Fate and stability of dissolved organic carbon in topsoils and subsoils under beech forests

Abstract

Dissolved organic carbon (DOC) from Oa horizons has been proposed to be an important contributor for subsoil organic carbon stocks. We investigated the fate of DOC by directly injecting a DOC solution from 13 C labelled litter into three soil depths at beech forest sites. Fate of injected DOC was quantified with deep drilling soil cores down to 2 m depth, 3 and 17 months after the injection. 27 ± 26% of the injected DOC was retained after 3 months and 17 ± 22% after 17 months. Retained DOC was to 70% found in the first 10 cm below the injection depth and on average higher in the topsoil than in the subsoil. After 17 months DOC in the topsoil was largely lost (-19%) while DOC in the subsoil did not change much (-4.4%). Data indicated a high stabilisation of injected DOC in the subsoils with no differences between the sites. Potential mineralisation as revealed by incubation experiments however, was not different between DOC injected in topsoil or subsoils underlining the importance of environmental factors in the subsoil for DOC stabilisation compared to topsoil. We conclude that stability of DOC in subsoil is primary driven by its spatial inaccessibility for microorganisms after matrix flow while site specific properties did not significantly affect stabilisation. Instead, a more fine-textured site promotes the vertical transport of DOC due to a higher abundance of preferential flow paths.

Impacts of Logging-Associated Compaction on Forest Soils: A Meta-Analysis

“…Thus, subsoil microorganisms have to adapt themselves to such energy and carbon limited conditions. One major source of growth resources for microorganisms is the transport of dissolved organic matter derived through preferential flow paths from the organic layer to top soil layers and, especially to subsoils in forest ecosystems (Kalks et al, 2020;Nazari et al, 2020). This major nutritional source for subsoil microorganisms may substantially decrease in its availability to subsoil microorganisms, due to the destruction of preferential flow paths by compaction.…”

Biogeochemical limitations of carbon stabilization in forest subsoils#

“…The laboratory batch experiments included two additional sites under beech, Ebergötzen (Dystric Cambisols) and Rüdershausen (Haplic Luvisols), as did the related DOC injection experiment from Kalks et al. (2020) in order to investigate the sorption behavior of soils which developed on different parent materials (more details are provided in the Supporting Information Methods). For the three study sites, we refer to a soil depth between 0 and 10 cm as topsoil, 10 and 50 cm as upper subsoil, and 50 and 150 cm as deeper subsoil based on recent publications describing these sites (Kalks et al., 2020; Leinemann et al., 2016; Liebmann et al., 2020).…”

Microbial Utilisation of Aboveground Litter-Derived Organic Carbon Within a Sandy Dystric Cambisol Profile

“…In line with this, Liebmann et al (24) found, in the same experiment as that of the present study, that a substantial part of the newly formed mineral-associated OC was labile. Pronounced C retention in topsoil has been further explained by preferential sorption of newly introduced C to already present organo-mineral clusters in a DOC injection experiment (45). Nevertheless, soil mineralogy and related physico-chemical properties can control the extent and temporal pattern of microbial assimilation of formerly mineral-bound C, but this may vary substantially between different soil types (46)(47)(48).…”