基于全球2479个土壤剖面资料的SOC在不同生态系统中的垂向分布差异及草地与森林深层碳库

… To evaluate the effect of vegetation on the vertical distribution of SOC, we grouped soil profiles into grasslands, shrublands, and forests. In some cases, the databases included these …

… The vertical distribution of SOC had a slightly stronger association with temperature than … the vertical distribution of SOC, we grouped soil profiles into grassland, shrubland, and forest …

Vegetation restoration has been conducted in the Chinese Loess Plateau (CLP) since the 1950s, and large areas of farmland have been converted to forest and grassland, which largely results in SOC change. However, there has been little comparative research on SOC sequestration and distribution between secondary forest and restored grassland. Therefore, we selected typical secondary forest (SF-1 and SF-2) and restored grassland (RG-1 and RG-2) sites and determined the SOC storage. Moreover, to illustrate the factors resulting in possible variance in SOC sequestration, we measured the soil δ13C value. The average SOC content was 6.8, 9.9, 17.9 and 20.4 g kg−1 at sites SF-1, SF-2, RG-1 and RG-2, respectively. Compared with 0–100 cm depth, the percentage of SOC content in the top 20 cm was 55.1%, 55.3%, 23.1%, and 30.6% at sites SF-1, SF-2, RG-1 and RG-2, suggesting a higher SOC content in shallow layers in secondary forest and in deeper layers in restored grassland. The variation of soil δ13C values with depth in this study might be attributed to the mixing of new and old carbon and kinetic fractionation during the decomposition of SOM by microbes, whereas the impact of the Suess effect (the decline of 13C atmospheric CO2 values with the burning of fossil fuel since the Industrial Revolution) was minimal. The soil δ13C value increased sharply in the top 20 cm, which then increased slightly in deeper layers in secondary forest, indicating a main carbon source of surface litter. However the soil δ13C values exhibited slow increases in the whole profile in the restored grasslands, suggesting that the contribution of roots to soil carbon in deeper layers played an important role. We suggest that naturally restored grassland would be a more effective vegetation type for SOC sequestration due to higher carbon input from roots in the CLP.

… in the vertical distribution of SOC occurred when pastures replaced native forests, with SOC gains in the surface soil but losses at greater depths. The changes in SOC stocks occurred …

In-depth understanding about the vertical distribution of soil organic carbon (SOC) density is crucial for carbon (C) accounting, C budgeting and designing appropriate C sequestration strategies. We examined the vertical distribution of SOC density under different land use/land cover (LULC) types, altitudinal zones and aspect directions in a montane ecosystem of Bhutan. Sampling sites were located using conditioned Latin hypercube sampling (cLHS) scheme. Soils were sampled based on genetic horizons. An equal-area spline function was fitted to interpolate the target values to predetermined depths. Linear mixed model was fitted followed by mean separation tests. The results show some significant effects of LULC, altitudinal zone and slope aspect on the vertical distribution of SOC density in the profiles. Based on the proportion of mean SOC density in the first 20 cm relative to the cumulative mean SOC density in the top meter, the SOC density under agricultural lands (34%) was more homogeneously distributed down the profiles than forests (39%), grasslands (59%) and shrublands (43%). Similarly, the SOC density under 3500–4000 m zone (35%) was more uniformly distributed compared to 3000–3500 m zone (43%) and 1769–2500 m and 2500–3000 m zones (41% each). Under different aspect directions, the north and east-facing slopes (38% each) had more uniform distribution of SOC density than south (40%) and west-facing slopes (49%).

Characterization of the vertical distribution of soil organic carbon (C), nitrogen (N), and phosphorus (P) may improve our ability to accurately estimate soil C, N, and P storage. Based on a database of 21 354 records in 74 long-term monitoring plots from 2004 to 2013 in the Chinese Ecosystem Research Network (CERN), we built fitting functions to quantify the vertical distribution of soil C, N, and P (up to 100 cm depth) in the typical Chinese terrestrial ecosystems. The decrease of soil C, N, and P content with depth can be well fitted with various mathematical functions. The fitting functions differed greatly between artificial (agriculture) and natural (desert, forest, and grassland) ecosystems, and also differed with respect to soil C, N, and P content. In both the artificial and natural ecosystems, the best fitting functions were exponential functions for C, quadratic functions for N, and quadratic functions for P. Furthermore, the stoichiometric ratios of soil C, N, and P were ranked in descending order: grassland > forest > agriculture > desert, and were also associated with climate. This study is the first to build the fitting functions for the profile distribution of soil C, N, and P in China at a national scale. Our findings provide a scientific basis to accurately assess the storage of C, N, and P in soils at a large scale, especially for the integrative analysis of historical data.

… than broadleaf forest … SOC changes in forestland than those in grassland here (Figure 1). However, we cannot preclude that there will be further SOC accumulation with increasing forest …

… : forest>grassland>shrub–grassland>shrub desert>desert; for density of soil inorganic carbon: forest, grassland<shrub–grassland<… In landscapes other than forest, more than 50% soil …

… contents within alpine forest and grassland soils along an elevation gradient (2600–3900 m … that the SOC contents in bulk soils and aggregates were higher within grassland soils than …

Accurate analysis and evaluation of the spatial distribution and the primary factors that affect regional soil organic carbon (SOC) together make an important step in assessing carbon sequestration potential. However, little information is available on distribution of regional SOC in deep soil layers. To analyze the spatial distribution of and factors influencing SOC in a 500 cm soil profile, 1440 soil samples were collected from 90 sites on the Loess Plateau in China. The primary factors dominating the spatial distribution of SOC were quantified using principal component analysis with multiple linear regression (PCA-MLR) analysis. Results showed that the mean SOC of the 500 cm soil profile ranged from 1.20 to 3.37 g kg-1, decreasing with increasing soil depth. The SOC in the deep soil profile decreased across the types of land use in the following order: forestland > cropland > grassland. Based on the factors analyzed in this study, land use accounted for 22% of the variation in SOC and was the dominant factor controlling the spatial distribution of organic carbon in shallow soils (0-100 cm); while soil factors (including soil clay, soil water content, and soil bulk density) were dominant in deep soil layers (200-500 cm), averagely accounting for 44.3%. The SOC stock in the 0-20 cm soil layer was 1.34 kg m-2, accounting for only a small proportion (8%) of the total carbon in the entire 500 cm soil profile. SOC stock in the 200-500 cm layer was 7.62 kg m-2, accounting for 40% of the total carbon in the 0-500 cm soil profile. This study demonstrates that a large amount of organic carbon is stored in deep soil, indicating that a better understanding of the reserves and cycles of deep soil carbon is a critical factor in the effective management of terrestrial ecosystems.

