Soil properties override climate controls on global soil organic carbon stocks

Global Soil ◽

Climate Controls ◽

Edaphic Properties ◽

Abstract. Soil organic carbon (SOC) accounts for two-thirds of terrestrial carbon. Yet, the role of soil physiochemical properties in regulating SOC stocks is unclear, inhibiting reliable SOC predictions under land use and climatic changes. Using legacy observations from 141,584 soil profiles worldwide, we disentangle the effects of biotic, climatic and edaphic factors (a total of 30 variables) on the global spatial distribution of SOC stocks in four sequential soil layers down to 2 m. The results indicate that the 30 variables can explain 70–80 % of the global variance of SOC in the four layers, to which edaphic properties contribute ~ 60 %. Soil lower limit is the most important individual soil properties, positively associated with SOC in all layers, while climatic variables are secondary. This dominant effect of soil properties challenges current climate-driven framework of SOC dynamics, and need to be considered to reliably project SOC changes for effective carbon management and climate change mitigation.

Similar importance of edaphic and climatic factors for controlling soil organic carbon stocks of the world

Biogeosciences ◽

10.5194/bg-18-2063-2021 ◽

2021 ◽

Vol 18 (6) ◽

pp. 2063-2073

Author(s):

Zhongkui Luo ◽

Raphael A. Viscarra-Rossel ◽

Tian Qian

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Properties ◽

Climatic Factors ◽

Net Primary Production ◽

Field Capacity ◽

Soil Layers ◽

Abstract. Soil organic carbon (SOC) accounts for two-thirds of terrestrial carbon. Yet, the role of soil physicochemical properties in regulating SOC stocks is unclear, inhibiting reliable SOC predictions under land use and climatic changes. Using legacy observations from 141 584 soil profiles worldwide, we disentangle the effects of biotic, climatic and edaphic factors (a total of 31 variables) on the global spatial distribution of SOC stocks in four sequential soil layers down to 2 m. The results indicate that the 31 variables can explain 60 %–70 % of the global variance of SOC in the four layers, to which climatic variables and edaphic properties each contribute ∼35 % except in the top 20 cm soil. In the top 0–20 cm soil, climate contributes much more than soil properties (43 % vs. 31 %), while climate and soil properties show the similar importance in the 20–50, 50–100 and 100–200 cm soil layers. However, the most important individual controls are consistently soil-related and include soil texture, hydraulic properties (e.g. field capacity) and pH. Overall, soil properties and climate are the two dominant controls. Apparent carbon inputs represented by net primary production, biome type and agricultural cultivation are secondary, and their relative contributions were ∼10 % in all soil depths. This dominant effect of individual soil properties challenges the current climate-driven framework of SOC dynamics and needs to be considered to reliably project SOC changes for effective carbon management and climate change mitigation.

Supplementary material to "Soil properties override climate controls on global soil organic carbon stocks"

10.5194/bg-2020-298-supplement ◽

2020 ◽

Author(s):

Zhongkui Luo ◽

Raphael Viscarra-Rossel

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Properties ◽

Carbon Stocks ◽

Global Soil ◽

Climate Controls ◽

Supplementary Material

Spatial heterogeneity and environmental predictors of permafrost region soil organic carbon stocks

Science Advances ◽

10.1126/sciadv.aaz5236 ◽

2021 ◽

Vol 7 (9) ◽

pp. eaaz5236 ◽

Cited By ~ 1

Author(s):

Umakant Mishra ◽

Gustaf Hugelius ◽

Eitan Shelef ◽

Yuanhe Yang ◽

Jens Strauss ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Spatial Heterogeneity ◽

Surface Air Temperature ◽

Spatially Explicit ◽

Soil Profiles ◽

Permafrost Region ◽

Environmental Predictors ◽

Large stocks of soil organic carbon (SOC) have accumulated in the Northern Hemisphere permafrost region, but their current amounts and future fate remain uncertain. By analyzing dataset combining >2700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated that 1014−175+194 Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.

Soil organic carbon stocks are systematically overestimated by misuse of the parameters bulk density and stone content

10.5194/soil-2016-78 ◽

2016 ◽

Author(s):

Christopher Poeplau ◽

Cora Vos ◽

Axel Don

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Bulk Density ◽

Agricultural Soils ◽

Soil Layer ◽

Future Studies ◽

Soc Stock ◽

The Mean ◽

Abstract. Estimation of soil organic carbon (SOC) stocks requires estimates of the carbon content, bulk density, stone content and depth of a respective soil layer. However, different application of these parameters could introduce a considerable bias. Here, we explain why three out of four frequently applied methods overestimate SOC stocks. In stone rich soils (> 30 Vol. %), SOC stocks could be overestimated by more than 100 %, as revealed by using German Agricultural Soil Inventory data. Due to relatively low stone content, the mean systematic overestimation for German agricultural soils was 2.1–10.1 % for three different commonly used equations. The equation ensemble as re-formulated here might help to unify SOC stock determination and avoid overestimation in future studies.

