Soil Inorganic Carbon Density Research Articles

Vulnerability and driving factors of soil inorganic carbon stocks in Chinese croplands

The long-term stability of soil inorganic carbon (SIC) and its minimum contribution towards global C cycle has been challenged, as recent studies have showed rapid decreases in SIC stocks in intensive agricultural systems. However, the extent of SIC losses and its driving factors remains unclear. Here, we compared changes in SIC density (SICD) in Chinese croplands between the 1980s and 2010s. The SIC contents in 1980s were obtained from second national soil survey (n = 949) and published studies (n = 47). The SIC contents in 2010s were based on resampling of soil profiles from the same locations during 2019 and 2020 (n = 30), as well as data from published studies and national soil survey (n = 903). We found that Chinese croplands have lost 27–38% of SICD from the 0–40 cm soil layer and that the soil pH has decreased by 0.53 units over the past 30 years. These SIC losses increased with the ratio of precipitation (P) to potential evapotranspiration (PET) and most notably with nitrogen (N) fertilization. The SICD decreased greatly in humid and semiarid regions, and these losses were enhanced by high N fertilization rates; however, the SICD increased in very arid regions. This analysis demonstrates that the water balance and N fertilization are major drivers leading to dramatic losses of SICD in croplands and, consequently, to decreases in soil fertility and functions.

Vertical Distribution and Controlling Factors of Soil Inorganic Carbon in Poplar Plantations of Coastal Eastern China

Afforestation is a strategy to protect croplands and to sequestrate carbon in coastal areas. In addition, inorganic carbon is a considerable constitute of the coastal soil carbon pool. However, the vertical distribution and controlling factors of soil inorganic carbon (SIC) in plantations of coastal areas have been rarely studied. We analyzed the SIC content as well as physiochemical properties along soil profiles (0–100 cm) in young (YP) and mature (MP) poplar plantations in coastal eastern China. The soil profile was divided into six layers (0–10, 11–20, 21–40, 41–60, 61–80 and 81–100 cm) and a total of 36 soil samples were formed. The SIC content first increased from 0–10 cm (0.74%) to 11–20 cm (0.92%) and then fluctuated in the YP. In contrast, the SIC content increased with increasing soil depth until 40 cm and then leveled off, and the minimum and maximum appeared at 0–10 cm (0.54%) and 81–100 cm (0.98%) respectively in the MP. The soil inorganic carbon density was 12.05 and 12.93 kg m−2 within 0–100 cm in the YP and MP, respectively. Contrary to SIC, soil organic carbon (SOC) first decreased then levelled off within the soil profiles. Compared with the YP, the SIC content decreased 27.8% at 0–10 cm but increased 13.2% at 21–40 cm, meanwhile the SOC content in MP decreased 70.6% and 46.7% at 21–40 cm and 61–80 cm, respectively. The water-soluble Ca2+ and Mg2+ gradually decreased and increased, respectively within the soil profiles. The soil water-soluble Ca2+ increased 18.3% within 41–100 cm; however, the soil water-soluble Mg2+ decreased 32.7% within 21–100 cm in the MP when compared to the YP. Correlation analysis showed that SIC was negatively correlated with SOC, but positively correlated with soil pH and water-soluble Mg2+. Furthermore, structural equation modeling (SEM) indicated that SOC was the most important factor influencing the SIC content in the studied poplar plantations, indicating SOC sequestration promoted the dissolution of SIC. Therefore, our study highlights the trade-off between SIC and SOC in poplar plantations of coastal Eastern China.

