Circumpolar assessment of rhizosphere priming shows limited increase in carbon loss estimates for permafrost soils but large regional variability

• Main Authors: Keuper, Frida, Wild, Birgit, Kummu, Matti, Beer, Christian, Blume-Werry, Gesche, Fontaine, Sébastien, Gavazov, Konstantin, Gentsch, Norman, Guggenberger, Georg, Hugelius, G., Jalava, Mika, Koven, C., Krab, Eveline J., Kuhry, P., Monteux, Sylvain, Richter, Andreas, Shazhad, Tanvir, Weedon, James, Dorrepaal, Ellen
• Other Authors: Agroressources et Impacts environnementaux (AgroImpact), Institut National de la Recherche Agronomique (INRA), Stockholm University, Aalto University, Universität Greifswald - University of Greifswald, Unité Mixte de Recherche sur l'Ecosystème Prairial - UMR (UREP), Institut National de la Recherche Agronomique (INRA)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS), Ecole Polytechnique Fédérale de Lausanne (EPFL), Leibniz University Hannover, Lawrence Berkeley National Laboratory Berkeley (LBNL), Umeå University, University of Vienna Vienna, Government College University of Faisalabad (GCUF), VU University Amsterdam
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2017
• Subjects: Biogeochemical cycles; processes; and modeling; Permafrost; Carbon cycling; global change; cryosphere; biogeosciences; Soils/pedology; [SDV]Life Sciences [q-bio]; [SDV.BV]Life Sciences [q-bio]/Vegetal Biology; [SDE]Environmental Sciences; Orleans; Brooks Range; permafrost; Tundra; Alaska
• Online Access: https://hal.inrae.fr/hal-02737495

International audience Predictions of soil organic carbon (SOC) losses in the northern circumpolar permafrost area converge around 15% (± 3% standard error) of the initial C pool by 2100 under the RCP 8.5 warming scenario. Yet, none of these estimates consider plant-soil interactions such as the rhizosphere priming effect (RPE). While laboratory experiments have shown that the input of plant-derived compounds can stimulate SOC losses by up to 1200%, the magnitude of RPE in natural ecosystems is unknown and no methods for upscaling exist so far. We here present the first spatial and depth explicit RPE model that allows estimates of RPE on a large scale (PrimeSCale). We combine available spatial data (SOC, C/N, GPP, ALT and ecosystem type) and new ecological insights to assess the importance of the RPE at the circumpolar scale. We use a positive saturating relationship between the RPE and belowground C allocation and two ALT-dependent rooting-depth distribution functions (for tundra and boreal forest) to proportionally assign belowground C allocation and RPE to individual soil depth increments. The model permits to take into account reasonable limiting factors on additional SOC losses by RPE including interactions between spatial and/or depth variation in GPP, plant root density, SOC stocks and ALT. We estimate potential RPE-induced SOC losses at 9.7 Pg C (5 - 95% CI: 1.5 - 23.2 Pg C) by 2100 (RCP 8.5). This corresponds to an increase of the current permafrost SOC-loss estimate from 15% of the initial C pool to about 16%. If we apply an additional molar C/N threshold of 20 to account for microbial C limitation as a requirement for the RPE, SOC losses by RPE are further reduced to 6.5 Pg C (5 - 95% CI: 1.0 - 16.8 Pg C) by 2100 (RCP 8.5). Although our results show that current estimates of permafrost soil C losses are robust without taking into account the RPE, our model also highlights high-RPE risk in Siberian lowland areas and Alaska north of the Brooks Range. The small overall impact of the RPE is largely ...