Total Soil Organic Carbon Storage Research Articles

Mapping Topsoil Carbon Storage Dynamics of Croplands Based on Temporal Mosaicking Images of Landsat and Machine Learning Approach

Understanding changes of soil organic carbon (SOC) in top layers of croplands and their driving factors is a vital prerequisite in decision-making for maintaining sustainable agriculture. However, high-precision estimation of SOC of croplands at regional scale is still an issue to be solved. Based on soil samples, synthetic image of bare soil and geographical data, this paper predicted SOC density of croplands using Random Forest model in the Black Soil Region of Jilin Province, China in 2005 and 2020, and analyzed its influencing factors. Results showed that random forest model that integrates bare soil composite images improve the accuracy and robustness of SOC density prediction. From 2005 to 2020, the total SOC storage in croplands decreased from 89.96 to 82.79 Tg C with an annual decrease of 0.48 Tg C yr−1. The mean value of SOC density of croplands decreased from 3.42 to 3.32 kg/m2, and high values are distributed in middle parts. Changes of SOC represented significant heterogeneity spatially. 62.14% of croplands with SOC density greater than 4.0 kg/m2 decreased significantly, and 38.60% of croplands with SOC density between 2.5 and 3.0 kg/m2 significantly increased. Climatic factors made great contributions to SOC density, however, their relative importance (RI) to SOC density decreased from 44.65% to 37.26% during the study period. Synthetic images of bare soil constituted 23.54% and 26.29% of RI in the SOC density prediction, respectively, and the contribution of each band was quite different. The RIs of topographic and vegetation factors were low but increased significantly from 2005 to 2020. This study can aid local land managers and governmental agencies in assessing carbon sequestration potential and carbon credits, thus contributing to the protection and sustainable use of black soils.

Tree diversity and arbuscular mycorrhizal trees increase soil carbon sequestration and stability in 1-m soils as regulated by microbial CAZymes-coworking in high-latitude Northern Hemisphere forests

Biodiversity loss and tree alternations often occurred in high-latitude Northern Hemisphere forests owing to climatic changes and human disturbance, while their effects on soil carbon sequestration remain unclear. In this paper, tree richness and arbuscular mycorrhizal (AM)-tree dominance experiments were settled in an experimental forest, and soil organic carbon (SOC) and glomalin-related soil protein carbon (Total, TG-C and easily extracted, EEG-C), stability (heterotrophic respiration, Rh, temperature sensitivity, Q10 and humidity sensitivity, Hs), in situ soil CO2, CH4, N2O fluxes, and CAZymes activities from the microbial metagenome technique were measured to identify their impacts and underlying mechanism. Both analysis of variance (ANOVA) and linear regression found tree richness and AM tree loss accompanied by soil carbon sequestration loss of total SOC storage, their mycorrhizal components (TG-C) and Rh. In 0–20 cm soils, high tree richness quadrats had 16–126.6 % higher SOC, TG-C, Rh, and in situ N2O flux, while AM-dominated stands had 34–39 % higher SOC and Rh than the EcM-dominated stands. In the 1 m soil profile, the effect size from tree richness and AM trees were more evident than the 0–20 cm soils. Compared with the richness gradient, much significant differences occurred between AM- and EcM-dominated stands. Structural equation modeling found that tree richness directly improved C stability, while the SOC accrual from the tree richness enrichment and AM-tree dominance were indirectly achieved by their decreasing in multiple CAZymes activities. Of CAZymes, glycoside hydrolases, polysaccharide lyases, carbohydrate esterases, glycosyl transferases, auxiliary activities, and carbohydrate-binding modules cooperated in their regulation of the soil C accrual. Our findings support carbon sequestration via biodiversity conservation and proper forest management related to tree mycorrhizal symbionts.

Regional topsoil organic carbon content in the agricultural soils of Slovakia and its drivers, as revealed by the most recent national soil monitoring data

