Organic carbon (OC) association with soil minerals stabilizes OC on timescales reflecting the strength of mineral\uffe2\uff80\uff93C interactions. We applied ramped thermal oxidation to subsoil B horizons with different mineral\uffe2\uff80\uff93C associations to separate OC according to increasing temperature of oxidation, i.e. thermal activation energy. Generally, OC released at lower temperatures was richer in bioavailable forms like polysaccharides, while OC released at higher temperatures was more aromatic. Organic carbon associated with pedogenic oxides was released at lower temperatures and had a narrow range of 14 C content. By contrast, N-rich compounds were released at higher temperatures from samples with 2\uffe2\uff80\uff89:\uffe2\uff80\uff891 clays and short-range ordered (SRO) amorphous minerals. Temperatures of release overlapped for SRO minerals and crystalline oxides, although the mean age of OC released was older for the SRO. In soils with more mixed mineralogy, the added presence of older OC released at temperatures greater than 450\uffc2\uffb0C from clays resulted in a broader distribution of OC ages within the sample, especially for soils rich in 2\uffe2\uff80\uff89:\uffe2\uff80\uff891 layer expandable clays such as smectite. While pedogenic setting affects mineral stability and absolute OC age, mineralogy controls the structure of OC age distribution within a sample, which may provide insight into model structures and OC dynamics under changing conditions.
This article is part of the Theo Murphy meeting issue \uffe2\uff80\uff98Radiocarbon in the Anthropocene\uffe2\uff80\uff99.Kalmia latifolia.\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 Within each of the 18 plots, we established paired 1-m radius subplots with and without K. latifolia in the understory ( \u201c+/- ErM subplot\u201d) within 2 m of the center of the 10-m radius plot. In each 1-m radius subplot, we measured trees \u22651 cm diameter at breast height (DBH; 1.37 m). We also measured DBH of all trees \u226520 cm DBH within 10 m and trees \u22655 cm DBH within 5 m of plot center. We calculated the percentage of EcM tree basal area out of total basal area, scaled to m2 ha-1. \u00a0 In June 2021, we collected and pooled two soil samples for each of three depths within the 36 paired subplots (i.e. 18 +ErM and 18 -ErM subplots). The three depths included: (1) the Oa horizon (depth varied depending on the thickness of the horizon); (2) the top 10 cm of the A horizon, beginning at the base of the Oa horizon; and (3) a second, contiguous A horizon sample that reached a cumulative sampling depth of 30 cm, inclusive of the depth of the Oa horizon. For the organic layer, we removed the litter layer (i.e. the Oi and Oe horizons) and collected and pooled two 25 by 25-cm areas of the Oa horizon using a square template. For the mineral layers, we collected two contiguous depth increments from the A horizon within the footprint of the 25 by 25-cm areas using a 5.08-cm diameter hammer corer. In each instance, we recorded the exact sampling depth. Two subplots did not have an Oa horizon, so we collected a total of 106 samples (3 sites \u00d7 6 plots \u00d7 2 subplots \u00d7 3 depths \u2212 2 Oa samples). Soils were stored at 4\u00b0C prior to their analysis. \u00a0 To prepare the soil samples for analysis, we weighed and homogenized each sample, air dried a representative subsample of non-sieved soil, and passed the remaining field-moist sample through a 4-mm sieve. Using the non-sieved subsample, we estimated the mass and volume of roots and stones and calculated soil bulk density values. For total soil organic matter (SOM) content, we heated samples at 550\u00b0C for 12-h in a muffle furnace and calculated loss on ignition. \u00a0 We used a modified substrate-induced respiration method as an indicator of active saprotrophic microbial biomass. Using autolyzed yeast extract solution as a labile C substrate, we measured rates of CO2 efflux over a 4-h incubation period with an Infra-Red Gas Analyzer and calculated the rate of C-CO2 production per unit of equivalent soil dry mass. For microbially-available C, we estimated potential CO2 production rates over a 14-d incubation period. We measured CO2 efflux over 24-h periods at days 1, 5, 8, and 14 and integrated the four measurements to calculate cumulative C-CO2 production. We estimated water holding capacity by saturating each field-moist sample with water and allowing it to drain freely for 2 h. To calculate the equivalent dry mass of field-moist samples, we measured gravimetric water