Recent advances have deepened our understanding of SOM fractionation and protection mechanisms, particularly the role of mineral-associated organic matter (MAOM), particulate organic matter (POM), and occluded POM (oPOM). Insights into the biotic and abiotic pathways leading to MAOM formation have expanded significantly, alongside the development of new-generation soil models that incorporate these processes into SOM turnover estimates.
At the same time, emerging evidence underscores the complex and context-dependent nature of the soil mineral–microbe–vegetation interface. In particular, studies beyond temperate systems reveal that organo-mineral interactions are more dynamic than previously assumed, and that POM can persist for centuries in certain ecosystems or soil horizons. These findings challenge conventional assumptions and highlight the need for tailored management strategies.
This session invites contributions that explore SOM dynamics across scales—from molecular mechanisms and microbial processes to ecosystem-level patterns and global models. We welcome studies that introduce novel insights, challenge established paradigms, or provide robust confirmations of existing theories. Whether your work is based on field observations, laboratory experiments, or computational modeling, we are eager to hear how it advances our understanding of SOM persistence and informs practical applications, from land management to climate policy.
We particularly encourage early career scientists to participate, including those with preliminary findings or innovative conceptual approaches. If your research touches on any aspect of SOM formation, transformation, or stabilization, join us for a lively and interdisciplinary discussion.
Soil organic carbon (SOC) is the largest terrestrial carbon reservoir and acknowledged to play an important role in climate mitigation. It has been advocated to store additional SOC in stable forms to provide efficient climate change mitigation. For this, mineral associated organic matter (MAOM) is considered to be relatively stable and has longer residence times than faster cycling particulate organic matter. However, we require a better mechanistic understanding of microscale interactions and the controlling factors of MAOM formation. Here we used arable soils across Germany representing three texture classes (sandy, loamy and clayey), two levels of SOC contents (low and high; 7-73 mg OC g-1 soil) and consequently a range of SOC loading in the MAOM fraction (2-122 mg OC g-1 fraction). The soils were incubated for two years after an addition of highly 13C labelled (8 atom%) barley-litter and fractionated by particle size to extract the MAOM (<20 µm). We applied mid-infrared spectroscopy and synchrotron-based scanning transmission X-ray microscopy coupled with near-edge X-ray absorption focusing on C K-edge spectra (STXM C NEXAFS) to investigate MAOM composition. Following the STXM C NEXAFS analysis, we conducted nano-scale secondary ion mass spectrometry imaging (NanoSIMS) to separate the labelled new from native organic matter. Organic matter composition derived from mid-infrared spectroscopy of the bulk MAOM fraction aligned well with the total STXM C NEXAFS spectra obtained for the different soils. Overall, the composition of the MAOM was controlled by SOC loading rather than texture with more processed and oxidized organic matter in soils with low organic carbon contents. On the microscale, organic matter was patchy distributed and the majority of the mineral surfaces were free of organic matter. Newly formed 13C-enriched patches that formed directly on mineral surfaces were more oxidatively-transformed (carboxylic groups) compared to 13C co-located with existing organic matter (dominant aromatic moieties). These findings provide direct evidence that soil carbon storage is governed by distinct and preferential accrual pathways shaping local ‘anchoring’ types, and thus, surface attachment mediates the composition of newly incorporated MAOM.
How to cite: Schiedung, M., Rowley, M., Colocho Hurtarte, L. C., Hu, Y., Beinik, I., Hoeschen, C., Begill, N., Poeplau, C., and Schweizer, S. A.: Soil organic matter and mineral surface interactions are governed by the anchoring pathway, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1627, https://doi.org/10.5194/egusphere-egu26-1627, 2026.
Buried soils (paleosols) represent vast but under-characterized reservoirs of long-term soil organic carbon (SOC) that can persist for millennia when isolated from surface processes (Marin-Spiotta et al., 2014; Berhe et al., 2018). Their stability depends on geomorphic protection and mineral–organic interactions that constrain microbial decomposition (Kleber et al., 2007; Kögel-Knabner et al., 2022), but this protection may be compromised when erosion, hydrologic variability, or land-use change reconnect buried carbon to the atmosphere (Doetterl et al., 2016; Berhe et al., 2012).
Using the late Pleistocene Brady paleosol in Nebraska (USA) as a model system, we combined geochemical, isotopic, and incubation approaches to examine mechanisms controlling SOC persistence and reactivation across burial and erosional settings. Radiocarbon and spectroscopic data show that millennia-old SOC is stabilized by fine-textured minerals and polyvalent cation bridging (Ca²⁺, Mg²⁺), which promote aggregation and organo-mineral bonding. Burial enhanced these stabilization mechanisms, whereas erosional exposure induced geochemical convergence toward modern surface soils and faster SOC turnover.
Incubation experiments further revealed that drying–rewetting cycles accelerate decomposition and destabilize even the slow-cycling pool, while continuously moist, deeply buried horizons retained low decomposition rates and greater mineral-associated carbon fractions. These results demonstrate that SOC persistence is jointly controlled by geomorphic position, ionic environment, and moisture regime, linking ancient pedogenesis with modern disturbance.
Because loess–paleosol sequences also occur throughout Central and Eastern Europe, these findings provide a valuable framework for assessing the vulnerability of deep-soil carbon pools to future climate and land-use change. Integrating paleosol processes into soil–climate models will improve predictions of carbon feedbacks and inform management of legacy carbon reservoirs.
How to cite: Nel, T., Dolui, M., McMurtry, A. R., Chacon, S., Phillips, L. M., Mason, J. A., Marin-Spiotta, E., de Graaff, M.-A., McFarlane, K., Tfaily, M., Moreland, K., Ghezzehei, T. A., and Berhe, A. A.: From time capsule to carbon source: Paleosol exposure as a missing component in soil-climate feedbacks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-168, https://doi.org/10.5194/egusphere-egu26-168, 2026.
Clay minerals are widely recognized as key regulators of soil organic matter (SOM) stabilization, yet their interactions with litter quality, soil fauna, and plant roots remain insufficiently understood. We investigated carbon (C) storage and partitioning among particulate (POM) and mineral-associated organic matter (MAOM) in substrates dominated by kaolinite, illite, and montmorillonite using two controlled microcosm and pot experiments. In the first experiments litter of contrasting quality (oak vs. alder) was added to clay minerals with and without earthworms, in second mineral organic matter was delivered by growing plants (Festuca rubra and Lotus corniculatus), in the same clay minerals.
Contrary to expectations based expectation that surface area (SBET) would be major predictor of SOM storage, illite consistently supported high C storage, particularly through enhanced incorporation of POM, while montmorillonite promoted MAOM accumulation. Earthworms and easily decomposable litter increased total C storage by facilitating transfer of litter-derived POM into mineral soil. Pore size distribution emerged as a critical factor: illite contained a higher proportion of micrometer-sized pores conducive to POM occlusion, whereas montmorillonite was dominated by nanometer-scale pores favoring MAOM formation.
How to cite: Irshad, S. and Frouz, J.: Specific surface area of clays affects accumulation of mineral associated organic matter while larger pore volume is crucial for particulate organic matter accumulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7476, https://doi.org/10.5194/egusphere-egu26-7476, 2026.
Process-based soil carbon (C) models are increasingly used to project regional and global C cycle responses to climate change. However, the development and evaluation of these models has largely focused on temperate regions of North America and Europe. This geographic bias raises a critical question: Do these models capture generalizable mechanisms that can be applied to underrepresented pedological regions, or do they encode processes specific to their developmental context? Through collaboration between modelers and experimentalists, we evaluated three process-based models—Century, Millennial, and MIMICS—across 777 topsoil samples spanning the climate and pedological diversity of sub-Saharan Africa. Despite their differences in mechanistic detail, all three models performed similarly (adjusted R² = 0.09–0.18) in predicting soil organic carbon (SOC) stocks. Using random forest algorithms trained on observed and modeled SOC data, we identified divergences between drivers of SOC. All three models overemphasized net primary productivity as a SOC driver and misrepresented the role of organo-mineral interactions. Bias analyses revealed that the three process-based models inadequately capture exchangeable calcium, which is increasingly recognized as an important control on SOC. Notably, increased mechanistic complexity did not improve transferability. Our results have significant implications for regional C budgets and global climate projections. They underscore the need for tighter feedback between modelers and experimentalists to incorporate region-specific biogeochemistry—particularly organo-mineral interactions and calcium dynamics—into future soil C models in (sub-)tropical regions. We propose that targeted experimental work on these mechanisms, coupled with model re-parameterization, offers a path toward more reliable climate projections.
How to cite: von Fromm, S. F., Rocci, K. S., Anuo, C. O., Asabere, S. B., Kanyiri, J., Kengdo, S. K., Mureva, A., Nketia, K. A., Zhang, L., and Abramoff, R. Z.: Reconciliation of Process-Based Models and Observations: Collaborative Pathways to Improve Soil Carbon Predictions Across Sub-Saharan Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12784, https://doi.org/10.5194/egusphere-egu26-12784, 2026.
Soil organic matter (SOM) stocks in mountain ecosystems play a crucial role in carbon and nutrient cycling, thereby mitigating climate change and providing many important ecosystem services. However, their response to rapid forest succession resulting from the combined effects of land abandonment and global warming, which is particularly pronounced in mountain areas, remains strongly context-dependent. The influence of soil-forming processes, represented by soil types, is still insufficiently understood. This study investigates how SOM stocks and their stability change along forest succession in the Gorce Mountains in southern Poland, with a specific focus on the role of soil type.
