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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 02 Jan 2020

Submitted as: research article | 02 Jan 2020

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Relevance of aboveground litter for soil organic matter formation – a soil profile perspective

Patrick Liebmann1, Patrick Wordell-Dietrich2, Karsten Kalbitz2, Robert Mikutta3, Fabian Kalks4, Axel Don4, Susanne K. Woche1, Leena R. Dsilva2, and Georg Guggenberger1 Patrick Liebmann et al.
  • 1Institute of Soil Science, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419, Hannover, Germany
  • 2Institute of Soil Science and Site Ecology, Technische Universität Dresden, Pienner Straße 19, 01737 Tharandt, Germany
  • 3Soil Science and Soil Protection, Martin Luther University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06210 Halle (Saale), Germany
  • 4Thünen Institute of Climate-Smart Agriculture, Bundesallee 65, 38116 Braunschweig, Germany

Abstract. In contrast to mineral topsoils, the origin and processes leading to the formation and stabilization of organic matter (OM) in subsoils is still not well known. This study addresses the fate of litter-derived carbon (C) in whole soil profiles with regard to the conceptual cascade model, which proposes that OM formation in subsoils is linked to sorption-microbial processing-remobilization cycles during the downward migration of dissolved organic carbon (DOC). Our main objectives were to quantify the contribution of recent litter to subsoil C stocks via DOC movement and to evaluate the stability of litter-derived OM in different functional OM fractions.

A plot-scale stable isotope labeling experiment was conducted in a temperate beech forest by replacing the natural litter layer with 13C enriched litter on an area of 20 m2 above a Dystric Cambisol. After 22 months of field exposure, the labeled litter was replaced again by natural litter and soil cores were drilled down to 180 cm soil depth. Water extraction and density fractionation were combined with stable isotope measurements in order to link the fluxes of recent litter-derived C to its allocation into different functional OM fractions. A second sampling was conducted 18 months later to further account for the stability of translocated young litter-derived C.

Almost no litter-derived particulate OM (POM) entered the subsoil, suggesting root biomass as the major source of subsoil POM. The contribution of aboveground litter to the formation of mineral-associated OM (MAOM) in topsoils (0–10 cm) was 0.99 ± 0.45 g C m−2 yr−1, and decreased to 0.37 ± 0.10 g C m−2 yr−1 in the upper subsoil (10–50 cm) and 0.01 ± 0.01 g C m−2 yr−1 in the deep subsoil > 100 cm soil depth. This finding suggests a subordinate importance of recent litter layer inputs via DOC translocation to subsoil C stocks, and implies that most of the OM in the subsoil is of older age. Smaller losses of litter-derived C within MAOM of about 66 % compared to POM (77–89 %) indicate that recent carbon can be stabilized by interaction with mineral surfaces; although the overall stabilization in the sandy study soils was low. Our isotope labeling approach supports the concept of OM undergoing a sequence of cycles of sorption, microbial processing, and desorption while migrating down a soil profile, which needs to be considered in models on soil OM formation and subsoil C cycling.

Patrick Liebmann et al.
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Patrick Liebmann et al.
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Short summary
Carbon input from a recent litter layer into a forest top- and subsoil was examined by adding a 13C enriched litter layer for a field exposure of 22 months. Annual C inputs were relatively low compared to the C already stored in soil and we did not find considerable translocation of recent litter-derived C into the deep subsoil (> 100 cm). Thus, our study supports the concept that C accumulation in deeper soil involves several (re)mobilization cycles of organic matter during downward migration.
Carbon input from a recent litter layer into a forest top- and subsoil was examined by adding a...