… (SOC) and inorganic carbon (SIC). The vertical distribution and transformation of SOC and … the vegetation and followed the order shrub > forest > grass. Compared to the shady slope, …

… (SOC), aggregate structure and SOC turnover processes. We studied the effects of a vegetation shift from forest to grassland … Total SOC stocks (0–50 cm) under forest (84 Mg C ha −1 ) …

… of grasslands can be an effective means of sequestering soil organic carbon (SOC) and … This study evaluated the vertical distribution and overall sequestration of SOC and total nitrogen …

… , this difference increased to 59.8% in SCS compared to ESP. The comparison between ESP and SCS showed the effect of mixing pedogenetic horizons when depth increments were …

… of soil organic carbon stocks from entire soil profiles … compared with cropland soils with 15 mg g −1 . Bulk density generally increased with depth in all soils, but considerable differences …

… layers may be more stable than that in surface soil due to differences … profile depth on soil organic matter (SOM) composition and stability by comparing soils which had received organic …

Soil organic carbon (OC) stocks are highly variable in space. This study aimed at analysing regional soil OC stock variability with direct measurements of OC stocks at 89 sampling …

… with many landscapes having soils that extend to depths of many … deep soils as those with profiles greater than 5 m deep. … When the SOC storage within the deep profiles was compared …

… The identification of soil management strategies as well as the evaluation of their … and temporal patterns of soil organic carbon storage. High-resolution SOC profile data are generally …

… The proportional differences in soil organic carbon (SOC) and … of aggregation and soil carbon sequestration mechanisms. A … related to comparison of SOC stock in soil profiles under …

Understanding spatial variation of soil organic carbon (SOC) in three-dimensional direction is helpful for land use management. Due to the effect of profile depths and soil texture on vertical distribution of SOC, the stationary assumption for SOC cannot be met in the vertical direction. Therefore the three-dimensional (3D) ordinary kriging technique cannot be directly used to map the distribution of SOC at a regional scale. The objectives of this study were to map the 3D distribution of SOC at a regional scale by combining kriging method with the profile depth function of SOC (KPDF), and to explore the effects of soil texture and land use type on vertical distribution of SOC in a fluvial plain. A total of 605 samples were collected from 121 soil profiles (0.0 to 1.0 m, 0.20 m increment) in Quzhou County, China and SOC contents were determined for each soil sample. The KPDF method was used to obtain the 3D map of SOC at the county scale. The results showed that the exponential equation well described the vertical distribution of mean values of the SOC contents. The coefficients of determination, root mean squared error and mean prediction error between the measured and the predicted SOC contents were 0.52, 1.82 and -0.24 g kg-1 respectively, suggesting that the KPDF method could be used to produce a 3D map of SOC content. The surface SOC contents were high in the mid-west and south regions, and low values lay in the southeast corner. The SOC contents showed significant positive correlations between the five different depths and the correlations of SOC contents were larger in adjacent layers than in non-adjacent layers. Soil texture and land use type had significant effects on the spatial distribution of SOC. The influence of land use type was more important than that of soil texture in the surface soil, and soil texture played a more important role in influencing the SOC levels for 0.2-0.4 m layer.

… SOC stocks at different depth intervals within the upper 1-m depth using profile depth distribution functions and ordinary … These comparisons further confirm the validity of our results. …

This paper proposes a method for mapping depth functions of soil organic matter (SOM) that combines general pedological knowledge with geostatistical modeling. A pedometric soil …

… and compare their effectiveness in achieving this aim. Using the conditioned Latin hypercube … method, 188 soil profiles in the study area were sampled and soil organic carbon content (…

… Soil organic carbon distribution within soil profile is highly influenced by management practices, especially tillage systems where soil … SOC stock differences with depth between tillage …

… of highly weathered soils usually found in tropical and subtropical regions. In the present work, soil organic matter (SOM) of six representative Brazilian Ferralsol profiles was examined …

… soil organic carbon and soil total nitrogen) after two crop rotational cycles over 11 years at 0–30-cm soil depth revealed no significant differences … whole soil profile (0–90-cm soil depth), …

Soils are the largest terrestrial pool of organic carbon, with up to 50% of soil organic carbon (SOC) stored below 30 cm. Knowledge of the impact of land use on the mechanisms by which SOC is stored in subsoils is critical to developing and delivering strategies to mitigate climate change. We characterized SOC under arable, grassland, and deciduous woodland land uses in lowland England to determine how land use affects the mechanisms by which topsoil and subsoil SOC are protected. Soil organic matter (SOM) physical fractionation and ammonium oxalate extractable Al, Fe and Mn were analysed to elucidate protection mechanisms. Results revealed that the mineral‐free particulate organic matter (fPOM) fraction was significantly greater in both the topsoil and subsoil under woodland than under grassland or arable. The mineral‐associated organic carbon (MinOC) fraction was proportionally greater in the subsoil compared with topsoil under all land uses, with arable >grassland > woodland. These findings indicate that land use affects the extent to which SOC is protected, with woodlands containing a higher proportion of carbon that has less protection from decomposition. Subsoil SOC is protected from decomposition by organo‐mineral interactions with amorphous Al, Fe and Mn, and may be susceptible to future pH shifts as a result of land use change. This study highlights the need to consider the impact of land use change on SOC, given policy and public interest in woodland planting for climate change mitigation.