We analyzed soils across different forest succession stages, ranging from grasslands through shrubs and young successional forests to permanent old-growth forests, and across different soil types (Cambisols, Gleysols, and Podzols). We assessed SOM stocks in the O horizons and in the 0–5 cm (topsoil) and 20–30 cm (subsoil) mineral soil layers. In addition, we performed soil density fractionation of the mineral topsoil and subsoil layers into free light fraction, occluded light fraction, and heavy fraction, the relative proportions of which were used as indicator of SOM stability. Our results show that both SOM quantity and stability vary significantly along the forest succession gradient; however, these patterns are strongly modified by soil type. In some soil-contexts, the transition from grassland to forest led to increased SOM stocks but also to a greater vulnerability to SOM decomposition, whereas in other soil types, the highest SOM stocks and greatest stability occurred at an intermediate forest succession stage (tall-shrub communities).
These findings highlight that soil type is a key contextual factor controlling SOM storage in mountain ecosystems. Accounting for soil-specific responses is therefore essential for predicting SOM sequestration potential under ongoing environmental change.
This project has received funding from the Central European Leuven Strategic Alliance (grant CELSA/24/002) and has been supported by a grant from the Priority Research Area Antropocene under the Strategic Programme Excellence Initiative at Jagiellonian University.
How to cite: Musielok, Ł., Nijdam, S., Gus-Stolarczyk, M., Kramarczuk, P., Vancampenhout, K., and Muys, B.: Soil type matters: forest succession and soil organic matter stability in the Gorce Mountains (S Poland), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13706, https://doi.org/10.5194/egusphere-egu26-13706, 2026.
The large carbon storage in terrestrial soils underscores the need for mechanistic soil process representations in Earth System Models (ESMs) aimed at simulating carbon-climate feedbacks under changing climate and land use. However, ESMs participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) still exhibit large uncertainties in simulating historical and future soil carbon stocks, reflecting incomplete process understanding and discrepancies between model assumptions and emerging empirical knowledge.
We present the recently developed NOAA/GFDL Global Integrated Microbial Interactions with Carbon in Soil (GIMICS) model, which integrates key advances in soil biogeochemistry and addresses limitations of the previous soil component, CORPSE, in GFDL ESM4.1. GIMICS has been incorporated into the CMIP7-class GFDL ESM4.5. GIMICS explicitly represents soil microbial dynamics and physicochemical stabilization mechanisms, as well as interactions among microbes, minerals, and vegetation, for both aboveground organic materials (leaf and coarse wood litter) and belowground, vertically resolved mineral soils (rhizosphere and bulk soil). GIMICS also accounts for the effects of spatially and vertically varying soil temperature and moisture on microbial processes and organic matter turnover, and represents redistribution and transport via bioturbation, diffusion, advection, and runoff to rivers.
GIMICS has been integrated with the GFDL Land Model LM4.2, which includes dynamic vegetation and wildfire processes. The resulting LM4.2-GIMICS configuration is evaluated in a stand-alone mode against a widely used, observationally derived global soil inventory dataset (Harmonized World Soil Database, HWSD), reported global synthesis estimates, and other global model results. Results show improved simulations of global and regional soil carbon stocks relative to models that do not explicitly represent microbial processes and mineral-associated organic matter (MAOM) stabilization. Analyses of pool–specific carbon stocks and fluxes highlight the critical role of soil mineral–microbe–vegetation interactions in regulating terrestrial carbon persistence.
How to cite: Lee, M., Shevliakova, E., and Malyshev, S.: Coupling vegetation dynamics, soil microbial processes, and physicochemical stabilization mechanisms within the new NOAA/GFDL Global Integrated Microbial Interactions with Carbon in Soil (GIMICS) model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13714, https://doi.org/10.5194/egusphere-egu26-13714, 2026.
The simulation of soil organic matter (SOM) dynamics, including SOM persistence, is a vital component of broader models representing vegetation dynamics or the impact of environmental change on the biosphere and climate. One of the biggest challenges in the application of SOM models is that their complexity is often not supported by sufficient data for parameter optimization. Inevitably, this leads to the calibration of more parameters than can be reliably optimised with available data, resulting in equifinality. This is the phenomenon that multiple parameter sets generate behavioural models: similarly well-performing models that cannot be ruled out.
This study assessed how equifinality affects the variability of predictions made by behavioural SOM models. We used a mechanistic, microbially-driven soil organic carbon and nitrogen model and evaluated it against an artificial data set. After the models were successfully calibrated and run into steady state, carbon inputs were doubled to evaluate how models with different mathematical formulations and different amounts of data used to optimize parameters reacted to this external forcing.
The key results are summarised as follows. (1) The accurate simulation of total SOM in steady state is an insufficient criterion to evaluate model performance. (2) The amount of calibration data determines how many model parameters can be jointly optimised without their values compensating for each other (i.e., identifiable parameters). And (3) the type of calibration data is equally important, as it dictates which pools can have their size and turnover rate constrained. For example, the size of particulate organic matter (POM) and mineral-associated organic matter (MAOM) can only be accurately simulated when data on these pool sizes are available. Similarly, the turnover rate of MAOM can only be reliably simulated if Δ14C data for MAOM are present. Our results emphasise the necessity of optimising only identifiable model parameters to avoid hidden uncertainty in model predictions. Adopting this approach consistently represents an important step forward to increase confidence in predictions made by SOM models.
How to cite: Van de Broek, M., Doetterl, S., and Six, J.: Equifinality and overparameterisation undermine confidence in predictions by soil organic matter models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14121, https://doi.org/10.5194/egusphere-egu26-14121, 2026.
Long-term bare fallow (LTBF) field experiments provide a unique framework to investigate soil organic carbon (SOC) persistence in the absence of fresh organic inputs. The Versailles 42-plots LTBF, established in 1928, is the oldest continuously managed bare fallow worldwide. Initially designed to assess the effects of fertilisers and amendments on loess-derived Luvisols, it offers a rare opportunity to quantify and isolate a centennially stable SOC pool. In 2008, total SOC in the reference plots was shown to equate estimated centennially stable SOC pool (Barré et al. 2010).
Here, we used repeated soil sampling to assess (i) whether the SOC content have stabilised over time and (ii) how long-term fertilisation and amendment practices affect the size of this pool. Treatments included mineral N fertilisers (ammonium, nitrate), basic amendments (lime, basic slag), mineral amendments containing P or K, an organic fertiliser (horse manure), and no-input reference plots. Topsoil (0–25 cm) was sampled in all 42 plots in 2008, 2014, 2017, 2021, and 2025 complemented by archived samples from 1929, 1949 and 1962.
In all plots except those receiving annual manure inputs, SOC contents have stabilised over recent decades, with no significant variation between 2008 and 2025. These steady values show that a centennially stable SOC pool has been reached but with different pool sizes across treatments. SOC contents were higher in plots receiving mineral N fertilisers or basic amendments than in no-input controls, whereas plots amended with monovalent cations (e.g. Na⁺, K⁺) or phosphates exhibited lower SOC levels.
These patterns suggest that long-term soil chemical and physical conditions, shaped by fertilisation and amendment regimes, influenced stabilisation processes and ultimately, SOC persistence. We suggest that low pHs (<5) resulting from with mineral N fertilisation may favour SOC stabilisation, while enhanced physical protection is promoted in lime- and carbonate-amended plots. Conversely, poor soil structure in monovalent cations amended plots may explain less SOC persistence.
These results underscore the high scientific value of long-term experiments, which need to be maintained and valorised, for understanding SOC dynamics and stabilisation.
How to cite: Delahaie, A., Plessis, C., Girardin, C., and Chenu, C.: Long-term bare fallows reveal centennially stable soil carbon pools under contrasting fertiliser and amendment regimes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16960, https://doi.org/10.5194/egusphere-egu26-16960, 2026.
Persistence of soil organic carbon (SOC) is largely controlled by interactions between organic matter and mineral surfaces, particularly iron oxides. These interactions are further influenced by the presence of competing species and various cations in soil systems. Despite their importance, the geochemical mechanisms by which competing species regulate organic matter and mineral interactions remain poorly understood, representing a critical knowledge gap in SOC stabilization processes. DNA is a ubiquitous biomolecule in soils and sediments. It is a key component of microbial necromass and extracellular polymeric substances. While DNA represents a small fraction of SOC, the mechanisms of DNA and mineral interaction can reveal broader principles applicable to other organic matter to elucidate mechanisms that contribute towards SOC formation and stabilization.
In this study, we used DNA of varying lengths representing organic matter fractions of different sizes, and phosphate as a model competing anion, to investigate the effects of phosphate on DNA adsorption to goethite. Batch adsorption experiments were complemented by enzymatic hydrolysis studies to assess the influence of phosphate and divalent cations (Ca²⁺ and Mg²⁺) on the degradation of DNA adsorbed on goethite. Our results show that DNA adsorption to goethite is strongly influenced by DNA length, phosphate concentration, and adsorption time. Phosphate significantly reduced DNA adsorption through competitive surface site occupation. Although the presence of Ca²⁺ and Mg²⁺ enhanced DNA adsorption under phosphate concentrations that were otherwise unfavorable for adsorption, this increased adsorption did not translate into protection against enzymatic hydrolysis.
These findings demonstrate that enhanced adsorption alone does not necessarily confer long-term protection of organic matter and highlight the complex roles of competing ions and cations in regulating mineral-associated SOC persistence. Our study provides mechanistic insights into how nutrient and cation availability may influence the stabilization and turnover of reactive, phosphorus-containing organic matter in soils.
How to cite: Brijit, A. J., Klier, P., Singh, V. V., Kumar, N., Kimber, R., Berthelemy, P., Rose, J., and Kraemer, S. M.: Controls on mineral-associated organic matter stability: Insights from DNA adsorption and degradation on goethite in the presence of phosphate and cations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17326, https://doi.org/10.5194/egusphere-egu26-17326, 2026.
