Relevance of aboveground litter for soil organic matter formation - A soil profile perspective

Research output: Contribution to journalReview articleContributedpeer-review

Contributors

  • Patrick Liebmann - , Leibniz University Hannover (LUH) (Author)
  • Patrick Wordell-Dietrich - , Chair of Soil Resources and Land Use (Author)
  • Karsten Kalbitz - , Chair of Soil Resources and Land Use (Author)
  • Robert Mikutta - , Martin Luther University Halle-Wittenberg (Author)
  • Fabian Kalks - , Johann Heinrich von Thunen Institute (Author)
  • Axel Don - , Johann Heinrich von Thunen Institute (Author)
  • Susanne K. Woche - , Leibniz University Hannover (LUH) (Author)
  • Leena R. Dsilva - , TUD Dresden University of Technology (Author)
  • Georg Guggenberger - , Leibniz University Hannover (LUH) (Author)

Abstract

In contrast to mineral topsoils, in subsoils the origin and processes leading to the formation and stabilization of organic matter (OM) are 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 translocation 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 20m2 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 180cm 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 (0-10cm) was 1.88±0.83gCm-2 and decreased to 0.69±0.19gCm-2 in the upper subsoil (10-50cm) and 0.01±0.02gCm-2 in the deep subsoil >100cm soil depth during the 22 months. 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%) over 18 months indicate that recent carbon can be stabilized by interaction with mineral surfaces; although the overall stabilization in the sandy study soils is limited. 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 of soil OM formation and subsoil C cycling.

Details

Original languageEnglish
Pages (from-to)3099-3113
Number of pages15
JournalBiogeosciences
Volume17
Issue number12
Publication statusPublished - 18 Jun 2020
Peer-reviewedYes

External IDs

Scopus 85088008252

Keywords

DFG Classification of Subject Areas according to Review Boards