Impacts of land use and salinization on soil inorganic and organic carbon in the middle-lower Yellow River Delta

Soil inorganic carbon (SIC) is an important reservoir of carbon (C) in arid, semi-arid, and semi-humid regions. However, knowledge is incomplete on the dynamics of SIC and its relationship with soil organic C (SOC) under different land use types in the semi-humid region, particularly in coastal zones impacted by soil salinization. We collected 170 soil samples from 34 profiles across various land use types (maize-wheat, cotton, paddy, and reed) in the middle-lower Yellow River Delta (YRD), China. We measured soil pH, electrical conductivity (EC), water-soluble salts, and SOC and SIC contents. Our results showed significant differences in both SOC and SIC among land use types. The dry cropland (maize-wheat and cotton) soils had significantly higher SOC and SIC densities (4.71 and 15.46 kg C m–2, respectively) than the paddy soils (3.28 and 14.09 kg C m–2, respectively) in the 0–100 cm layer. Compared with paddy soils, reed soils contained significantly higher SOC (4.68 kg C m–2) and similar SIC (15.02 kg C m–2) densities. There was a significant positive correlation between SOC and SIC densities over a 0–100 cm soil depth in dry cropland soils, but a negative relationship in the paddy soils. On average, SOC and SIC densities under maize-wheat cropping were 15% and 4% lower, respectively, in the salt-affected soils in the middle-lower YRD than the upper YRD. This study indicated that land use types had great influences on both SOC and SIC and their relationship, and salinization had adverse effect on soil C storage in the YRD.

Spatial Pattern of Soil Carbon Density in Cultivated Land of Different Domains of Madhya Pradesh

Present study was conducted in the Department of Soil Science JNKVV, Jabalpur during 2018-2020. GPS based 531 soil samples were collected from each domain viz., Bhopal, Jabalpur, Vidisha and Hoshangabad of 10.1 Agro ecological sub region (AESR). The samples analyzed for soil organic carbon (SOC) and calcium carbonate (CaCO3) then soil organic carbon density (SOCD), total organic carbon density (TOCD), soil inorganic carbon density (SICD) and total carbon density (TCD) in Mg C ha-1 were calculated. The results of SOCD, TOCD, SICD and TCD ranged from 4.73 to 25.12, 9.22 to 48.98, 1.00 to 21.29 and 11.08 to 68.80 Mg C ha-1 with mean value of 12.19, 23.78, 7.58 and 31.36 Mg C ha-1 in AESR 10.1 and Coefficient of variation (CV) 37.58, 37.58, 50.88 and 31.24 %. The overall trend in SOCD was Bhopal > Vidisha > Jabalpur > Hoshanagabad and SICD was Vidisha > Hoshanagabad > Jabalpur >Bhopal while TCD was in trend of Bhopal > Vidisha > Hoshangabad> Jabalpur.
 Geo-statistical indicated that Ordinary Kriging used and all variogram were in isotropic form. In Bhopal domain, Gaussian model best fitted for of SOCD, TOCD, and TCD but spherical model for SICD. In Jabalpur domain, exponential domain best fitted for TCD and TOCD but for SICD, spherical model and for SOCD, Gaussian model is best fitted. In Vidisha domain, exponential model best fitted for all. In Hoshangabad domain, exponential model is best fitted for SOCD and TOCD and Gaussian and J-Bessel model best fitted for TCD and SIC, respectively. The nugget/ sill (N/S) ratio was <25% which exhibit strong SD only for SICD in Bhopal domain. The N/S ratio was found to be >25% but <75% which showed moderate SD, for SOCD, TOCD and TC, TOCD, SICD and TCD; SOCD, TOCD, SICD and TCD and SOCD, TOCD, SICD and TCD in Bhopal, Jabalpur, Vidisha and Hoshangabad domain, respectively. The correlation range (m) for SOCD, TOCD, SICD and TCD are 5448.413, 4809.535, 360.522, and 5113.050; 7201.044, 6601.044, 611.651, and 8438.711; 5734.559, 7334.398, 1323.773, and 7881.289 and 5418.684, 5433.206, 8887.656, and 1836.274 in Bhopal, Jabalpur, Vidisha and Hoshangabad domain, respectively. The carbon density was found in order of Jabalpur> Hoshangabad >Vidisha > Bhopal.