Soil organic carbon (SOC) is a primary constituent of soil organic matter and plays an important role in the regulation of many soil processes, including greenhouse gas emissions. Recently, SOC also became an indicator for monitoring climate change mitigation policies in the agricultural sector. The availability of up-to-date SOC inventories is thus crucial in terms of supporting SOC–related actions at country or sub-country scales. Currently, the National Monitoring System of the Agricultural Soils of Slovakia (CMS-P), whose network of 318 monitoring sites was last surveyed in 2018, is the only available source of up-to-date topsoil SOC data for agricultural land in Slovakia. Although very useful at the national scale, the number of CMS-P observations it contains is too limited for much needed sub-national SOC inventories. We hypothesized that with the aid of well-chosen macro-scale drivers of topsoil SOC accumulation in agricultural land in Slovakia, and by mapping those drivers geographically, we could upscale the CMS-P observations and produce a regional estimate of topsoil SOC. Altitude, land cover, topsoil texture, and soil type were assumed to be the key factors controlling topsoil SOC accumulation in Slovakia, and based on these, the country was classified into 14 macro-scale geographical regions. Typical ranges and mid-class values of 0–30cm topsoil SOC concentrations (%) and stocks (t ha−1) were calculated for each macro-scale region from CMS-P data. The average topsoil SOC content in agricultural land was estimated to be 2.13% (72.9 t ha−1). The highest topsoil SOC stock (> 90 t ha−1) was estimated for the lowlands of Slovakia, and the lowest (< 50 t ha−1) for the shallow and stony soils of mountain regions. When aggregated to 78 administrative regions at LAU1 level, the area-weighted averages ranged between 39.20 t ha−1 and 80.0 t ha−1, with the highest values (> 65 t ha−1) being in LAU1 regions in the south-west, south-east, and north of Slovakia where arable land is most prevalent. Total SOC storage in 0–30cm topsoil of agricultural land in Slovakia was estimated at 118.39 Mt, with two-thirds of this amount stored in arable soils in 33 south-west, south-east, and south LAU1 administrative regions. As there is no alternative and up-to-date dataset on topsoil SOC content in Slovakia, the upscaling algorithm presented in this study is an important step toward utilizing CMS-P data for sub-national SOC inventories. It may also offer a new way of providing inputs to help predict future or alternative regional topsoil SOC accumulation trajectories in Slovakian agricultural land using process-based or statistical models.

Soil Organic Carbon Dynamics and Influencing Factors in the Zoige Alpine Wetland from the 1980s to 2020 Based on a Random Forest Model

Wetlands provide important ecosystem services, such as water conservation, biodiversity protection, and carbon sequestration. The Zoige alpine wetland is the largest high-altitude swamp in the world and plays a critical role in regional ecological balance and climate change. However, little is known about the fate of its soil organic carbon (SOC) storage. In this study, we estimated the degradation status of the wetland over the past 35 years and used machine learning to investigate the dynamics and driving factors of SOC at different soil depths of the Zoige wetland in 1985, 2000, and 2020. We also simulated the future SOC balance under different scenarios. The results showed that the area of Zoige wetland has degraded by 378.71 km2 in the past 35 years. Increased precipitation and solar radiation offset the adverse effects of global warming, making the soil act as a carbon sink in the past 35 years. The total SOC storage of the wetland soils in 1985, 2000, and 2020 was estimated to be 2.03 Pg, 2.05 Pg, and 2.21 Pg, respectively, with 46.95% of SOC distributed in the subsoil layers. Climate change was the most important driving factor controlling the SOC storage of the Zoige wetland, explaining 51.33% of the SOC changes in the soil. Temperature change was always the most important factor controlling wetland SOC, and precipitation had a greater impact on the topsoil. Under the temperature control targets of 1.5 °C and 2 °C, the SOC pool of the Zoige wetland will decrease by 60.21 Tg C and 69.19 Tg C, respectively. Under scenarios of a 10% and 20% increase in precipitation, the wetland soil will accumulate an additional 46.53 Tg C and 118.89 Tg C, respectively. The study results provide important references for the sustainable management of the Zoige wetland under the background of global climate change.

Deep soil water depletion and soil organic carbon and total nitrogen accumulation in a long‐term alfalfa pasture

AbstractDeep soil resources are essential for improving the production and ecological functions of dryland ecosystems. Relationships between deep soil water depletion and carbon and nitrogen accumulation in long‐term dryland pastures were not well quantified and understood. This study aimed to quantify the changes in deep soil water, soil organic carbon (SOC), and total nitrogen (TN) in alfalfa pasture and identify their relationships with root density. We conducted a field experiment in the south Loess Plateau in 2020 and 2021. Soil water, SOC, and TN contents and alfalfa root length density to 1000‐cm‐depth were measured in alfalfa pastures and annual crop reference fields. Soil water depletion by alfalfa mainly occurred in the first 6 years with a depletion rate of 41.6, 49.1, and 62.1 mm yr−1 in the shallow (0–200 cm), middle (200–500 cm) and deep (500–1000 cm) soil layers, respectively. Total depletion after 6 and 19 years were 916.8 and 1049.4 mm, respectively. SOC and TN storages in the shallow and middle layers continuously increased and peaked at 19 years after planting, and those in the deep soil increased quickly in the early ages but showed few changes in the following years. Final SOC and TN storages in the 0–1000 cm profile in alfalfa pasture reached 61.1 and 5.4 kg m−2, respectively, 13.7% and 20.4% higher than the reference field. Soil in 200–1000 cm contributed to 60.7% and 47.8% of the total SOC and TN storage increments, respectively. The deep rooting system of alfalfa derived soil water depletion and SOC and TN increments, as indicated by the significant relationships between fine root length density and the changes in soil water, SOC and TN storages. Therefore, the deep soil contributed substantially to the carbon and nitrogen sequestration in alfalfa early ages but the contribution was limited by water shortage in the middle and late ages. We suggest stopping alfalfa early (≤6 years) to increase water sustainability and maintain carbon and nitrogen sequestration efficiencies in the alfalfa pasture and crop rotation system on Loess Plateau.