Quantitative data on carbon stock (C stock) in and beyond the topsoil (0–30 cm) under natural terrestrial ecosystems in West African savanna could provide information about their relative potential, and management options, for C sequestration, but these data are still scanty in the region. In selected locations (Nsukka, Obimo, and Ibagwa-aka) in the derived savanna zone of south-eastern Nigeria, secondary forest (SFT), grassland fallow (GLF), and bare footpath (BFP) were sampled from the topsoils (0–30 cm) and subsoils (30–60 cm) in triplicate. The soils are generally sandy, with low (1.4–13.8%) mean silt content. Mean bulk density ranged from 1.30 to 1.83 Mg/m3. The soils were acidic (pHwater 4.0–4.8) and low in organic C (0.10–1.14%). There was a consistent trend in C stock (SFT &amp;gt; GLF &amp;gt; BFP) in the topsoil, whereas only higher values in SFT than BFP were consistent in the subsoil. In both soil layers, the scale of the differences among the land-cover types was location-specific. Values of C stock were higher in the topsoil than subsoil, except for GLF and BFP at Obimo due to recent bush burning. Irrespective of location, the mean topsoil–subsoil values under SFT, GLF, and BFP were 45.7–30.6, 27.7–25.8, and 19.0–18.8 Mg/ha, respectively. Soil structural stability, indexed as the ratio of organic matter to silt + clay, explained roughly 61 and 89% of the variability in C stock of topsoils and subsoils, respectively. These results should benefit the planning of C sequestration projects in savanna agroecosystems of West Africa.

Abstract. The net loss of soil organic carbon (SOC) from terrestrial ecosystems is a likely consequence of global warming and may affect key soil functions. The strongest changes in temperature are expected to occur at high northern latitudes, with forest and tundra as prevailing land cover types. However, specific soil responses to warming in different ecosystems are currently understudied. In this study, we used a natural geothermal soil warming gradient (0–17.5  ∘ C warming intensity) in an Icelandic spruce forest on Andosol to assess changes in the SOC content between 0 and 10 cm (topsoil) and between 20 and 30 cm (subsoil) after 10 years of soil warming. Five different SOC fractions were isolated, and their redistribution and the amount of stable aggregates were assessed to link SOC to changes in the soil structure. The results were compared to an adjacent, previously investigated warmed grassland. Soil warming depleted the SOC content in the forest soil by −2.7  g kg −1 ∘ C −1 ( −3.6  %  ∘ C −1 ) in the topsoil and −1.6  g kg −1 ∘ C −1 ( −4.5  %  ∘ C −1 ) in the subsoil. The distribution of SOC in different fractions was significantly altered, with particulate organic matter and SOC in sand and stable aggregates being relatively depleted and SOC attached to silt and clay being relatively enriched in warmed soils. The major reason for this shift was aggregate breakdown: the topsoil aggregate mass proportion was reduced from 60.7±2.2  % in the unwarmed reference to 28.9±4.6  % in the most warmed soil. Across both depths, the loss of one unit of SOC caused a depletion of 4.5 units of aggregated soil, which strongly affected the bulk density (an R2 value of 0.91 and p when correlated with SOC, and an R2 value of 0.51 and p when correlated with soil mass in stable aggregates). The proportion of water-extractable carbon increased with decreasing aggregation, which might indicate an indirect protective effect of aggregates larger than 63  µ m on SOC. Topsoil changes in the total SOC content and fraction distribution were more pronounced in the forest than in the adjacent warmed grassland soils, due to higher and more labile initial SOC. However, no ecosystem effect was observed on the warming response of the subsoil SOC content and fraction distribution. Thus, whole profile differences across ecosystems might be small. Changes in the soil structure upon warming should be studied more deeply and taken into consideration when interpreting or modelling biotic responses to warming.

… primarily lost from the subsoil. Afforestation effects on SOC … C turnover under forest did not increase SOC storage—at … production in forests are considerably lower than in grasslands, …

Soils store large quantities of carbon in the subsoil (below 0.2 m depth) that is generally old and believed to be stabilized over centuries to millennia, which suggests that subsoil carbon sequestration (CS) can be used as a strategy for climate change mitigation. In this article, we review the main biophysical processes that contribute to carbon storage in subsoil and the main mathematical models used to represent these processes. Our guiding objective is to review whether a process understanding of soil carbon movement in the vertical profile can help us to assess carbon storage and persistence at timescales relevant for climate change mitigation. Bioturbation, liquid phase transport, belowground carbon inputs, mineral association, and microbial activity are the main processes contributing to the formation of soil carbon profiles, and these processes are represented in models using the diffusion–advection–reaction paradigm. Based on simulation examples and measurements from carbon and radiocarbon profiles across biomes, we found that advective and diffusive transport may only play a secondary role in the formation of soil carbon profiles. The difference between vertical root inputs and decomposition seems to play a primary role in determining the shape of carbon change with depth. Using the transit time of carbon to assess the timescales of carbon storage of new inputs, we show that only small quantities of new carbon inputs travel through the profile and can be stabilized for time horizons longer than 50 years, implying that activities that promote CS in the subsoil must take into consideration the very small quantities that can be stabilized in the long term.

Woody encroachment is a widespread phenomenon resulting from the abandonment of mountain agricultural and pastoral practices during the last century. As a result, forests have expanded, increasing biomass and necromass carbon (C) pools. However, the impact on soil organic carbon (SOC) is less clear. The main aim of this study was to investigate the effect of woody encroachment on SOC stocks and ecosystem C pools in six chronosequences located along the Italian peninsula, three in the Alps and three in the Apennines. Five stages along the chronosequences were identified in each site. Considering the topsoil (0-30 cm), subsoil (30 cm-bedrock) and whole soil profile, the temporal trend in SOC stocks was similar in all sites, with an initial increment and subsequent decrement in the intermediate phase. However, the final phase of the woody encroachment differed significantly between the Alps (mainly conifers) and the Apennines (broadleaf forests) sites, with a much more pronounced increment in the latter case. Compared to the previous pastures, after mature forest (>62 years old) establishment, SOC stocks increased by: 2.1(mean) ± 18.1(sd) and 50.1 ± 25.2 Mg C·ha-1 in the topsoil, 7.3 ± 17.4 and 93.2 ± 29.7 Mg C·ha-1 in the subsoil, and 9.4 ± 24.4 and 143.3 ± 51.0 Mg C·ha-1 in the whole soil profile in Alps and Apennines, respectively. Changes in SOC stocks increased with mean annual air temperature and average minimum winter temperature, and were negatively correlated with the sum of summer precipitation. At the same time, all other C pools (biomass and necromass) increased by 179.1 ± 51.3 and 304.2 ± 67.6 Mg C·ha-1 in the Alps and the Apennines sites, respectively. This study highlights the importance of considering both the subsoil, since deep soil layers contributed 38% to the observed variations in carbon stocks after land use change, and the possible repercussions for the carbon balance of large areas where forests are expanding, especially under pressing global warming scenarios.

