Abstract
The role of DOC for the build-up of soil organic carbon pools is still not well known, but it is thought to play a role in the transport of carbon to a greater depth where it becomes more stable. The aim of this study was to elucidate within-year dynamics of carbon transport from litter to the O (Oe and Oa) and A horizons. Mesocosms with constructed soil profiles were used to study dynamics of C transport from 14C-enriched (about 1000‰) leaf litter to the Oe/Oa and A horizons as well as the mineralization of leaf litter. The mesocosms were placed in the field for 17 months during which time fluxes and 14C content of DOC and CO 2 were measured. Changes in 14C in leaf litter and bulk soil C pools were also recorded. Significant simultaneous release and immobilization of DOC occurring in both the O and A horizons was hypothesized. Contrary to our hypothesis, DOC released from the labeled Oi horizon was not retained within the Oe/Oa layer. DOC originating in the unlabeled Oe/Oa layer was also released for transport. Extensive retention of DOC occurred in the A horizon. DOC leaching from A horizon consisted of a mix of DOC from different sources, with a main fraction originating in the A horizon and a smaller fraction leached from the overlaying horizons. The C and 14C budget for the litter layer also indicated a surprisingly large amount of carbon with ambient Δ 14C -signature to be respired from this layer. Data for this site also suggested significant contributions from throughfall to dissolved organic carbon (DOC) transport into and respiration from the litter layer. The results from this study showed that DOC retention was low in the O horizon and therefore not important for the O horizon carbon budget. In the A horizon DOC retention was extensive, but annual DOC input was small compared to C stocks and therefore not important for changes in soil C on an annual timescale.
Highlights
Transport and retention of dissolved organic carbon (DOC) has been suggested to be an important mechanism for build-up of soil organic C pools in forest soils (e.g. Kalbitz et al, 2005)
The data presented in this paper suggested that retention of DOC in the O horizon, contrary to our hypothesis, was not significant and that extensive retention and release of DOC occurred in the A horizon
DOC derived from the litter layer was not to a significant degree retained in the O horizon
Summary
Transport and retention of DOC has been suggested to be an important mechanism for build-up of soil organic C pools in forest soils (e.g. Kalbitz et al, 2005). Transport and retention of DOC has been suggested to be an important mechanism for build-up of soil organic C pools in forest soils E.g. adsorption, there is typically a reduction in DOC flux from approximately 10–40 g m− 2 under the O horizon to about 1–20 g m− 2 in the B horizon (Kalbitz et al, 2000, Michalzik et al, 2001). DOC retained in the mineral soil is thought to a large extent to be stabilized in slow turnover carbon pools (Kalbitz et al, 2005). Been suggested to be a significant substrate for soil microorganisms (Marschner and Noble, 2000) and DOC leached from undecomposed substrates has been shown to be especially labile (Kalbitz et al, 2005).
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