Variability Of Organic Carbon Research Articles

Assessing spatiotemporal variations of soil organic carbon and its vulnerability to climate change: a bottom-up machine learning approach

Soil organic carbon (SOC) is a crucial component of the terrestrial carbon cycle and essential for agricultural productivity. Quantifying its sensitivity to future climate change is vital for sustaining agricultural practices and mitigating greenhouse gas emissions. However, this remains a challenge as long-term SOC data are scarce and substantial uncertainties regarding future climate scenarios. This study presents a bottom-up machine learning framework to assess the spatiotemporal variations of SOC and its vulnerability to climate change in the Jinghe River Basin, a typical loess hilly and gully watershed. Firstly, the long-term (2000-2023) dynamics of SOC was estimated by integrating in-situ measurements with machine learning techniques. Results show that the high SOC values are primarily distributed in the farmland of the mountain-loess transition zone, while the low-value areas are mainly found in the loess region. During the study period, the SOC content exhibited a slight increasing trend with a rate of 0.02 g kg⁻1 yr⁻1 (p = 0.449). The vulnerability of farmland surface SOC to future climate change was then evaluated by combining a robust machine learning model with the bottom-up framework. To this end, the study explored a wide range of possible future climates to identify critical climate thresholds and their spatial variation across the basin’s farmlands. Based on this analysis, this research found that the farmland in the northern basin is generally more susceptible to changing climate with even marginal rises in temperature could lead to severe loss in SOC. These results highlight the need for proactive climate adaptation strategies to safeguard SOC in vulnerable agricultural landscapes, ensuring soil health and resilience in the face of climate change.

Differential Spatiotemporal Patterns of Major Ions and Dissolved Organic Carbon Variations from Non-Permafrost to Permafrost Arctic Basins: Insights from the Severnaya Dvina, Pechora and Taz Rivers

The Arctic river basins, among the most sensitive regions to climate warming, are experiencing rapid temperature rise and permafrost thawing that profoundly affect their hydrological and hydrochemical systems. However, our understanding of chemical export from Arctic basins to oceans remains limited due to scarce data, particularly in permafrost-dominated regions. This study examines the spatiotemporal variations and seasonal dynamics of major ions (Na+, K+, Mg2+, Ca2+, Cl−, SO42−) and dissolved organic carbon (DOC) concentrations across three river basins with varying permafrost extents: the Severnaya Dvina (2006–2008, 2012–2014), the Pechora (2016–2019) and the Taz Rivers (2016–2020). All the data were sourced from published Chemical Geological researches and were taken from Mendeley and PANGAEA datasets. Our results showed that DOC concentrations ranged from 1.75 to 26.40 mg/L, with the Severnaya Dvina River exhibiting the highest levels of DOC concentrations, alongside significantly elevated ion concentrations compared to the other two basins. A positive correlation was observed between DOC concentrations and river discharge, with peaks during the spring flood and summer baseflow due to leaching processes. The Severnaya Dvina and Pechora Rivers exhibited the highest DOC values during the spring flood, reaching 26.40 mg/L and 8.07 mg/L, respectively. In contrast, the Taz River had the highest runoff during the spring flood season, but the DOC concentration reached its highest value of 11.69 mg/L in the summer. Specifically, a 1% increase in river discharge corresponded to a 1.25% rise in DOC concentrations in the Severnaya Dvina River and a 1.04% increase in the Pechora River, while there was no significant correlation between runoff and DOC concentrations in the Taz River. Major ion concentrations demonstrated a negative correlation with river discharge, remaining relatively high during winter low-flow period. A robust power-law relationship between river discharge and concentration of DOC and major ions was observed, with distinct variations across the three river basins depending on permafrost extent. The Pechora and Taz Rivers, characterized by extensive permafrost, exhibited increasing trends in river discharge and DOC concentrations, accompanied by decreasing major ion concentrations, whereas the non-permafrost-dominated Severnaya Dvina River basin showed the opposite pattern. The Taz River, with the most extensive permafrost, also displayed a delayed DOC peak and more complex seasonal ion concentration patterns. These findings highlight the importance of varying permafrost extents and their implications for water quality and environmental protection in these vulnerable regions.

