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 Stable isotopic constraints on global soil organic carbon turnover

2018 ◽  
Vol 15 (4) ◽  
pp. 987-995 ◽  
Author(s):  
Chao Wang ◽  
Benjamin Z. Houlton ◽  
Dongwei Liu ◽  
Jianfeng Hou ◽  
Weixin Cheng ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Linear Relationship ◽  
Root Decomposition ◽  
Mean Annual Precipitation ◽  
Mean Annual Temperature ◽  
Turnover Rates ◽  
Decomposition Rates ◽  
Soil C ◽  
C Stocks

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 on 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 (176 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 rates 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 = 0.76; p < 0.001) linear relationship between ln( − β) and estimates of litter and root decomposition rates suggests similar controls over rates of organic matter decay among the generalized soil C stocks. Overall, these findings demonstrate the utility of soil δ13C for independently benchmarking global models of soil C turnover and thereby improving predictions of multiple global change influences over terrestrial C-climate feedback.

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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&amp;#8211;20 cm and 20&amp;#8211;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.&lt;/p&gt;&lt;p&gt;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 &gt; 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 &lt; 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.&lt;/p&gt;

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.

scholarly journals Estimation of Soil Organic Carbon Contents in Croplands of Bavaria from SCMaP Soil Reflectance Composites

2021 ◽  
Vol 13 (16) ◽  
pp. 3141
Author(s):  
Simone Zepp ◽  
Uta Heiden ◽  
Martin Bachmann ◽  
Martin Wiesmeier ◽  
Michael Steininger ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Spatial Resolution ◽  
Large Scale ◽  
High Spatial Resolution ◽  
Global Climate ◽  
Machine Learning Algorithms ◽  
Data Source ◽  
Soil Reflectance

For food security issues or global climate change, there is a growing need for large-scale knowledge of soil organic carbon (SOC) contents in agricultural soils. To capture and quantify SOC contents at a field scale, Earth Observation (EO) can be a valuable data source for area-wide mapping. The extraction of exposed soils from EO data is challenging due to temporal or permanent vegetation cover, the influence of soil moisture or the condition of the soil surface. Compositing techniques of multitemporal satellite images provide an alternative to retrieve exposed soils and to produce a data source. The repeatable soil composites, containing averaged exposed soil areas over several years, are relatively independent from seasonal soil moisture and surface conditions and provide a new EO-based data source that can be used to estimate SOC contents over large geographical areas with a high spatial resolution. Here, we applied the Soil Composite Mapping Processor (SCMaP) to the Landsat archive between 1984 and 2014 of images covering Bavaria, Germany. Compared to existing SOC modeling approaches based on single scenes, the 30-year SCMaP soil reflectance composite (SRC) with a spatial resolution of 30 m is used. The SRC spectral information is correlated with point soil data using different machine learning algorithms to estimate the SOC contents in cropland topsoils of Bavaria. We developed a pre-processing technique to address the issue of combining point information with EO pixels for the purpose of modeling. We applied different modeling methods often used in EO soil studies to choose the best SOC prediction model. Based on the model accuracies and performances, the Random Forest (RF) showed the best capabilities to predict the SOC contents in Bavaria (R² = 0.67, RMSE = 1.24%, RPD = 1.77, CCC = 0.78). We further validated the model results with an independent dataset. The comparison between the measured and predicted SOC contents showed a mean difference of 0.11% SOC using the best RF model. The SCMaP SRC is a promising approach to predict the spatial SOC distribution over large geographical extents with a high spatial resolution (30 m).

scholarly journals Influence of trees and associated variables on soil organic carbon: a review

2021 ◽  
Vol 45 (1) ◽  
Author(s):  
Angom Sarjubala Devi
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Significant Negative Correlation ◽  
Mean Annual Temperature ◽  
Forest Stands ◽  
Mixed Stands ◽  
Silt Fraction ◽  
Different Types ◽  
Soil Climate ◽  
Associated Variables

AbstractThe level of soil organic carbon (SOC) fluctuates in different types of forest stands: this variation can be attributed to differences in tree species, and the variables associated with soil, climate, and topographical features. The present review evaluates the level of SOC in different types of forest stands to determine the factors responsible for the observed variation. Mixed stands have the highest amount of SOC, while coniferous (both deciduous-coniferous and evergreen-coniferous) stands have greater SOC concentrations than deciduous (broadleaved) and evergreen (broadleaved) tree stands. There was a significant negative correlation between SOC and mean annual temperature (MAT) and sand composition, in all types of forest stands. In contrast, the silt fraction has a positive correlation with SOC, in all types of tree stands. Variation in SOC under different types of forest stands in different landscapes can be due to differences in MAT, and the sand and silt fraction of soil apart from the type of forests.

scholarly journals Upside-down fluxes Down Under: CO<sub>2</sub> net sink in winter and net source in summer in a temperate evergreen broadleaf forest

2018 ◽  
Vol 15 (12) ◽  
pp. 3703-3716 ◽  
Author(s):  
Alexandre A. Renchon ◽  
Anne Griebel ◽  
Daniel Metzen ◽  
Christopher A. Williams ◽  
Belinda Medlyn ◽  
...  
Keyword(s):  
Large Scale ◽  
Vegetation Index ◽  
Ecosystem Respiration ◽  
Vapour Pressure Deficit ◽  
Summer Rainfall ◽  
Mean Annual Precipitation ◽  
Surface Conductance ◽  
Mean Annual Temperature ◽  
Eddy Covariance Method ◽  
Area Index