Impacts of Spartina alterniflora invasion on soil inorganic carbon in coastal wetlands in China

AbstractBiological invasion has profoundly influenced coastal soil reservoirs of carbon. Previous carbon studies regarding biological invasion in coastal wetlands mainly focused on soil organic carbon; however, little is known about the mechanisms that control soil inorganic carbon (SIC, e.g., carbonates) variation. In order to explore our understanding, we used structural equation modeling (SEM) to evaluate controlling mechanisms of SIC in response to Spartina alterniflora (Loisel) invasion in the east‐central China coast, where there is a lack of native salt marsh species. A space‐for‐time substitution method was used to identify sampling sites, assuming it has the capability to quantify the soil‐vegetation relationship along a gradient of the increasing S. alterniflora age (17 year). The results showed that soil inorganic carbon density (SICD) at the 0.3–0.6 m depth exhibited a decline under S. alterniflora invasion, while there was no substantial change at the depths of 0–0.3 m and 0.6–1 m. The majority of the variances in SICD changes could be explained by S. alterniflora invasion and key soil physicochemical variables. In SEM, S. alterniflora invasion, soil water content, and soil texture presented direct influence on SICD throughout the soil profile (i.e., to 1 m depth). Soil salinity presented direct influence on SICD in the upper 0.6 m soil, while pH played an important role in the depth of 0.6–1 m. These results highlight that dynamics of SIC processes are probably controlled by interactions among S. alterniflora invasion and key soil physicochemical variables.

Shrub encroachment decreases soil inorganic carbon stocks in Mongolian grasslands

Abstract Widespread shrub encroachment in global drylands may increase plant biomass and change soil organic carbon stocks of grassland ecosystems. However, the response of soil inorganic carbon (SIC), which is a major component of dryland carbon pools, to this vegetation shift remains unknown. We conducted a systematic field survey in 75 pairs of shrub‐encroached grassland (SEG) and control plots at 25 sites in the grasslands of the Inner Mongolia Plateau to evaluate how shrub encroachment affects SIC density (SICD) in these ecosystems. We found that shrub encroachment significantly reduced SICD in the upper 100 cm (3.85 vs. 4.74 kg C m−2, p < .05), especially in the subsurface soil (20–50 cm layer). The magnitude of SICD changes was related to the change in soil pH, shrub patch size and initial SICD, reflecting that the reduction in SICD might be attributed to the shrub encroachment‐related soil acidification. Our results also revealed that the lost SIC was mainly released into the atmosphere rather than redistributed into deeper soil layers. Synthesis. We provide the first evidence for the soil acidification‐induced SIC loss caused by shrub encroachment. Our findings highlight the non‐negligible role of SIC dynamics in the C budget of SEG ecosystems and the need to consider these dynamics in terrestrial C cycle research.

Profile storage and vertical distribution (0–150 cm) of soil inorganic carbon in croplands in northeast China

In addition to soil organic carbon (SOC), soil inorganic carbon (SIC) is also an important reservoir of carbon (C) in arid and semiarid areas, and often contributes a large amount to total soil C. Despite carbonate soils distributed in some regions of northeast China, few data are available on SIC stock, especially in deep soils, resulting underestimation of total soil C. Based on 25 soil profiles (>150 cm) sampled from cropping lands of Lindian County, a typical region of carbonate soils in northeast China, we calculated SIC stock and its distribution in soil profiles and explored their relationship with soil physical and chemical properties. Results showed that SIC density (SICD) within 0–150 cm depth ranged from 109.0 to 331.7 Mg ha−1, with an average of 259.0 Mg ha−1, accounting for 68% of total soil C stock. The ratio of SIC to SOC ranged from 0.1 to 8.0 across soil profiles and was less than 1.0 on average in the upper 40 cm. The SICD in soil profiles were 55.6, 114.4, and 88.9 Mg ha−1 in the 0–40, 40–100, and 100–150 cm, respectively. The stocks of SIC and SOC in the 100–150 cm depth accounted for 23% and 6%, respectively, of the total soil C stock across soil profile. The SIC/SOC ratio was negatively correlated with total nitrogen, available phosphorus and potassium. A structural equation model analysis showed that soil depth combined with soil physical and chemical properties significantly affected the SIC/SOC ratio. Our study highlights the importance of SIC in total C stocks, and indicates SIC stock below 40 cm dominates the total C in soil profile, and SIC stock in deep layers (100–150 cm) can contribute one third to the total stock in the profile (0–150 cm). The distribution of soil C components throughout soil profiles as influenced by soil properties depends on soil layers.

