EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Additional carbon stabilization in temperate subsoils impeded by biogeochemical and hydraulic constraints

Georg Guggenberger1, Patrick Liebmann1, Robert Mikutta2, Karsten Kalbitz3, Patrick Wordell-Dietrich3, Timo Leinemann1, Sebastian Preusser4, Jörg Bachmann1, Axel Don5, Ellen Kandeler4, Bernd Marschner6, and Frank Schaarschmidt1
Georg Guggenberger et al.
  • 1Leibniz Universität Hannover, Germany
  • 2Martin-Luther University Halle-Wittenberg, Germany
  • 3Technical University Dresden, Germany
  • 4University of Hohenheim, Germany
  • 5Thünen Institute of Climate-Smart Agriculture, Braunschweig, Germany
  • 6Ruhr-Universität Bochum, Germany

Formation of mineral-associated organic matter (MAOM) is a decisive process in the stabilization of OM against rapid microbial decomposition and thus in the soils’ role as global carbon (C) sink. Sorption experiments of dissolved OM (DOM) repeatedly showed that particularly mineral subsoils have a large sorption capacity to retain more C. However, there is also an increasing body of literature, revealing an increasing output of dissolved organic C (DOC) from soils. Here, we investigated into this paradox in forest soil under beech by a combination of a field labelling experiment with 13C-enriched litter with a unique DO13C and 13CO2 monitoring, an in-situ C exchange experiment with 13C-coated minerals, and batch sorption experiments.

Within two years of 13C monitoring, only 0.5% of litter-derived DO13C entered the subsoil, where it was only short-term stabilized by formation of MAOM but prone to fast microbial mineralization. The 13C monitoring, sorption/desorption experiments in the laboratory, and also the in-situ C exchange on buried soil minerals revealed that there is a frequent exchange of DOM with native OM and a preferential desorption of recently retained OM. Hence, there appeared to be a steady-state equilibrium between C input and output, facilitated by exchange and microbial mineralization of an adopted microbial community. The remobilized OM was also richer in less sorptive carbohydrates. Along with transport of most of DOM along preferential paths, this further increased the discrepancy between laboratory-measured sorption capacities of subsoil and the actual C loading of minerals. Finally, the 13C labeling experiments revealed that input of fresh litter-derived OM into subsoil may even mobilize old-soil derived OM. Hence, in the field different biogeochemical constraints are acting that prevent that the laboratory-based C sink can be reached in the field.  We conclude, that forest subsoils can hardly be considered as additional C sink, even at management options that increase DOC input to subsoil.

How to cite: Guggenberger, G., Liebmann, P., Mikutta, R., Kalbitz, K., Wordell-Dietrich, P., Leinemann, T., Preusser, S., Bachmann, J., Don, A., Kandeler, E., Marschner, B., and Schaarschmidt, F.: Additional carbon stabilization in temperate subsoils impeded by biogeochemical and hydraulic constraints, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14580,, 2021.

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