Relationship between Soil Organic Carbon, Soil Nutrients, and Land Use in Linyi City (East China)

The distribution characteristics of soil organic carbon (SOC) and soil nutrients under different land-use types in Linyi City, East China, were studied. The spatial distribution of SOC under different land-use types and the relationship between SOC and soil nutrients were analyzed using remote sensing interpretation and soil sample analyses. The results showed that SOC in Linyi was mainly stored in drylands and paddy fields. SOC and total nitrogen (TN) levels were positively correlated for most land use types. There was a positive linear correlation between SOC and total K in the paddy fields. The coefficients of variation for SOC and TN differed greatly among the land use types studied. Total SOC storage was 8772.73 × 103 kg in the surface 0.2 m soil layer. The order of total SOC storage was drylands (6771.45 × 103 ton) &gt; paddy field (764.67 × 103 ton) &gt; nurseries (510.79 × 103 ton) &gt; forest land (413.49 × 103 ton) &gt; low-cover grasslands (238 × 103 ton) &gt; bare land (74.35 × 103 ton). With the largest SOC storage, and C density, respectively, drylands and paddy fields are conducive to enhancing soil C sequestration, achieving low-carbon goals, and mitigating climate change.

Soil Organic Carbon Storage in Urban Green Space and Its Influencing Factors: A Case Study of the 0–20 cm Soil Layer in Guangzhou City

Urban soils can contribute to organic carbon sequestration. The socioeconomic drivers of soil organic carbon (SOC) in urban areas may differ between regions due to the different land tenure and its derived green space management regimes. Currently, few studies focus on regions where public ownership of land was implemented. We examined the SOC storage and driving factors of urban green spaces in Guangzhou, China at 0–20 cm depth by variance and regression analysis. Our results showed that the total SOC storage did not vary significantly among green space types, with an average value of 2.59 ± 1.31 kg/m2. SOC increased with plot age (2–87 years) by 0.025 kg/m2/year (p = 0.026) and plot size (63–2058 m2) by 0.001 kg/m2/m2 (p = 0.026). Disturbance intensity was negatively correlated to SOC storage. Green space maintenance practices could promote SOC sequestration, but this benefit may be offset by high-intensity disturbances such as trampling, litter and debris removal and fragmentation of green spaces. To increase urban residential SOC storage, except for remediation of compacted soils, it is essential to promote house owners’ initiative in green space management and conservation by improving the current residential green space management regimes.

Soil organic carbon stock capacity in karst dolines under different land uses

The soil organic carbon (SOC) was determined in soils of enclosed karst depressions (dolines) (NW Dinaric Mts.) to define their potential for organic carbon sequestration. SOC was measured in the forest, succession (scrubland), and grassland plots at the bottom of dolines at four depths (0–40 cm) and for 40 cm soil layer SOC stock was calculated. We demonstrated that the prevailing fine soil fractions, the C/N ratio and soil thickness play a positive role in the storage capacity of SOC in dolines regardless land use type. Grasslands have the lowest SOC storage capacity (106 t/ha/40 cm), while the highest SOC storage capacity is in succession plots (130 t/ha/40 cm). The last are covered by shrub communities dominated by Prunus spinosa, forming dense communities, and are typical of abandoned croplands or meadows that have been impacted by high levels of nutrients during cultivation phase. At this stage, there is no additional nutrient input in studied plots, which lowers the nutrient content and increases the C/N ratio. C/N ratio is the highest in the forest, where SOC stock capacity is 116 t/ha/40 cm. Given the trend towards the abandonment of agricultural land at Kras Plateau (SW Slovenia), we can expect more overgrowth of dolines, and thus an increase in carbon stocks and stabilization of organic carbon in forest soils. In contrary, we noticed the alarming decrease in grasslands and increase in urban land. The SOC storage in 2020 was for 12,538 t/ha/40 cm lower than in 2002. Although grasslands showed the lowest SOC storage, their contribution to total SOC storage in dolines is very important. Since there is a lack of studies on carbon stocks in doline soils, our research is of great importance and a novelty and gives an important background for further research on SOC stock in karst landscapes worldwide.

