Soil carbon loss in warmed subarctic grasslands is rapid and restricted to topsoil

• Published in: Biogeosciences
• Main Authors: Verbrigghe, Niel, Leblans, Niki I.W., Sigurdsson, Bjarni D., Vicca, Sara, Fang, Chao, Fuchslueger, Lucia, Soong, Jennifer L., Weedon, James T., Poeplau, Christopher, Ariza-Carricondo, Cristina, Bahn, Michael, Guenet, Bertrand, Gundersen, Per, Gunnarsdóttir, Gunnhildur E., Kätterer, Thomas, Liu, Zhanfeng, Maljanen, Marja, Marañón-Jiménez, Sara, Meeran, Kathiravan, Oddsdóttir, Edda S., Ostonen, Ivika, Peñuelas, Josep, Richter, Andreas, Sardans, Jordi, Sigurðsson, Páll, Torn, Margaret S., Van Bodegom, Peter M., Verbruggen, Erik, Walker, Tom W.N., Wallander, Håkan, Janssens, Ivan A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2022
• Subjects: Soil Science; Subarctic
• Online Access: https://lup.lub.lu.se/record/3b16e899-6fd1-4252-b05a-6debf4aa1003; https://doi.org/10.5194/bg-19-3381-2022

Global warming may lead to carbon transfers from soils to the atmosphere, yet this positive feedback to the climate system remains highly uncertain, especially in subsoils . Using natural geothermal soil warming gradients of up to +6.4C in subarctic grasslands , we show that soil organic carbon (SOC) stocks decline strongly and linearly with warming (-2.8tha-1C-1). Comparison of SOC stock changes following medium-term (5 and 10 years) and long-term (>50 years) warming revealed that all SOC stock reduction occurred within the first 5 years of warming, after which continued warming no longer reduced SOC stocks. This rapid equilibration of SOC observed in Andosol suggests a critical role for ecosystem adaptations to warming and could imply short-lived soil carbon-climate feedbacks. Our data further revealed that the soil C loss occurred in all aggregate size fractions and that SOC stock reduction was only visible in topsoil (0-10cm). SOC stocks in subsoil (10-30cm), where plant roots were absent, showed apparent conservation after >50 years of warming. The observed depth-dependent warming responses indicate that explicit vertical resolution is a prerequisite for global models to accurately project future SOC stocks for this soil type and should be investigated for soils with other mineralogies.