Organic Carbon Density Research Articles

Factors controlling the spatial distribution of soil organic carbon in the Chinese medicine producing area of NW China1

Soil organic carbon is an important factor for the cultivation and production of traditional Chinese medicine. This study aimed to reveal the spatial distribution of the soil organic carbon density (SOCD) and the effects of the climatic and topographic factors in Longxi County (Gansu Province, China). The soil organic carbon (SOC) from 200 sampling points were collected and analyzed in 2018. Results showed that the total SOCD was 26.7 ± 10.2 Mg ha-1, while the SOCDs at a soil depth of 0–10, 10–30, and 30–50 cm were 6.3 ± 1.7, 11.0 ± 3.8, and 9.3 ± 4.8 Mg ha-1, respectively. The temperature, precipitation, elevation, and stream power index showed significant correlations with the SOCD at each soil layer. With an increasing soil depth, the correlation between the slope, relief amplitude, surface roughness, and SOCD gradually decreased. From the central plains to the mountainous areas, the SOCD increased with rising elevation, while the valley plain that formed by the river basin showed low levels of SOCD. Therefore, the scientific management of soil fertility and the development of precision agriculture, combined in a soil testing fertilization formula, will guarantee the healthy development of the Chinese herbal medicine planting.

A comprehensive assessment of diversified cropping systems on agro-environmental sustainability in three Mediterranean long-term field experiments

The intensification of agricultural systems has caused a noticeable impact on agro-ecosystem services. Thus, the adoption of more sustainable agricultural practices such as crop diversification and reduction of external inputs represent an alternative strategy to minimize the impacts of intensive agricultural systems to the environment. This study aimed at evaluating the effects of crop rotation, conservation tillage, and low-input strategies on soil quality and farming performance using a set of 7 indicators based on a fuzzy logic approach. Data were collected from three Mediterranean long-term field experiments (LTEs) mostly oriented on cereal-based and vegetables cropping systems, located in Spain and Italy. The selected agro-environmental indicators clearly discriminated both from a geographical point of view and between monoculture and diversification, showing their suitability for the evaluation of diversified cropping systems. Such indicators highlighted that implementing crop diversification and reducing soil disturbance and chemical inputs enhanced soil quality. In this context, the most significant effects of diversified cropping strategies were the increase of crucial variables such as soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Pav), and bulk density (BD) maintaining a stability of yields in all the three LTEs. These results provide strong evidence for the benefits of crop diversification in Mediterranean areas, highlighting that diversification represents a very promising strategy for more sustainable land management. Simple and composite indicators calculated using fuzzy method can be proposed as tool to assess the effects of diversification strategies on cropping systems performance. This approach can be used to define local solutions to help the re-design of cropping system through crop diversification transition across Europe.

Precipitation drives the accumulation of soil organic carbon in the sandy desert of the Junggar Basin, Northwest China

Accurate quantitative estimation of soil organic carbon (SOC) and its storage is crucial for ecosystem response over desert areas, and is an important component of understanding dryland climate change, which can effectively reflect the processes and regulatory mechanisms in the carbon cycle. Nevertheless, the relationship between carbon sources and carbon sinks in sandy soils is a hotly debated subject. In particular, how plants and environmental conditions interact to affect SOC remains unclear in sandy deserts. Here, we investigated 77 sites at depths of 0–100 cm (soil depth was divided by 0–5 cm, 5–10 cm, 10–20 cm,20–30 cm, 30–50 cm, 50–70 cm and 70–100 cm intervals), collected 1617 soil samples, and obtained the climatic conditions, vegetation types, and edaphic factors associated with the sampling sites. This study aims to determine whether there are divisions in the allocation strategies of SOC by various vegetation types, and to analyze the mechanisms of environmental factors on the soil carbon pool in sandy deserts. Our results found that (1) the mean value of SOC in the sandy desert was 2.19 g·kg−1, which differed significantly among different vegetation types (P < 0.05), yet there were no significant changes in aboveground biomass and litter biomass. (2) SOC did not significantly differ among soil layers except for the Ceratoides latent (P = 0.04), and Seriphidium terrae-albae (P = 0.02) communities. (3) The mean value of soil organic carbon density (SOCD) was 3.38 kg·m−2 and increased exponentially with soil depth (R2 = 0.23, P < 0.05). (4) Mean annual precipitation controlled the spatial distribution of SOC variation in sandy desert. Vegetation types, soil variables, topographic factors did not control SOC, but had a strong interactive effect with climatic factors. The explanatory power of interaction effects often showed an improvement over single variables, manifested as nonlinear enhancement and bivariate enhancement. Our results highlighted the nature of the desert’s position in the global carbon cycle and provide key information on missing carbon sinks in the driest zone.