Evaluating the impacts of area closure on soil properties in south central highland of Ethiopia

Soil degradation affects its quality and productivity of the land. To control soil degradation, various soil and water conservation (SWC) measures, including area closure are implemented. Understanding the impacts of SWC measures could support planning and implementation of land management practices. This study aimed to investigate impacts of area closure on soil properties in south central highland of Ethiopia. To acquire the necessary data, we conducted interviews with 80 households. Furthermore, nine years old area closure with physical soil and water conservation (AC-SWC), open grazing with physical SWC (OG-SWC), and open grazing without physical SWC (OG) were identified and each divided into upper, middle, and lower slope positions. In each slope position, 3 sample plots were established at 25–50 m intervals. A total of 27 composite samples and other 27 core samples for bulk density (3 treatments∗3 slope position∗3 replications) were collected and analyzed for soil properties. The data were analyzed using descriptive statistics and one-way ANOVA. The results showed that about 98 % of the respondents perceived that area closure would be an effective way to restore degraded land. Majority of the farmers (86 %) believed that area closure could reduce soil erosion and replenish soil fertility and thus, is beneficial in improving land productivity. Soil test results revealed that AC-SWC had significantly greater (P < 0.05) clay fractions, pH, available potassium, and available phosphorus than OG-SWC and OG. Variations of soil organic carbon (SOC) and total nitrogen (TN) were more pronounced. The SOC in AC-SWC was 83 % and 314 % greater than OG-SWC and OG, respectively. In the AC-SWC, TN was three and seven times higher than that of OG-SWC and OG, respectively. This could be due to vegetation restoration that reduces erosion, and enhances organic matter, moisture, and nutrient. The SOC, TN, pH, available potassium, and clay were significantly greater (P < 0.05) at lower slope position than upper in all forms of land management, which could be due to deposition at downslope. About 12 % and 11 % variations of clay fractions and SOC were, respectively, observed in between upper and lower slope positions at AC-SWC, but they varied by 25 % and 57 %, respectively, in OG. These imply area closure has had a beneficial effect on soil properties even on sloping land. AC-SWC is an important option to integrate in land management for rehabilitation of degraded soil.

Distribution characteristics of soil active organic carbon at different elevations and its effects on microbial communities in southeast Tibet.

Global mountain ecosystems have garnered significant attention due to their rich biodiversity and crucial ecological functions; however, there is a dearth of research on the variations in soil active organic carbon across altitudinal gradients and their impacts on microbial communities. In this study, soil samples at an altitude of 3,800 m to 4,400 m were collected from Sejira Mountain in the southeast Tibet, and soil active organic carbon components, soil microbial community diversity, composition and structure distribution and their relationships were systematically analyzed. The results revealed a non-linear relationship between the elevation and the contents of soil organic carbon (SOC) and easily oxidized organic carbon (ROC), with an initial increase followed by a subsequent decrease, reaching their peak at an altitude of 4,200 m. The Shannon diversity of bacteria exhibited a significant decrease with increasing altitude, whereas no significant change was observed in the diversity of fungi. The bacterial community primarily comprised Acidobacteria, Proteobacteria, Chloroflexi, and Actinobacteriota. Among them, the relative abundance of Proteobacteria exhibited a negative correlation with increasing altitude, whereas Actinobacteriota demonstrated a positive correlation with elevation. The fungal communities primarily consisted of Basidiomycota, Ascomycota, and Mortierellomycota, with Ascomycota prevailing at lower altitudes and Basidiomycota dominating at higher altitudes. The diversity and composition of bacterial communities were primarily influenced by altitude, SOC, ROC, and POC (particulate organic carbon). Soil carbon-to-nitrogen ratio (C/N), dissolved organic carbon (DOC), and available phosphorus (AP) emerged as key factors influencing fungal community diversity, while POC played a pivotal role in shaping the composition and structure of the fungal community. In conclusion, we believe that soil active organic carbon components had a greater impact on the bacterial community in the primary forest ecosystem in southeast Tibet with the elevation gradient increasing, which provided a theoretical basis for further understanding of the relationship between the microbial community and soil carbon cycle in the plateau mountain ecosystem under the background of climate change.