Factor contribution to soil organic and inorganic carbon accumulation in the Loess Plateau: Structural equation modeling

The effects of climate, soil characteristics and management on soil carbon accumulation have been extensively investigated. However, the relative importance of these factors remains unclear, especially in arid and semiarid regions. Here we evaluated the contribution of the environmental variables (geographical location, climate, soil type, and land use type) to soil organic and inorganic carbon accumulation in the 0–100 cm soil layers across the Loess Plateau in China. A structural equation modeling (SEM) was used to distinguish direct from indirect effects of factors on soil carbon accumulation based on covariance structures. The results showed that environmental temperature and moisture were the primary controls of soil organic carbon density (SOCD) variation. The total effects (the sum of direct and indirect effect) of soil type and land use on SOCD were less than half of those of environmental temperature and moisture. In addition, the direct and negative effect of environmental temperature on SOCD increased, and the direct and positive effect of environmental moisture on SOCD decreased with soil depth. For the soil inorganic carbon densities in the 0–100 cm soil layers, soil organic carbon (SOC) content acted as the most important factor controlling the variations in soil inorganic carbon density (SICD). Environmental temperature and moisture mainly affected indirectly SICD by mediating through its impacts on soil type, SOC content, or soil pH. Less than 40% of variation in soil carbon accumulation for 0–100 cm soil depth is explained in the model. The unexplained variance highlights the need for the data on soil physicochemical properties, quality of organic carbon inputs, and soil microorganisms.

Soil carbon storage along a 46-year revegetation chronosequence in a desert area of northern China

Soil contains the majority of terrestrial carbon; however, most studies only focus on soil organic carbon (SOC) in the first meter or even shallower layers, and soil inorganic carbon (SIC) and root-derived carbon (RDC) are often overlooked. Here, we investigated the distribution of soil carbon at a depth of 0–3.0 m over a 46-year revegetation chronosequence on moving sand dunes and evaluated the potential influence of soil water content on soil carbon. The SOC density increased significantly along the 0–3.0 m profile, and showed a faster increasing rate in shallow layer (0–0.4 m) than that of the deep layers below 0.4 m. Although the SIC density did not increase significantly, it accounted for >65% of the total soil carbon in shallow layer and at least 82% in deep layer. The live and dead RDC increased significantly over the chronosequence in both shallow and deep layers. The RDC accounted for a small amount of the total soil carbon at an average of 3.19%. The SOC was closely linked with live RDC in both the shallow and deep layers. The soil water content was only positively correlated with the SOC in the shallow layer. The SOC storage in the shallow layer required 57.4 years to reach the level at the natural vegetation site, whereas the storage in the deep layers required >100 years. Our results indicated that soil carbon accumulation is a slow process in both shallow and deep layers after revegetation, and the most notable increase in soil carbon was accounted by SOC. We suggest that SOC, SIC and RDC should be considered when assessing the effects of revegetation on soil carbon in water-limited ecosystems.