Variation of soil organic carbon and bulk density during afforestation regulates soil hydraulic properties

Variation of soil organic carbon and bulk density during afforestation regulates soil hydraulic properties

Spatiotemporal Changes and Driver Analysis of Ecosystem Respiration in the Tibetan and Inner Mongolian Grasslands

Ecosystem respiration (RE) plays a critical role in terrestrial carbon cycles, and quantification of RE is important for understanding the interaction between climate change and carbon dynamics. We used a multi-level attention network, Geoman, to identify the relative importance of environmental factors and to simulate spatiotemporal changes in RE in northern China’s grasslands during 2001–2015, based on 18 flux sites and multi-source spatial data. Results indicate that Geoman performed well (R2 = 0.87, RMSE = 0.39 g C m−2 d−1, MAE = 0.28 g C m−2 d−1), and that grassland type and soil texture are the two most important environmental variables for RE estimation. RE in alpine grasslands showed a decreasing gradient from southeast to northwest, and that of temperate grasslands showed a decreasing gradient from northeast to southwest. This can be explained by the enhanced vegetation index (EVI), and soil factors including soil organic carbon density and soil texture. RE in northern China’s grasslands showed a significant increase (1.81 g C m−2 yr−1) during 2001–2015. The increase rate of RE in alpine grassland (2.36 g C m−2 yr−1) was greater than that in temperate grassland (1.28 g C m−2 yr−1). Temperature and EVI contributed to the interannual change of RE in alpine grassland, and precipitation and EVI were the main contributors in temperate grassland. This study provides a key reference for the application of advanced deep learning models in carbon cycle simulation, to reduce uncertainties and improve understanding of the effects of biotic and climatic factors on spatiotemporal changes in RE.

Spatial-Temporal Variability of Soil Organic Carbon Density and Its Related Factors in Fengqiu County of Yellow River Basin, China: A Model and GIS Technique Approach

The accurate estimation of the soil organic carbon (SOC) sequestration rate is very important for studying farmland soil fertility and environmental effects. In this research, a typical fluvor-aquic soil area, Fengqiu county, located in the Yellow River basin of the Huang-Huai-Hai Plain of China, was chosen as a study area. The physicochemical properties of 70 soil samples collected from the surface layer (at a depth of 0–20 cm) in 2011 were analyzed, and related data about the sampling sites were also collected from the Second State Soil Survey of China (SSSSC), conducted in 1981. The results revealed that the SOC density (SOCD) in Fengqiu county increased greatly on a spatio-temporal scale. The average SOCD increased from 15.66 to 26.09 Mg ha−1, and the SOCD sequestration rate was more than 0.20 Mg C ha−1 year−1 in most regions. Few areas showed lost carbon in the past 30 years (1981–2011). In addition, the study suggested that all the areas present strong carbon sequestration potential in the coming decades from 2011, and the carbon sequestration potential was mainly between 32–40 Mg ha−1. Finally, the SOCD sequestration rate was not only affected by natural factors, such as soil type and pH, but also positively correlated with artificial soil management measures, such as fertilization and straw returning. Therefore, we concluded that the farmland in Fengqiu county showed significant carbon sequestration characteristics in the past 30 years (1981–2011). Considering that soil has a great potential for carbon sequestration in the future, the trend of carbon sequestration in farmland soil might continue for a period of time. Furthermore, the results of this study emphasized that strengthening soil scientific management may play a positive role in improving soil carbon sequestration.