Plant roots contribute substantially to soil organic matter (SOM) formation via litter inputs, exudation, and stimulation of microbial activity. Increasing plant species richness has been proposed as a strategy to enhance soil organic carbon (SOC) storage by promoting greater variation in root functional traits and associated carbon (C) inputs. Root traits may influence C partitioning between particulate organic matter (POM) and mineral-associated organic matter (MAOM) pools. Specific root length (SRL) reflects a do-it-yourself resource acquisition strategy characterized by fine, short-lived roots that primarily contribute plant-derived inputs, whereas greater root diameter (RD) indicates increased investment in microbial symbionts that can enhance microbial processing and stabilization of C in mineral-associated pools.
Here, we examined whether root morphological traits associated with the root economic space (RES) collaboration gradient provide a mechanistic link between plant roots and SOM partitioning, and the role of plant diversity therein. We hypothesized that root traits regulate SOC fractions, with SRL positively associated with POM, and RD associated with MAOM. We utilised the 1- and 12-species mixtures in BioCliVE, a large-scale grassland diversity experiment on sandy soil at Utrecht University (Netherlands). We measured community-level root traits for each plot, performed wet sieving to separate soils into particulate and mineral-associated fractions, and quantified C concentrations using elemental analysis to derive particulate organic carbon (POC) and mineral-associated organic carbon (MAOC).
Initial analyses showed that RD had a marginal positive association with MAOC, supporting the conceptual expectation that root traits linked to microbial collaboration may influence MAOM formation. SRL, however, was not related to POC, contrary to our hypothesis. There was no detectable effect of plant species richness on C stored in either the particulate or mineral-associated pools. Our research demonstrates the complexity of SOM partitioning and suggests that trait-based and diversity-driven controls on SOM are limited or context-dependent in sandy grassland soils. By testing root trait pathways within a diversity experiment, our study contributes to ongoing discussions on the mechanisms governing SOM across ecosystems.
How to cite: Kingsland-Mengi, A., de Boer, E., Kowalchuk, G., Barel, J., and Barry, K.: Linking Root Traits and Soil Organic Matter Pools in a Grassland Diversity Experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18950, https://doi.org/10.5194/egusphere-egu26-18950, 2026.
Mineral-associated organic matter (OM) exhibits a heterogeneous arrangement in soils at the microscale and nanoscale as revealed by high-resolution imaging techniques. The arrangement of OM at the microscale has broad implications for biogeochemical cycles of major elements such as C and N by compartmentalizing their dynamics into distinct micropatches and a few µm-sized hotspots. It is crucial to understand the organization of this heterogeneous microscale arrangement across diverse soil systems. Here, we present a meta-analysis of spatial patterns of OM patches based on unsupervised segmentation of nanoscale secondary ion mass spectrometry (NanoSIMS) measurements. Using a dataset of over 450 measurements of fine fractions from soils with different texture and C content, we evaluated the spatial coverage, clustering, and heterogeneity of OM micropatches across mineral surfaces. The OM coverage across mineral surfaces linearly correlated with the bulk soil C content, indicating a spatially expanding arrangement of OM whereas large parts of mineral-dominated surface remain. Higher OM coverage was related to more connected and more clustered OM patches. Within the OM patches, we found evidence of recurring µm-sized distinct C-rich and N-rich subunits based on a fractal geography approach. Within more homogeneous OM patches, subunits showed stronger differentiation in C and N composition, whereas subunits within more heterogeneous patches exhibited less differentiated C and N composition. The distinct spatial organization of OM micropatches observed here suggests a compartmentalized framework of OM dynamics with implications for C and N cycling in soils.
How to cite: Schweizer, S. A., Hu, Y., Zollner, J. M., Inagaki, T., Höschen, C., and Werner, M.: Spatial pattern analysis of soil organic matter micropatches show distinct µm-sized C-rich and N-rich subunits, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20930, https://doi.org/10.5194/egusphere-egu26-20930, 2026.
Forest soils play a key role in global carbon (C) storage. Important for long-term C storage in soil is the formation of mineral-associated organic matter (MAOM), which is protected through chemical bonds and occlusion from decomposition. Recent research demonstrated shifts in forest C cycles depending on tree diversity and mycorrhizal type, but we still lack mechanistic knowledge about the role of tree diversity and associated mycorrhizal symbiosis in soil C stabilization.
This study aims to quantify particulate organic matter (POM) and MAOM in relation to tree diversity and mycorrhizal type, i.e., ectomycorrhiza (ECM) and arbuscular mycorrhiza (AM) and to investigate the contributions of plant and microbial residues to POM and MAOM. It was conducted in the MyDiv tree experiment (Bad Lauchstädt, Germany), established in 2015 with 10 different deciduous tree species planted across a gradient of species richness. After density separation of POM and MAOM fractions, their mass, carbon and nitrogen (N) contents as well as 13C and 15N isotopic composition were determined. Soil samples were also taken from the grassland next to the site as background values. In addition, we measured 13C and 15N natural abundances of leaf litter, fine roots, saprotrophic and ectomycorrhizal sporocarps as well as ectomycorrhizal and soil hyphae.
There was no significant difference in the amount and C content of POM and MAOM between treatments. However, there was a tendency towards more POM (and POM-C) in diverse - especially ECM - systems. Compared to the grassland, C and N contents in POM were lower, which may result from reduced litter input after planting trees (soil was covered with a weed tarp until canopy closure). In line with this, POM of forest soil samples was enriched in 13C and 15N compared to grassland POM, suggesting a higher share of microbial residues in forest POM due to litter exclusion. Interestingly, also C content in MAOM declined due to litter exclusion, whereas 13C in MAOM seemed unaffected by the transition from grassland to forest.
The higher C/N ratio of POM compared to MAOM aligned with the expected greater contribution of plant residues to POM and microbial residues to MAOM. This is in accordance with a higher 13C-enrichment of MAOM compared to POM, especially in diverse systems and irrespective of the mycorrhizal type.
All in all, the analysis of natural stable isotope abundances is a powerful tool to elucidate the composition of POM and MAOM in temperate forests, which may change depending on forest age, mycorrhizal type and tree diversity.
How to cite: Marburger, C., Kochniss, L., Meier, I., Mohamed, A., and Pausch, J.: How tree species diversity and mycorrhizal association type influence contributions of plant and microbial residues to soil organic matter fractions in temperate forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21021, https://doi.org/10.5194/egusphere-egu26-21021, 2026.
Soil organic matter persistence has been recognized as an ecosystem property emerging from environmental and biological controls rather than intrinsic molecular recalcitrance. Yet a theoretical framework operationalizing this insight into predictive equations remains elusive. Here we present a coupled transport-reaction model where persistence emerges from the dynamic interplay of water, heat, and oxygen transport with kinetically-controlled mineral associations. The framework explicitly couples: (1) environmental state variables (θ, T, O₂) that modulate all reaction rates, (2) transformation kinetics from particulate to dissolved to reactive intermediates, (3) two-stage mineral association with direction-dependent sorption and desorption rates (αs > αd) following Langmuir-Freundlich kinetics, and (4) diffusive and advective transport controlling substrate accessibility. Analytical steady-state solutions in dimensionless form reveal fundamental parameter groupings—including a combined affinity parameter β that governs saturation behavior.
The model predicts distinct persistence regimes: environmental (decomposition suppressed by moisture, temperature, or oxygen limitation), kinetic (asymmetric mineral association creates hysteresis and path-dependence), and transport-limited (micro-site isolation restricts accessibility). These regimes explain why particulate organic matter can persist for centuries under certain conditions while mineral-associated carbon exhibits dynamic exchange in others. The framework also resolves apparent contradictions between saturation theory and field observations—total soil carbon can increase linearly while mineral-associated efficiency declines. Validation against long-term field experiments demonstrates predictive capability across contrasting sites and input regimes. We show that persistence is not a property to be measured but an outcome to be predicted from coupled dynamics—providing a quantitative foundation for the paradigm shift from intrinsic to emergent controls on soil carbon.
How to cite: Ghezzehei, T. and Berhe, A. A.: Kinetic and Transport Controls on Soil Organic Matter Persistence: A Coupled Framework for an Emergent Ecosystem Property, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15388, https://doi.org/10.5194/egusphere-egu26-15388, 2026.
Fen peatlands are essential ecosystems that support high biodiversity, buffer hydrological extremes such as droughts and flooding, sequester carbon (C), and contribute to human well-being. However, increasing climate anomalies and anthropogenic disturbances are accelerating peat degradation, potentially triggering abrupt shifts in peat integrity and function – with significant implications for the global C cycle. Our study investigated the rapid peat subsidence observed in Belgium’s oldest nature reserve ‘De Zegge’, which represents an unheard form of fen ecosystems deterioration, and an environmental alarm. Thus, this case study may provide insights for land managers and researchers working in similar peat systems worldwide. To determine how hydrological stress, coupled with chronic hydro-chemical pressures − may push the system beyond a critical threshold, and lead to peat collapse, we: (1) estimated the loses in elevation and C stocks using field-based digital elevation models, (2) compared peat characteristics between collapsed, adjacent non-collapsed and distant non-collapsed areas, and (3) experimentally assessed the effects of potential collapse triggers,- hydrological alterations and hydro-chemical additions (control, ditchwater, and sulfate [SO42-])- as on peat stability using a mesocosm experiment by measuring greenhouse gases (GHGs) emissions and porewater chemistry as indicators. Our findings demonstrate that fen peatland collapse led to significant lowering of the surface level (-12.8 ± 2.3 cm) accompanied by significant carbon losses (-21.6 ± 6.1 kg−C m-2), alongside structural and functional shifts across biological, vegetative, physiochemical, and molecular dimensions (P < 0.05). In the mesocosm experiment, hydrologically perturbed peat exhibited reduced stability compared to undisturbed monoliths, particularly in regulating GHGs fluxes. During the successional phase, SO42- emerged as a key stressor, exerting pressure on system-wide stability. SO42- intrusion indirectly increased N2O emissions during the re-saturation, with high spatial variability. Collectively, our study provides new insights into long-term pedological shifts affecting peat integrity and function in fen ecosystems.
