Land use drives the distribution of free, physically protected, and chemically protected soil organic carbon storage at a global scale
Data files
Oct 10, 2024 version files 2.37 MB
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README.md
52.97 KB
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Willard_GCB_2024_processed_data_081024.csv
1.13 MB
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Willard_GCB_2024_raw_data_081024.csv
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Abstract
Soil organic carbon (SOC) sequestration is increasingly emphasized as a climate mitigation solution, as scientists, policy makers, and land-managers prioritize enhancing belowground C storage. To identify key underlying drivers of total SOC distributions, we compiled a global dataset of soil C stocks held in three chemical forms, reflecting different mechanisms of organic C protection: free particulate organic C (fPOC), physically protected particulate organic C (oPOC), and mineral-protected soil organic C (mSOC). In our dataset, these three SOC pools were differentially sensitive to effects of climate, soil mineralogy, and ecosystem type, emphasizing the importance of distinguishing between physical and chemical C protection mechanisms. C stocks in all three pools varied among ecosystems: cropland soils stored the least amount in each pool, with forest and grassland soils both containing significantly more fPOC (40-60% greater in each ecosystem) than croplands. oPOC stocks did not significantly differ from zero in croplands, but were substantial in forest and grassland soils. Meanwhile, mSOC stocks were the greatest in grasslands and shrublands (90-100% greater than croplands). In cropland soils, there were no major effects of tillage on C storage in any of the three pools, while manure addition enhanced mSOC stocks, especially when added with inorganic N. Thus, the human land use intensity in croplands appears to reduce SOC storage in all major pools, depending upon management; retaining native vegetation should be emphasized to maintain current global SOC stocks.
https://doi.org/10.5061/dryad.b5mkkwhp0
Files and variables
File: Willard_GCB_2024_processed_data.csv
Description:
Variables
- UniqueObsCodeThreePool: Code to denote each unique datapoint featuring: Study ID, simplified ecosystem, USDA soil order, Treatment name, fractionation type (fLF, oLF, mSOC), and topsoil or subsoil
- Study_ID: Author name and published year
- Citation: Author name, published year, journal name, and edition information
- Year_sampled: Sampled year
- Field_or_Lab: Study system
- Latitude: Latitude of sampled location
- Longitude: Longitude of sampled location
- Country: Country of sampled location
- Elevation: Sample elevation
- Ecosystem_type: Ecosystem of sampled location
- Ecosystem_simplified: Simplified ecosystem of sampled location
- Crop_or_forest_type_reported: Cropping or forest type of sampled location
- Cropland_addition: Nutrient addition of sampled soil
- Cropland_addition_N.kg.ha.yr: Inorganic nitrogen addition of sampled soil in units of kg/ha/yr.
- Cropland_addition_Manure.Mg.ha.yr: Manure addition of sampled location in units of kg/ha/yr.
- Cropland_tillage: Tillage regimen of sampled soil
- Soil_order_reported: Reported soil order including USDA and World Reference Base
- Soil_order_simplified: USDA simplified soil order
- Soil_texture: Reported soil texture
- Horizon: Sampled soil horizon
- Soil_volume: Calculated soil volume (100cm *100cm * soil depth)
- Top_depth: Top soil depth (cm)
- bottom_depth: Bottom soil depth (cm)
- Soil_pH_reported: Reported soil pH
- Treatment: Treatment name
- Rotation: Reported cropland rotation information
- Fraction_reported: SOC fraction reported in study
- Fraction_harmonized: Harmonized fraction name for dataset unification
- Floatation_density: Reported density flotation in units of g/cm^3
- Two_pool: Harmonized fraction for two pool sorting (HF and LF)
- Three_pool: Harmonized fraction for three pool sorting (fLF, oLF, mSOC; note manuscript uses terms fPOC, oPOC, and mSOC to convey geochemical characteristics)
- Method_used_C: Reported methodology used to differentiate SOC fraction
- Primary_C_pool: Primary C pool data reported from study: used to calculate data found in C_stock_for_analysis_three_pool. Obsoleted in Willard_GCB_2024_processed_data.csv due to data recombining.