Effects of vegetation succession on soil organic carbon fractions and stability in a karst valley area, Southwest China

A series of complex organic fractions with different physical and chemical properties make up soil organic carbon (SOC), which plays a vital role in climate change and the global carbon cycle. Different SOC fractions have different stability and respond differently to vegetation succession. This research was carried out to assess the impacts of vegetation succession on SOC dynamics in the Qingmuguan karst valley area, southwest China. Soil samples were collected from four typical vegetation succession stages, including farmland, grassland, shrubland, and forest. The total SOC content and four oxidizable SOC fractions were measured. Results showed that the total SOC content and storage under farmland were highest, followed by forest and shrubland, and the grassland had the lowest total SOC content and storage. The SOC sequestration potential under different vegetation types in the study area was grassland (26.32Mg C ha-1) > shrubland (9.64Mg C ha-1). All SOC content, storage, and fractions showed a decrease with the increase of soil depth over the 0-50cm in the study area. The four SOC fractions under forest at topsoil (0-10cm) were higher than that under the other vegetation types. Compared with the other land uses, the farmland had the highest stable oxidizable SOC fractions (F3 and F4) at the 10-50-cm depth, while the shrubland had the highest active oxidizable SOC fractions (F1 and F2). In terms of the lability index of SOC, shrubland was the largest, followed by grassland and forest, and farmland was the smallest. These results provide essential information about SOC fractions and stability changes resulting from changes of vegetation types in a karst valley area of southwest China. It also supplements our understanding of soil carbon sequestration in vegetation succession.

Soil organic carbon stocks in the high mountain permafrost zone of the semi-arid Central Andes (Cordillera Frontal, Argentina)

This study presents the first detailed soil organic carbon (SOC) inventory for a high mountain permafrost zone in the semi-arid Central Andes of South America. We describe plant cover and soil profiles at 31 sites representing the main land cover and landform types in the Veguitas catchment (Cordillera Frontal, Argentina), which ranges in elevation from c. 3000 to 5500 m. The vegetated area with soil development is largely confined to altitudes of < 3650 m and represents only 8.2% of the total catchment area. Mean SOC 0–100 cm storage for the vegetated portion of the catchment is 3.62 kg C m−2, which is reduced to 0.33 kg C m−2 if we consider negligible SOC stocks in the extensive bare ground and glaciated areas at higher elevations. Hotspots of SOC storage are wet meadow areas, with peat deposits up to 102 cm deep and a maximum observed total SOC storage of 53.07 kg C m−2. These wet meadow areas, however, occupy only 0.11% of the total catchment area and their contribution to mean SOC storage is limited. Among soils at well-drained sites, highest mean SOC 0–100 cm storage is found on backslope positions of moraines that predate the Last Glacial Maximum (6.87 kg C m−2). Only 2% of all SOC stocks in the catchment are found in permafrost terrain and none are located in the permafrost layer itself. The main ecoclimatic control on SOC storage is plant cover, with vegetation limits being sensitive to ambient temperature. Projected increases in temperatures will not remobilize any frozen SOC stocks but will likely result in an upward shift of the upper vegetation belt with soil development creating new areas of phytomass carbon and SOC storage. The area is expected to represent a net C sink and thus a negative feedback on future global warming.

Effects of Spartina alterniflora Invasion on Soil Organic Carbon Storage in the Beihai Coastal Wetlands of China

The invasion of Spartina alterniflora (S. alterniflora) has changed the carbon cycle process of local ecosystems. In order to clarify the effect of S. alterniflora invasion on coastal soil carbon pool in Northern Beibu Gulf, the distribution characteristics and influencing factors of soil organic carbon (SOC) and SOC storage (SOCS) at different intrusion stages were investigated and analyzed. The results showed that the SOC content in S. alterniflora wetlands (2.65–21.54 g/kg) was higher than that in mudflats (0.85–1.19 g/kg). SOC content in 0–20 cm depth was highest than that in 20–40 cm and 40–60 cm depth. The total SOCS increased by 72.11%, 78.45%, 77.56%, 80.42%, and 90.63% in 3a, 12a, 15a, 16–19a, and 26a compared with mudflats, respectively. S. alterniflora invasion increased SOC and SOCS both in surface soil and deep soil. SOCS increased rapidly during the initial stage of invasion, and remained in a relatively stable and continuous growth state after 12–15 years. The distributions and accumulation of SOC and SOCS were affected mainly by soil texture, soil bulk density, moisture content, total nitrogen and total phosphorus. The source of SOC from S. alterniflora was increasing with invasion ages and would be mainly input in 26a, while marine sources was mainly imported in other invasion ages. Our data indicated that S. alterniflora continuously enhances the SOC sequestration over the years in coastal wetland ecosystems.