How to cite: Kim, K., Emsens, W.-J., Ottoy, S., Schellekens, J., Deswert, T., Desie, E., Muys, B., J. I. Briones, M., Jansen, B., and Vancampenhout, K.: Peat Collapse as a new threat to fen hydrological stability: the case of Nature reserve De Zegge (Belgium), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20252, https://doi.org/10.5194/egusphere-egu26-20252, 2026.
Understanding the persistence, stability and turnover time of soil organic carbon (SOC) is essential for predicting terrestrial carbon storage, ecosystem responses to climate change, and strategies to enhance sequestration. However, linking SOC stability to specific soil properties remains challenging, with global models often underestimating SOC residence times compared to empirical observations (e.g., Shi et al., 2020). Radiocarbon (14C) provides a powerful tool for addressing these gaps by adding a temporal dimension to SOC studies.
Conventional approaches typically use physical or chemical fractionation to create operational pools for 14C analysis (e.g., Haddix et al., 2020), such as mineral-associated organic matter (MAOM). While informative, these pools themselves represent mixtures of diverse chemical components. An emerging approach is that of thermal-based methods such as ramped oxidation (ROx). These offer an alternative by partitioning SOC according to activation energy (e.g., Hanke et al., 2023), providing valuable insights into mechanisms of SOC stabilization (Stoner et al., 2023).
We applied ROx combined with 14C analysis to samples from a study that examined how converting temperate grassland to coniferous forest influences below-ground carbon dynamics in Scotland (Joly et al., 2025). As part of this work, we also quantified pyrogenic carbon (PyC), a fire-derived SOC fraction known for its long environmental residence times, in bulk soils and sub-fractions to assess its contribution to SOC persistence. By comparing 14C signatures from conventional fractionation with those from thermal fractions, including PyC, we evaluate the added value of ROx in revealing SOC age structure and persistence. These insights advance understanding of SOC stabilization processes and inform predictions of land-use change impacts on soil carbon storage.
Acknowledgments
We acknowledge support from the UK Natural Environment Research Council (NERC) via the National Environmental Isotope Facility (NEIF) grant (NE/S011587/1) and the NERC project grant NE/P011098/1.
References
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How to cite: Ascough, P., Garnett, M., Subke, J.-A., Street, L., Joly, F.-X., Harman, N., and Murdoch, I.: Evaluating Soil Carbon Persistence Using Ramped Oxidation and Radiocarbon Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11600, https://doi.org/10.5194/egusphere-egu26-11600, 2026.
Mediterranean mountain regions provide essential ecosystem services and resources to surrounding urban areas. Since the mid-20th century, however, rural depopulation has led to widespread land abandonment, triggering natural revegetation and consequent shrub encroachment. These changes have been associated with increased wildfire risk, reduced agro-pastoral resources, and altered hydrological functioning. Soil, a non-renewable resource on human timescales, plays a key role in ecosystem resilience due to its influence on biogeochemical cycles and carbon accumulation, making it a potential tool in Climate Change adaptation strategies.
This study, grounded in the MANMOUNT project (PID2019-105983RB-I00) investigates post-abandonment land management strategies in marginal Mediterranean mountain areas, focusing on their effects on soil quality and soil organic carbon (SOC) storage. The Leza Valley (Iberian System, Spain) was selected as the study area due to its representativeness of the historical and ecological context of Mediterranean mountains. Three management strategies were evaluated: passive management through secondary succession; forest management through conifer afforestation and dehesa systems; and shrub clearing to establish pastures for extensive grazing. Analyses considered soil environment (acid or alkaline), soil depth (0–40 cm), time since management implementation, and the presence of active management practices (e.g., thinning, selective cutting).
A total of 453 soil composite samples were collected and analysed to assess physicochemical properties and SOC stocks. Carbon stabilization mechanisms were examined using aggregate stability tests and fractionation techniques. Future SOC dynamics were projected under different Climate Change scenarios using the CarboSOIL predictive model, while integrated soil–water balance was evaluated with the RHESSys model.
Results revealed significant effects of post-abandonment management on soil quality and SOC storage. All management strategies increased carbon stocks compared to the initial unmanaged shrubland. Forest systems accumulated higher total SOC, whereas pasture systems promoted greater mineral-associated carbon, indicating enhanced long-term stability. Soil environment was a major driver of SOC responses, with marked differences between acid and alkaline soils. Model projections highlight the importance of sustained active management to maintain soil functions in abandoned areas under future climatic conditions.
These findings provide valuable insights for land managers and policymakers, underlining the potential of post-abandonment management in marginal Mediterranean mountain landscapes as an important tool for Climate Change adaptation. The promotion of mosaic landscapes is proposed as an effective strategy to achieve both ecological resilience and socio-economic sustainability.
Acknowledgement: This research project was supported by the MANMOUNT (PID2019-105983RB-100/AEI/ 10.13039/501100011033) project funded by the MICINN-FEDER, and the SOLPYR (POCTEFA 2021-2027 (EFA045/01)) project funded by Interreg Poctefa and European Union.
Keywords: Mediterranean mountains; carbon sequestration; natural revegetation; extensive grazing; forest practices.
How to cite: Cortijos-López, M., Lasanta, T., Zabalza-Martínez, J., Muñoz-Rojas, M., Cammeraat, E., Sánchez-Navarrete, P., and Nadal-Romero, E.: Management of marginal landscapes in the Mediterranean mountains: Driving soil regulatory functions towards Global Change adaptation., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17958, https://doi.org/10.5194/egusphere-egu26-17958, 2026.
Although conservation tillage practices generally do not enhance soil organic carbon sequestration in temperate arable soils, they substantially modify the vertical distribution and composition of soil organic matter compared to conventional tillage. Yet, the implications of these tillage-induced alterations for soil organic matter stability remain poorly understood. Gaining a deeper understanding of soil organic matter stability is essential in the context of global warming and increasingly variable rainfall patterns.
Here, we investigated depth-dependent patterns of soil respiration and its temperature sensitivity under conventional tillage (CT) and reduced tillage (RT) as well as under current (100%) and reduced rainfall (50%) in a temperate cropland. Soils were sampled in January 2025 from a long-term tillage experiment established in 1970 in central Germany on a Haplic Luvisol under a humid temperate climate (mean annual air temperature 9.6 ± 0.7°C; mean annual precipitation ~610 ± 120 mm). The field trial follows a randomized block design with 16 plots, including eight managed under CT with mouldboard ploughing to 27–30 cm and eight under RT with rotary harrowing to 7–10 cm. Rainout shelters, designed to remove 50% of rainfall, were installed in 2022 in half of the plots. Soils for the incubation experiment were collected from four replicate plots per tillage treatment and under 100% rainfall at four depths (i.e., 0–10, 10–20, 20–30, and 30–60 cm). Additional samples from rainfall-exclusion plots were collected in August 2025 and are currently being analysed.
Laboratory incubations were performed under controlled conditions using an automated Respicond system. Soils were sieved, adjusted to 60% water holding capacity, and incubated under stepwise temperature changes from 5 to 25°C, followed by a cooling phase back to 5°C, with temperature sensitivity analyses primarily based on the second incubation phase.
Preliminary results under normal rainfall conditions showed that respiration rates were highest in surface soils and declined with depth, while the deepest layer (i.e., 30–60 cm) showed comparatively low and less temperature-responsive respiration. Depth patterns differed between tillage systems: reduced tillage enhanced respiration in the topsoil, whereas conventional tillage showed higher respiration at intermediate depths (10–30 cm), reflecting contrasting vertical distributions of SOC and organic matter fractions. No significant tillage effects on respiration were observed below the plough layer.
Across both tillage practices, temperature sensitivity declined significantly with soil depth, indicating weaker relative temperature responses in subsoils. Mean temperature sensitivity values did not differ between CT and RT when averaged across depths. Normalisation to organic matter fractions showed lower temperature sensitivity of MAOM-associated respiration compared to POM-associated respiration, consistent with differences in substrate quality and energetic constraints on decomposition.
Overall, tillage primarily redistributed organic matter within the topsoil, while subsoil carbon exhibited lower temperature sensitivity, suggesting reduced responsiveness to short-term warming with important implications for modelling soil carbon–climate feedbacks. Ongoing analyses will assess how two years of reduced rainfall modify the vertical distribution and temperature sensitivity of soil organic matter.
How to cite: Iddris, N. A.-A., Apostolakis, A., Hanczaryk, J. S., Tyystjärvi, V., Schimmel, H., Bauke, S., and Meijide, A.: Depth-dependent temperature sensitivity of heterotrophic soil respiration under long-term tillage and reduced rainfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19558, https://doi.org/10.5194/egusphere-egu26-19558, 2026.
Organic nitrogen (ON) represents the majority of nitrogen compounds found in soil systems, although often overlooked in favour of the minority of more bioaccessible inorganic nitrogen compounds. One of the main pools of soil ON is mineral-associated organic matter (MAOM), in these complexes organic compounds chemically and physically interact with soil mineral surfaces. Understanding ON cycling in soils is paramount to ensuring sustainable management of soil resources and predicting pollutant nitrogen outgassing. A key aspect of this, is understanding ON vulnerability to microbial breakdown. Previous work has shown how organic matter in MAOM complexes can persist in soils for centuries, protected from microbial degradation. However, more recent research has highlighted that organic matter can be mobilised from soil mineral surfaces and become accessible to microbes once more. MAOM complexes therefore can represent a far more dynamic pool of nitrogen than previously thought and the drivers of their formation need more robust characterisation. Our research focused on abiotic soil properties as potential drivers of ON adsorption to soil mineral surfaces, as well as the influence of time and the identity (chemistry and size) of investigated nitrogen compounds. Soil mineralogy data, from XRF analysis, as well as soil texture and pH data were coupled with adsorption assays and mixed effects modelling. This revealed the dominant influence of adsorbate identity on total adsorption and rate of adsorption to soil mineral surfaces. The presence of aluminium and iron, both common in soils and reactive with organic matter, and soil pH also had significant influences on nitrogen compound adsorption. These findings add to the growing body of literature on the drivers of MAOM complex formation, support the use of newer adsorption potential proxies, and highlight the importance of considering organic matter identity when predicting nitrogen recalcitrance in soils.