Tree-planting is increasingly presented as a cost-effective strategy to maximise ecosystem carbon (C) storage and thus mitigate climate change. Its success largely depends on the associated response of soil C stocks, where most terrestrial C is stored. Yet, we lack a precise understanding of how soil C stocks develop following tree planting, and particularly how it affects the form in which soil C is stored and its associated stability and resistance to climate change. Here, we present changes in C and nitrogen (N) stored as mineral-associated organic matter (OM), occluded particulate OM, free particulate OM and dissolved OM, from four regional chronosequences of Scots pine (Pinus sylvestris L.) forests planted on former grasslands across Scotland. We found that c. 58-68 years after the plantation, bulk soil C and N stocks in the organic layer and the top 20 cm of mineral soil decreased by half relative to unforested grasslands - a decrease roughly equivalent to a third of the simultaneous C gain in the tree biomass. This pattern was driven predominantly by a decrease in the amount of C and N stored as mineral-associated OM, an OM fraction considered as relatively long-lived. Our findings demonstrate the need to estimate C storage in response to tree planting based both on soil C stocks and tree biomass, as the use of the latter alone may significantly over-estimate net C benefits of tree planting on permanent grasslands.

… Grasslands and forests may be preferable systems in terms of … Stabilised carbon in subsoil horizons is located in spatially distinct parts of the soil profile. Soil Biology and Biochemistry 41…

… carbon sequestration in subsoil horizons in order to explore the possibility to increase soil carbon stocks by carbonising subsoil … oak forest, which was growing at the site in former times. …

… Jacob M, Viedenz K and Polle A 2010b Leaf litter decomposing in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica) Oecologia 164 1083–94 …

Forest restoration and its capacity to enhance soil carbon sequestration constitute critical mechanisms for augmenting global soil carbon pools. However, the distinct regulatory roles of plant‐derived versus microbial‐derived carbon in restoration‐driven carbon sequestration remain poorly understood. Here, we collected whole‐profile soils from over 180 years of forest restoration sequences, including coniferous, mixed, secondary and old‐growth forests. We measured soil microbial necromass carbon (MNC) and lignin phenols to identify the key factors that influence the variation of carbon sequestration in surface (0–20 cm), subsurface (20–60 cm) and deep soil (60–100 cm). We systematically revealed depth‐dependent soil organic carbon (SOC) dynamics: Subsurface and deep SOC accumulation contributed disproportionately to total SOC stock increases during restoration, supplementing the conventional surface‐centric perspective. Through coupled measurements of MNC and lignin phenols, we uncovered divergent transformation pathways—while surface soils exhibited declining plant‐derived carbon proportions, microbial‐derived carbon progressively dominated deeper layers (27.4%–53.4% of SOC in late‐stage restoration). This microbial dominance is driven by depth‐specific conditions (nutrient scarcity, mineral protection) rather than being universal across all soil depths. Crucially, the coupling of lignin degradation and microbial assimilation in deep soils enhanced MNC stabilization, providing empirical evidence for the ‘microbial carbon pump’ theory through vertically resolved lignin–MNC linkages. Mechanistically, lignin distribution correlated with microbial‐mediated liberation and vertical transport, whereas depth‐specific nutrient‐microbe interactions governed MNC accumulation. The proportion of microbial‐derived carbon positively predicted SOC stocks in subsurface and deep soils ( R 2  = 0.63–0.80), contrasting with negative correlations of plant‐derived carbon in surface layers. Synthesis and applications . These findings establish a tripartite framework for precision restoration: (1) prioritizing subsurface carbon sequestration by alleviating nutrient limitations in deep soils, (2) steering plant–microbe‐derived carbon coupling through tree species mixtures that balance lignin inputs and microbial turnover and (3) optimizing vertical carbon allocation by synchronizing root traits with microbial stoichiometric needs. Our work redefines restoration strategies to harness depth‐specific biogeochemical processes, offering a pathway to maximize SOC sequestration across the whole soil profile.

The conversion of primary forests to cultivation brings a significant change in soil carbon (C) forms. In the foothills of the Eastern Himalayan Region of India (Manipur), such conversions are prevalent. However, little is known about the response of C forms, particularly in deep soil, to land use conversion in the region. We evaluated changes in soil C forms (total organic, inorganic, and pools) and microbiological properties (up to 1.0 m depth) mediated by C when the 45-year-old forest had been cultivated for 18-25 years. The cultivated land uses were tree-based agroforestry (LAF: legumes, NAF: non-legumes), horticultural fruits (WHF: woody, NHF: non-wood, mainly vegetables), and paddy agriculture system (AUS: upland, ALS: lowlands). Forest conversion significantly (p < 0.05) decreased the total carbon (TC) in the surface soil (0.0-0.15 m) from 4.88 % to 3.04-3.93 % in the tree-based land uses (LAF, NAF, and WHF). TC further declined to 2.05-2.81 % under seasonal crops (NHF, AUS, and ALS). Seasonal crop cultivation also caused a higher decline in microbial biomass carbon, soil enzymes, and carbon pools (active and passive) than the tree-based land use with the soil depth. The vertical distribution of C in the soil profile was inconsistent: organic C (including C pools) decreased, while inorganic C increased. The profile TC stock to a depth of 1.0 m in the forest was 358.8 Mg ha-1, of which 81 % were organic C, and 19 % were inorganic C. In comparison with forest soil, total soil C stocks (organic and inorganic) decreased more (-44.1 to -55.1 %) in seasonal crops than in tree-based (-15.4 to -36.3 %) land uses. The degradation index (DI) also confirmed that seasonal crop cultivation caused a larger decline in surface soil quality (DI: -423 % to -623 %) than tree-based land use (DI: -243 % to -317 %). The topsoil (up to 0.45 m) of seasonal crops was more degraded than that of the subsoil (>0.45 m-1.0 m). Forests converted to seasonal cultivation (upland rice and vegetables) caused higher degradation of soil C forms and overall soil health in the Himalayan foothills of northeastern India. We suggest the promotion of Agroforestry based on legumes (Parkia spp.) and woody fruits (mango/citrus/guava) in the uplands to minimize soil C degradation while ensuring nutritional security in the hill agro-ecosystems of the Indian Himalayas.

