Density fractions versus size separates: does physical fractionation isolate functional soil compartments?

Moni, Christophe; Derrien, Delphine; Hatton, Pierre‐Joseph; Zeller, Bernd; Kleber, Markus

doi:10.5194/bg-9-5181-2012

Cited by 67 publications

(46 citation statements)

References 75 publications

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“…7a and b). The limited effects of OM occlusion in aggregates are not consistent with the general view of aggregate-controlled OM stabilization (Lehmann and Kleber, 2015;Wiesmeier et al, 2019), as well as other studies revealing aggregate-protected OM using similar aggregate destruction methods (Mueller et al, 2012;Wang et al, 2014). However, Goebel et al (2009) and Juarez et al (2013) reported limited roles of soil aggregates in protecting OM from decomposition.…”

Section: Organic Matter Stabilization Mechanismscontrasting

confidence: 57%

“…(1) OM adsorption on the mineral surfaces and (2) physical occlusion of OM within soil water-stable aggregates (Lützow et al, 2006;Six et al, 2002). In general, OM occluded in water-stable aggregates is isolated using wet-sieving followed by density fractionation plus sonication (Cerli et al, 2012;Moni et al, 2012). However, these methods were not applicable for our acid igneous rock soils because the application of ultrasound caused severe dispersion of OM into the dense solution (i.e., NaPT).…”

Section: Organic Matter Stabilization Mechanismsmentioning

confidence: 99%

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Lithology- and climate-controlled soil aggregate-size distribution and organic carbon stability in the Peruvian Andes

Yang

Jansen

Absalah

et al. 2020

SOIL

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Recent studies indicate that climate change influences soil mineralogy by altering weathering processes and thus impacts soil aggregation and organic carbon (SOC) stability. Alpine ecosystems of the Neotropical Andes are characterized by high SOC stocks, which are important for sustaining ecosystem services. However, climate change in the form of altered precipitation patterns can potentially affect soil aggregation and SOC stability with potentially significant effects on the soil's ecosystem services. This study aimed to investigate the effects of precipitation and lithology on soil aggregation and SOC stability in the Peruvian Andean grasslands, and it assessed whether occlusion of organic matter (OM) in aggregates controls SOC stability. For this, samples were collected from soils on limestone and soils on acid igneous rocks from two sites with contrasting precipitation levels. We used a dry-sieving method to quantify aggregate-size distribution and applied a 76 d soil incubation with intact and crushed aggregates to investigate SOC stability's dependence on aggregation. SOC stocks ranged from 153 ± 27 to 405 ± 42 Mg ha −1 , and the highest stocks were found in the limestone soils of the wet site. We found lithology rather than precipitation to be the key factor regulating soil aggregate-size distribution, as indicated by coarse aggregates in the limestone soils and fine aggregates in the acid igneous rock soils. SOC stability estimated by specific SOC mineralization rates decreased with precipitation in the limestone soils, but only minor differences were found between wet and dry sites in the acid igneous rock soils. Aggregate destruction had a limited effect on SOC mineralization, which indicates that occlusion of OM in aggregates played a minor role in OM stabilization. This was further supported by the inconsistent patterns of aggregate-size distribution compared to the patterns of SOC stability. We propose that OM adsorption on mineral surfaces is the main OM stabilization mechanism controlling SOC stocks and stability. The results highlight the interactions between precipitation and lithology on SOC stability, which are likely controlled by soil mineralogy in relation to OM input.

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Section: Organic Matter Stabilization Mechanismscontrasting

confidence: 57%

Section: Organic Matter Stabilization Mechanismsmentioning

confidence: 99%

Lithology- and climate-controlled soil aggregate-size distribution and organic carbon stability in the Peruvian Andes

Yang

Jansen

Absalah

et al. 2020

SOIL

View full text Add to dashboard Cite

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“…Although we observed large impacts of grazing on BCA and SOC pools, future work will be needed to gain greater mechanistic insight into the processes regulating SOC turnover, and thus long-term implications of grazing for carbon sequestration. For instance, our findings support that plant tissue inputs account for a disproportionate fraction of SOC under grazing, but we do not have data to link this pattern to any particular fraction of SOC (von L€ utzow et al, 2007;Moni, Derrien, Hatton, Zeller, & Kleber, 2012). We speculate that it is possible that particulate forms of SOC are promoted by grazing, while the absolute concentration of mineral-associated C is similar due to saturation of physical-protection capacity in coarse sandy soils.…”

Section: Discussionmentioning

confidence: 60%

Grazing enhances belowground carbon allocation, microbial biomass, and soil carbon in a subtropical grassland