How to cite: Vaughan, A., Purchase, M., and Mushinski, R.: MAOM Formation: Abiotic Drivers of Soil Organic Nitrogen Adsorption to Soil Mineral Surfaces, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7560, https://doi.org/10.5194/egusphere-egu26-7560, 2026.
High organic carbon (OC) in agricultural sandy soils (>85% sand) is generally unexpected under prevailing paradigms of organic matter (OM) formation and stabilisation, which emphasise mineral protection. Nevertheless, so-called “black sand” soils are widespread in north-western Europe and store exceptionally large amounts of OC. Much of this OC resides in the finest soil fractions and is chemically enriched in alkyl C, likely reflecting historic heathland vegetation, but it remains unclear whether this enrichment is associated with minerals or occurs within largely organic microstructures. To address this, we combined particle-size fractionation, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, optical photothermal infrared (O-PTIR) microscopy, and nanoscale secondary ion mass spectrometry (NanoSIMS) to investigate OM organisation and composition at the microscale. Fine fractions stored a disproportionate amount of OC, showing pronounced alkyl enrichment and a decline in O/N-alkyl C. NanoSIMS revealed that OM occurred as finely divided domains rather than intact particles. OM-dominated areas expanded with increasing OC, and while some OM was associated with Al-rich domains, much showed no clear mineral association, indicating that OM accumulation is not solely driven by organo-mineral interactions. O-PTIR revealed alkyl-rich microdomains reflecting the chemical signature of historic vegetation. Aliphatic signals increased with OC content and OM coverage, indicating that SOC in black sand soils is stored as micrometre-scale, alkyl-rich micro-particulate OM. This challenges mineral-centric concepts of SOC stabilisation and highlights the importance of OM–OM interactions and land-use legacy in controlling carbon storage in sandy soils.
How to cite: Colocho Hurtarte, L. C., Sandt, C., Höschen, C., Kögel-Knabner, I., Lugato, E., Urbanski, L., and Schweizer, S. A.: High organic matter accrual in black sand soils linked to microscale aliphatic hotspots, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20000, https://doi.org/10.5194/egusphere-egu26-20000, 2026.
Molecular diversity has been proposed as a critical factor controlling soil organic matter (SOM) persistence. However, in contrast to dissolved organic matter, molecular diversity of solid phase organic matter remains largely unexplored. Here, we show the molecular diversity features of solid phase organic matter through a direct mass spectrometric scan of particulate and mineral associated organic matter (POM and MAOM) that show a strong relationship with carbon turnover rates, collected from a long-term grassland recovery experiment after 0, 23, and 43 years. We found that the highest molecular diversity (Hill Number = 1603±124) existed in SOM that had the slowest carbon turnover rate. Molecular diversity of MAOM exhibits greater correlation (R2 = 0.95, p < 0.001) with SOM persistence than that of POM. Molecular diversity became increasingly enriched from top to subsoil horizons (360% increase), consistent with a breaking down of large molecules into a range of low- to high-molecular-weight molecules. Soil depth and total iron content were main factors impacting the diversity change of POM and MAOM, highlighting the combined control of microbial decomposition and mineral interaction in shaping molecular features of solid phase organic matter. Together, these results suggest that molecular diversity may not operate as a limiting factor for carbon utilization by decomposers but as an ecosystem property that incorporates organo-mineral interactions.
How to cite: Yang, Z. and Sun, T.: Solid Phase Molecular Diversity Enhances Soil Organic Matter Persistence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21126, https://doi.org/10.5194/egusphere-egu26-21126, 2026.
Posters on site: Tue, 5 May, 10:45–12:30 | Hall X3
Soil respiration is a widely used indicator of microbial activity and soil organic matter dynamics, reflecting both intrinsic biochemical processes and external disturbances. This contribution presents an optimised approach for soil respiration measurement using the OxiTop®-IDS respirometric system (DIN ISO 16072), with emphasis on improving experimental sensitivity and reproducibility. Key incubation parameters, including soil moisture, temperature, sample mass, and incubation time, were systematically optimised under controlled laboratory conditions. The refined methodology was applied to soils from the Czech Republic and to soils collected in selected regions of Ukraine partially affected by armed conflict, enabling a comparative assessment of microbial activity across contrasting environmental conditions. The method was further tested by evaluating the effects of soil amendments, including biochar and hydrogel-based preparations containing soil bacteria, on respiration rates. Automated carbon dioxide monitoring allowed continuous quantification of microbial responses to organic matter inputs. Results demonstrate that both soil origin and amendment type significantly influence soil respiration, confirming the suitability of optimised respirometric techniques for assessing soil biochemical status and microbial functioning in non-disturbed as well as disturbed and degraded soils.
Acknowledgement
This work was supported by the NATO Science for Peace and Security Programme, project Nr. G6296. https://land-security.org/.
How to cite: Kalina, M., Hlavackova, B., Svecova, M., and Pekar, M.: Optimisation of Soil Respiration Measurement Using OxiTop®-IDS as a Tool for Assessing Microbial Activity and Organic Matter Dynamics in Soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3072, https://doi.org/10.5194/egusphere-egu26-3072, 2026.
Forest conversion to plantations represents a major global land-use change with profound consequences for soil nutrient cycling and strongly impacts coupled carbon (C), nitrogen (N), and phosphorus (P) stoichiometry across ecosystem compartments. Building on stoichiometric homeostasis theory and ecosystem feedback concepts, we conducted a global meta-analysis of 126 studies to quantify how forest-to-plantation conversion alters C:N:P ratios in plant litter, soil pools, microbial biomass, and extracellular enzyme activities, and to identify the key drivers of these responses.
Overall, forest conversion to plantations was associated with declines in soil C and N contents, microbial biomass, enzyme activities, and soil C:P ratios, whereas microbial biomass C:P ratios increased. These contrasting responses indicate a decoupling of P from C and N cycling following conversion, reflecting enhanced P recycling and intensified P limitation for soil microorganisms. Soil and microbial C:N and N:P ratios had stabilizing feedbacks, showing limited directional change despite large shifts in pool sizes, whereas C:P ratios displayed intensifying feedbacks, particularly within microbial biomass and enzyme activities. These patterns suggested weak microbial stoichiometric homeostasis in response to changes in resource quality and availability within plantation systems. Plant functional traits strongly modulated stoichiometric outcomes. Narrow C:P and N:P ranges in coniferous species pointed to tighter nutrient regulation compared with broadleaf systems, and conversion effects differed markedly depending on plantation type. Litter quantity and quality emerged as key regulators of soil C and N pools, whereas soil P pools responded weakly to conversion, highlighting efficient internal P recycling. Microbial and enzymatic stoichiometric imbalances increased after conversion, indicating growing nutrient divergences between microbial demand and resource supply, except in coniferous-to-coniferous conversions, where some imbalances decreased. Random Forest analyses identified soil pH and climatic variables as dominant abiotic controls of soil stoichiometric responses, while leaf, root, and litter C:N:P ratios were the primary biotic drivers of microbial biomass and enzyme stoichiometry.
This meta-analysis provided the first global, cross-compartment synthesis of C:N:P stoichiometry responses to forest-to-plantation conversion. By linking biogeochemical shifts to microbial homeostasis and ecosystem feedback mechanisms, our findings revealed multidirectional and decoupled nutrient responses that challenge simplified assumptions of uniform nutrient limitation. These insights underscore the importance of species selection, residue management, and long-term monitoring to mitigate stoichiometric imbalances and sustain nutrient cycling in plantation ecosystems.
How to cite: Gunina, A., Wang, Y., and Sun, T.: Forest-to-plantation conversion reshapes C:N:P coupling across soil–microbe–enzyme systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5186, https://doi.org/10.5194/egusphere-egu26-5186, 2026.
The mountain soils of the Andes, especially in the Puna ecoregion (above 3500 m elevation), have been shown to maintain disproportional soil carbon stocks derived from an abundance of soil organic matter (SOM). However, the mechanisms governing the stabilization of SOM in this understudied tropical high-alpine region remain elusive; in particular with respect to the interplay with human land management in the area. Here we present the results of a study in the Miraflores area of the Peruvian Andes where soils are cultivated on terraces under a rotational system that has been in place for 9,000 years. This system alternates 2-4 years of cultivation with 9-11 years of regeneration, In our study, we quantified soil carbon stocks in several soil carbon fractions—total organic carbon, labile carbon, soluble organic carbon—as well as associated aluminium, iron and calcium pools. Moreover, we examined the molecular composition of SOM under different land-use types within the region.
The results show pronounced differences in carbon accumulation and decomposition between terraced soils (cropped, cropped but outside the rotation, regenerating and abandoned terraces) and non-terraced soils (grazing land, natural grassland and peatland). We found the rotational crop management to exert a more beneficial effect on SOM accumulation and composition than continuous agriculture without rotation. The preservation of organic was driven primarily by land-use practices, plant-derived litter inputs and microbial activity, while soil mineralogy appeared to play only a minor role in carbon stabilization in this landscape.
Overall, our findings underscore the importance of sustainable land management in high-altitude ecosystems for strengthening carbon sequestration and reducing the impacts of climate change, particularly in highly susceptible mountain regions.
