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Abstract

Aims Subsoil organic carbon (OC) tends to be older and is presumed to be more stable than topsoil OC, but the
reasons for this are not yet resolved. One hypothesis is
that decomposition rates decrease with increasing soil
depth. We tested whether decomposition rates of beech
fine root litter varied with depth for a range of soils using
a litterbag experiment in German beech forest plots.
Methods In three study regions (Schorfheide-Chorin,
Hainich-Dün and Schwäbische-Alb), we buried 432
litterbags containing 0.5 g of standardized beech root
material (fine roots with a similar chemical composition
collected from 2 year old Fagus sylvatica L. saplings,
root diameter<2mm) at three different soil depths (5, 20
and 35 cm). The decomposition rates as well as the
changes in the carbon (C) and nitrogen (N) concentrations
of the decomposing fine root litter were determined at a 6 months interval during a 2 years field experiment. Results The amount of root litter remaining after 2 years
of field incubation differed between the study regions
(76 ± 2 % in Schorfheide-Chorin, 85 ± 2 % in
Schwäbische-Alb, and 88±2 % in Hainich-Dün) but
did not vary with soil depth.
Conclusions Our results indicate that the initial fine root
decomposition rates are more influenced by regional
scale differences in environmental conditions including
climate and soil parent material, than by changes in
microbial activities with soil depth. Moreover, they
suggest that a similar potential to decompose new resources in the form of root litter exists in both surface and deep soils.