Abstract. Predicting the seasonal dynamics of ecosystem carbon fluxes is challenging in broadleaved evergreen forests because of their moderate climates and subtle changes in canopy phenology. We assessed the climatic and biotic drivers of the seasonality of net ecosystem–atmosphere CO2 exchange (NEE) of a eucalyptus-dominated forest near Sydney, Australia, using the eddy covariance method. The climate is characterised by a mean annual precipitation of 800 mm and a mean annual temperature of 18 ∘C, hot summers and mild winters, with highly variable precipitation. In the 4-year study, the ecosystem was a sink each year (−225 g C m−2 yr−1 on average, with a standard deviation of 108 g C m−2 yr−1); inter-annual variations were not related to meteorological conditions. Daily net C uptake was always detected during the cooler, drier winter months (June through August), while net C loss occurred during the warmer, wetter summer months (December through February). Gross primary productivity (GPP) seasonality was low, despite longer days with higher light intensity in summer, because vapour pressure deficit (D) and air temperature (Ta) restricted surface conductance during summer while winter temperatures were still high enough to support photosynthesis. Maximum GPP during ideal environmental conditions was significantly correlated with remotely sensed enhanced vegetation index (EVI; r2 = 0.46) and with canopy leaf area index (LAI; r2 = 0.29), which increased rapidly after mid-summer rainfall events. Ecosystem respiration (ER) was highest during summer in wet soils and lowest during winter months. ER had larger seasonal amplitude compared to GPP, and therefore drove the seasonal variation of NEE. Because summer carbon uptake may become increasingly limited by atmospheric demand and high temperature, and because ecosystem respiration could be enhanced by rising temperatures, our results suggest the potential for large-scale seasonal shifts in NEE in sclerophyll vegetation under climate change.

Soil organic carbon quality in forested mineral wetlands at different mean annual temperature

2009 ◽  
Vol 41 (3) ◽  
pp. 458-466 ◽  
Author(s):  
Cinzia Fissore ◽  
Christian P. Giardina ◽  
Randall K. Kolka ◽  
Carl C. Trettin
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Mean Annual Temperature ◽  
Carbon Quality

scholarly journals Microspectroscopic visualization of how biochar elevates the soil organic carbon ceiling

2021 ◽  
Author(s):  
Zhe (Han) Weng ◽  
Lukas Van Zwieten ◽  
Michael Rose ◽  
Bhupinder Pal Singh ◽  
Ehsan Tavakkoli ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Molecular Diversity ◽  
Three Dimensional ◽  
Specific Enzyme ◽  
Eucalyptus Saligna ◽  
Soil C ◽  
Decadal Scale ◽  
Use Efficiency ◽  
Microbial C

Abstract The soil carbon saturation concept suggests an upper limit to store soil organic carbon (SOC), set by the mechanisms that protect soil organic matter from decomposition. Biochar has the capacity to protect new C including rhizodeposits and microbial necromass. However, the decadal scale mechanisms by which biochar influences the molecular diversity, spatial heterogeneity, and temporal changes of SOC persistence remain unresolved. Here we show that the soil C saturation ceiling of a Ferralsol under subtropical pasture could be elevated by 2 Mg (new) C ha-1 by the application of Eucalyptus saligna biochar 8.2 years after the first application. Using one, two-, and three-dimensional analyses, significant increases were observed in the spatial distribution of root-derived 13C in microaggregates (53-250 µm, 11 %) and new C protected in mineral fractions (<53 µm, 5 %). Microbial C-use efficiency was concomitantly improved by lowering specific enzyme activities, contributing to the decreased mineralization of native SOC by 18 %. We provide evidence that the global SOC ceiling can be elevated using biochar in Ferralsols by 0.01-0.1 Pg new C yr-1.

scholarly journals Permafrost-Affected Soils of the Russian Arctic and their Carbon Pools

2014 ◽  
Vol 6 (1) ◽  
pp. 619-655
Author(s):  
S. Zubrzycki ◽  
L. Kutzbach ◽  
E.-M. Pfeiffer
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Carbon Sink ◽  
Global Climate ◽  
Fundamental Property ◽  
Climate System ◽  
The Arctic ◽  
Quaternary Period ◽  
Permafrost Regions

Abstract. Permafrost-affected soils have accumulated enormous pools of organic matter during the Quaternary Period. The area occupied by these soils amounts to more than 8.6 million km2, which is about 27% of all land areas north of 50° N. Therefore, permafrost-affected soils are considered to be one of the most important cryosphere elements within the climate system. Due to the cryopedogenic processes that form these particular soils and the overlying vegetation that is adapted to the arctic climate, organic matter has accumulated to the present extent of up to 1024 Pg (1 Pg = 1015 g = 1 Gt) of soil organic carbon stored within the uppermost three meters of ground. Considering the observed progressive climate change and the projected polar amplification, permafrost-affected soils will undergo fundamental property changes. Higher turnover and mineralization rates of the organic matter are consequences of these changes, which are expected to result in an increased release of climate-relevant trace gases into the atmosphere. As a result, permafrost regions with their distinctive soils are likely to trigger an important tipping point within the global climate system, with additional political and social implications. The controversy of whether permafrost regions continue accumulating carbon or already function as a carbon source remains open until today. An increased focus on this subject matter, especially in underrepresented Siberian regions, could contribute to a more robust estimation of the soil organic carbon pool of permafrost regions and at the same time improve the understanding of the carbon sink and source functions of permafrost-affected soils.

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