How to cite: Jansen, B., Hansen, J., and Cammeraat, E.: The effects of traditional rotational terrace agriculture in the high Andes on the dynamics of their soil organic matter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5698, https://doi.org/10.5194/egusphere-egu26-5698, 2026.
Mineral-associated organic carbon (MAOC) constitutes the largest and most persistent pool of soil organic carbon, yet the pathways through which new plant inputs are stabilised in MAOC remain actively debated. In particular, the relative contributions of microbial processing versus direct physical transfer from particulate organic carbon (POC) from the plant are still poorly constrained. Here, we combined rare earth oxide (REO) labelling, stable carbon isotopes (δ¹³C), and controlled soil incubations to trace carbon redistribution between POC and MAOC in two soils with contrasting carbon status. Reconstituted soils containing independently REO-labelled POC and MAOC were amended with sugarcane mulch that had undergone different water-processing treatments to systematically manipulate carbon solubility and microbial accessibility. Carbon dynamics were monitored over a 180-day incubation using physical fractionation, respiration measurements, isotopic mass balance, and REO recovery, and interpreted within a POC–MAOC phase-space framework to track the different pathways of carbon stabilization (Manzoni and Cotrufo, 2024). To better align this framework with the objectives of the present study, we adapted its application to explicitly resolve the fate of newly added plant-derived carbon. Rather than treating POC as a single composite pool, we quantified the incorporation of mulch-derived carbon separately within POC and MAOC using isotope-based partitioning. This integrated approach enables direct comparison of physical redistribution and microbial transformation pathways, providing new mechanistic constraints on MAOC formation under contrasting input bioavailability and soil conditions.
How to cite: Liu, J., Farrell, M., Karunaratne, S., Wright, C., and Pasut, C.: Tracing carbon stabilization pathways in soil incubation using isotopes, REOs, and phase-space modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8637, https://doi.org/10.5194/egusphere-egu26-8637, 2026.
There is a growing interest in characterising distinct forms of soil organic carbon (SOC) with contrasting turnover times. In Australia, a well-established approach combining physical size fractionation (coarse >50 µm and fine <50 µm) with chemical characterisation has been developed to quantify a resistant organic carbon (ROC) fraction, commonly referred to as ‘char-like’ carbon. This fraction is typically characterised by 13C nuclear magnetic resonance (NMR) spectroscopy. However, hydrofluoric acid (HF) pre-treatment is often needed to remove paramagnetic soil minerals that interfere with magnetic resonance measurements and to concentrate carbon sufficiently to generate a detectable 13C NMR signal. It is recognised that this pre-treatment, while necessary to enable NMR analysis, may affect SOC chemistry, generating artefacts. While the combined size-fractionation scheme followed by NMR analysis has evolved over nearly two decades, increasing attention is now being given to comparisons between ‘char-like’ carbon estimates derived from combining size fractionation with 13C NMR analysis and those obtained using thermal step-ramping methods. In this study, we hypothesised that removing mineral particles (clay + silt) from the fine fraction does not significantly affect estimates of ROC derived using stepwise thermal ramping, quantified between 400°C and 600°C. To this end, we analysed a total of 111 soil samples collected from diverse soil types across Australian agricultural production regions. Topsoil samples were collected at three depth intervals (0-10 cm, 10-20 cm, and 20-30 cm). Fine-fraction 13C NMR-based ROC estimates were directly compared with the thermal step-based ramping ROC estimates, analysed both before and after HF pre-treatment of the fine fraction. Key findings of this research will provide underpinning knowledge to assess whether the removal of the mineral phase by HF treatment affects estimates of the ROC fraction derived from stepwise thermal ramping. The results further enable evaluation of similarities and differences between ROC or ‘char-like’ carbon concentrations estimated using 13C NMR and thermal step-ramping methods for the fine fraction of soils, with important implications for method application and inter-model comparisons.
How to cite: Damatirca, C., Farquharson, R., Asanopoulos, C., Mcgowan, J., Farrell, M., Macdonald, B., and Karunaratne, S.: Mineral removal and its influence on thermal step-ramping estimates of resistant organic carbon in fine soil fractions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8914, https://doi.org/10.5194/egusphere-egu26-8914, 2026.
Grassing of arable land is a widely adopted restoration strategy to rebuild soil fertility and enhance soil organic carbon (SOC) stabilization, but the contribution of plant species richness during the initial phases of restoration remains unclear. In a four-year field experiment, we compared a species-poor clover–grass mixture and a species-rich regional mixture, using permanent grasslands as control, to assess changes in soil physical properties, soil biota, and SOC fractions. Root biomass in permanent grassland was initially 2241% higher than in both seed mixtures but rapidly converged, with differences declining to 101% after four years. Both seed mixtures significantly increased soil organic matter content and water-holding capacity while reducing bulk density, indicating rapid recovery of soil structure driven by grass-dominated root systems. Soil microbial activity, microbial biomass carbon, and nitrogen were initially 62%, 286%, and 304% higher in permanent grassland, respectively, but these differences diminished substantially over time, demonstrating rapid microbial recovery independent of species richness. SOC fractionation revealed comparable increases in particulate and mineral-associated organic matter under both mixtures, indicating that early SOC stabilization was primarily controlled by root-derived carbon inputs rather than plant diversity. Strong correlations among root biomass, microbial properties, and SOC fractions highlight the key role of root–microbe interactions in driving early SOC stabilization during grassland restoration. Overall, early soil recovery and SOC stabilization after grassing are driven primarily by continuous root-derived C inputs and biotic transformations, while higher plant diversity may enhance long-term soil multifunctionality and C persistence.
How to cite: Roy, A., Tajovský, K., Devetter, M., Libra, M., Pižl, V., Tuma, J., Tůmová, M., and Jílková, V.: Root-derived carbon inputs dominate early soil recovery after grassing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9621, https://doi.org/10.5194/egusphere-egu26-9621, 2026.
Climate change and forest management are expected to alter plant carbon allocation and dissolved organic carbon (DOC) inputs to soils, with potentially strong but poorly constrained consequences for soil organic carbon (SOC) dynamics. While DOC inputs can stimulate microbial decomposition through priming effects, they may also contribute to SOC stabilization via microbial processing and mineral association. However, the relative roles of aboveground and belowground DOC inputs, their chemistry, and interactions with soil biotic communities across forest types and soil depths remain insufficiently understood.
Here, we investigated the effects of plant-derived DOC inputs on SOC dynamics using a field manipulation experiment that disentangled aboveground (leaf leachates) and belowground (root exudates) DOC inputs in broadleaf (European beech) and coniferous (Norway spruce) forest stands. We quantified short-term responses of SOC fractions—free particulate organic matter (fPOM), occluded particulate organic matter (oPOM), and mineral-associated organic matter (MAOM)—in mineral topsoil (0–10 cm) and subsoil (50–60 cm), and related these responses to DOC input chemistry as well as microbial and faunal properties.
Despite the relatively short experimental duration (two years), DOC inputs exerted pronounced effects on SOC fraction dynamics, with responses strongly dependent on organic matter fraction and soil depth. Both leaf leachates and root exudates induced SOC formation as well as loss, depending on the fraction considered. Regarding soil depth, SOC fractions in the subsoil were generally less responsive to DOC inputs than those in the topsoil, indicating greater short-term vulnerability of topsoil SOC to DOC-induced losses. In contrast, forest type had only minor influence on DOC-driven SOC dynamics, suggesting that DOC input chemistry and point of entry outweigh tree species identity as short-term controls of SOC dynamics.
Our results demonstrate that short-term SOC responses to DOC inputs are governed primarily by DOC input chemistry, organic matter fraction stability, and soil depth rather than forest type. Explicit consideration of above- and belowground DOC pathways and microbial mediators is therefore essential for predicting forest SOC responses to environmental change.
How to cite: Libra, M., Jílková, V., Čápová, K., Devetter, M., Hubáček, T., Jandová, K., Kukla, J., and Starý, J.: Short-term changes in plant dissolved organic carbon inputs are fundamental inmediating soil organic carbon dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11788, https://doi.org/10.5194/egusphere-egu26-11788, 2026.
Biochar is widely promoted as a climate-mitigation strategy, yet its effects on carbon persistence in subsoil remain poorly constrained. Here we show that long-term surface biochar application substantially increases soil organic carbon (SOC) storage in subsoil by suppressing SOC decomposition. In a 14-year field experiment with compound-specific δ13C and Δ14C analyses, SOC increased by 40 ± 3.7 Mg C ha–1 across a one-meter profile, with 17% of this increase occurring below 20 cm. Biochar stabilized plant-derived carbon in topsoil via enhanced microbial transformation and mineral association, while the reduced vertical carbon transport constrained carbon supply to subsoil, suppressing native SOC decomposition and extending its radiocarbon age by 690 ± 57 years. These patterns were confirmed by five additional biochar experiments and a global meta-analysis, indicating broad applicability. Globally, this mechanism could offset 2.2–6.9% of annual agricultural greenhouse-gas emissions, highlighting subsoil as a resilient, underappreciated carbon sink under long-term biochar management.
How to cite: Chen, Y., Sun, K., and Chen, J.: Biochar suppresses subsoil carbon decomposition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11869, https://doi.org/10.5194/egusphere-egu26-11869, 2026.
The capacity and long-term stability of soil organic carbon (SOC) are governed by its composition. SOC is commonly conceptualized as two major pools: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). While POC represents a labile fraction that responds rapidly to management and environmental change, MAOC is stabilized through physical and chemical associations with soil minerals, resulting in substantially longer turnover times.
Although the concept of carbon saturation has been widely discussed, empirical information on the spatial distribution of POC and MAOC contrasting pedo-climatic conditions remains limited, particularly at regional scales. As a result, the extent to which agricultural soils are able to further accumulate SOC under different environmental settings is still poorly constrained.
