Radiocarbon Isotopic Disequilibrium Shows Little Incorporation of New Carbon in Mineral Soils of a Boreal Forest Ecosystem

• Published in: Journal of Geophysical Research: Biogeosciences
• Main Authors: Tangarife‐escobar, Andrés, Guggenberger, Georg, Feng, Xiaojuan, Muñoz, Estefanía, Chanca, Ingrid, Peichl, Matthias, Smith, Paul, Sierra, Carlos, A
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), ICOS-RAMCES (ICOS-RAMCES), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA))
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2024
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Northern Sweden
• Online Access: https://hal.science/hal-04692243; https://hal.science/hal-04692243/document; https://hal.science/hal-04692243/file/JGR%20Biogeosciences%20-%202024%20-%20Tangarife%E2%80%90Escobar%20-%20Radiocarbon%20Isotopic%20Disequilibrium%20Shows%20Little%20Incorporation%20of%20New.pdf; https://doi.org/10.1029/2024jg008191

International audience Boreal forests fix substantial amounts of atmospheric carbon (C). However, the timescales at which this C is cycled through the ecosystem are not yet well understood. To elucidate the temporal dynamics between photosynthesis, allocation and respiration, we assessed the radiocarbon ( 14 C) disequilibrium (D) between different C pools and the current atmosphere to understand the fate of C in a boreal forest ecosystem. Samples of vegetation, fungi, soil and atmospheric CO 2 were collected at the Integrated Carbon Observation System station Svartberget in northern Sweden. Additionally, we analyzed the Δ 14 C-CO 2 from incubated topsoil and forest floor soil respiration (FFSR) collected over a 24-hr cycle, and calculated the Δ 14 C signature of the total ecosystem respiration (Re) using the Miller-Tans method. We found that vegetation pools presented a positive D enriched with bomb 14 C, suggesting a fast-cycling rate (months to years) for living biomass and intermediate (years to decades) for dead biomass. In contrast, mineral soils showed a negative D, indicating minimal incorporation of bomb 14 C. FFSR showed diurnal Δ 14 C variability (mean = 8.5‰), suggesting predominance of autotrophic respiration of recently fixed labile C. Calculations for Δ 14 C in Re (median = 12.7‰) demonstrate the predominance of C fixed from days to decades. Although the boreal forest stores significant amounts of C, most of it is in the soil organic layer and the vegetation, where it is cycled relatively fast. Only minimal amounts of recent C are incorporated into the mineral soil over long timescales despite the current stocks in soils being relatively old. Plain Language Summary Boreal forests play a key role as an alternative to sequester carbon dioxide (CO 2 ) from the atmosphere and mitigate climate change. However, there is uncertainty on where this CO 2 is stored and the timescales at which it remains. To understand this, we studied the fate of the atmospheric CO 2 since the beginning of the nuclear era ...