Inorganic carbon sequestration capacity and soil carbon assimilation pathway of deserts in arid region

The inorganic carbon sequestration capacity of deserts in an arid region is now still questioned for their accuracy. The key question is whether the result of CO2 absorption from aboveground flux observation can be reflected in the soil carbon pool or not. In the arid region of northwest China, desert is divided into three types based on the landscape and vegetation characteristics, namely gravel desert (Gobi), sand desert, and silt desert. By measuring and analyzing the soil particle composition, total salt content, organic carbon and inorganic carbon content, the changes in soil organic carbon (SOC) and soil inorganic carbon (SIC) density and their storage in different type deserts were studied, and then they were compared with that in the alpine ecosystem of southwest China. The results showed that the average SIC densities in 0–30 cm surface soil layer and 1 m soil depth in different type deserts were 2.8 and 10.1 kg C m−2, respectively. Comparatively, the SIC density of silt desert was the highest, and the value over 12 kg C m−2 in 1 m soil depth. In our study, the average total carbon densities in 0–30 cm desert soil layer was 3.5 kg C m−2, and in 1 m soil depth was 12.1 kg C m−2. According to the value of 100 g C m−2 a−1 to calculate, the carbon accumulation in 0–30 cm surface soil layer and 1 m soil depth need 35 years and 121 years, respectively. If the value is less than 100 g C m−2 a−1, a longer period is required, showed that it will take a long time for the formation of desert inorganic carbon pool. In terms of material content, the average bulk density in 1 m soil depth was 1.52 g cm−3, and the total carbon accumulated in desert soil accounted for 0.8% of soil mass in 121 years, of which the inorganic carbon accounted for 0.7% of soil mass. For the soil absorption and inorganic sequestration to CO2, we proposed the concept of soil carbon assimilation. Carbon sequestration in desert ecosystems is plant carbon assimilation and soil carbon assimilation, which is a combination of organic and inorganic processes. The SIC density and storage of desert soil are five times that of SOC. The pathway of soil carbon assimilation can be divided into three stages: the reaction stage between CO2 and H2O, the reaction stage between CO2 or weak carbonic acid and soil solution cation, and the stage that is the dissolved and precipitated carbonates which attached to soil particles and downward deposition. The soil carbon assimilation capacity was enhanced by increasing the soil organic carbon, salt content, water content, and soil silt and clay content. To recovering and conservation of desert vegetation, the desert is reclaimed into farmland under the carrying capacity of water resources, the SOC density was not only increased, the soil carbon assimilation capacity, SIC density and storage are also enhanced greatly. Under conditions of future climatic warming, soil inorganic carbon sequestration capacity will be increased and carbon sequestration capacity of the desert ecosystem will be enhanced with increasing precipitation in the arid region. The development of irrigated agriculture in the arid desert region will be beneficial to a collaborative improvement in production and ecological functions in the arid region.

Profile Distribution of Soil Organic and Inorganic Carbon Under Different Land Use Types in the Loess Plateau of Northern Shaanxi

Carbon storage in the Loess Plateau is affected by land use. In order to assess the differences in soil organic carbon (SOC) and soil inorganic carbon (SIC) under different land use patterns in deep soil profiles, we investigated the distribution characteristics of SOC and SIC at 0-20.0 m soil depth at three locations in the northern Shaanxi province (i.e., an economical plantation in Mizhi, a reforestation area in Shenmu, and a wind break and sand fixation forest district in Yuyang). The results showed that the order for SOC content was:pruning jujube tree (2.00 g·kg-1) > jujube tree (1.54 g·kg-1) > Caragana (0.97 g·kg-1) > degraded artificial grassland (0.81 g·kg-1) > pine forests (0.70 g·kg-1) > natural grass field (0.45 g·kg-1), which indicated significant differences between SOC content and land use types (P<0.05). Similarly, the order of SIC content was:pruning jujube tree (11.66 g·kg-1) > jujube tree (11.59 g·kg-1) > Caragana (9.62 g·kg-1) > degraded artificial grassland (8.07 g·kg-1) > pine forests (4.32 g·kg-1) > natural grass field (0.47 g·kg-1). There were no significant differences between SIC content and soil profiles under the economical plantation of Mizhi and the reforestation area of Shenmu. There were significant differences for SIC content between an artificial economic forest, an area returning farmland to a forest (grass) profile, and a windbreak and sand fixation forest (P<0.05). The SIC densities for pruning jujube tree, jujube tree, Caragana, degraded artificial grassland, pine forest, and natural grass field were 6.19, 7.71, 10.70, 10.78, 5.91, and 1.03 times that of its corresponding SOC density, respectively. It has been concluded that the soil carbon storage was significantly different for different land use patterns, and the SIC content was much higher than the SOC content in the soil profile.