Effects of land use and land cover change on soil organic carbon storage in the Hexi regions, Northwest China

Soil organic carbon (SOC) storage in arid inland regions is significantly affected by land use and land cover change (LUCC) associated with climate change and agricultural activities. A systematic evaluation to the LUCC effects on SOC storage could enable us to better manage soil carbon pools in arid inland regions. Here, we evaluated the effects of LUCC on SOC storage in the Hexi Regions based on high-resolution SOC and LUCC maps derived from Landsat imagery and digital soil mapping using machine learning algorithm and environmental covariates. The results showed that SOC generally increased from northwest to southeast over the Hexi Regions with an average stock of 7.15 kg C m−2 at a soil depth of 100 cm and a total storage of 2783.05 Tg C. The SOC stock and storage in the Qilian Mountains (mountains) was about 3.90 and 4.55 times higher than that in the Hexi Corridor (plains), respectively. It was estimated that LUCC over the past four decades caused a net increase of 23.41 and 18.19 Tg C in total SOC storage for the Qilian Mountains and Hexi Corridor, respectively. Specifically, the development in grasslands quality as well as the land-use category conversion from the bare land to grassland mainly contributed to the increase in SOC storage of the Qilian Mountains, where the LUCC was mainly driven by climate change. By contrast, the SOC storage change in the Hexi Corridor was mainly associated with the conversion from sandy land and low-cover grassland to cropland as well as sandy land to grassland, being mainly affected by intense cropland expansion and desertification control. Our results highlighted the importance of climate change and cropland expansion in enhancing SOC storage of the Qilian Mountains and Hexi corridor, respectively.

Persistent soil carbon enhanced in Mollisols by well-managed grasslands but not annual grain or dairy forage cropping systems

Intensive crop production on grassland-derived Mollisols has liberated massive amounts of carbon (C) to the atmosphere. Whether minimizing soil disturbance, diversifying crop rotations, or re-establishing perennial grasslands and integrating livestock can slow or reverse this trend remains highly uncertain. We investigated how these management practices affected soil organic carbon (SOC) accrual and distribution between particulate (POM) and mineral-associated (MAOM) organic matter in a 29-y-old field experiment in the North Central United States and assessed how soil microbial traits were related to these changes. Compared to conventional continuous maize monocropping with annual tillage, systems with reduced tillage, diversified crop rotations with cover crops and legumes, or manure addition did not increase total SOC storage or MAOM-C, whereas perennial pastures managed with rotational grazing accumulated more SOC and MAOM-C (18 to 29% higher) than all annual cropping systems after 29 y of management. These results align with a meta-analysis of data from published studies comparing the efficacy of soil health management practices in annual cropping systems on Mollisols worldwide. Incorporating legumes and manure into annual cropping systems enhanced POM-C, microbial biomass, and microbial C-use efficiency but did not significantly increase microbial necromass accumulation, MAOM-C, or total SOC storage. Diverse, rotationally grazed pasture management has the potential to increase persistent soil C on Mollisols, highlighting the key role of well-managed grasslands in climate-smart agriculture.

