligninolyticMycenaandKuehneromycesfungi, and positively related to Microbacteriaceae. Our findings suggest that by altering the composition of microbial communities on decaying fine roots such that their capacity for lignin degradation is reduced, experimental N deposition has slowed fine root litter decay, and increased the contribution of lignin‐derived compounds from fine roots to SOM. The microbial responses we observed may explain widespread findings that anthropogenic N deposition increases soil C storage in terrestrial ecosystems. More broadly, our findings directly link composition to function in soil microbial communities, and implicate compositional shifts in mediating biogeochemical processes of global significance.
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Characterizing natural variability of lignin abundance and composition in fine roots across temperate trees: a comparison of analytical methods
Summary Lignin is an important root chemical component that is widely used in biogeochemical models to predict root decomposition. Across ecological studies, lignin abundance has been characterized using both proximate and lignin‐specific methods, without much understanding of their comparability. This uncertainty in estimating lignin limits our ability to comprehend the mechanisms regulating root decomposition and to integrate lignin data for large‐scale syntheses.We compared five methods of estimating lignin abundance and composition in fine roots across 34 phylogenetically diverse tree species. We also assessed the feasibility of high‐throughput techniques for fast‐screening of root lignin.Although acid‐insoluble fraction (AIF) has been used to infer root lignin and decomposition, AIF‐defined lignin content was disconnected from the lignin abundance estimated by techniques that specifically measure lignin‐derived monomers. While lignin‐specific techniques indicated lignin contents of 2–10% (w/w) in roots, AIF‐defined lignin contents werec.5–10‐fold higher, and their interspecific variation was found to be largely unrelated to that determined using lignin‐specific techniques. High‐throughput pyrolysis–gas chromatography–mass spectrometry, when combined with quantitative modeling, accurately predicted lignin abundance and composition, highlighting its feasibility for quicker assessment of lignin in roots.We demonstrate that AIF should be interpreted separately from lignin in fine roots as its abundance is unrelated to that of lignin polymers. This study provides the basis for informed decision‐making with respect to lignin methodology in ecology.
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- Award ID(s):
- 1754679
- PAR ID:
- 10377094
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 236
- Issue:
- 6
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 2358-2373
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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