… Some previous studies suggested that soil C storage … soil organic C (SOC) stocks along an altitudinal gradient spanning a 3000m altitude difference. In addition, we sampled soils in …

Abstract. The global soil organic carbon (SOC) mass is relevant for the carbon cycle budget and thus atmospheric carbon concentrations. We review current estimates of SOC stocks and mass (stock × area) in wetlands, permafrost and tropical regions and the world in the upper 1 m of soil. The Harmonized World Soil Database (HWSD) v.1.2 provides one of the most recent and coherent global data sets of SOC, giving a total mass of 2476 Pg when using the original values for bulk density. Adjusting the HWSD's bulk density (BD) of soil high in organic carbon results in a mass of 1230 Pg, and additionally setting the BD of Histosols to 0.1 g cm−3 (typical of peat soils), results in a mass of 1062 Pg. The uncertainty in BD of Histosols alone introduces a range of −56 to +180 Pg C into the estimate of global SOC mass in the top 1 m, larger than estimates of global soil respiration. We report the spatial distribution of SOC stocks per 0.5 arcminutes; the areal masses of SOC; and the quantiles of SOC stocks by continents, wetland types, and permafrost types. Depending on the definition of "wetland", wetland soils contain between 82 and 158 Pg SOC. With more detailed estimates for permafrost from the Northern Circumpolar Soil Carbon Database (496 Pg SOC) and tropical peatland carbon incorporated, global soils contain 1325 Pg SOC in the upper 1 m, including 421 Pg in tropical soils, whereof 40 Pg occurs in tropical wetlands. Global SOC amounts to just under 3000 Pg when estimates for deeper soil layers are included. Variability in estimates is due to variation in definitions of soil units, differences in soil property databases, scarcity of information about soil carbon at depths > 1 m in peatlands, and variation in definitions of "peatland".

… and regional databases that already exist. We calculated global and regional soil carbon … databases (SoilGrids, the Harmonized World Soil Database, and the Northern Circumpolar …

We developed a comprehensive, gridded Global Soil Dataset for use in Earth System Models (GSDE) and other applications. The GSDE provides soil information, such as soil particle‐size distribution, organic carbon, and nutrients, and quality control information in terms of confidence level at 30″ × 30″ horizontal resolution and for eight vertical layers to a depth of 2.3 m. The GSDE is based on the Soil Map of the World and various regional and national soil databases, including soil attribute data and soil maps. We used a standardized data structure and data processing procedures to harmonize the data collected from various sources. We then used a soil type linkage method (i.e., taxotransfer rules) and a polygon linkage method to derive the spatial distribution of the soil properties. To aggregate the attributes of different compositions of a mapping unit, we used three mapping approaches: the area‐weighting method, the dominant soil type method, and the dominant binned soil attribute method. The data set can also be aggregated to a lower resolution. In this paper, we only show the vertical and horizontal variations of sand, silt and clay contents, bulk density, and soil organic carbon as examples of the GSDE. The GSDE estimates of global soil organic carbon stock to the depths of 2.3, 1, and 0.3 m are 1922.7, 1455.4, and 720.1 Gt, respectively. This newly developed data set provides more accurate soil information and represents a step forward to advance earth system modeling.

… In addition, a subset of sites from the ISRIC-WISE international soil profile dataset was included in this study (Batjes 1995). To ensure the best coverage of the globe, we also included …

… of global SOC stocks and their spatial distribution, in particular highlighting recently published global soil carbon … ▪ Uncertainty in SOC distribution data due to reliance on soil maps …

… consideration of the underlying data lineage, generalizations, and the associated uncertainties. As an example, the database was used to calculate the global soil organic carbon (SOC) …

Soil microbial biomass carbon (SMBC) is important in regulating soil organic carbon (SOC) dynamics along soil profiles by mediating the decomposition and formation of SOC. The dataset (VDMBC) is about the vertical distributions of SOC, SMBC, and soil microbial quotient (SMQ = SMBC/SOC) and their relations to environmental factors across five continents. Data were collected from literature, with a total of 289 soil profiles and 1040 observations in different soil layers compiled. The associated environment data collectd include climate, ecosystem types, and edaphic factors. We developed this dataset by searching the Web of Sciene and the China National Knowledge Infrastructure from the year of 1970 to 2019. All the data in this dataset met two creteria: 1) there were at least three mineral soil layers along a soil profile, and 2) SMBC was measured using the fumigation extraction method. The data in tables and texts were obtained from literature directly, and the data in figures were extracted by using the GetData Graph digitizer software version 2.25. When climate and soil properties were not available from publications, we obtainted the data from the World Weather Information Service (https://worldweather.wmo.int/en/home.html) and SoilGrids at a spatial resolution of 250 meters (version 0.5.3, https://soilgrids.org). The units of all the variables were converted to the standard international units or commonly used ones and the values were transformed correspondingly. For example, the value of soil organic matter (SOM) was converted to SOC by using the equation (SOC = SOM × 0.58). This dataset can be used in predicting global SOC changes along soil profiles by using the multi-layer soil carbon models. It can also be used to analyse how soil microbial biomass changes with plant roots as well as the composition, structure, and functions of soil microbial communities along soil profiles at large spatial scales. This dataset offers opportunities to improve our prediction of SOC dynamics under global changes and to advance our understanding of the environmental controls.