In this study, we investigate the distribution of POC and MAOC in cropland soils across Czechia by combining physical size fractionation method with digital soil mapping. Soil samples from a nationwide sampling network are separated to quantify POC and MAOC stocks down to 0.6 m soil depth. These data will be integrated with spatially explicit, high-resolution environmental covariates, including climate variables, soil properties, and terrain attributes, to model the distribution of carbon fractions across 25 major pedo-climatic zones.
These results will provide insights into the current carbon saturation of cropland soils under different pedo-climatic conditions. This further allow identification of regions with a high potential for additional carbon sequestration, as well as areas where SOC stocks may already be constrained by mineralogical or climatic limitations. The expected outcomes will contribute to a process-based understanding of SOC stabilization at the landscape scale and provide a basis for region-specific soil carbon management and climate-mitigation strategies.
How to cite: Margoldová, A., Skála, J., Žížala, D., Chuman, T., Vindušková, O., and Frouz, J.: Carbon stability of cropland soils in Czechia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11958, https://doi.org/10.5194/egusphere-egu26-11958, 2026.
Assessing the chemical composition of soil organic matter (OM) inputs is essential to understand and simulate soil OM decomposition dynamics and thus better evaluate the soil contribution to the global C balance. The Van Soest (VS) chemical extraction distinguishes four fractions of the OM namely “soluble”, “hemicellulose-”, “cellulose-” and “lignin-”like compounds. However, this procedure is time-consuming, costly, and requires acids, solvents and detergents. The Rock-Eval® (RE) thermal analysis consists of pyrolysis of the sample followed by oxidation of the residue. Since the 2000s, it has been increasingly used in soil science to quantify soil organic carbon (SOC) via the TOC parameter and to characterize SOC thermal stability, a proxy of biological stability, through various indices. Although several studies have investigated the relationship between SOC thermal stability and the chemical composition of soil OM, it has to be consolidated in order to identify and quantify the main components of OM, especially for OM of litters. In this study, we further explored this relationship by comparing the chemical composition (VS fractions) and the RE-derived parameters determined on various agricultural and forestry litters. The RE signals obtained before (bulk sample) and after the VS extraction (lignin-like compound residue) were compared. The effect of the VS extraction was reflected on the RE signals of the lignin-like compound residue. The thermolabile compounds emitted during the pyrolysis were lost and the CO and CO2 signals obtained during the oxidation resembled those of pure lignin. Correlation matrix between the RE parameters and the VS fractions were performed. The cellulose and hemicellulose proportions were positively correlated to the hydrocarbon compounds (HC) emitted below 340 °C (named A1, Spearman coefficient = 0.75, p-value < 0.05) and the CO2 emitted during pyrolysis (named S3CO2, Spearman coefficient = 0.76, p-value < 0.05), respectively. These results confirmed the previous assumptions that the A1 proportion and the S3CO2 signal are tightly related to the amount of carbohydrates in OM. The lignin proportion was positively correlated to the temperature at which 50 % of the total HC signal is emitted (Spearman coefficient = 0.75, p-value < 0.05). Additional insights about these relationships will be provided by Fourier-Transform Infra-Red spectroscopy (FTIR). A multivariate modelling approach will be developed to explore the predictive performance of RE data for estimating the chemical composition of OM assessed with VS fractions and with FTIR.
How to cite: Hazera, J., Baudin, F., Delarue, F., Chevallier, T., Barre, P., and Sebag, D.: Bridging Rock-Eval® thermal signature and Van Soest chemical composition of litters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12285, https://doi.org/10.5194/egusphere-egu26-12285, 2026.
Mountain soils are important carbon reservoirs, yet the distribution and stability of soil organic carbon (SOC) in deep soil horizons remain poorly understood, particularly in temperate mid-elevation mountain regions. Although vegetation is recognized as a key control on the vertical distribution and stabilization of SOC, its influence on deep soil carbon pools remains largely unexplored. This study investigates the content, composition and stability of SOC in topsoil and deep soil horizons under different vegetation types in the Bieszczady Mountains (Eastern Carpathians, SE Poland).
The research was conducted under four contrasting vegetation types representing forest and non-forest ecosystems: Vaccinietum myrtilli, Calamagrostietum arundinaceae, Dentario glandulosae–Fagetum and Campanulo serratae-Agrostietum. For each vegetation type, representative soil profiles were excavated and sampled by genetic horizons from surface organic layers to deep mineral horizons. Basic soil properties, including pH, soil texture and mineral composition, were determined to characterize environmental controls on SOC stabilization.
Soil organic carbon and total nitrogen contents were measured using elemental analysis. The chemical composition of soil organic matter (SOM) was examined using Fourier-transform infrared (FTIR). To evaluate SOC stability, soil organic matter (SOM) was separated using a density-based physical fractionation method, which allows the isolation of labile particulate organic matter from mineral-associated, more stable carbon pools. Additionally, soil respiration measurements were used to assess microbial activity and potential SOC mineralization.
This approach helps to understand how different types of vegetation influence both the quantity and stability of SOC in topsoil and subsoil layers. The results can provide new insights into carbon sequestration mechanisms in temperate mountain ecosystems and hightlight the significant role of deep soil horizons in long-term carbon storage.
How to cite: Kramarczuk, P.: Content and stability of topsoil and deep soil organic carbon under different vegetation types in the Bieszczady Mountains (Eastern Carpathians, SE Poland), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13971, https://doi.org/10.5194/egusphere-egu26-13971, 2026.
Paddy soils represent a globally significant agroecosystem, functioning both as the primary environment for irrigated rice (Oryza sativa L.) production and as extensive anthropogenic wetlands with a major role in soil organic carbon (SOC) sequestration. Under climate change, increasing temperatures and reduced water availability threaten soil health, carbon (C) stability, and the long-term resilience of these systems.
This study evaluates how anaerobic digestate application influences soil organic matter (SOM) dynamics in paddy soils under simulated climate stress. A factorial field experiment tested amendment application (digestate, DS; unamended control, UN), temperature (ambient, AM; warming, +2 °C, WR), and water regime (normal flooding, NF; reduced flooding, - 30%, RF). SOM was fractionated into particulate (POM) and mineral-associated organic matter (MAOM) pools, which were characterized using Fe K-edge XANES and k²-weighted EXAFS to resolve Fe speciation and coordination environments controlling C stabilization.
Across treatments, SOC declined under warming, with WR plots losing up to 15% more SOC than AM, while digestate under NF partially mitigated SOC losses and reduced C/N ratios, indicating enhanced microbial processing.
XANES revealed strong fraction- and management-dependent shifts in Fe speciation, showing that POM was enriched in redox-sensitive Fe phases and Fe-organic complexes that responded markedly to reduced flooding and warming, whereas MAOM was dominated by illite-associated Fe and Fe (III) oxyhydroxides. Complementarily, k²-weighted EXAFS resolved the short-range Fe coordination environment, indicating that POM contained mixed crystalline Fe (III) phases (hematite and lepidocrocite) embedded within a variable mineral matrix, while MAOM was systematically enriched in poorly ordered Fe (III) phases, including ferrihydrite-like and Fe (III)-organic associations, indicative of persistent mineral-protected C pools. Together, XANES and EXAFS demonstrate that climate stress primarily destabilizes SOC by disrupting redox-controlled Fe-organic associations in the labile POM fraction, whereas long-term carbon persistence under future warming scenarios depends on the maintenance of Fe (III) oxyhydroxide-mediated protection within MAOM, only weakly modulated by organic amendment and water regime.
How to cite: Giannetta, B., Oliveira de Souza, D., and Zaccone, C.: Redox-driven iron mechanisms regulating soil organic carbon stabilization in paddy soils under warming and altered flooding, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16484, https://doi.org/10.5194/egusphere-egu26-16484, 2026.
Pyrogenic organic matter (PyOM) significantly contributes to soil carbon (C) sequestration, yet its stability in terrestrial ecosystems is more dynamic and biologically responsive than previously assumed. A thorough understanding of mechanisms governing PyOM stability is critical, given increased wildfire occurrence and associated PyOM production in a warming climate and the potential feedbacks to the global C cycle. This review highlights how warming-driven changes in soil biological processes directly and indirectly influence PyOM persistence. Our synthesis reveals that long-term soil warming initiates a cascade of competing biological processes. For example, warming enhances microbial oxidative enzyme activity and stimulates co-metabolic breakdown of labile PyOM components, notably its dissolved fraction, via greater plant-derived labile C input. Conversely, soil warming promotes mechanisms of stabilization, as microbial surface oxidation strengthens organo-mineral bonds and increased bioturbation by soil fauna transports PyOM fragments into deeper, mineral-protected soil layers. These opposing processes operate simultaneously, resulting in a dynamic balance between decomposition and stabilization. This balance may be further modified by warming-associated changes in soil moisture, which can suppress both decomposition and stabilization processes. Critically, the prevailing outcome is dictated by the intrinsic heterogeneity of the PyOM in question. Low-temperature PyOM is more vulnerable to enhanced decomposition, while high-temperature, lignin-rich PyOM is more resistant to decomposition and enters stabilization pathways. We conclude that the net persistence of PyOM in a warming climate depends on the dynamic balance between biological decomposition and physicochemical stabilization, controlled by interactions among PyOM properties, soil biota, and environmental drivers.
How to cite: Zhao, Y., DeLuca, T. H., and Jílková, V.: Warming-Driven Biological Mechanisms Governing the Fate of Pyrogenic Organic Matter in Soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17618, https://doi.org/10.5194/egusphere-egu26-17618, 2026.