Digital mapping of soil organic and inorganic carbon status in India

Reliable mapping of soil organic carbon (SOC) and Soil Inorganic Carbon (SIC) densities and estimates of their pool size are important from global warming perspective to understand the sequestration potential and losses. In this study, first spatially explicit mapping of SOC and SIC at 250m resolution and an estimate of their pool size in India was undertaken using a large number of remote sensing derived data layers and data mining approach. The SOC and SIC densities up to 100cm depth or paralithic contact (whichever is shallower) were estimated for 1198 soil samples located across India using a stratified random sampling that integrated land use, soil, topography and agro-ecological regions.Using Random forests (RF) based spatial prediction procedure with climatic, land cover, rock type, soil type, multi-year NDVI, irrigation status as independent input variables, models for predicting carbon density at 250m spatial resolution were developed. For modelling with RF algorithm, about 898 soil profile observations (75% observations) were used, while the rest of 300 (25% of total observations) were used for validation. It was observed that the data distribution of sample points don't have significant influence on RF model predictions. The relationship between observed and predicted values was characterized by Mean Squared Deviation (MSD) and Root Mean Squared Error (RMSE) parameters. The SOC, SIC and total soil carbon pool size of India has been estimated at 22.72±0.93 Pg,12.83±1.35 Pg and 35.55±1.87 Pg, respectively, which are comparable to previous studies while providing first spatially explicit 250m map of their distribution. The spatial distribution indicates that majority of the carbon stock resides in the northern part of India. The soil carbon stock of eastern India has contribution from organic carbon, while the western portion has contribution mainly from inorganic carbon.

Comparison on soil carbon stocks between urban and suburban topsoil in Beijing, China

The urban population and urbanized land in China have both increased markedly since the 1980s. Urban and suburban developments have grown at unprecedented rates with unknown consequences for ecosystem functions. In particular, the effect of rapid urbanization on the storage of soil carbon has not been studied extensively. In this study, we compared the soil carbon stocks of different land use types in Beijing Municipality. We collected 490 top-soil samples (top 20 cm) from urban and suburban sites within the Sixth Ring Road of Beijing, which cover approximately 2400 km2, and the densities of soil organic carbon (SOC), soil inorganic carbon (SIC), and total carbon (TC) were analyzed to determine the spatial distribution of urban and suburban soil carbon characteristics across seven land use types. The results revealed significant differences in soil carbon densities among land use types. Additionally, urban soil had significantly higher SOC and SIC densities than suburban soil did, and suburban shelterbelts and productive plantations had lower SIC densities than the other land use types. The comparison of coefficients of variance (CVs) showed that carbon content of urban topsoil had a lower variability than that of suburban topsoil. Further findings revealed that soil carbon storage increased with built-up age. Urban soil built up for more than 20 years had higher densities of SOC, SIC and TC than both urban soil with less than 10 years and suburban soil. Correlation analyses indicated the existence of a significantly negative correlation between the SOC, SIC, and TC densities of urban soil and the distance to the urban core, and the distance variable alone explained 23.3% of the variation of SIC density and 13.8% of the variation of TC density. These results indicate that SOC and SIC accumulate in the urban topsoil under green space as a result of the conversion of agricultural land to urban land due to the urbanization in Beijing.

