Dr Yannick Agnan1, Dr Marie A. Alexis1, Ms Alice Kohli2, Dr Edith Parlanti3, Dr Sylvie Derenne1, Ms Mahaut Sourzac3, Ms Christelle Anquetil1, Pr Daniel Obrist4, Dr Maryse Castrec-Rouelle1
1Sorbonne Université, Paris, France, 2Agrocampus Ouest, Angers, France, 3Université de Bordeaux, Talence, France, 4University of Massachusetts, Lowell, Lowell, USA
Soil organic matter in Arctic and Subarctic regions plays a key role for the global carbon cycling. The objective of this study was to evaluate the structure and fate of soil organic matter in the high latitudes by jointly quantifying and characterizing both bulk and water-extractable organic matter in surface soil samples. We compared two study sites with similar tussock tundra ecosystems and distinct mean annual air temperature and permafrost conditions: Abisko, Sweden (−1 °C, discontinuous permafrost) and Toolik, Alaska, USA (<−8 °C, continuous permafrost). Both sites presented different bulk soil organic matter compositions: higher C/N and alkyl C/O-alkyl C ratios were reported at Abisko (27.1 ± 8.6 and 0.57 ± 0.17, respectively) compared to Toolik (17.4 ± 2.3 and 0.44 ± 0.11, respectively). These patterns are attributed to either distinct decomposition stages linked to climate conditions or distinct organic matter inputs with local vegetation influences. Extractable fractions indicated higher water-extractable organic matter concentrations in the colder site (i.e., at Toolik with 4.38 mg gsoil−1 of water-extractable organic carbon and 0.25 mg gsoil−1 of water-extractable total nitrogen) that we attribute to a higher pool of potentially mobilizable matter from a more preserved soil organic matter. Overall, the most significant result is that the intra-site heterogeneity of the soil organic matter quality was higher than the inter-site heterogeneity, in the bulk as well as in the water-extractable fractions. Finally, the qualities of both bulk and extractable fractions were not directly linked together: some specific patterns observed in the bulk fraction (e.g., locally lower alkyl C/O-alkyl C ratios) were not observed in the extractable one, and reciprocally (e.g., singular fluorescence signature).
Since 2008, M. A Alexis is assistant professor in Biogeochemistry at the Sorbonne Université (Paris – France). Her studies focus on the characterization of soil organic matter (at elementary, isotopic, or molecular scales) to understand its dynamics and its response to global changes. She especially studied the quality and features of thermally altered organic matter, in soils naturally affected by biomass fires, and in hearths after prehistorical human use. She presently also works on the production of dissolved organic matter through soil leaching and on the consequences for carbon storage and for transfer and dynamics of trace elements in high latitude environments.