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Topsoil organic matter build‐up in glacier forelands around the world

Norine Khedim 1 Lauric Cecillon 2, 3 Jérôme Poulenard 1 Pierre Barré 3 François Baudin 4 Silvio Marta 5 Antoine Rabatel 6 Cédric Dentant 7 Sophie Cauvy‐fraunié 8 Fabien Anthelme 9 Ludovic Gielly 10 Roberto Ambrosini 5 Andrea Franzetti 5 Roberto Sergio Azzoni 5 Marco Stefano Caccianiga 5 Chiara Compostella 5 John Clague 11 Levan Tielidze 12 Erwan Messager 1 Philippe Choler 10 Gentile Francesco Ficetola 10, 5
1 EDYTEM - Environnements, Dynamiques et Territoires de la Montagne
2 ECODIV - Étude et compréhension de la biodiversité
3 LGE - Laboratoire de géologie de l'ENS
4 iSTeP - Institut des Sciences de la Terre de Paris
5 University of Milan
6 IGE - Institut des Géosciences de l’Environnement
7 Parc national des Ecrins
8 UR Riverly - RiverLy
9 UMR AMAP - Botanique et Modélisation de l'Architecture des Plantes et des Végétations
10 LECA - Laboratoire d'Ecologie Alpine
11 SFU.ca - Simon Fraser University
12 Victoria University of Wellington
Abstract : Since the last glacial maximum, soil formation related to ice-cover shrinkage has been one major sink of carbon accumulating as soil organic matter (SOM), a phenomenon accelerated by the ongoing global warming. In recently deglacierized forelands, processes of SOM accumulation, including those that control carbon and nitrogen sequestration rates and biogeochemical stability of newly sequestered carbon, remain poorly understood. Here, we investigate the build-up of SOM during the initial stages (up to 410 years) of topsoil development in 10 glacier forelands distributed on four continents. We test whether the net accumulation of SOM on glacier forelands (i) depends on the time since deglacierization and local climatic conditions (temperature and precipitation); (ii) is accompanied by a decrease in its stability and (iii) is mostly due to an increasing contribution of organic matter from plant origin. We measured total SOM concentration (carbon, nitrogen), its relative hydrogen/oxygen enrichment, stable isotopic (C-13, N-15) and carbon functional groups (C-H, C=O, C=C) compositions, and its distribution in carbon pools of different thermal stability. We show that SOM content increases with time and is faster on forelands experiencing warmer climates. The build-up of SOM pools shows consistent trends across the studied soil chronosequences. During the first decades of soil development, the low amount of SOM is dominated by a thermally stable carbon pool with a small and highly thermolabile pool. The stability of SOM decreases with soil age at all sites, indicating that SOM storage is dominated by the accumulation of labile SOM during the first centuries of soil development, and suggesting plant carbon inputs to soil (SOM depleted in nitrogen, enriched in hydrogen and in aromatic carbon). Our findings highlight the potential vulnerability of SOM stocks from proglacial areas to decomposition and suggest that their durability largely depends on the relative contribution of carbon inputs from plants.
Keywords : Carbon stability Chronosequence Climate sensitivity Soil organic matter Topsoil development
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https://hal.inrae.fr/hal-03125455
Déposant : Yannick Brohard <>
Soumis le : vendredi 29 janvier 2021 - 14:47:48
Dernière modification le : mercredi 10 février 2021 - 09:53:42

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Norine Khedim, Lauric Cecillon, Jérôme Poulenard, Pierre Barré, François Baudin, et al.. Topsoil organic matter build‐up in glacier forelands around the world. Global Change Biology, Wiley, In press, ⟨10.1111/gcb.15496⟩. ⟨hal-03125455⟩

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