Abstract. High-latitude terrestrial ecosystems are key components in the global carbon (C) cycle. Estimates of global soil organic carbon (SOC), however, do not include updated estimates of SOC storage in permafrost-affected soils or representation of the unique pedogenic processes that affect these soils. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify the SOC stocks in the circumpolar permafrost region (18.7 × 106 km2). The NCSCD is a polygon-based digital database compiled from harmonized regional soil classification maps in which data on soil order coverage have been linked to pedon data (n = 1778) from the northern permafrost regions to calculate SOC content and mass. In addition, new gridded datasets at different spatial resolutions have been generated to facilitate research applications using the NCSCD (standard raster formats for use in geographic information systems and Network Common Data Form files common for applications in numerical models). This paper describes the compilation of the NCSCD spatial framework, the soil sampling and soil analytical procedures used to derive SOC content in pedons from North America and Eurasia and the formatting of the digital files that are available online. The potential applications and limitations of the NCSCD in spatial analyses are also discussed. The database has the doi:10.5879/ecds/00000001 . An open access data portal with all the described GIS-datasets is available online at: http://www.bbcc.su.se/data/ncscd/ .

… carbon stocks. Applying GlobalSoilMap specifications to France, using a large soil dataset and all the exhaustive spatially available data … and carbon stocks (> 75% for the total carbon …

Abstract Small changes in soil organic carbon (SOC) may have great influences on the climate-carbon (C) cycling feedback. However, there are large uncertainties in predicting the dynamics of SOC in soil profiles at the global scale, especially on the role of soil microbial biomass in regulating the vertical distribution of SOC. Here, we developed a database of soil microbial biomass carbon (SMBC), SOC, and soil microbial quotient (SMQ = SMBC/SOC) from 289 soil profiles globally, as well as climate, ecosystem types, and edaphic factors associated with these soil profiles. We assessed the vertical distribution patterns of SMBC and SMQ and the contributions of climate, ecosystem type, and edaphic condition to their vertical patterns. Our results showed that SMBC and SMQ decreased exponentially with soil depth, especially within the 0–40 cm soil depth. SOC also decreased exponentially with depth but in different magnitudes compared to SMBC and SMQ. Edaphic factors (e.g., soil clay content and C/N ratio) had the strongest control on the vertical distributions of SMBC and SMQ, probably by mediating substrate and nutrient supplies for microbial growth in soils. Mean annual temperature and ecosystem types (i.e., forests, grasslands, and croplands) had weak influences on SMBC and SMQ. In contrast, the vertical distribution of SOC was significantly affected by climate and edaphic factors. Climate and ecosystem types likely simultaneously affected multiple factors that control SMBC, such as the distribution of soil clay and nutrients along soil profiles. Overall, our data synthesis provides quantitative information of how SMBC, SMQ, and SOC changed along soil profiles at large spatial scales and identifies important factors that influence their vertical distributions. The findings can help improve the prediction of C cycling in terrestrial ecosystems by incorporating the contribution of soil microbes in Earth system models.

Most of our terrestrial carbon (C) storage occurs in soils as organic C derived from living organisms. Therefore, the fate of soil organic C (SOC) in response to changes in climate, land use, and management is of great concern. Here we provide a unified conceptual model for SOC cycling by gathering the available information on SOC sources, dissolved organic C (DOC) dynamics, and soil biogeochemical processes. The evidence suggests that belowground C inputs (from roots and microorganisms) are the dominant source of both SOC and DOC in most ecosystems. Considering our emerging understanding of SOC protection mechanisms and long-term storage, we highlight the present need to sample (often ignored) deeper soil layers. Contrary to long-held biases, deep SOC—which contains most of the global amount and is often hundreds to thousands of years old—is susceptible to decomposition on decadal timescales when the environmental conditions under which it accumulated change. Finally, we discuss the vulnerability of SOC in different soil types and ecosystems globally, as well as identify the need for methodological standardization of SOC quality and quantity analyses. Further study of SOC protection mechanisms and the deep soil biogeochemical environment will provide valuable information about controls on SOC cycling, which in turn may help prioritize C sequestration initiatives and provide key insights into climate-carbon feedbacks.

… Agriculture ecosystems have 37.0% of the total SOC of the … In contrast, for wetland ecosystems most of total SOC is in … SOC and SIC was found for any ecosystem at any soil depth. Most …

… -based observation of the actual depth distribution of soil carbon ages. … For the subsoil, by contrast, we found no relationship … of, first, the SOC age distribution over the soil profile (Fig. 2), …

Abstract Soil organic carbon (SOC) decomposition can potentially feedback to climate change. However, the biotic, abiotic and inherent factors controlling the stability of soil carbon, and changes in these factors with soil depth, remain poorly understood. In this study, we combined a number of complementary methods to quantify the biological, thermal, chemical, molecular and isotopic indices of soil organic matter (SOM) stability along the soil profile (0–70 cm) in two contrasting alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. Firstly, we conducted an aerobic lab–incubation experiment on root–free, sieved soils. The number of days to respire 5% of initial SOC, a biological index of SOM stability, decreased with soil depth. Moreover, the temperature at which half of SOM mass loss (TG–T50), a thermal index of SOM stability, increased with soil depth. Additionally, hot–water extractable organic carbon (HWEOC) per gram SOC, a chemical index of SOM stability, showed weak (meadow) and little (shrubland) declining trend with depth. Further, we used Fourier–transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy to characterize the molecular composition of SOM. The index of recalcitrance of FTIR spectra and the combined index of aliphaticity and aromaticity of NMR spectra both increased with depth, suggesting that the molecular composition of SOM was more complex with increasing depth. Finally, the isotopic values of SOM (13C and 15N) and the 14C–based SOC turnover time both increased with depth, indicating that the isotopic indices of SOM stability also increased with depth. Overall, our results suggest that the thermal, chemical, molecular and isotopic indices of SOM stability were mutually correlated and all showed increasing trend with increasing soil depth in the two alpine ecosystems, although the biological index (as measured by aerobic incubation of root–free sieved soils) showed the opposite results.