Soil inorganic carbon stock under different soil types and land uses on the Loess Plateau region of China

The soil carbon reservoir is the largest carbon reservoir in terrestrial ecosystems and consists of soil organic and inorganic carbon stocks. Previous studies have mainly focused on the soil organic carbon (SOC) stock, and limited information is available about the soil inorganic carbon (SIC) stock. The Chinese Loess Plateau (CLP), which is located in the arid and semi-arid region of China, is an important inorganic carbon reservoir, with a thick soil layer that is rich in calcium carbonate. However, there are few reports on the SIC stock and its spatial distribution in this region. In the current study, the SIC densities and stocks for various soil types and land use patterns were evaluated based on 495 profiles with 2470 soil samples across the CLP, which were collected from the Chinese Second National Soil Survey. The results showed that in the top 1m of soil across the CLP, the average SIC density is 17.04kg/m2, and the total SIC stock is approximately 10.20 Pg C (1 Pg=1015g). The SIC stock of the CLP accounts for approximately 18.4% of the total SIC stock throughout China. The average values of the SIC stock in the 0–20, 20–50 and 50–100cm depths of the CLP are 2.39, 2.92 and 4.89 Pg, respectively. Under different land use patterns, the order of the average SIC density is farmland≈grassland>forest in all soil layers. For the various soil types, the SIC density in the 0–100cm layer is the highest in alkaline soil and lowest in subalpine meadow soil, whereas the SIC stock is highest in loessial soil, eolian sandy soil and sierozem, and the lowest in subalpine meadow soil. These differences are largely a result of the area occupied by each soil type and the climate conditions. The results of this study provide basic information about carbon reservoir in China and contribute to our understanding of the SIC stock on the CLP as it relates to the carbon balance of terrestrial ecosystems.

Spatial Distribution of Soil Inorganic Carbon in Urbanized Territories

Soil carbon stock changes induced by land-use change play an essential role in the global greenhouse effect and carbon circulation. This paper studies the spatial characteristics of soil inorganic carbon (SIC) distribution in urbanized territories of main cities in Jiangsu Province, China, based on the data of regional geochemical survey. Urbanization process in study area has been quickened greatly since the 1980s. The SIC density in urban area is 0.64±0.70 kg m-2, which mean density is 1.33 times of that in suburban and 1.52 times of that in countryside, and SIC distribution in urbanized area shows accumulation and obvious spatial variability. By comparison of SIC distribution in the central urban area, urbanized area during 1980-2000, 2000-2005 and suburban, the SIC obviously accumulates in central urban area, furthermore, the SIC density increases with urban land use duration extending and urban ecosystem evolving. This paper provides the characteristics of SIC distribution and evolution during the course of urbanization, which may be useful for assessing the impact of land-use and urban development on SIC pools in urban ecosystem.

Urban expanding pattern and soil organic, inorganic carbon distribution in Shanghai, China

Soil carbon stock changes induced by land-use change play an essential role in the global greenhouse effect and carbon circulation. This paper studies the urban expanding patterns and spatial characteristics of soil organic carbon (SOC) and soil inorganic carbon (SIC) distribution and evolution during the urbanization process of Shanghai, China, based on the data of the regional geochemical survey. Urbanization process in Shanghai, China, has been quickening greatly since the 1980s. The urban area expanded from 193.08 km2 in 1980 to 1,570.52 km2 in 2005, or up from 3.05 to 24.77% in the past 25 years, and the urban expansion circled the central city region according to the RS images acquired in the periods of 1980, 2000 and 2005. The urban topsoil is slightly enriched with SOC and SIC, which shows obvious spatial variability. By comparison of SOC and SIC distribution in the central urban area, urbanized area during 1980–2000, 2000–2005 and the suburban area, the SOC obviously accumulates in the central urban area, while SOC density in the urbanized area decreases; similarly, the SIC obviously accumulates in central urban area; furthermore, the SIC density increases with urban land use duration extending and urban ecosystem evolving. This paper provides the characteristics of SOC and SIC distribution and evolution during the course of urbanization, which may be useful for assessing the impact of land use and urban development on SOC and SIC pools in urban ecosystem.

