scholarly journals Large-scale controls of soil organic carbon in (sub)tropical soils

2020 ◽  
Author(s):  
Sophie F. von Fromm ◽  
Alison M. Hoyt ◽  
Asmeret Asefaw Berhe ◽  
Keith D. Shepherd ◽  
Tor-Gunnar Vågen ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Large Scale ◽  
Experimental Studies ◽  
Clay Content ◽  
Carbon Stocks ◽  
Sub Saharan Africa ◽  
Mean Annual Precipitation ◽  
Tropical Regions ◽  
Continental Scale

<p>Soil organic carbon (SOC) is a key component of terrestrial ecosystems. Experimental studies have shown that soil texture and geochemistry have a strong effect on carbon stocks. However, those findings primarily rely on data from temperate regions or use model approaches that are often based on limited data from tropical and sub-tropical regions.</p><p>Here, we evaluate the controls on soil carbon stocks in Africa, using a dataset of 1,580 samples. These were collected across Sub-Saharan Africa (SSA) within the framework of the Africa Soil Information Service (AfSIS) project, which was built on the well-established Land Degradation Surveillance Framework (LDSF). Samples were taken from two depths (0–20 cm and 20–50 cm) at 46 LDSF sites that were stratified according to Koeppen-Geiger climate zones. The different pH-values, clay content, exchangeable cations and extractable elements across various soils of the different climatic zones (i.e. from arid to humid (sub)tropical) allow us to identify different soil and climate parameters that best explain SOC variance across SSA.</p><p>We tested if these SOC predictors differed across climatological conditions, using the ratio of potential evapotranspiration (PET) to mean annual precipitation (MAP) as indicator. For water-limited regions (PET/MAP > 1), the best predictors were climatic variables, likely because of their effect on the quantity of carbon inputs. Geochemistry dominated SOC storage in energy-limited systems (PET/MAP < 1), reflecting its effect on carbon protection. On a continental scale, climate (e.g. PET) is key to predicting SOC content in topsoil, whereas geochemistry, particularly iron-oxyhydroxides and aluminum-oxides, is more important in subsoil. Clay content had little influence on SOC at both depths. These findings contribute to an improved understanding of the controls on SOC stocks in tropical and sub-tropical regions.</p>

scholarly journals Continental-scale controls on soil organic carbon across sub-Saharan Africa

SOIL ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 305-332
Author(s):  
Sophie F. von Fromm ◽  
Alison M. Hoyt ◽  
Markus Lange ◽  
Gifty E. Acquah ◽  
Ermias Aynekulu ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Land Cover ◽  
Soil Texture ◽  
Sub Saharan Africa ◽  
Continental Scale ◽  
Weathered Soils ◽  
Exchangeable Ca ◽  
Extractable Metals ◽  
Sub Saharan

Abstract. Soil organic carbon (SOC) stabilization and destabilization has been studied intensively. Yet, the factors which control SOC content across scales remain unclear. Earlier studies demonstrated that soil texture and geochemistry strongly affect SOC content. However, those findings primarily rely on data from temperate regions where soil mineralogy, weathering status and climatic conditions generally differ from tropical and subtropical regions. We investigated soil properties and climate variables influencing SOC concentrations across sub-Saharan Africa. A total of 1601 samples were analyzed, collected from two depths (0–20 and 20–50 cm) from 17 countries as part of the Africa Soil Information Service project (AfSIS). The data set spans arid to humid climates and includes soils with a wide range of pH values, weathering status, soil texture, exchangeable cations, extractable metals and land cover types. The most important SOC predictors were identified by linear mixed-effects models, regression trees and random forest models. Our results indicate that geochemical properties, mainly oxalate-extractable metals (Al and Fe) and exchangeable Ca, are equally important compared to climatic variables (mean annual temperature and aridity index). Together, they explain approximately two-thirds of SOC variation across sub-Saharan Africa. Oxalate-extractable metals were most important in wet regions with acidic and highly weathered soils, whereas exchangeable Ca was more important in alkaline and less weathered soils in drier regions. In contrast, land cover and soil texture were not significant SOC predictors on this large scale. Our findings indicate that key factors controlling SOC across sub-Saharan Africa are broadly similar to those in temperate regions, despite differences in soil development history.