- Units_Primary: Units of primary data (e.g.: g/kg, %)
- Units_Primary_Annotated: Annotation of primary units
- Secondary_C_pool: Secondary C pool data reported from study (used to calculate to g m^2) : used to calculate data found in C_stock_for_analysis_three_pool. Obsoleted in Willard_GCB_2024_processed_data.csv due to data recombining
- Units_Secondary: Units of secondary data (e.g.: g/kg, %)
- MAT_reported: Mean annual temperature (degrees Celsius) reported (used when available)
- MAP_reported: Mean annual precipitation (mm) reported (used when available)
- MAT_added: Mean annual temperature (degrees Celsius) extracted from Terra Climate
- MAP_added: Mean annual precipitation (mm) extracted from Terra Climate
- MAT_used: Mean annual temperature (degrees Celsius) used
- MAP_used: Mean annual precipitation (mm) used
- T_PH_H2O: HWSD topsoil pH; extracted from Harmonized World Soil Database
- S_PH_H2O: HWSD subsoil pH; extracted from Harmonized World Soil Database
- T_CLAY: HWSD topsoil clay percentage; extracted from Harmonized World Soil Database
- S_CLAY: HWSD subsoil clay percentage; extracted from Harmonized World Soil Database
- T_BULK_DEN: HWSD topsoil bulk density (g/cm^3); extracted from Harmonized World Soil Database
- S_BULK_DEN: HWSD subsoil bulk density (g/cm^3); extracted from Harmonized World Soil Database
- BD_reported: Bulk density reported (g cm^3; used when available)
- BD_used: Bulk density used (g cm^3)
- Calculated_C_pool: Calculated C pool size (Primary_C_pool multiplied by Secondary_C_pool C * BD_used * summed_vol where appropriate to units of g m^2; calculated prior to combining along UniqueObsCodeThreePool)
- layer: topsoil (0-30cm) or subsoil (31+cm)
- UniqueObsCodeTwoPool: Code to denote each unique datapoint featuring: Study ID, simplified ecosystem, USDA soil order, Treatment name, fractionation type (HF or LF), and topsoil or subsoil
- C_stock_for_analysis_three_pool: Combined C pool along UniqueObsCodeThreePool: used as response C pool data in manuscript models and in units of g m^2
- PH_three_pool: Combined soil pH along UniqueObsCodeThreePool
- summed_vol: summed soil volume along UniqueObsCodeThreePool and in units of cm^3
Note: NA’s denote unreported data from publications
File: Willard_GCB_2024_raw_data.csv
Description:
Variables
- Study_ID: Author name and published year
- Citation: Author name, published year, journal name, and edition information
- Year_sampled: Sampled year
- Field_or_Lab: Study system
- Latitude: Latitude of sampled location
- Longitude: Longitude of sampled location
- Country: Country of sampled location
- Elevation: Sample elevation
- Ecosystem_type: Ecosystem of sampled location
- Ecosystem_simplified: Simplified ecosystem of sampled location
- Crop_or_forest_type_reported: Cropping or forest type of sampled location
- Cropland_addition: Nutrient addition of sampled soil
- Cropland_addition_N kg/ha/yr: Inorganic nitrogen addition of sampled soil in units of kg/ha/yr.
- Cropland_addition_Manure Mg ha yr: Manure addition of sampled location in units of kg/ha/yr.
- Cropland_tillage: Tillage regimen of sampled soil
- Soil_order_reported: Reported soil order including USDA and World Reference Base
- Soil_order_simplified: USDA simplified soil order
- Soil_texture: Reported soil texture
- Horizon: Sampled soil horizon
- Soil_volume: Calculated soil volume (100cm100cm * soil depth)
- Top_depth: Top soil depth (cm)
- bottom_depth: Bottom soil depth (cm)
- Soil_pH_reported: Reported soil pH
- Treatment: Treatment name
- Rotation: Reported cropland rotation information
- Fraction_reported: SOC fraction reported in study
- Fraction_harmonized: Harmonized fraction name for dataset unification
- Floatation_density: Reported density flotation in units of g/cm^3
- Two_pool: Harmonized fraction for two pool sorting (HF and LF)
- Three_pool: Harmonized fraction for three pool sorting (fLF, oLF, mSOC; note manuscript uses terms fPOC, oPOC, and mSOC to convey geochemical characteristics)
- Method_used_C: Reported methodology used to differentiate SOC fraction
- Primary_C_pool: Primary C pool data reported from study: used to calculate data found in C_stock_for_analysis_three_pool. Obsoleted in Processed_data file due to data recombining.