Soil inorganic carbon stock in the Tibetan alpine grasslands

As the largest carbon pool in the terrestrial biosphere, soil carbon stock consists of organic and inorganic components. However, previous studies dominantly concentrated on soil organic carbon (SOC) stock, and little is known about the magnitude and patterns of soil inorganic carbon (SIC). In this study, we evaluated the magnitude of SIC stock in the Tibetan alpine grasslands using data from 405 profiles surveyed from 135 sites across the plateau during 2001–2004. Kriging interpolation was conducted to interpolate site‐level observations to the regional level. We also compared spatial and vertical distributions of SIC stock with the corresponding patterns of SOC stock in the Tibetan alpine grasslands. Our results showed that SIC stock in the top 1 meter in the Tibetan alpine grasslands was approximately 15.2 Pg C (1 Pg = 1015 g), with an average density (amount per area) of 13.46 kg C m−2. SIC density exhibited different spatial and vertical distributions in comparison with SOC density. Spatially, SIC density in the alpine steppe was larger than that in the alpine meadow, in contrast to SOC distribution. Vertically, SIC stock in the upper 30 and 50 cm accounted for 47.6% and 71.6%, respectively, of that in the upper 1 meter, with lower proportions than that of SOC stock in the same interval (67.8% and 83.3%). In total, SIC stock in the Tibetan alpine grasslands was about 2.1 times the corresponding SOC stock, accounting for 28.5% of the total SIC stock in China. These results highlight that SIC stock in the Tibetan grasslands could make a significant contribution to China's terrestrial carbon balance.

Carbon storage and spatial distribution patterns of paddy soils in China

Carbon storage in agricultural soils plays a key role in terrestrial ecosystem carbon cycles. Paddy soil is one of the major cultivated soil types in China and is of critical significance in studies on soil carbon sequestration. This paper estimated the organic and inorganic carbon density and storage in paddy soils, and analyzed the paddy soil stock spatial distribution patterns in China based on subgroups and regions using the newly compiled 1:1 000 000 digital soil map of China as well as data from 1 490 paddy soil profiles. Results showed that paddy soils in China cover an area of about 45.69 Mhm2, accounting for 4.92% of total soil area in China. Soil organic and inorganic carbon densities of paddy soils in China showed a great heterogeneity. Paddy soil organic carbon densities (SOCD) in soil profile ranged from 0.53 to 446.2 kg/m2 (0 to 100 cm) while the paddy soil inorganic carbon densities (SICD) ranged from 0.05 to 90.03 kg/m2. Soil organic carbon densities of paddy soils in surface layer ranged from 0.17 to 55.38 kg/m2 (0 to 20 cm), with SICD of paddy soils ranging from 0.01 to 21.85 kg/m2. Profile based and surface layer based paddy soil carbon storages (SCS) are 5.39 Pg and 1.79 Pg, respectively. Paddy soil organic carbon storage (SOCS) accounts for 95% of the total carbon storage. Profile based and surface layer based SOCS of paddy soils are 5.09 Pg and 1.72 Pg, respectively. Soil inorganic carbon storage (SICS) of paddy soils accounts for 5% of the total carbon storage in China. Profile based and surface layer based paddy SICS are 0.30 Pg and 0.07 Pg respectively. Among all the eight paddy soil subgroups, hydromorphic, submergenic and percogenic paddy soils account for 85.2% of the total paddy soil areas all over China. Consequently, profile based carbon storages of these three subgroups account for 78.1% of the total profile based paddy SCS in China. Most paddy soils in China are distributed in the East-China, South-China and South-west China regions, therefore, 92.6% of China’s profile based paddy SCS focuses on these three regions. The estimates of soil carbon stocks in paddy soils will help to identify areas or soil subgroups which are of particular interest for soil carbon gains and losses.