scholarly journals Density-Based Soil Organic Carbon Fractionation: Experimental Method Comparison and Influential Factors

2021 ◽  
Author(s):  
Xiaolu Sun ◽  
Michael G. Ryan ◽  
Osbert Jianxin Sun ◽  
Zuoxin Tang
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Experimental Method ◽  
Soil Type ◽  
Vegetation Type ◽  
Clay Content ◽  
Mean Annual Precipitation ◽  
Mean Annual Temperature ◽  
Climate Condition ◽  
Soc Fractions

Abstract Background: Because soil organic carbon (SOC) variation is a result of its physicochemical protection, fractionating SOC into different functional subpools according to its protection mechanism and studying the mechanism of different SOC fractions’ responses to environmental change will help guide the study of SOC dynamics. Therefore, we conducted an analysis of density-based SOC fractionation of 107 study sites from 35 literature sources to answer the following questions: (1) Will different fractionation methods yield different amounts in the three organic carbon pools: free organic carbon (FOC), occluded organic carbon (OOC) and mineral associated organic carbon (MOC)? (2) Does the distribution of these three SOC fractions differ with climate (mean annual temperature, MAT; mean annual precipitation, MAP), soil characteristics (e.g., soil layer, soil type, clay content) or vegetation type when controlling for any method differences?Results: Experimental method significantly affected OOC and MOC but not FOC results, and OOC separated by density and soil physical dispersion (density+disperse) was underestimated, thus a suitable SOC fractionation method should be carefully selected. SOC and MOC contents were negatively related to MAT; and highest SOC content appeared at moderate MAP, and when MAP increased or decreased, SOC decreased. SOC, FOC, and MOC were significantly affected by vegetation type; presumably due to anthropogenic disturbance or precipitation, plantations, grass and rainforest had the lower SOC contents and higher OOC and MOC percentages; and conifer, broadleaf, and mixed forests had similar FOC, OOC and MOC percentages, indicating less effect of tree species on SOC variation. The contents of both SOC and each fraction decreased in deeper sol layer; SOC, FOC and OOC contents were significantly affected by soil type; and SOC and MOC contents were negatively related to soil clay content, but the influences of soil characters on SOC and its fractions were less than experimental method and climate condition.Conclusion: Experimental methods for fractionation of SOC significantly affected fraction results. Climate, vegetation type and soil character also significantly influenced SOC and its factions, but the influences of soil characters on SOC and its fractions were not as strong as experimental method and climate condition.

Large-scale spatial variability and distribution of soil organic carbon across the entire Loess Plateau, China

Soil Research ◽  
2012 ◽  
Vol 50 (2) ◽  
pp. 114 ◽  
Author(s):  
Z. P. Liu ◽  
M. A. Shao ◽  
Y. Q. Wang
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Loess Plateau ◽  
Soil Ph ◽  
Environmental Variables ◽  
Large Scale ◽  
Linear Regression Analysis ◽  
Clay Content ◽  
Soil Productivity ◽  
Wide Range

Soil organic carbon (SOC) plays an important role in soil productivity and the global carbon cycle. However, little is known about the regional distribution of SOC across the entire Loess Plateau region of China. We investigated 382 sampling sites across the region (620 000 km2) and collected 764 soil samples from the topsoil (0–20 cm) and subsoil (20–40 cm). Standard statistics were used to identify the regional SOC content and the relationships with 11 selected environmental variables. Concentrations of SOC varied within a wide range throughout the region from 0.38 to 54.03 g kg–1, with mean values of 10.34 and 6.78 g kg–1 for the topsoil and subsoil, respectively. Coefficient of variation values showed moderate variation for SOC in both soil layers. Significant correlations were detected between SOC and these environmental variables, notably with soil total nitrogen (TN), soil pH, and clay content. Multiple linear regression analysis indicated that TN, clay content, soil pH, elevation, and temperature had greatest effects on regional SOC variability among all the selected soil and site variables. Geostatistical analysis showed that the maximum autocorrelation ranges were 384 and 393 km for SOC in the topsoil and subsoil, respectively. Nugget-to-sill ratios were 0.52 and 0.50, which also indicated moderate spatial dependence. Maps of SOC distribution produced by the geostatistical method showed that the overall spatial pattern was characterised by an area of low SOC content surrounded by bands with higher values, which generally increased towards the region’s boundaries. The distribution pattern corresponded to that of the major regional landforms, which also influenced land use, whereby the sandy Ordos Plateau is surrounded by relatively fertile plains and valleys, where the human population density is highest, and the regional boundary is mountainous. The spatial data of SOC could be useful as an important initial state in regional SOC modelling and possibly be used in calibration and prediction processes in the remote sensing method to estimate SOC content for large-scale areas.