亚热带红壤区森林土壤剖面微生物残体碳分布及影响因素

土壤剖面中20cm以下土壤有机碳（SOC）储量占土壤剖面总SOC储量50%左右，由于土壤微生物残体碳（MRC）是稳定土壤碳库的重要来源，因此研究土壤剖面中MRC对SOC的贡献对于评估土壤碳储量具有重要意义。然而，目前关于MRC含量及其对SOC贡献的研究多数集中在土壤表层，在土壤剖面和母质中尚不清楚。选取江西省千烟洲亚热带典型森林红壤剖面，通过氨基糖与磷脂脂肪酸（PLFA）微生物标志物分析方法，分析红壤剖面和母质中MRC的影响机制及其对SOC贡献的分布特征。研究结果表明：（1）MRC含量随着土壤剖面深度增加而显著降低（P<0.05），在整个土壤剖面中，细菌MRC对SOC贡献为6%-12%，真菌MRC对SOC贡献为12%-36%，MRC对SOC贡献为18%-46%。从土壤表层至母质，真菌MRC对SOC贡献高于细菌MRC。（2）结构方程模型结果表明，在土壤剖面中，MRC含量主要受到微生物-PLFA含量、容重和溶解态有机碳含量的影响。研究量化了红壤剖面中MRC对SOC的贡献，表明在20cm以下土壤及母质中，微生物残体碳对红壤地区生态系统碳库具有重要贡献。;In soil profiles, soil organic carbon (SOC) storage beneath 20cm accounts for about 50% of the total SOC storage in the terrestrial ecosystem. Microbial residue carbon (MRC) is considered as an important constituent of persistent soil organic carbon. It is important to learn the role of MRC for soil carbon storage in deep soil as the main source of soil stable carbon pool. Until now, most studies involving MRC content and the contribution of MRC to SOC have mainly focused on surface soil, but seldom in deep soil and parent material. In this study, we selected typical red soil profiles in Qianyanzhou, Jiangxi province in subtropical region. We measured the microbial biomarkers of amino sugars and phospholipid fatty acids (PLFAs) which represent microbial residue carbon content and living microbial biomass content, respectively. The objective of the study was to analyze the influence factors of MRC and to quantify the contributions of MRC to SOC along the soil profiles from the surface to parent material. The results showed that (1) bacterial residue carbon (MRC_B), fungal residue carbon (MRC_F) and MRC contents decreased significantly with soil depth (P<0.05), and were about 0.08, 0.18, 0.25 g/kg at the parent material, respectively. The contributions of MRC to SOC along the soil profiles remained unchanged because of the same variation trend of MRC and SOC contents. Along the whole soil profiles, the contributions of MRC_B, MRC_F and MRC to SOC were about 6%-12%, 12%-36% and 18%-46%, respectively. The contribution of MRC_F to SOC was higher than that of MRC_B to SOC from surface soil to parent material. This may be caused by different components of cell walls in bacteria and fungi. The chitin in cell wall of fungi is more difficult to decompose than peptidoglycan in cell wall of bacteria. In addition, MRC_F could have more physical protection than MRC_B by soil aggregates since extracellular mycelia and polysaccharides are involved in the formation of soil aggregates. (2) The structural equation model showed that MRC content was largely determined by microbial biomass content of PLFA biomarkers, soil bulk density (Db) and dissolved organic carbon (DOC) content in the soil profiles, while Db and DOC indirectly influenced but microbial-PLFA content directly influenced the MRC content. Our study quantified the contribution of MRC to SOC along the soil profile and emphasized the contribution of MRC to the formation of ecosystem carbon pool beneath 20cm and in the parent material in red soil region.

Soil organic carbon storage, distribution, and influencing factors at different depths in the dryland farming regions of Northeast and North China

The knowledge of the spatial distribution of soil organic carbon (SOC) and of its influencing factors is crucial for understanding the global carbon cycle. Although the influence of climate, soil properties, and soil management on the SOC content has been extensively explored, their relative importance remains unclear, especially under dryland farming. Herein, we investigated the SOC density (SOCD) at different depths (0–10, 10–20, 20–30, and 30–40 cm) across an area of 37.79 × 104 km2 (420 sites) located in the dryland farming regions of Northeast and North China. The total SOC storage (SOCS) was estimated to be 1922.38 Tg, with a mean density of 5.78 kg C m−2 for the entire area. The three soil groups with the largest SOCS were Fluvo-aquic, Black, and Chernozem soils, accounting for 63.34% of the total SOCS in the study area. Overall, both the SOCD and SOCS increased from southwest to northeast at all investigated depths. A structural equation model was used to distinguish direct from indirect effects of different factors on SOCD. Soil properties (e.g., bulk density and pH) and natural conditions (e.g., mean annual temperature and mean annual precipitation) were found to be the main factors controlling the SOCD variation at depths of 10–20, 20–30, and 30–40 cm. However, the total (direct and indirect) effect of soil management on SOCD at a 0–10 cm depth was greater than that of natural conditions, and smaller than that of soil properties. With increasing soil depth, the total effect of natural conditions on SOCD changed from –0.33 to –0.58, whereas the indirect effect of soil management decreased from 0.47 to 0. These results indicate that compared with environmental factors, soil management practices such as tillage and fertilization had a greater influence on SOCD in the surface soil of dryland. Our study provides a valuable reference for future research on the long-term evolution of SOC in dryland farming regions.

