In:
Biogeosciences, Copernicus GmbH, Vol. 17, No. 12 ( 2020-06-18), p. 3099-3113
Abstract:
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 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 1.88±0.83 g C m−2 and decreased to
0.69±0.19 g C m−2 in the upper subsoil (10–50 cm) and 0.01±0.02 g C m−2 in the deep subsoil 〉100 cm 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.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-17-3099-2020
DOI:
10.5194/bg-17-3099-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2158181-2