Soil Aggregate Stability and Carbon Density in Three Plantations in the Loess Plateau, China

Afforestation plays an important role in mitigating soil erosion and improving soil quality in the Loess Plateau. However, there is no consistent conclusion about the effect of tree species on soil properties. Robinia pseudoacacia, Pinus tabulaeformis, and Malus pumila plantations were selected as the research objects. Soil indices such as the content of soil organic carbon (SOC) and inorganic carbon (SIC), carbon density, soil aggregate stability, and bulk density were selected to study the effects of different plantations on soil properties. The mean weight diameter (MWD) was calculated to evaluate soil aggregate stability. The results showed that: (1) MWD of R. pseudoacacia was 22%–67% lower than that of P. tabuliformis across the 0–80 cm soil layers. MWD of M. pumila was 27%–45% and 57%–78% lower than that of R. pseudoacacia and P. tabuliformis across 0–50 cm layers. (2) SOC of P. tabuliformis was 61%–127% and 67%–148% higher than that of R. pseudoacacia and M. pumila, respectively, while SIC was 55%–82% and 12%–14% lower than that of R. pseudoacacia and M. pumila. (3) Soil carbon density, including soil organic carbon density and inorganic carbon density, of P. tabuliformis was 36%–49% and 3%–31% lower than that of R. pseudoacacia and M. pumila, respectively. (4) Aggregate organic carbon increased with increasing aggregate size, while inorganic carbon decreased. Water-stable aggregates with larger sizes had higher soil organic carbon and lower carbonate calcium. (5) The inorganic carbon in soil was both a binder and a dispersant of soil aggregates, which depends on its content. P. tabuliformis should be planted in the semi-arid area of the Loess Plateau in China, because this species was able to increase soil organic matter and improve soil structure compared with the other two species.

Spatial distribution and the influencing factors of organic carbon of biological crusts on regional scale in Mu Us sandy land, China

As an important soil cover in deserts, biological crusts play a central role in ecosystem function such as nutrient cycling, nitrogen fixation, and carbon sequestration. Many biological crust organisms could fix CO2 through photosynthesis to improve soil organic carbon content. There is a knowledge gap in the origin of soil organic carbon (SOC) from biological crusts on a regional level, which restricts the prediction of soil carbon pool. Based on 45 plots in the Mu Us sandy land (42200 km2), we measured the SOC content and soil organic carbon density (SOCD) of two types of typical biological crusts (moss crusts, algal crusts) and their underlying soils, and analyzed together with the climate data, soil and vegetation factors to investigate the spatial distribution characteristics and controlling factors of organic carbon of biological crusts at the regional scale. The results showed that: 1) biological crusts significantly increased SOC and SOCD compared with bare ground. Moss crusts and the underlying SOC (4.93 g·kg-1) and SOCD (0.41 kg·m-2) were higher than those of algal crusts (1.89 g·kg-1, 0.18 kg·m-2). 2) On the regional scale, the SOC and SOCD of biological crusts had clear spatial distribution characteristics, demonstrating a banded distribution and block mosaic from northeast to central and west to southeast. 3) The SOC and SOCD of biological crusts and their underlying soils were mainly affected by climate, soil and vegetation conditions, while the main controlling factors depended on the types of biological crusts. The SOC and SOCD of moss crust were controlled by annual maximum temperature and potential evapotranspiration, whereas those of algal crusts were controlled by water vapor pressure.