Wilson

Strickland

Hutchings

et al. 2018

Global Change Biology

197

135

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Despite the large contribution of rangeland and pasture to global soil organic carbon (SOC) stocks, there is considerable uncertainty about the impact of large herbivore grazing on SOC, especially for understudied subtropical grazing lands. It is well known that root system inputs are the source of most grassland SOC, but the impact of grazing on partitioning of carbon allocation to root tissue production compared to fine root exudation is unclear. Given that different forms of root C have differing implications for SOC synthesis and decomposition, this represents a significant gap in knowledge. Root exudates should contribute to SOC primarily after microbial assimilation, and thus promote microbial contributions to SOC based on stabilization of microbial necromass, whereas root litter deposition contributes directly as plant-derived SOC following microbial decomposition. Here, we used in situ isotope pulse-chase methodology paired with plant and soil sampling to link plant carbon allocation patterns with SOC pools in replicated long-term grazing exclosures in subtropical pasture in Florida, USA. We quantified allocation of carbon to root tissue and measured root exudation across grazed and ungrazed plots and quantified lignin phenols to assess the relative contribution of microbial vs. plant products to total SOC. We found that grazing exclusion was associated with dramatically less overall belowground allocation, with lower root biomass, fine root exudates, and microbial biomass. Concurrently, grazed pasture contained greater total SOC, and a larger fraction of SOC that originated from plant tissue deposition, suggesting that higher root litter deposition under grazing promotes greater SOC. We conclude that grazing effects on SOC depend on root system biomass, a pattern that may generalize to other C4-dominated grasslands, especially in the subtropics. Improved understanding of ecological factors underlying root system biomass may be the key to forecasting SOC and optimizing grazing management to enhance SOC accumulation.

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“…Conceptual pools were sometimes associated to functional pools tentatively separated from soils according to chemical or physical fractionation (e.g. Balesdent 1996;Zimmermann et al 2007;Crow et al 2007;Moni et al 2012). In recent years, the significance of the chemical fractions obtained after the so-called humic substances separation have been questioned since they are probably artefacts formed during the drastic chemical extraction treatment (Schmidt et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Increasing soil carbon storage: mechanisms, effects of agricultural practices and proxies. A review

Dignac

Derrien

Barré

et al. 2017

Agron. Sustain. Dev.

378

170

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The international 4 per 1000 initiative aims at supporting states and non-governmental stakeholders in their efforts towards a better management of soil carbon (C) stocks. These stocks depend on soil C inputs and outputs. They are the result of fine spatial scale interconnected mechanisms, which stabilise/destabilise organic matter-borne C. Since 2016, the CarboSMS consortium federates French researchers working on these mechanisms and their effects on C stocks in a local and global change setting (land use, agricultural practices, climatic and soil conditions, etc.). This article is a synthesis of this consortium's first seminar. In the first part, we present recent advances in the understanding of soil C stabilisation mechanisms comprising biotic and abiotic processes, which occur concomitantly and interact. Soil organic C stocks are altered by biotic activities of plants (the main source of C through litter and root systems), microorganisms (fungi and bacteria) and 'ecosystem engineers' (earthworms, termites, ants). In the meantime, abiotic processes related to the soil-physical structure, porosity and mineral fraction also modify these stocks. In the second part, we show how agricultural practices affect soil C stocks. By acting on both biotic and abiotic mechanisms, land use and management practices This synthesis of the CarboSMS French consortium's first seminar was already published in French: Derrien D, Dignac M-F, Basile-Doelsch I, Barot S, Cécillon L, Chenu C, Chevallier T, Freschet GT, Garnier P, Guenet B, Hedde M, Klumpp K, Lashermes G, Maron P-A, Nunan N, Roumet C, Barré P (2016) (choice of plant species and density, plant residue exports, amendments, fertilisation, tillage, etc.) drive soil spatiotemporal organic inputs and organic matter sensitivity to mineralisation. Interaction between the different mechanisms and their effects on C stocks are revealed by meta-analyses and long-term field studies. The third part addresses upscaling issues. This is a cause for major concern since soil organic C stabilisation mechanisms are most often studied at fine spatial scales (mm-μm) under controlled conditions, while agricultural practices are implemented at the plot scale. We discuss some proxies and models describing specific mechanisms and their action in different soil and climatic contexts and show how they should be taken into account in large scale models, to improve change predictions in soil C stocks. Finally, this literature review highlights some future research prospects geared towards preserving or even increasing C stocks, our focus being put on the mechanisms, the effects of agricultural practices on them and C stock prediction models.

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Density fractions versus size separates: does physical fractionation isolate functional soil compartments?

Cited by 67 publications

References 75 publications

Lithology- and climate-controlled soil aggregate-size distribution and organic carbon stability in the Peruvian Andes

Lithology- and climate-controlled soil aggregate-size distribution and organic carbon stability in the Peruvian Andes

Grazing enhances belowground carbon allocation, microbial biomass, and soil carbon in a subtropical grassland

Increasing soil carbon storage: mechanisms, effects of agricultural practices and proxies. A review

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