content by oven-drying the samples to constant mass at 105\u00b0C. \u00a0 We separated the >53 and <53\u2009\u00b5m particle size fractions to quantify particulate (POM) and mineral-associated soil organic matter fractions. We passed air-dried samples through a 2-mm sieve and then dispersed soil aggregates by shaking ~30 g of the sieved, air-dried sample with 30\u2009mL of sodium hexametaphosphate (NaHMP) solution for 18 h. We rinsed each sample over a 53-\u00b5m sieve with deionized water until the water passing through the sieve ran clear. We oven-dried the >53-\u00b5m fraction retained on the top of the sieve and a representative subsample of the <53-\u00b5m fraction suspended in solution at 70\u00b0C. To estimate the mass of the <53-\u00b5m fraction, we calculated the difference between the initial soil mass (105\u00b0C equivalent) and the recovered mass of the >53-\u00b5m fraction (105\u00b0C equivalent). To convert air-dried soil mass to oven-dried mass we dried a subsample of each air-dried sample at 105\u00b0C. Fractions were ground to a fine powder and analyzed for total carbon (C) and nitrogen (N) concentrations using a Costech ESC 4010 Elemental Analyzer. \u00a0 We used an equivalent soil mass approach to calculate soil C, N, SOM, microbial biomass, and microbially-available C stocks in three equivalent soil mass layers as well as the sum of the three layers to estimate cumulative stocks at the subplot level. Following this approach, we report stocks to a standard soil mass and therefore allow the depth of the equivalent soil mass layers to vary depending on soil bulk density. To calculate equivalent soil mass stocks, we added or subtracted elemental stocks of the deeper soil layer to the upper soil layer in 1-mm increments until the soil mass from the upper layer is closest to that of the target soil mass. We chose reference soil masses using the median or target field sampling depth and the mean bulk density value for each of the three depth increments to make them roughly equivalent to the sampled depths. Based on this method, the organic layer had an equivalent mass of ~2.5 kg soil m-2 (median Oa depth = 2.5 cm; mean Oa bulk density = 0.10 g cm-3), the surface mineral layer had an equivalent mass of ~37 kg soil m-2 (target sampling depth = 10 cm; mean bulk density = 0.37 g cm-3), and the subsurface mineral layer had an equivalent mass of ~126 kg soil m-2 (the target sampling depth was 17.5 cm for a sample with a 2.5 cm Oa depth; mean bulk density = 0.72 g cm-3). The cumulative equivalent soil mass for the subplot-level stocks was the sum of the three layers, or ~166 kg soil m-2.", "keywords": ["equivalent soil mass", "ericoid mycorrhizal fungi", "13. Climate action", "ectomycorrhizal fungi", "Particulate organic matter", "FOS: Biological sciences", "soil nitrogen", "Arbuscular mycorrhizal fungi", "Mineral-associated organic matter", "soil carbon stocks", "15. Life on land"], "contacts": [{"organization": "Ward, Elisabeth", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.5061/dryad.4qrfj6qg2"}, {"rel": "self", "type": "application/geo+json", "title": "10.5061/dryad.4qrfj6qg2", "name": "item", "description": "10.5061/dryad.4qrfj6qg2", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.5061/dryad.4qrfj6qg2"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2023-07-12T00:00:00Z"}}, {"id": "10.5061/dryad.ncjsxksxj", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-27T16:22:32Z", "type": "Dataset", "title": "Data for: Cover crop functional types differentially alter the content and composition of soil organic carbon in particulate and mineral-associated fractions", "description": "Cover crops (CCs) can increase soil organic carbon (SOC) sequestration by providing additional OC residues, recruiting beneficial soil microbiota, and improving soil aggregation and structure. The various CC species that belong to distinct plant functional types (PFTs) may differentially impact SOC formation and stabilization. Biogeochemical theory suggests that selection of PFTs with distinct litter quality (C:N ratio) should influence the pathways and magnitude of SOC sequestration. Yet, we lack knowledge on the effect of CCs from different PFTs on the quantity and composition of physiochemical pools of SOC. We sampled soils under monocultures of three CC PFTs (legume [crimson clover]; grass [triticale]; and brassica [canola]) and a mixture of these three species, from a long-term CC experiment in Pennsylvania, USA. We measured C content in bulk soil and C content and composition in contrasting physical