Preprints
https://doi.org/10.5194/bg-2022-199
https://doi.org/10.5194/bg-2022-199
 
26 Sep 2022
26 Sep 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Recently fixed carbon fuels microbial activity several meters below the soil surface

Andrea Scheibe1, Carlos Sierra2,3, and Marie Spohn1,4 Andrea Scheibe et al.
  • 1Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Germany
  • 2Department of Biogeochemical Processes, Max Planck Institute for Biogeochemistry, Jena, Germany
  • 3Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden
  • 4Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Abstract. The deep soil, >1 meter, harbors a substantial share of the global microbial biomass. Currently, it is not known whether microbial activity several meters below the surface is fueled by recently fixed carbon or by old carbon that persisted in soil for several hundred years. Understanding the carbon source of microbial activity in deep soil is important to identify the drivers of biotic processes in the critical zone. Therefore, we explored carbon cycling in soils in three climate zones (arid, mediterranean, and humid) of the Coastal Cordillera of Chile down to a depth of six meters, using carbon isotopes. Specifically, we determined the 13C : 12C ratio (δ13C) of soil and roots, and the 14C : 12C ratio (Δ14C) of soil and CO2 respired by microorganisms. We found that the Δ14C of the respired CO2-C was higher than of the soil organic carbon in all soils (except for two topsoils). Further, we found that the δ13C of the soil organic carbon changed only in the upper decimeters (by less than 6 ‰). Our results show that microbial activity several meters below the soil surface is mostly fueled by recently fixed carbon that is on average much younger than the total soil organic carbon present in the respective soil depth increments, in all three climate zones. Further, our results indicate that strong microbial decomposition of the soil organic matter only occurs in the upper decimeters of the soils, which is likely due to stabilization of organic carbon in the deep soil. In conclusion, our results demonstrate that microbial processes in the deep soil several meters below the surface are closely tied to primary production aboveground.

Andrea Scheibe et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-199', Karis McFarlane, 19 Oct 2022
    • AC1: 'Reply on RC1', Marie Spohn, 02 Dec 2022
  • RC2: 'Comment on bg-2022-199', Hannah Holland-Moritz, 28 Nov 2022
    • AC2: 'Reply on RC2', Marie Spohn, 02 Dec 2022
    • AC3: 'Reply on RC2', Marie Spohn, 02 Dec 2022

Andrea Scheibe et al.

Andrea Scheibe et al.

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Short summary
We explored carbon cycling in soils in three climate zones in Chile down to a depth of six meters, using carbon isotopes. Our results show that microbial activity several meters below the soil surface is mostly fueled by recently fixed carbon and that strong decomposition of the soil organic matter only occurs in the upper decimeters of the soils. The study shows that different layers of the Critical Zone are tightly connected, and that processes in the deep soil depend on plant growth.
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