Application of soil quality index to determine the effects of different vegetation types on soil quality in the Yellow River Delta wetland

Assessment of soil quality in different vegetation types of wetland ecosystems is essential for soil functioning, such as nutrient cycling and vegetation growth, particularly the maintenance of wetland ecosystem sustainability. Wetland degradation can extremely influence soil quality. However, prediction of soil quality in terms of soil quality index in wetland soils remains obscure. In this study with the fundamental goal to assess soil quality, we have intended to assemble a range of soil quality indicators to characterize the soil quality index (SQI). The minimum data set (MDS) from the Principal component analysis (PCA) was used to determine the SQI. With such objectives, three vegetation types: Robinia pseudoacacia community (tree), Tamarix chinensis community (bush), and Suaeda salsa community (grass) were selected in the Yellow River Delta wetland, eastern of China. A total of 108 soil samples [3 sites (tree, bush and grass)—3 field plots—3 replicates—4 soil depth layers: 0–10 cm, 10–20 cm, 20–40 cm, and 40–60 cm] were collected for laboratory analyses. This study showed that there were high variations in soil physical and chemical properties among the three sites. Soil organic carbon (SOC), silt, clay, and pH at tree site, total soil porosity (TSP), soil organic carbon (SOC), pH, and soil bulk density (SBD) at bush site, and total soil porosity (TSP), silt, and soil electronic conductivity (SEC) at grass site were retained in the MDS. SOC and TSP were the key soil quality indicators. The values of the SQI at 0–10 cm soil depth at all three sites (2.236, 0.895, and 2.573 respectively) were the highest compared with other soil depths, indicating the best soil quality in the upper soil layers (0–10 cm). The values of the SQI at 0–10 cm soil depth at both tree site and grass site were similar, and they were higher than those at bush site. At tree site, the values of the SQI decreased with increasing soil depth, which indicated that soil quality became worse with depth. At bush site, the values of the SQI decreased with increasing soil depth (0–40 cm), while the values increased at 40–60 cm depth, indicating better soil quality in the deeper soil layers (40–60 cm). At grass site, the values of the SQI at 10–20 cm and 40–60 cm soil depth were lower than those at 20–40 cm soil depth, indicating better soil quality at 20–40 cm soil depth. It is concluded that the SQI can be compared more accurately in different vegetation types of wetland ecosystems based on its simplicity and quantitative flexibility. These findings are of importance because the assessment of the SQI allows to quantify different vegetation effects on soil quality.

Effect of No Tillage System on Soil Fungal Community Structure of Cropland in Mollisol: A Case Study.

Conservation tillage is generally regarded as a sustainable farming system for the future. The fungal community structure has a strong response to conservation tillage. However, how the conservation tillage system affects the soil fungal community structure is little known. Using the high-throughput sequencing technology, the soil fungal community was explored under no tillage (NT) and conventional tillage (CT) in Northeast China Mollisol. The copy number of fungal genes in NT20 was significantly lower than that in other treatments. NT changed the composition of soil fungal communities at the taxonomic level of phylum and genus. The diversity indices of the soil fungal community in no tillage at soil depths of 0–5 cm (NT5) were significantly higher than those in soil depths of 5–20 cm (NT20). The fungal community under NT and CT could form a good cluster distribution and NT5, conventional tillage at soil depths of 0–5 cm (CT5) and 5–20 cm (CT20) had specific indicator species. Most of the potential pathogens were significantly higher in NT5 than in NT20. Tillage and soil depth could explain 64% of the diversity and 95% of the composition of the fungal community, which indirectly changed the diversity and composition of fungi by using soil organic carbon, pH value, and soil bulk density. Furthermore, soil organic carbon (SOC) best explained the soil fungal community, followed by soil pH. The study indicated that the NT system had a comprehensive effect on the soil fungal community and SOC is the most crucial factor in determining this community.