Long‐term vegetation restoration increases carbon sequestration of different soil particles in a semi‐arid desert

AbstractVegetation restoration in desert areas has an important influence on soil carbon sequestration. To understand the long‐term effects of vegetation restoration on soil particle composition and carbon sequestration of different soil particles in semi‐arid deserts, we collected the topsoil of different types of vegetation restored for different periods at the southeast margin of Mu Us Desert and analyzed the soil organic carbon (SOC) and soil inorganic carbon (SIC) contents in soil particles of different sizes. The results demonstrated that after vegetation restoration, soil particles of &lt;0.05 mm and aggregates in arbor lands and shrub lands increased 8 and 4 times and 4.67 and 4 times than shifting sandy land (CK), respectively. The SOC and SIC in different soil particles under vegetation increased with the restoration period. Among different vegetation forms, arbor land had significant effect on SIC fixation. Soil particles of &lt;0.05 mm contained the highest SOC and SIC contents (16.8 and 0.78 g/kg), followed by aggregates (8.26 and 6.79 g/kg), 0.05–0.25 mm (8.24 and 4.55 g/kg), and &gt;0.25 mm (5.23 and 2.25 g/kg). As for total SOC storage, it was positively correlated with the organic carbon storage of &lt;0.05 mm particles. We concluded that SOC and SIC of &lt;0.05 mm soil particles and aggregates increase with the restoration period and play a leading role in soil carbon sequestration. From the perspective of long‐term soil carbon sequestration, the best vegetation restoration mode in Mu Us Desert would be arbor forest.

Simulating Grassland Carbon Dynamics in Gansu for the Past Fifty (50) Years (1968–2018) Using the Century Model

China is one of the countries most impacted by desertification, with Gansu Province in the northwest being one of the most affected areas. Efforts have been made in recent decades to restore the natural vegetation, while also producing food. This has implications for the soil carbon sequestration and, as a result, the country’s carbon budget. Studies of carbon (C) dynamics in this region would help to understand the effect of management practices on soil organic carbon (SOC) as well as aboveground biomass (ABVG), and to aid informed decision-making and policy implementation to alleviate the rate of global warming. It would also help to understand the region’s contribution to the national C inventory of China. The CENTURY model, a process-based model that is capable of simulating C dynamics over a long period, has not been calibrated to suit Gansu Province, despite being an effective model for soil C estimation. Using the soil and grassland maps of Gansu, together with weather, soil, and reliable historical data on management practices in the province, we calibrated the CENTURY model for the province’s grasslands. The calibrated model was then used to simulate the C dynamics between 1968 and 2018. The results show that the model is capable of simulating C with significant accuracy. Our measured and observed SOC density (SOCD) and ABVG had correlation coefficients of 0.76 and 0.50, respectively, at p &lt; 0.01. Precipitation correlated with SOCD and ABVG with correlation coefficients of 0.57 and 0.89, respectively, at p &lt; 0.01. The total SOC storage (SOCS) was 436.098 × 106 t C (approximately 0.4356% of the national average) and the average SOCD was 15.75 t C/ha. There was a high ABVG in the southeast and it decreased towards the northwest. The same phenomenon was observed in the spatial distribution of SOCD. Among the soils studied, Hostosols had the highest SOC sequestration rate (25.6 t C/ha) with Gypsisols having the least (7.8 t C/ha). Between 1968 and 2018, the soil carbon stock gradually increased, with the southeast experiencing the greatest increase.

The Impact of Impervious Surface Expansion on Soil Organic Carbon: A Case Study of 0–300 cm Soil Layer in Guangzhou City

Empirical evidence shows that the expansion of impervious surface threatens soil organic carbon (SOC) sequestration in urbanized areas. However, the understanding of deep soil excavation due to the vertical expansion of impervious surface remains limited. According to the average soil excavation depth, we divided impervious surface into pavement (IS20), low-rise building (IS100) and high-rise building (IS300). Based on remote-sensing images and published SOC density data, we estimated the SOC storage and its response to the impervious surface expansion in the 0–300 cm soil depth in Guangzhou city, China. The results showed that the total SOC storage of the study area was 8.31 Tg, of which the top 100 cm layer contributed 44%. The impervious surface expansion to date (539.87 km2) resulted in 4.16 Tg SOC loss, of which the IS20, IS100 and IS300 contributed 26%, 58% and 16%, respectively. The excavation-induced SOC loss (kg/m2) of IS300 was 1.8 times that of IS100. However, at the residential scale, renovating an IS100 plot into an IS300 plot can substantially reduce SOC loss compared with farmland urbanization. The gains of organic carbon accumulation in more greenspace coverage may be offset by the loss in deep soil excavation for the construction of underground parking lots, suggesting a need to control the exploitation intensity of underground space and promote residential greening.