fractions: particulate organic matter, POM; and mineral-associated organic matter, MAOM. The bulk SOC content was higher in all CC treatments compared to the fallow. Compared to the legume, monocultures of grass and brassica with lower litter quality (wider C:N) had higher proportion of plant-derived C in POM, indicating selective preservation of complex structural plant compounds. In contrast, soils under legumes had greater accumulation of microbial-derived C in MAOM. Our results for the first time, revealed that the mixture contributed to a higher concentration of plant-derived compounds in POM relative to the legume, and a greater accumulation of microbial-derived C in MAOM compared to monocultures of grass and brassica. Mixtures with all three PFTs can thus increase the short- and long-term SOC persistence balancing the contrasting effects on the chemistries in POM and MAOM imposed by monoculture CC PFTs. Thus, despite different cumulative C inputs in CC treatments from different PFTs, the total SOC stocks did not vary between CC PFTs, rather PFTs impacted whether C accumulated in POM or MAOM fractions. This highlights that CCs of different PFTs may shift the dominant SOC formation pathways (POM vs. MAOM), subsequently impacting short- and long-term SOC stabilization and stocks. Our work provides a strong applied field test of biogeochemical theory linking litter quality to pathways of C accrual in soil.", "keywords": ["2. Zero hunger", "soil organic carbon", "Plant functional types", "Particulate organic matter", "FOS: Agricultural sciences", "Mineral-associated organic matter", "cover crops", "legume", "15. Life on land", "Biomarkers"], "contacts": [{"organization": "Suseela, Vidya, Zhang, Ziliang, Kaye, Jason, Bradley, Brosi, Amsili, Joseph,", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.5061/dryad.ncjsxksxj"}, {"rel": "self", "type": "application/geo+json", "title": "10.5061/dryad.ncjsxksxj", "name": "item", "description": "10.5061/dryad.ncjsxksxj", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.5061/dryad.ncjsxksxj"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2023-04-17T00:00:00Z"}}, {"id": "10.5281/zenodo.5987644", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-27T16:24:31Z", "type": "Dataset", "title": "Supporting data for review article: The Global Distribution, Formation, and Fate of Mineral-Associated Soil Organic Matter Under a Changing Climate \u2013 A Trait-Based Perspective", "description": "Supporting data and code for review article: Sokol N.W., Whalen E.D., Kallenbach C., Pett-Ridge J., Georgiou K. The Global Distribution, Formation, and Fate of Mineral-Associated Soil Organic Matter Under a Changing Climate \ufffd\ufffd\ufffd A Trait-Based Perspective. Functional Ecology, 2022. We leveraged data from a global synthesis of soil fractionation measurements (DOI: 10.5281/zenodo.5987415). For this review article, we specifically focused on measurements of bulk and mineral-associated soil organic carbon concentrations (reported in units of gC/kg soil) and the proportion of bulk soil organic carbon that is mineral-associated (reported as a %). This subset also includes auxiliary data regarding climate and biome characteristics extracted from the synthesized papers; for more variables, see the original full dataset. K\ufffd\ufffdppen-Geiger climate zones were extracted from a georeferenced global database (using R package 'kgc' v1.0.0.2) with site coordinates, where available. Three files are provided in this repository: (1) data file, (2) metadata file, and (3) code for manuscript figures and summary statistics.", "keywords": ["2. Zero hunger", "mineral-associated organic matter", "climate change", "13. Climate action", "biogeochemistry", "15. Life on land", "soil fractions", "particulate organic matter"], "contacts": [{"organization": "Georgiou, Katerina", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.5281/zenodo.5987644"}, {"rel": "self", "type": "application/geo+json", "title": "10.5281/zenodo.5987644", "name": "item", "description": "10.5281/zenodo.5987644", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.5281/zenodo.5987644"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2022-01-01T00:00:00Z"}}, {"id": "10.5281/zenodo.6539765", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-27T16:24:33Z", "type": "Dataset", "title": "Globally-gridded data for manuscript: Global stocks and capacity of mineral-associated soil organic carbon", "description": "Supporting globally-gridded data products for manuscript: Georgiou K., Jackson R. B., Vindu\u0161kov\u00e1 