Effects of the Main Ecological Restoration Projects on Grassland Carbon Sequestration in Ningxia on the Loess Plateau

The temperate steppe experienced degradation and desertification as a result of long-term heavy grazing and excessive reclamation. Some major ecological projects, such as the Grain for Green Program (GGP) and Grazing Exclosure (GE), have been implemented to promote ecological restoration in grassland ecosystems. With the goal of carbon neutrality, the effects of the GGP and GE on grassland carbon sequestration need to be further explored. Based on soil data from the second soil survey in the 1980s, a field survey in 2021, and the land-use/land-cover datasets of 2000–2018, we characterized the changes in soil C stock following grazing exclosure, analyzed the effect of GGP on land-use changes and soil C accumulation, and then estimated the overall grassland carbon sequestration in Ningxia on the Loess Plateau of China. From 2000 to 2018, GE increased the grassland SOCD from 49.60 Mg ha−1 to 90.71 Mg ha−1, and the C stock increased by 65.55 T g. Under the influence of the GGP, 347.62 km2 of cultivated land was converted into grasslands, increasing the grassland soil carbon sequestration by 1.31 T g. Subsequently, the grassland organic carbon storage increased by 66.86 T g, which accounted for approximately 4.26% of the grassland organic carbon storage in the Loess Plateau of China. In the southern Loess hilly area, which experienced high precipitation and low temperatures, grasslands increased by 95.55 km2; the average organic carbon density increased 46.95 Mg ha−1 due to a rate of increase of 2.61 Mg ha−1 yr−1; and the corresponding values for those in the middle arid zone were 36.25 Mg ha−1 and 2.01 Mg ha−1 yr−1, with grasslands decreasing by 147.41 km2. The follow-up policies of the GGP and GE should be implemented and improved according to local conditions to improve the carbon sink and ecological services in grassland ecosystems.

Temporal and Spatial Dynamics of Carbon Storage in Qinghai Grasslands

Accurate quantification of ecosystem carbon storage dynamics is very important in regional ecological management. However, the dynamics of grassland carbon storage in Qinghai, China, are still unexplored. We investigated the temporal and spatial dynamics of carbon storage in the Qinghai grasslands from 1979 to 2018, using the spatially explicit Biome-BGCMuSo model. The average annual value of vegetation carbon density (VCD) was 52.71 gC·m−2. After 2000, VCD showed an overall increasing trend, with an average rate of 2.14 gC·m−2. The VCD was relatively high in the eastern and southeastern regions of Qinghai compared with that in the western and central areas. The increasing trend in VCD was mainly observed in the eastern and southeastern regions, while a decreasing trend was evident in western and central Qinghai. Annual soil organic carbon density (SOCD) in Qinghai grasslands generally increased from 1979 to 2018. After 2001, the SOCD increased by an average rate of 7.07 gC·m−2. The SOCD was relatively high in eastern and southeastern Qinghai compared with that in western and central Qinghai. The pronounced increasing trend of SOCD was mainly distributed in the southeast and northeast parts of Qinghai, while the decreasing trend was mainly distributed in the area between southeast and northeast Qinghai, and in the central and western regions. This study deepened our understanding of carbon dynamics in the Qinghai grasslands and provided data for guiding the ecological restoration and carbon management of local grasslands.

Sensitivities of Physical and Chemical Attributes of Soil Quality to Different Tillage Management

Tillage management is a direct factor in affecting soil quality, which is a key factor in sustainable agriculture. However soil quality evaluation needs significant manpower, material resources and time. To explore the sensitive indicators of soil quality affected by tillage management, eight soil physical and chemical properties under three tillage managements, including plow tillage, subsoiling tillage and rotary tillage, were determined under a long-term experiment in North China Plain. The results showed that subsoiling tillage management had the highest soil organic carbon and total nitrogen in the 0–20 cm layer and the lowest soil bulk density in the 30–40 cm layer. Rotary tillage management had the highest soil water content in the 0–40 cm layer. Meanwhile, compared to 2002, the soil organic carbon, total nitrogen and soil bulk density had varied greatly in 2012, but there was no significant difference between 2012 and 2018. However, other property concentrations tended to increase in 2002, 2012 and 2018. In addition, there was a significant linear relationship between soil quality index and grain yield. Subsoiling tillage management had the highest soil quality index and gain yield both in 2012 and 2018. The soil quality can be evaluated through the sensitive indicator of soil organic carbon, total nitrogen, soil bulk density, total phosphorus and soil water content, which provides a scientific basis for selecting reasonable tillage management and evaluating soil quality in this agricultural production area or other similar areas.