The resilience of soil organic carbon stocks under contrasting hill country pasture management practices

NZGA: Research and Practice Series ◽

10.33584/rps.17.2021.3449 ◽

2021 ◽

Vol 17 ◽

Author(s):

Alec Mackay ◽

Ronaldo Eduardo Vibart ◽

Catherine McKenzie ◽

Brian Devantier ◽

Emma Noakes

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Management Practices ◽

Pasture Management ◽

Single Superphosphate ◽

Hill Country ◽

Environmental Goals ◽

The Stability ◽

In 2020 we measured the stability of soil organic carbon (SOC) concentrations and stocks under contrasting hill country pasture regimes, by sampling three slope classes and three aspect locations on each of three farmlets of a long-term phosphorus fertiliser and sheep grazing experiment. The farmlets included no annual phosphorus (NF), 125 kg of single superphosphate/ha (LF), or 375 kg superphosphate/ha (HF) that has been applied on an annual basis since 1980. Results from the 2020 sampling event were added to previous results reported from soil samples collected in 2003 and 2014. The SOC concentrations in the topsoil (0-75 mm depth), ranging from 4.23 to 5.99% across all slopes and aspects of the farmlets, fell within the normal range (≥3.5 and <7.0%) required for sustaining production and environmental goals. A trend was shown for greater SOC stocks in the topsoil in the HF farmlet (34.0 Mg/ ha) compared with the other two farmlets (31.6 Mg/ha), but this trend was not evident in the deeper soil layers (75-150, 150-300, 0-300 mm). Under the current conditions, topographical features such as slope and aspect had a more profound influence on SOC stocks than management history.

Afforestation changes soil organic carbon stocks on sloping land: The role of previous land cover and tree type

Ecological Engineering ◽

10.1016/j.ecoleng.2020.105860 ◽

2020 ◽

Vol 152 ◽

pp. 105860 ◽

Cited By ~ 3

Author(s):

Guolong Hou ◽

Claudio O. Delang ◽

Xixi Lu

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Land Cover ◽

Carbon Stocks ◽

Sloping Land ◽

Tree Type

Divergent controls of soil organic carbon between observations and process-based models

Biogeochemistry ◽

10.1007/s10533-021-00819-2 ◽

2021 ◽

Author(s):

Katerina Georgiou ◽

Avni Malhotra ◽

William R. Wieder ◽

Jacqueline H. Ennis ◽

Melannie D. Hartman ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Primary Productivity ◽

Net Primary Productivity ◽

Global Scale ◽

Mean Annual Temperature ◽

Biogeochemical Models ◽

Soc Stocks ◽

Process Based Models

AbstractThe storage and cycling of soil organic carbon (SOC) are governed by multiple co-varying factors, including climate, plant productivity, edaphic properties, and disturbance history. Yet, it remains unclear which of these factors are the dominant predictors of observed SOC stocks, globally and within biomes, and how the role of these predictors varies between observations and process-based models. Here we use global observations and an ensemble of soil biogeochemical models to quantify the emergent importance of key state factors – namely, mean annual temperature, net primary productivity, and soil mineralogy – in explaining biome- to global-scale variation in SOC stocks. We use a machine-learning approach to disentangle the role of covariates and elucidate individual relationships with SOC, without imposing expected relationships a priori. While we observe qualitatively similar relationships between SOC and covariates in observations and models, the magnitude and degree of non-linearity vary substantially among the models and observations. Models appear to overemphasize the importance of temperature and primary productivity (especially in forests and herbaceous biomes, respectively), while observations suggest a greater relative importance of soil minerals. This mismatch is also evident globally. However, we observe agreement between observations and model outputs in select individual biomes – namely, temperate deciduous forests and grasslands, which both show stronger relationships of SOC stocks with temperature and productivity, respectively. This approach highlights biomes with the largest uncertainty and mismatch with observations for targeted model improvements. Understanding the role of dominant SOC controls, and the discrepancies between models and observations, globally and across biomes, is essential for improving and validating process representations in soil and ecosystem models for projections under novel future conditions.

Soil organic carbon stocks are systematically overestimated by misuse of the parameters bulk density and rock fragment content

SOIL ◽

10.5194/soil-3-61-2017 ◽

2017 ◽

Vol 3 (1) ◽

pp. 61-66 ◽

Cited By ~ 51

Author(s):

Christopher Poeplau ◽

Cora Vos ◽

Axel Don

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Bulk Density ◽

Agricultural Soils ◽

Soil Layer ◽

Rock Fragment ◽

Rock Fragments ◽

Soc Stocks ◽

Rock Fragment Content

Abstract. Estimation of soil organic carbon (SOC) stocks requires estimates of the carbon content, bulk density, rock fragment content and depth of a respective soil layer. However, different application of these parameters could introduce a considerable bias. Here, we explain why three out of four frequently applied methods overestimate SOC stocks. In soils rich in rock fragments (> 30 vol. %), SOC stocks could be overestimated by more than 100 %, as revealed by using German Agricultural Soil Inventory data. Due to relatively low rock fragments content, the mean systematic overestimation for German agricultural soils was 2.1–10.1 % for three different commonly used equations. The equation ensemble as re-formulated here might help to unify SOC stock determination and avoid overestimation in future studies.

Global distribution of soil organic carbon – Part 1: Masses and frequency distributions of SOC stocks for the tropics, permafrost regions, wetlands, and the world

SOIL ◽

10.5194/soil-1-351-2015 ◽

2015 ◽

Vol 1 (1) ◽

pp. 351-365 ◽

Cited By ~ 138

Author(s):

M. Köchy ◽

R. Hiederer ◽

A. Freibauer

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Carbon ◽

Bulk Density ◽

Tropical Soils ◽

Frequency Distributions ◽

Tropical Regions ◽

The World ◽

Global Soil ◽

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".