Management of soil organic carbon (SOC) has attracted attention because of its critical role in maintaining soil health and mitigating global climate change. In tropical and subtropical soils, where SOC decomposes quickly, long-term SOC accumulation depends on stabilizing organic carbon (OC) as mineral-associated organic carbon (MAOC). Previous studies suggest that binding agents of MAOC vary with soil pH: clay content and exchangeable Ca/Mg are key controls in alkaline soils, whereas active Al/Fe (hydr)oxides in acidic soils. Meanwhile, MAOC is regulated not only by the abundance of these binding agents but also by their OC-stabilization capacity, both of which are likely pH-dependent yet remain poorly quantified. Thus, this study aims to (1) clarify the controls (e.g., precipitation, net primary production (NPP), binding agents) on MAOC, (2) quantify OC-stabilization capacity of main binding agents, with the investigation of their OC-stabilization mechanism across soil pH gradients.
A total 72 soil samples spanning strongly acidic (pH ≤ 5.5), weakly acidic (5.5 < pH ≤ 7), and alkaline (pH > 7) conditions were collected from Indonesia (n=14), Japan (n=12), Cameroon (n=16), Tanzania (n=13), and India (n=17). MAOC was quantified using density and particle-size fractionation (density > 1.7 g cm⁻³, particle size < 53 μm). Correlation analyses and structural equation models (SEM) were used to identify the primary controls on MAOC contents, incorporating NPP, precipitation, soil pH, exchangeable Ca/Mg, clay content and active Al/Fe as candidate explanatory variables for each pH class. Based on the unstandardized SEM coefficients, the OC-stabilization capacity of main binding agents was quantified. To assess the OC-stabilization mechanism, necromass C and non-necromass C (i.e., MAOC − necromass) were quantified and investigated relationship with the binding agents using correlation/regression analyses.
MAOC contents were 78 % of total SOC across all samples, with alkaline soils showing lower MAOC and active Al/Fe than strongly acidic and weakly acidic (42 vs. 181 vs. 238 cmol kg⁻1, respectively) (4.6 vs. 9.2 vs. 17 cmol kg⁻1, respectively). Correlation and SEM analysis identified active Al/Fe content as the primary control of MAOC content rather than clay content and NPP, across all pH classes. Exchangeable Ca/Mg showed no significant contribution even in alkaline conditions. These results indicate that lower MAOC in alkaline soils is due to the lower active Al/Fe content. Furthermore, the SOC stabilization capacity of active Al/Fe was also 28% lower in alkaline soil than in weakly acidic and strongly acidic. In strongly and weakly acidic soils, active Al/Fe was positively correlated with both necromass and non-necromass C, whereas active Al/Fe was positively correlated with non-necromass C but showed no relationship with necromass C in alkaline soils. These results suggest that in alkaline soils, active Al/Fe stabilizes non-necromass C but not necromass C, causing the low OC-stabilization capacity. Thus, in tropical and subtropical regions, active Al/Fe are the primary control on MAOC binding in all pH class, and their low abundance and low OC-stabilization capacity in alkaline soils partly explain the low MAOC and SOC contents.
How to cite: Tokunaga, A., Lyu, H., Seki, M., Tanaka, H., Hartono, A., Muniandi, J., Pandian, K., Shibata, M., Watanabe, T., Funakawa, S., and Sugihara, S.: Same Binding Agent with Different Stabilization Capacities Regulates Soil Organic Carbon Across pH Gradients in Tropical and Subtropical Soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17787, https://doi.org/10.5194/egusphere-egu26-17787, 2026.
How to cite: Vancampenhout, K., Cordaro, T., Muys, B., and Desie, E.: Restoration effects on forest soil carbon dynamics and overall soil health: a management perspective, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18879, https://doi.org/10.5194/egusphere-egu26-18879, 2026.
Organically managed grass-clover leys are often claimed to improve soil quality and are considered as a cornerstone of sustainable agricultural practice. However, our earlier results from an organically managed farm in Tingvoll (NW Norway) demonstrated soil organic matter (SOM) content declined over the 35 years following the adoption of organic management, in parallel with increase in temperature and decrease in phosphor availability. In 2011, a field experiment was established on part of the grass-clover ley to study the effects of anaerobic digestion of dairy cattle slurry, i.e. waste product of a biogas reactor, on crop yield and soil characteristics. Slurry application, both treated and untreated, was normalized on the nitrogen content. As part of the global C-arouNd consortium, which aims to investigate how short- and long-term agricultural management practices affect SOM persistence, we are investigating how the long-term slurry applications have affected that and other nutrients.
Since spring 2024, greenhouse gas emissions were recorded and plant material and soil were sampled. Preliminary results showed a higher SOM concentration with slurry application compared to the control, whereby anaerobic digested slurry let to significantly higher carbon and nitrogen contents in the soil than untreated slurry and unamended soil
More detailed analysis of the soil, using an advanced density-thermal fractionation protocol, should give more insight into the long-term persistence of SOM. We expect that by first separating the Particulate from Mineral-Associated OM we will find a more thermally stable Mineral-Associated OM fraction under anaerobically digested slurry application, highlighting changes in SOM composition.
How to cite: Zethof, J. H. T., Zimmermann, J. M., Schützenmeister-Rex, K., Rittl, T. F., and Jungkunst, H. F.: Anaerobic digestation turns the tide: Does long-term digested slurry input boost SOM persistence in a Norwegian grass-clover ley?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20841, https://doi.org/10.5194/egusphere-egu26-20841, 2026.
Biopolymers, including nucleic acids, proteins, and carbohydrates, constitute a substantial fraction of soil organic matter (SOM). The adsorption of these biopolymers to mineral surfaces is widely regarded as a key protection mechanism against environmental decay, particularly from ubiquitous microbial enzymes, thereby facilitating long-term persistence.1 While extensive research has examined how the chemical composition governs organic matter adsorption and stability, the role of molecular size, particularly biopolymer length, remains poorly understood.2
Using DNA as a model biopolymer and minerals with diverse surface properties (goethite, ferrihydrite, kaolinite, montmorillonite, and hydroxyapatite), we investigated how polymer length affects both adsorption and protection against enzymatic decay. Results show that under competing conditions, shorter polymers exhibited preferential adsorption to all mineral surfaces. Furthermore, we examined enzymatic hydrolysis using DNase I as a model endonuclease. In solution, hydrolysis followed second-order kinetics with rate constants scaling linearly with the polymer length. Remarkably, while adsorbed DNA also showed length-dependent hydrolysis rates, hydrolysis ceased entirely for fragments below 50 base pairs—a threshold absent in solution.
This critical length threshold agrees very well with the median DNA polymer length observed across diverse environmental samples, providing experimental evidence for adsorption-driven enhanced protection of ultrashort biopolymers in soil and sediments.3,4 Our findings demonstrate that polymer length is a fundamental determinant of biopolymer persistence at mineral surfaces, with important implications for understanding MAOM stability. These results suggest that molecular properties, especially size and polymer length of organic matter, warrant greater consideration in SOM stabilization models and management strategies.
References
1. Kleber, M. et al. Dynamic interactions at the mineral–organic matter interface. Nat. Rev. Earth Environ. 2, 402–421 (2021).
2. Yu, W. H. et al. Adsorption of proteins and nucleic acids on clay minerals and their interactions: A review. Appl. Clay Sci. 80–81, 443–452 (2013).
3. Sawyer, S., Krause, J., Guschanski, K., Savolainen, V. & Pääbo, S. Temporal Patterns of Nucleotide Misincorporations and DNA Fragmentation in Ancient DNA. PLOS One 7, e34131 (2012).
4. Herzschuh, U. et al. Dynamic land-plant carbon sources in marine sediments inferred from ancient DNA. Commun. Earth Environ. 6, 78 (2025).
How to cite: Singh, V. V., Kumar, N., Kimber, R., Pinhasi, R., and Kraemer, S.: A Critical Length Threshold for Biopolymer Protection in Mineral-Associated Organic Matter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21244, https://doi.org/10.5194/egusphere-egu26-21244, 2026.
Soil incubation experiments are widely used to investigate soil organic carbon (SOC) decomposition and persistence. However they frequently exhibit short-term respiration pulses following disturbances such as rewetting, flask manipulation and/or carbon inputs events that reflect rapid changes in substrate availability and microbial activity. The original formulation of PROCS, a system model of two ordinary differential equations (ODEs) designed to describe SOC dynamics, was unable to accurately represent abrupt state changes, therefore amplifying uncertainty, particularly in the estimation of SOC decomposability parameters. We extended the PROCS model to improve its ability to reproduce short-term respiration pulses observed in soil incubation experiments. A decaying function was added as a new differential equation to represent the transient effect of rewetting on SOC decomposability, with a rapid initial response that smoothly relaxed back to standard PROCS dynamics. We estimated all parameters of the extended PROCS model within a Bayesian inference framework using 30-month soil incubation data with no carbon inputs from three long-term cropland experimental sites across contrasting Brazilian climatic regions, explicitly accounting for three rewetting cycles and jointly fitting observed CO₂ emissions and SOC stocks. The extended model accurately reproduced observed decomposability pulses associated with incubation disturbance events, substantially improving model–data compatibility, and yielded well-constrained posterior distributions for SOC concentration and decomposability and turnover-related parameters across sites. The introduction of a post-disturbance decaying function in the PROCS model, combined with Bayesian calibration, enabled the fitting of a parsimonious statistical model that accurately represented the transient disturbances effects and provided posterior distributions of model parameters. The model’s ability to fit all sequential rewetting cycles consistently suggests that the disturbance effect was compartment-independent. Our model extension enhanced the robustness of the PROCS model for its application in soil incubation experiments.
How to cite: Camolesi, J., Ruiz Potma Gonçalves, D., G. Barioni, L., Lopes Garcia, N., and Freguglia, V.: Bayesian Calibration of a Dynamic Model with Sequential Rewetting Disturbances Incubation Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21829, https://doi.org/10.5194/egusphere-egu26-21829, 2026.