- Units_Primary: Units of primary data (e.g.: g/kg, %)
- Units_Primary_Annotated: Annotation of primary units
- Secondary_C_pool: Secondary C pool data reported from study (used to calculate to g m^2) : used to calculate data found in C_stock_for_analysis_three_pool. Obsoleted in Processed_data file due to data recombining.
- Units_Secondary: Units of secondary data (e.g.: g/kg, %)
- MAT_reported: Mean annual temperature (degrees Celsius) reported (used when available)
- MAP_reported: Mean annual precipitation (mm) reported (used when available)
- MAT_added: Mean annual temperature (degrees Celsius) extracted from Terra Climate
- MAP_added: Mean annual precipitation (mm) extracted from Terra Climate
- MAT_used: Mean annual temperature (degrees Celsius) used
- MAP_used: Mean annual precipitation (mm) used
- T_PH_H2O: HWSD topsoil pH; extracted from Harmonized World Soil Database
- S_PH_H2O: HWSD subsoil pH; extracted from Harmonized World Soil Database
- T_CLAY: HWSD topsoil clay percentage; extracted from Harmonized World Soil Database
- S_CLAY: HWSD subsoil clay percentage; extracted from Harmonized World Soil Database
- T_BULK_DEN: HWSD topsoil bulk density (g/cm^3); extracted from Harmonized World Soil Database
- S_BULK_DEN:HWSD subsoil bulk density (g/cm^3); extracted from Harmonized World Soil Database
- BD_reported: Bulk density reported (g cm^3; used when available)
- BD_used: Bulk density used (g cm^3)
- Calculated_C_pool: Calculated C pool size (Primary_C_pool multiplied by Secondary_C_pool C * BD_used * summed_vol where appropriate to units of g m^2; calculated prior to combining along UniqueObsCodeThreePool) and in units of g m^2
- layer: topsoil (0-30cm) or subsoil (31+cm)
Note: NA’s denote unreported data from publications
Code/software
Data analysis was done in R (version 4.3.1). Packages for statistics and graphing included: lme4, lmerTest, MuMIn, plotrix, stringr, dplyr, tidyverse, ggplot2, and lsmeans.
Access information
Data was derived from the following sources:
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Provided is the list of publications from which data was extracted and utilized within the analysis:
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We collected data from papers which utilized a density fractionation methodology to measure soil organic C (SOC) within the three fraction pools: free particulate organic fraction (fPOC), occluded particulate organic fraction (oPOC), and mineral soil organic carbon (mSOC). To filter through published studies reporting SOC stocks, we chose to extract data from papers which cited one of the following rigorous and influential fractionation methodologies: (Golchin et al., 1994; Shaymukhametov et al., 1984; Six et al., 1998; Sollins et al., 1984, 2006, 2009; Spycher et al., 1983; Steffens et al., 2009). On Google Scholar, there were 3915 papers citing one of the above papers through September 2020. We examined each publication and only extracted data from empirical studies, published in a peer-review journal in English, that measured SOC via density fractionation. When recording oPOC or mSOC data, we only collected data from papers which utilized sonication, sodium hexametaphosphate dispersion, or physical disruption (e.g., from glass beads) to separate oPOC from mSOC (Figure S1). Unless it was specified for a particular soil and reported in the respective study, we set a density cutoff of 1.85 g cm-3 for classifying mSOC. Since some studies isolated C pools along a density gradient, we summed SOC stored in fractions above or below the density cutoff.
To make meaningful global comparisons, we chose to only include papers which reported enough information to calculate the C stock in units of g C m2. In cases where C concentrations but not stocks were reported, we used soil depth and bulk density (BD, g cm-3) to calculate the C stock in a given pool (fPOC, oPOC, mSOC). Data were recorded separately for different locations, ecosystem types, treatments, soil depths, and fractions. Because there was a wide range in soil depth increments used within studies, we summed C stocks from specific depth intervals (e.g. 0-10 cm, 10-30 cm) into two categories: ‘topsoil’ (0-30cm) or subsoil (31+cm). Soil volume associated with each observation was calculated assuming a 1x1 m sampling area and the sampling depth increment reported by the study authors (e.g. 0-10 cm, 15-30 cm).