Wildfire drives the transition from deterministic- to stochastic-dominated community assembly of abundant bacterial in forest soils

Wildfires are ecological disturbances that shift soil microbes and the ecosystem functions they drive in forests. The temporal dynamics and assembly processes of the bacterial community following fire are essential but remain unknown. This study aimed to investigate how the assembly processes and their associated factors mediate the abundant and rare bacterial communities across temporal trajectories (21 months from 2019 to 2020) in severely burned and contiguous unburned forest soils. Results revealed that the temporal turnover rate of abundant sub-community in unburned soils was lower than that of rare sub-community, and abundant taxa exhibited a wider niche breadth than rare taxa; null model analyses indicated that variable selection made a paramount contribution to bacterial community assembly, with stronger phylogenetic clustering of the rare taxa; soil ammonium nitrogen and pH were the most decisive factor for community assembly of abundant and rare taxa, as evidenced by how divergences in them decreased the proportion of stochasticity. Compared with the unburned soils, the temporal turnover of the soil bacterial community was accelerated in burned soils; moreover, determinism had more important roles in rare taxa, whereas the abundant taxa were primarily dominated by dispersal limitation; soil dissolved organic carbon and bulk density regulated the balance between deterministic and stochastic assembly of the abundant and rare bacteria, respectively. Overall, these findings suggested distinct community assembly of abundant taxa in burned and unburned forest soils, which is of great significance to understand the establishment and maintenance mechanism of the soil bacterial community in forests following wildfire.

Ecosystem organic carbon storage and their drivers across the drylands of China

Earth’s drylands store large amounts of organic carbon and thus play an important role in regulating atmospheric CO2 concentrations and mitigating climate change. However, little is known about the magnitude and the drivers of organic carbon stocks because of limited data, in particular in desert ecosystems. To fill this gap, we surveyed 763 plots and collected 5091 soil samples from 170 sites covering grassland and desert ecosystems across the drylands of China. The results show that 10.96 Pg organic carbon is stored in these ecosystems (7.07 Pg in grasslands and 3.89 Pg in deserts). The effects of environmental variables on carbon density were found to be contingent on ecosystem type and soil depth. Mean annual precipitation had a strong positive effect on the spatial distributions of vegetation carbon density in both types of ecosystems. The spatial variations of surface (0–40 cm) and subsurface (40–100 cm) soil organic carbon (SOC) density in grasslands were mainly correlated with plant productivity and mean annual temperature (MAT), respectively, while in desert ecosystems, they were mainly correlated with soil salinity (electrical conductivity). The spatial sensitivities (linear regression slopes) of the surface SOC density versus MAT increased from dry subhumid to semi-arid regions and then gradually shifted to decrease from semi-arid to hyper-arid regions, indicating that the surface SOC stock is more sensitive to temperature in semi-arid regions. This study provides a comprehensive survey of ecosystem carbon stocks in China’s drylands, fills a gap in our knowledge about carbon stocks in deserts, complements estimates of ecosystem carbon stocks throughout China, and provides insights into our understanding of the carbon cycle in drylands.