Effect of land cover change on total SOC and soil PhytOC accumulation in the karst subtropical forest ecosystem, SW China

Soil organic carbon (SOC), especially the stable SOC, have the important ecological function in the carbon cycle. As a typical stable SOC, soil phytolith-occluded organic carbon (PhytOC) is one of the important mechanisms of long-term soil carbon sink in terrestrial ecosystems. However, the distribution characteristics, accumulation law, and cycle process of soil PhytOC in fragile karst ecosystems are still not cognized. The purpose of the present study is to obtain the distribution pattern and change law of total SOC and soil PhytOC in different land cover types and to clarify the influencing factors and driving mechanism of land cover change on total SOC and soil PhytOC content and storage in the karst ecosystem. In the typical karst area of Southwest China, five representative land cover types, including bamboo forest (BF), coniferous and broad-leaved mixed forest (CBF), shrub (SH), grassland (GL), and agricultural abandoned land (AAL), were selected as the research objects. The total SOC contents, soil PhytOC contents, and soil physical and chemical properties were determined in the lab. Soil PhytOC and total SOC storage were calculated by the formulas. Data were analyzed statistically by linear regression, Pearson correlation analysis, LSD multiple comparison, and principal component analysis. Land cover change can affect obviously total SOC and soil PhytOC content and storage in the karst subtropical forest. Among the five land cover types, soil phytolith content, soil PhytOC content and storage, and total SOC storage of each soil profile in the BF were all significantly higher than those of the other four land covers. Among the three different soil profiles of 0~10, 10~20, and 20~30 cm, total SOC and soil PhytOC contents of the surface soil layer in the five land cover types were all the most, and the content decreased obviously with the increase of soil depth. There were significant positive correlation between the contents of soil available silicon, phytolith, and PhytOC. Soil available silicon content, soil phytolith content, and soil C/N were significantly positive related with the accumulation of total SOC and soil PhytOC. Soil PhytOC content or storage was significant or extremely significant related with total SOC content or storage. The results of the present study provided scientific bases for further evaluating the carbon sink capacity of soil PhytOC in the karst ecosystem, in SW China, and have important values in the reduction of carbon emission and increase of carbon sink to combat the global warming. In addition, the results of the present study also can provide theoretical references for the vegetation restoration of karst rocky desertification in Southwest China.

Prosopis juliflora management and grassland restoration in Baringo County, Kenya: Opportunities for soil carbon sequestration and local livelihoods

Abstract Climate change, land degradation and invasive alien species (IAS) threaten grassland ecosystems worldwide. IAS clearing and grassland restoration would help to reduce the negative effects of IAS, restore the original vegetation cover and sustain livelihoods while contributing to climate change mitigation, but uncertain financial benefits to local stakeholders hamper such efforts. This study assessed where and when net financial benefit could be realized from Prosopis juliflora management and subsequent grassland restoration by combining ecological, social and financial information. Impacts of Prosopis invasion and grassland degradation on soil organic carbon (SOC) in nine sublocations in Baringo County, Kenya, were evaluated. Then the financial impacts of Prosopis removal and grassland restoration in the area were calculated and spatially explicit management scenarios for each sublocation modelled, combining geographical information derived from satellite images taken in different years of the invasion with SOC data and socio‐economic data collected in the sublocations. The expanding Prosopis distribution and density since 1995 have increased cumulated SOC storage on former bare land or degraded grasslands. On former pristine or restored grasslands, however, Prosopis invasion has reduced total SOC storage. Prosopis removal and grassland restoration are predicted to yield financial benefits through charcoal made from removed trees, increased cattle numbers and carbon credits. However, a trade‐off between increased SOC and net financial benefit was found. The predicted net SOC increase would contribute around one‐tenth, at most, to the net financial benefit. The available budget, based on Baringo households’ average willingness to pay, would enable removal, on average, of one‐fifth of Prosopis per sublocation in a single year. A larger area can be cleared if Prosopis is sparse than if it is dense. The analyses show that in some sublocations, households’ annual investments could result in restoration of all former grassland areas. Synthesis and applications. This study shows how integrating and linking detailed ecological, social and financial geodata to develop accurate and realistic invasive alien species management scenarios can illustrate costs and benefits of management interventions in a spatial context. Such scenarios should be used more extensively to support land management decisions.