O., Abramoff R. Z., Ahlstr\u00f6m A., Feng W., Harden J. W., Pellegrini A. F. A., Polley H. W., Soong J. L., Riley W. J., Torn M. S. Global stocks and capacity of mineral-associated soil organic carbon. Nature Communications, 2022. We leveraged data from a global synthesis of soil fractionation measurements (DOI: 10.5281/zenodo.5987415) along with ancillary data on climate, vegetation, and soil characteristics to produce spatially-explicit global estimates of mineral-associated soil organic carbon stocks (MOC) and mineralogical carbon capacity (MOCmax) in non-permafrost, non-desert mineral soils. Globally-gridded datasets are given in kgC/m2 for topsoil (0-30cm) and subsoil (30-100cm) at 0.5 degree by 0.5 degree spatial resolution.", "keywords": ["2. Zero hunger", "mineral-associated organic matter", "biogeochemistry", "soil organic matter", "15. Life on land", "carbon storage", "soil fractions"], "contacts": [{"organization": "Georgiou, Katerina, Jackson, Robert B., Vindu\u0161kov\u00e1, Olga, Abramoff, Rose Z., Ahlstr\u00f6m, Anders, Feng, Wenting, Harden, Jennifer W., Pellegrini, Adam. F. A., Polley, H. Wayne, Soong, Jennifer L., Riley, William J., Torn, Margaret S.,", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.5281/zenodo.6539765"}, {"rel": "self", "type": "application/geo+json", "title": "10.5281/zenodo.6539765", "name": "item", "description": "10.5281/zenodo.6539765", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.5281/zenodo.6539765"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2022-01-01T00:00:00Z"}}, {"id": "10.5281/zenodo.8090465", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-27T16:24:49Z", "type": "Dataset", "title": "Data for the manuscript 'Cover crop root morphology rather than quality controls the fate of root and rhizodeposition C into distinct soil C pools'", "description": "Data for manuscript The data provided in the present document corresponds to the manuscript: Engedal, T., Magid, J., Hansen, V., Rasmussen, J., S\u00f8rensen, H., Jensen, L. S. (2023): Cover crop root morphology rather than quality controls the fate of root and rhizodeposition C into distinct soil C pools. Global Change Biology, in press. Short abstract In order to investigate the fate of cover crop-derived belowground C as rhizodeposition and, over time, into the distinct soil organic carbon pools of particulate- and mineral-associated organic carbon (POC and MAOC), a column trial was esblished with 0.25 m top soil and 0.25 m sub soil. Four cover crops were grown for 3 months and 14CO2-labelled twice a week. Four out of eight replicate columns were destructively harvested to quantify root C and the carbon lost via rhizodeposition in absolute (qClvR) and relative terms (%ClvR) in bulk soil and rhizosphere soil from top- and subsoil (t1). The other four replicate columns were harvested for undisturbed incubation for one year, before final sampling (t2). Bulk soil from both sampling times were subject to a simple fractionation protocol by size, where particles larger from 50 microns were assigned to POC and smaller than 50 microns assigned to MAOC after dispersion in NaHMP. All fractions were dried, weighed and analyzed for 14C activity as disintegrations per minute (DPM). Further details Column ID 1-16 refer to columns sampled at t1, while column ID 17-32 refer to columns sampled at t2. Underlying assumptions and detailed descriptions of the different fractions are to be found in the manuscript.", "keywords": ["2. Zero hunger", "MOAM", "POM", "MAOC", "cover crop", "15. Life on land", "soil organic fractionation", "soil organic carbon", "mineral-associated organic matter", "rhizodeposition", "root morphology", "particulate organic matter", "root carbon", "POC"], "contacts": [{"organization": "Engedal, Tine, Magid, Jakob, Hansen, Veronika, Rasmussen, Jim, S\u00f8rensen, Helle, Jensen, Lars Stoumann,", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.5281/zenodo.8090465"}, {"rel": "self", "type": "application/geo+json", "title": "10.5281/zenodo.8090465", "name": "item", "description": "10.5281/zenodo.8090465", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.5281/zenodo.8090465"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2023-06-28T00:00:00Z"}}, {"id": "11369/445129", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-27T16:26:13Z", "type": "Journal Article", "created": "2023-05-09", "title": "The effects of biochar on soil organic matter pools are not influenced by climate change", "description": "The sustainability of Mediterranean croplands is threatened by climate