Urban soil management in the strategies for adaptation to climate change of cities in the Tropical Andes

The unique characteristics of a city amplify the impacts of climate change; therefore, urban planning in the 21st century is challenged to apply mitigation and adaptation strategies that ensure the collective well-being. Despite advances in monitoring urban environmental change, research on the application of adaptation-oriented criteria remains a challenge in urban planning in the Global South. This study proposes to include urban land management as a criterion and timely strategy for climate change adaptation in the cities of the Tropical Andes. Here, we estimate the distribution of the soil organic carbon stock (OCS) of the city of Quito (2,815 m.a.s.l.; population 2,011,388; 197.09 km2) in the following three methodological moments: i) field/laboratory: city-wide sampling design established to collect 300 soil samples (0–15 cm) and obtain data on organic carbon (OC) concentrations in addition to 30 samples for bulk density (BD); ii) predictors: geographic, spectral and anthropogenic dimensions established from 17 co-variables; and iii) spatial modeling: simple multiple regression (SMRM) and random forest (RFM) models of organic carbon concentrations and density as well as OCS stock estimation. We found that the spatial modeling techniques were complementary; however, SMRM showed a relatively higher fit both (OC: r2 = 20%, BD: r2 = 16%) when compared to RFM (OC: r2 = 8% and BD: r2 = 5%). Thus, soil carbon stock (0–0.15 m) was estimated with a spatial variation that fluctuated between 9.89 and 21.48 kg/m2; whereas, RFM showed fluctuations between 10.38 and 17.67 kg/m2. We found that spatial predictors (topography, relative humidity, precipitation, temperature) and anthropogenic predictors (population density, roads, vehicle traffic, land cover) positively influence the model, while spatial predictors have little influence and show multicollinearity with relative humidity. Our research suggests that urban land management in the 21st century provides key information for adaptation and mitigation strategies aimed at coping with global and local climate variations in the cities of the Tropical Andes.

Effects of forest fire disturbance on carbon density of eucalyptus forest ecosystem in Guangdong Province

Forest fire, as a discontinuous ecological factor of forest, causes the changes of carbon storage and carbon distribution in forest ecosystem, and affects the process of forest succession and national carbon capacity. Taking the burned land with different forest fire interference intensity as the research object, using the comparison method of adjacent sample plots, and taking the combination of field investigation sampling and indoor test analysis as the main means, this paper studies the influence of different forest fire interference intensity on the carbon pool of forest ecosystem and the change and spatial distribution pattern of ecosystem carbon density, and discusses the influence mechanism of forest fire interference on ecosystem carbon density and distribution pattern. The results showed that forest fire disturbance reduced the carbon density of vegetation (P &lt; 0.05). The carbon density of vegetation in the light, moderate and high forest fire disturbance sample plots were 67.88, 35.68 and 15.50 t∙hm-2, which decreased by 15.86%, 55.78% and 80.79% respectively compared with the control group. In the light, moderate and high forest fire disturbance sample plots, the carbon density of litter was 1.43, 0.94 and 0.81 t∙hm-2, which decreased by 28.14%, 52.76% and 59.30% respectively compared with the control group. The soil organic carbon density of the sample plots with different forest fire disturbance intensity is lower than that of the control group, and the reduction degree gradually decreases with the increase of soil profile depth. The soil organic carbon density of the sample plots with light, moderate and high forest fire disturbance is 103.30, 84.33 and 70.04 t∙hm-2 respectively, which is 11.670%, 27.899% and 40.11% lower than that of the control group respectively; the carbon density of forest ecosystem was 172.61, 120.95 and 86.35 t∙hm-2 after light, moderate and high forest fire disturbance, which decreased by 13.53%, 39.41% and 56.74% respectively compared with the control group; forest fire disturbance reduced the carbon density of eucalyptus forest, which showed a law of carbon density decreasing with the increase of forest fire disturbance intensity. Compared with the control group, the effect of light forest fire disturbance intensity on the carbon density of eucalyptus forest was not significant (P &gt; 0.05), while the effect of moderate and high forest fire disturbance intensity on the carbon density of eucalyptus forest was significant (P &lt; 0.05).