scholarly journals Stable isotopic constraints on global soil organic carbon turnover

2017 ◽  
Author(s):  
Chao Wang ◽  
Benjamin Z. Houlton ◽  
Dongwei Liu ◽  
Jianfeng Hou ◽  
Weixin Cheng ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Large Scale ◽  
Global Climate ◽  
Mean Annual Precipitation ◽  
Complex Polynomial ◽  
Mean Annual Temperature ◽  
Turnover Rates ◽  
Soil C ◽  
Spatial And Temporal Scales

Abstract. Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2 concentrations and global climate change. However, reliably measuring SOC turnover rates at large spatial and temporal scales remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ13C of vegetation and soil reported in the literature (182 separate soil profiles), to examine large-scale controls of climate, soil physical properties and nutrients over patterns of SOC turnover across terrestrial biomes worldwide. We report a significant relationship between β and calculated soil C turnover rates (k), which were estimated by dividing soil heterotrophic respiration by SOC pools. ln(-β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with mean annual precipitation, implying strong-feedbacks of SOC turnover to climate changes. Soil nitrogen (N) and clay content correlate strongly and positively with ln(-β), revealing the additional influence of nutrients and physical soil properties on SOC decomposition rates. Furthermore, a strong (R2 = 0.85; p 

scholarly journals Continental-scale controls on soil organic carbon across sub-Saharan Africa

2020 ◽  
Author(s):  
Sophie F. von Fromm ◽  
Alison M. Hoyt ◽  
Gifty E. Acquah ◽  
Ermias Aynekulu ◽  
Asmeret Asefaw Berhe ◽  
...  
Keyword(s):  
Random Forest ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Texture ◽  
Aridity Index ◽  
Climatic Conditions ◽  
Sub Saharan Africa ◽  
Continental Scale ◽  
Wide Range ◽  
Sub Saharan

Abstract. Earlier studies have demonstrated that soil texture and geochemistry strongly affect soil organic carbon (SOC) content. However, those findings primarily rely on data from temperate regions with soil mineralogy, weathering status and climatic conditions that generally differ from tropical and sub-tropical regions. We investigated soil properties and climate variables influencing SOC concentrations across sub-Saharan Africa. A total of 1,601 samples were analyzed, collected from two depths (0–20 cm and 20–50 cm) at 45 sentinel sites from 17 countries as part of the Africa Soil Information Service (AfSIS) project. The dataset spans climatic conditions from arid to humid and includes soils with a wide range of pHH20 values, weathering status, soil texture, exchangeable cations, extractable metals and a variety of important land cover types. The most important SOC predictors were identified by linear mixed effects models, regression trees and random forest models. Our results indicate that SOC is primarily controlled by aridity index (PET/MAP), exchangeable calcium (Caex) and oxalate-extractable aluminum (Alox); this was found across both depth intervals. Oxalate-extractable iron (Feox) emerged as the most important predictor for both depth intervals in the regression tree and random forest analyses. However, its influence on SOC concentrations was strong only below Feox concentrations of 0.25 wt %. This suggests that Feox can act as a pedogenic threshold – even on a continental scale. Across model-ling approaches, clay and fine silt content (

scholarly journals Supplementary material to "Continental-scale controls on soil organic carbon across sub-Saharan Africa"

2020 ◽  
Author(s):  
Sophie F. von Fromm ◽  
Alison M. Hoyt ◽  
Gifty E. Acquah ◽  
Ermias Aynekulu ◽  
Asmeret Asefaw Berhe ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Sub Saharan Africa ◽  
Continental Scale ◽  
Supplementary Material ◽  
Sub Saharan
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