warming and rainfall reduction. The use of biochar as an amendment represents a tool to store organic carbon (C) in soil. The vulnerability of soil organic C (SOC) to the joint effects of climate change and biochar application needs to be better understood by investigating its main pools. Here, we evaluated the effects of partial rain exclusion (\u223c30%) and temperature increase (\u223c2\u00a0\u00b0C), combined with biochar amendment, on the distribution of soil organic matter (SOM) into particulate organic matter (POM) and the mineral-associated organic matter (MAOM). A set of indices suggested an increase in thermal stability in response to biochar addition in both POM and MAOM fractions. The MAOM fraction, compared to the POM, was particularly enriched in labile substances. Data from micro-Raman spectroscopy suggested that the POM fraction contained biochar particles with a more ordered structure, whereas the structural order decreased in the MAOM fraction, especially after climate manipulation. Crystalline Fe oxides (hematite) and a mix of ferrihydrite and hematite were detected in the POM and in the MAOM fraction, respectively, of the unamended plots under climate manipulation, but not under ambient conditions. Conversely, in the amended soil, climate manipulation did not induce changes in Fe speciation. Our work underlines the importance of discretely taking into account responses of both MAOM and POM to better understand the mechanistic drivers of SOC storage and dynamics.", "keywords": ["Particulate organic matter", " Mineral-associated organic matter", " Open top chambers", " Fe EXAFS", " Raman spectroscopy", " Thermal analysis", "Take urgent action to combat climate change and its impacts", "550", "Climate Change", "Fe EXAFS", "15. Life on land", "6. Clean water", "Carbon", "Soil", "Open top chamber", "13. Climate action", "Particulate organic matter", "Charcoal", "Raman spectroscopy", "Mineral-associated organic matter", "Particulate Matter", "Thermal analysis", "http://metadata.un.org/sdg/13", "Open top chambers"]}, "links": [{"href": "https://iris.univr.it/bitstream/11562/1093186/2/JEMA%2c%202023%20-%20The%20effects%20of%20biochar%20on%20SOM%20pools%20are%20not.pdf"}, {"href": "https://doi.org/11369/445129"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Journal%20of%20Environmental%20Management", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "11369/445129", "name": "item", "description": "11369/445129", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/11369/445129"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2023-09-01T00:00:00Z"}}, {"id": "20.500.11850/638608", "type": "Feature", "geometry": null, "properties": {"license": "Open Access", "updated": "2026-07-27T16:26:45Z", "type": "Journal Article", "created": "2023-10-10", "title": "Relating mineral\u2013organic matter stabilization mechanisms to carbon quality and age distributions using ramped thermal analysis", "description": "
Organic carbon (OC) association with soil minerals stabilizes OC on timescales reflecting the strength of mineral\uffe2\uff80\uff93C interactions. We applied ramped thermal oxidation to subsoil B horizons with different mineral\uffe2\uff80\uff93C associations to separate OC according to increasing temperature of oxidation, i.e. thermal activation energy. Generally, OC released at lower temperatures was richer in bioavailable forms like polysaccharides, while OC released at higher temperatures was more aromatic. Organic carbon associated with pedogenic oxides was released at lower temperatures and had a narrow range of 14 C content. By contrast, N-rich compounds were released at higher temperatures from samples with 2\uffe2\uff80\uff89:\uffe2\uff80\uff891 clays and short-range ordered (SRO) amorphous minerals. Temperatures of release overlapped for SRO minerals and crystalline oxides, although the mean age of OC released was older for the SRO. In soils with more mixed mineralogy, the added presence of older OC released at temperatures greater than 450\uffc2\uffb0C from clays resulted in a broader distribution of OC ages within the sample, especially for soils rich in 2\uffe2\uff80\uff89:\uffe2\uff80\uff891 layer expandable clays such as smectite. While pedogenic setting affects mineral stability and absolute OC age, mineralogy controls the structure of OC age distribution within a sample, which may provide insight into model structures and OC dynamics under changing conditions.
This article is part of the Theo Murphy meeting issue \uffe2\uff80\uff98Radiocarbon in the Anthropocene\uffe2\uff80\uff99.