Land use and land cover change influence on soil organic carbon content for a pastoral area: use of geographical information system

Data on land use and cover change and soil organic carbon (SOC) in rangelands are essential. This is because rangelands ecosystems are fragile, and poor land-use practices can significantly threaten their sustainability by depleting SOC and increasing atmospheric carbon dioxide. This study investigated soil organic carbon variations as influenced by land use/land cover changes in the unprotected area of the Sanga agropastoral ecosystem, southwestern Uganda. Landsat images provided data for land use and cover for 1987 and 2020. Soil organic carbon contents were investigated in farmland (FL), grassland (GL), woodland (WL), and bare land (BL) as control at 0-15 cm and 15-30 cm depths. Soil samples were analyzed for organic carbon and bulk density using the colorimetric and core ring methods, respectively. Total soil organic carbon content was significantly high in grassland (31.55 Mg C ha-1), p=0.005, and woodland (27.89 Mg C ha-1), p=0.028 compared to bare land (16.17 Mg C ha-1). Additionally, total soil organic carbon concentration in grassland (2.10%) was higher than SOC concentration in farmland (1.39%) p=0.001 and bare land (1.00%), p&lt;0.001, respectively. Similarly, woodlands soil organic carbon concentration (1.98%) was higher than soil organic concentrations in bare lands, p=0.003 and farmlands, p=0.028. Bulk density was significantly different at lower horizons, with farmland having a higher bulk density than other land use types, p=0.013. Roots and litter inputs in woodlands and grasslands contributed to higher organic carbon than farmland and eroded/bare lands. Cultivation also increased the soil bulk density. This study concludes that land use and the land cover change affected soil organic carbon sequestration and bulk density. Therefore, farmers need to increase farm management practices to avoid an increase in bulk density. Further study to compare the effects of grazing intensity on SOC and modeling future SOC content in the study area is recommended.

Influences of Environmental Variables and Their Interactions on Chinese Farmland Soil Organic Carbon Density and Its Dynamics

Farmland is one of the most important and active components of the soil carbon pool. Exploring the controlling factors of farmland soil organic carbon density (SOCD) and its sequestration rate (SOCDSR) is vital for improving carbon sequestration and addressing climate change. Present studies provide considerable attention to the impacts of natural factors and agricultural management on SOCD and SOCDSR. However, few of them focus on the interaction effects of environmental variables on SOCD and SOCDSR. Therefore, using 64 samples collected from 19 agricultural stations in China, this study explored the effects of natural factors, human activities, and their interactions on farmland SOCD and SOCDSR by using geographical detector methods. Results of geographical detectors showed that SOCD was associated with natural factors, including groundwater depth, soil type, clay content, mean annual temperature (MAT), and mean annual precipitation. SOCDSR was related to natural factors and agricultural management, including MAT, groundwater depth, fertilization, and their interactions. Interaction effects existed in all environmental variable pairs, and the explanatory power of interaction effects was often greater than that of the sum of two single variables. Specifically, the interaction effect of soil type and MAT explained 74.8% of the variation in SOCD, and further investigation revealed that SOCD was highest in Luvisols and was under a low MAT (&lt;6 °C). The interaction effect of groundwater depth and fertilization explained 40.4% of the variation in SOCDSR, and fertilization was conducive to SOCD increase at a high groundwater depth (&lt;3 m). These findings suggest that low soil temperature, high soil moisture, and fertilization are conducive to soil carbon accumulation. These findings also highlight the importance of agricultural management and interaction effects in explaining SOCD and SOCDSR, which promote our knowledge to better understand the variation of SOCD and its dynamics.

Reassession of Topsoil Organic Carbon Density in China by Diagnostic Surface Horizon Method and Comparison of Two Topsoil Delineation Methods

Reassession of Topsoil Organic Carbon Density in China by Diagnostic Surface Horizon Method and Comparison of Two Topsoil Delineation Methods