This study was carried out in three kinds of salt marshes according to the vegetation covers, including Phragmites australis salt marsh (PSM), Suaeda salus salt marsh (SSM) and Tamarix chinensis-Suaeda salus salt marsh (TSSM). We applied allometric function, exponential function and logistic function to model the depth distribution of the SOCv and SOCc for each salt marsh, respectively. The results showed that the exponential function fits the depth distribution of the SOCv more well than other two functions. The SOCc can be fitted very well by all three functions for three salt marsh (Adj. R2 > 0.99), of which the allometric function was the best one. The mean topsoil concentration factors (TCFs) of three salt marshes were beyond 0.1, which means the SOC enrichment in surface soils due to plant cycling, but TCFs in PSM were significantly higher than those in SSM (P < 0.05). Nearly 30% of SOC was concentrated in the top 20 cm soils. The results of general linear model (GLM) suggested that four soil properties (soil water content, pH, soil salt content and silt+clay) and their interactive effects explained about 80% of the total variation of SOC stock in the top 20 cm soils and the 20–100 cm soil layers.

… depth at which high/low amounts of SOC … depth distribution of SOC in relation to land use and soil type based on a large dataset for Flanders (Belgium). Soil type determines the SOC …

Subsurface soil organic carbon (SOC) is a large but still poorly understood component of the global carbon cycle. We investigated the depth distribution of SOC in eastern Australia, testing the hypotheses that SOC content near the surface is linked with water availability, whereas the distribution of SOC with depth is linked with land use, site factors and temperature. To do this, we measured SOC concentration to 1 m at 100 sites across eastern Australia, and fitted three parameter exponential depletion models to the results. Three machine learning algorithms were used to identify predictors important to the model parameters. Multiple regression models were then created based upon the machine learning results using bootstrapped stepwise regressions and the relative importance of the selected variables was assessed using proportional marginal variance decomposition. Surface SOC concentration was influenced predominantly by climate variables, of which seasonal rainfall was by far the most important. At depth, SOC storage was most influenced by site factors (mainly bulk density and soil type), and both land use and climate contributed similar amounts to model explained variance. The depth distribution of SOC was most influenced by land use, which accounted for ~60% of model explained variance, with site and climate factors being approximately equally important. These results support our hypotheses regarding the drivers of SOC depth distribution in eastern Australia and can be used to identify regions with the potential for additional subsurface soil carbon storage.

Abstract. Determining the dynamics of organic carbon in subsoil (SOC, depth of 20–100 cm) is important with respect to the global C cycle and warming mitigation. However, there is still a huge knowledge gap in the dynamics of spatiotemporal changes in SOC in this layer. Combining traditional depth functions and machine-learning methods, we achieved soil β values and SOC dynamics at high resolution for global ecosystems (cropland, grassland, and forestland). First, quantified the spatial variability characteristics of soil β values and driving factors by analyzing 1221 soil profiles (0–100 cm) of globally distributed field observations. Then, based on multiple environmental variables and soil profile data, we mapped the grid-level soil β values with machine-learning approaches. Lastly, we evaluated the SOC density spatial distribution in different soil layers to determine the subsoil SOC stocks of various ecosystems. The subsoil SOC density values of cropland, grassland, and forestland were 63.8, 83.3, and 100.4 Mg ha–1, respectively. SOC density decreased with increasing depth, ranging from 5.6 to 30.8 Mg ha–1 for cropland, 7.5 to 40.0 Mg ha–1 for grassland, and 9.6 to 47.0 Mg ha–1 for forestland. The global subsoil SOC stock was 912 Pg C (cropland, grassland, and forestland were 67, 200, and 644 Pg C), in which an average of 54 % resided in the top 0–100 cm of the soil profile. Our results provide information on the vertical distribution and spatial patterns of SOC density at a 10 km resolution for areas of Global ecosystems, which providing a scientific basis for future studies pertaining to Earth system models. The dataset is open-access and available at https://doi.org/10.5281/zenodo.10846543 (Wang et al., 2024).

Abstract The soils of shrublands are important for organic carbon storage in terrestrial ecosystems, but geographical patterns and environmental controls of soil organic carbon (SOC) remain largely understudied compared to other terrestrial ecosystems, leaving a significant gap in our understanding of terrestrial ecosystem carbon budgets. Here, we quantified SOC density (SOCD) and its potential determinants based on a comprehensive dataset with a consistent stratified random sampling of extensive soil profiles down to the parent material or to one meter depth across 1211 sites across China. Our up-to-date estimate of SOCD in Chinese shrublands is an average of 8.36 kg m−2, and ca. 43% of SOC is stored in the upper 20 cm relative to the one meter top soil, which is higher than estimates for shrublands globally. We also observed that SOCD was positively related to shrubland biomass and more so with belowground biomass. Furthermore, SOCD was positively related to mean annual precipitation (MAP), soil total nitrogen (N), phosphorus (P), clay and silt percent, but decreased with increasing mean annual temperature (MAT). Dark felty soils stored the highest SOCD and frigid desert soils stored the lowest. Soil total nitrogen (N), MAP, soil type, MAT, and belowground biomass, soil clay, and pH were the best predictors of total SOCD in Chinese shrublands. We concluded that Chinese shrubland soils store the lowest density of organic carbon so far recorded compared to forests and grasslands, and that the vertical distribution of SOC in Chinese shrublands was much shallower. While both climate (in particular MAP) and soil total N exerted dominant control over geographical patterns of SOCD across Chinese shrublands, soil type also played a significant role. Our study also emphasizes this key role of edaphic variables in determining the SOCD of shrublands and that they should be better incorporated into large-scale assessments of SOC dynamics. Our study extends existing work conducted in forest and grasslands and provides the most up-to-date knowledge on benchmark values for SOCD in Chinese shrublands, with important implications for predicting the fate of C stored in shrubland soils in response to climate change.

The objectives of this study were to investigate effects of land use on accumulation of soil organic matter (SOM) in the soil profile (0–100 cm) and to determine pattern of SOM stock distribution in soil profiles. Soil samples were collected from five soil depths at 20 cm intervals from 0 to 100 cm under four adjacent land uses including forest, cassava, sugarcane, and paddy lands located in six districts of Maha Sarakham province in the Northeast of Thailand. When considering SOM stock among different land uses in all locations, forest soils had significantly higher total SOM stocks in 0–100 cm (193 Mg·C·ha−1) than those in cassava, sugarcane, and paddy soils in all locations. Leaf litter and remaining rice stover on soil surfaces resulted in a higher amount of SOM stocks in topsoil (0–20 cm) than subsoil (20–100 cm) in some forest and paddy land uses. General pattern of SOM stock distribution in soil profiles was such that the SOM stock declined with soil depth. Although SOM stocks decreased with depth, the subsoil stock contributes to longer term storage of C than topsoils as they are more stabilized through adsorption onto clay fraction in finer textured subsoil than those of the topsoils. Agricultural practices, notably applications of organic materials, such as cattle manure, could increase subsoil SOM stock as found in some agricultural land uses (cassava and sugarcane) in some location in our study. Upland agricultural land uses, notably cassava, caused high rate of soil degradation. To restore soil fertility of these agricultural lands, appropriate agronomic practices including application of organic soil amendments, return of crop residues, and reduction of soil disturbance to increase and maintain SOM stock, should be practiced.

