Factors controlling the variability of organic matter in the top- and subsoil of a sandy Dystric Cambisol under beech forest

Heinze, Stefanie; Ludwig, Bernard; Piepho, Hans‐Peter; Mikutta, Robert; Don, Axel; Wordell‐Dietrich, Patrick; Helfrich, Mirjam; Hertel, Dietrich; Leuschner, Christoph; Kirfel, Kristina; Kandeler, Ellen; Preußer, Sebastian; Guggenberger, Georg; Leinemann, Timo; Marschner, Bernd

doi:10.1016/j.geoderma.2017.09.028

Cited by 65 publications

(36 citation statements)

References 63 publications

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“…decreasing role of root input and bioturbation in subsoil horizons (Heinze et al, 2018). Our results suggest that the majority of POM in the topsoil is not strongly connected to annual litter inputs as these are very small compared to the total POM pool.…”

Section: Particulate Om In the Soil Profile And Contribution Of Littementioning

confidence: 64%

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Relevance of aboveground litter for soil organic matter formation – a soil profile perspective

Liebmann¹,

Wordell‐Dietrich²,

Kalbitz³

et al. 2020

Preprint

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Abstract. In contrast to mineral topsoils, the origin and processes leading to the formation and stabilization of organic matter (OM) in subsoils is 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 movement 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 0.99 ± 0.45 g C m−2 yr−1, and decreased to 0.37 ± 0.10 g C m−2 yr−1 in the upper subsoil (10–50 cm) and 0.01 ± 0.01 g C m−2 yr−1 in the deep subsoil > 100 cm soil depth. 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 %) indicate that recent carbon can be stabilized by interaction with mineral surfaces; although the overall stabilization in the sandy study soils was low. 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 on soil OM formation and subsoil C cycling.

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Section: Particulate Om In the Soil Profile And Contribution Of Littementioning

confidence: 64%

“…4b). The so called humification index derived from fluorescence spectra first increased from the topsoil to its maximum in the heavily rooted upper subsoil (Heinze et al, 2018;Wordell-Dietrich et al, 2019). Below, a constant decrease with increasing soil depth was observed (Fig.…”

Section: Depth Distribution and Properties Of Socmentioning

confidence: 90%

Relevance of aboveground litter for soil organic matter formation – a soil profile perspective

Liebmann¹,

Wordell‐Dietrich²,

Kalbitz³

et al. 2020

Preprint

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“…Recently, evidence is growing that it is of similar importance for the stabilization of SOM in topsoils and subsoils (Rasmussen et al, 2005;Moni et al, 2010;Sanaullah et al, 2010;Rumpel et al, 2012). Because roots have been shown to play a significant role in the input and dynamics of OC in subsoils (Angst et al, 2016;Heinze et al, 2018), the question remains to what extent soluble root exudates drive the C allocation and soil aggregation in subsoil vs. topsoils.…”

Section: Introductionmentioning

confidence: 99%

Root Exudates Induce Soil Macroaggregation Facilitated by Fungi in Subsoil

Baumert

Vasilyeva

Vladimirov

et al. 2018

Front. Environ. Sci.

154

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Subsoils are known to harbor large amounts of soil organic carbon (SOC) and may represent key global carbon (C) sinks given appropriate management. Although rhizodeposition is a major input pathway of organic matter to subsoils, little knowledge exists on C dynamics, particularly stabilization mechanisms, such as soil aggregation, in the rhizosphere of different soil depths. The aim of this study was to investigate the influence of natural and elevated root exudation on C allocation and aggregation in the topsoil and subsoil of a mature European beech (Fagus sylvatica L.) forest. We experimentally added model root exudates to soil at two different concentrations using artificial roots and analyzed how these affect SOC, nitrogen, microbial community composition, and size distribution of water-stable aggregates. Based on the experimental data, a mathematical model was developed to describe the spatial distribution of the formation of soil aggregates and their binding strength. Our results demonstrate that greater exudate additions affect the microbial community composition in favor of fungi which promote the formation of macroaggregates. This effect was most pronounced in the C-poor subsoil, where macroaggregation increased by 86% and SOC content by 10%. Our modeling exercise reproduced the observed increase in subsoil SOC at high exudate additions. We conclude that elevated root exudation has the potential to increase biotic macroaggregation and thus the C sink strength in the rhizosphere of forest subsoils.

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“…Organic C content was calculated by the difference between total and inorganic C. Carbonate was present in only very few samples and in very low concentrations (\ 0.025 weight %). Respective values for bulk density, pH and stone content were obtained from a formerly conducted regional site grid sampling at the same sites (Heinze et al 2018). Oxalate extractions were conducted according to Schwertmann (1964) and McKeague and Day (1966) by using a 0.2 M ammonium oxalate solution (pH 3) to dissolve poorly crystalline aluminosilicates and Fe hydroxides like ferrihydrite as well as organic complexes (Fe o , Al o ).…”

Section: Chemical Analyses and Calculationsmentioning

confidence: 99%

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

et al. 2020

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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.

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Factors controlling the variability of organic matter in the top- and subsoil of a sandy Dystric Cambisol under beech forest

Cited by 65 publications

References 63 publications

Relevance of aboveground litter for soil organic matter formation – a soil profile perspective

Relevance of aboveground litter for soil organic matter formation – a soil profile perspective

Root Exudates Induce Soil Macroaggregation Facilitated by Fungi in Subsoil

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

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