It has been demonstrated that the high bulk densities of clayey subsoils of Sodosols can result from a process involving shrink/swell cycles and the development of ped coatings containing topsoil material. Our objective was to study this process according to land use and to compute the amount of organic carbon introduced into the subsoil as a consequence of ped coating in the subsoil. In an area located east of Katanning, we carried out an intensive soil survey and selected 2 closely adjacent sites with similar soils but differing in their land use: a cultivated soil and a never cultivated soil in an undisturbed strip of land. Pit faces and horizontal planes of the top of the subsoil were studied. The polygonal network corresponding to the cross-section of the prismatic peds was described. The clay content and bulk density of the prisms was determined. The carbon contents of the coatings and of the sandy material rich in organic carbon that corresponded to remnants of native vegetation was measured. Results showed that the coating process has occurred under native vegetation but is more active when the land has been used for agricultural and pastoral activities, as indicated by thicker sandy-clay coatings on the vertical faces of prisms and the higher bulk densities in the subsoil. The mean bulk density was 1.71 g/cm3 at 20-25 cm depth at the undisturbed site and was 1.86 and 1.82 g/cm3 at 20-25 and 25-30 cm depth, respectively, at the cultivated site. The total soil organic carbon stock was estimated to be close to 68.9 and 61.0 Mg/ha at the undisturbed and cultivated sites, respectively. The organic carbon stock in the subsoil was 38.5 and 23.3% of the respective total stocks. One fourth of the carbon stock in the subsoil corresponded to materials rich in organic carbon that originated from roots of native vegetation. The organic carbon stock in the ped coatings was &amp;lt;1% of the total stock at the 2 sites. Finally, our results support the adoption of zero-till agricultural system for the soil studied to restrict subsoil densification.

Soil organic carbon (SOC) and nitrogen (N) contents are controlled partly by plant inputs that can be manipulated in agricultural systems. Although SOC and N pools occur mainly in the topsoil (upper 0.30 m), there are often substantial pools in the subsoil that are commonly assumed to be stable. We tested the hypothesis that contrasting long‐term management systems change the dynamics of SOC and N in the topsoil and subsoil (to 0.75 m) under temperate conditions. We used an established field experiment in the UK where control grassland was changed to arable (59 years before) and bare fallow (49 years before) systems. Losses of SOC and N were 65 and 61% under arable and 78 and 74% under fallow, respectively, in the upper 0.15 m when compared with the grass land soil, whereas at 0.3–0.6‐m depth losses under arable and fallow were 41 and 22% and 52 and 35%, respectively. The stable isotopes 13C and 15N showed the effects of different treatments. Concentrations of long‐chain n‐alkanes C27, C29 and C31 were greater in soil under grass than under arable and fallow. The dynamics of SOC and N changed in both topsoil and subsoil on a decadal time‐scale because of changes in the balance between inputs and turnover in perennial and annual systems. Isotopic and geochemical analyses suggested that fresh inputs and decomposition processes occur in the subsoil. There is a need to monitor and predict long‐term changes in soil properties in the whole soil profile if soil is to be managed sustainably.

This study aims to investigate soil organic carbon (SOC) and total nitrogen (TN) contents and stocks, CO_2 emissions and selected soil properties in croplands, grazing lands, exclosures and forest lands of semi-arid Ethiopia. Sampling was done at 0–30, 30–60 and 60–90 cm soil depths and concentration and stocks of SOC, TN and selected soil properties were determined using standard routine laboratory procedures. There were variations in distribution of SOC and TN stock over 90 cm depth across land use types and locations, decreasing from topsoils to subsoil, with average values ranging from 48.68 Mg C ha^−1 and 4.80 Mg N ha^−1 in Hugumburda cropland to 303.53 Mg C ha^−1 and 24.99 Mg N ha^−1 in Desa’a forest respectively. Forest sequestered significant higher SOC and TN stock, decreasing with depth, compared with other land use types. In Desa'a and Hugumburda, the conversion of forest to cropland resulted in a total loss of SOC stock of 9.04 Mg C ha^−1 and 2.05 Mg C ha^−1, respectively, and an increase in CO_2 emission of 33.16 Mg C ha^−1 and 7.52 Mg C ha^−1 yr^−1, respectively. The establishment of 10 years (Geregera) and 6 years (Haikihelet) exclosures on degraded grazing land increased SOC stock by 13% and 37% respectively.

… carbon globally is in the subsoil, but data are scarce. We updated estimates of subsoil organic carbon ( … Differences in depth distributions between land uses were small, but subsoil OC …

… of young carbon down the entire soil profile. Our results indicate that organic carbon storage … whole profile, challenging the concept of subsoils as a repository of stable organic carbon. …

Abstract Our objective was to determine how biophysical drivers impact on C sequestration and dynamics in Mollisols and Oxisols under grassland of South-America. We performed a literature review to obtain data on soil C stocks in grasslands and tree plantations on Mollisols and Oxisols and combined it with information from a local soil survey. A simple estimate of the C retention efficiency (CRE) was calculated as the ratio between soil C pool size data and modeled C inputs. Although soil C inputs were higher in tree plantations than in grasslands, this only translated to higher soil C stocks in temperate climates. The CRE was generally much lower in tree plantations as compared to grasslands, and this difference was strongest in tropical sites The CRE was much higher in the subsoil than in the topsoil, probably associated with a more effective physico-chemical protection of soil C by minerals. Our analysis suggests that a combination of trees and grasses in silvopastoral system might be a solution for soil C sequestration in tropical soils.