Pre-ozonation coupled with forward osmosis with fertilizer as draw solution for simultaneous wastewater treatment and agricultural irrigation

Membrane-based processes have emerged as effective solutions for treating tannery wastewater. Persistent membrane fouling remains a significant obstacle to long-term operational sustainability, and residual pollutants often persist in the treated effluent. To address these challenges, we investigated an integrated ozone-forward osmosis (O3-FO) process, with a focus on evaluating the efficacy of pre-ozonation in alleviating membrane fouling, as well as exploring the possibilities of this integrated process for the reuse of tannery wastewater. Fertilizer, specifically 2 M Ca(NO3)2, served as the draw solution (DS) in this process. The findings reveal that the integrated system demonstrated remarkable pollutant retention capabilities. Notably, no metal was detected in the fertilizer. Therefore, the integrated process not only dilutes the fertilizer but also minimizes the risk of heavy metal contamination to both crops and soil. Furthermore, pre-ozonation effectively mitigated membrane fouling, resulting in an increase in membrane flux with a maximum increase of 20.98 % at 0.6 L/min. Orthogonal partial least squares-discriminant analysis (OPLS-DA) revealed pre-ozonation has the most significant impact on four parameters: water flux (Jw), chemical oxygen demand (COD), fouling resistance (Rf) and oxidation reduction potential (ORP). Meanwhile, ammonium nitrogen (NH4-N) variation, dissolved organic carbon (DOC) variation and ORP played an important role in the four systems. Multi-criteria decision analysis (MCDA) showed that the 0.2 L/min O3-FO system achieved the highest score (0.66), followed by 0.6 L/min (0.53), 0.4 L/min (0.41) and 0 L/min (0.29). This research offers a theoretical framework for the synergistic integration of advanced oxidation and membrane technology in the treatment of industrial wastewater.

Temporal and Spatial Variations of Soil Organic Carbon and the Influencing Factors in Shaanxi Province in Recent 30 Years

Soil organic carbon （SOC） variation is a significant indicator for the soil quality dynamic and global carbon cycle. Therefore, it is necessary to study the regional temporal and spatial distribution of SOC pool and the influencing factors. In this study, a total of 540 soil data and environmental variables were collected from Shaanxi Province during a 30-year period from 1985 to 2015, and univariate analysis of variance and path analysis were used to explore the temporal and spatial distribution characteristics of SOC content and the influencing factors of SOC change. The results showed that the SOC contents of Shaanxi Province in both 1985 and 2015 were the highest in central Shaanxi, followed by those in southern Shaanxi, and they were significantly higher than those in northern Shaanxi. From 1985 to 2015, the increase in SOC in southern Shaanxi was the highest （21.28%）, and that in central Shaanxi was 15.33%. The content of SOC in northern Shaanxi was decreased by 10.23%, caused by significant decrements in the bottom horizons of 60-80 cm and 80-100 cm. Compared with that in 1985, the increases in SOC content in the 0-100 cm soil profile （with every 20 cm as a horizon） ranged from 3.21% to 29.39% in 2015. The increase in SOC content of skeletal soils was largest, followed by that of alluvial soils. Correlation analysis and path analysis showed that SOC content was positively correlated with altitude, average annual precipitation, normalized vegetation index, and total nitrogen content and was in significant negative correlation with curvature, bulk density, and pH. Total nitrogen content was the main controlling factor affecting SOC content. The results of the study can provide reference for future carbon management measures in the region.

Salinity increases under sea level rise strengthens the chemical protection of SOC in subtropical tidal marshes

The rise in sea levels due to global warming could significantly impact the soil organic carbon (SOC) pool in coastal tidal marshes by altering soil salinity and flooding conditions. However, the effects of these factors on SOC protection in coastal tidal marshes are not fully understood. In this study, we employed a space-for-time approach to investigate the variations in soil active carbon components and mineral-associated organic carbon under different salinity gradients (freshwater and brackish) and flooding frequencies (high and low tidal flats).The soil organic carbon (SOC) and easily oxidizable organic carbon (EOC) contents at the low-flooding frequency sites were higher than those at the high-flooding frequency sites. The dissolved organic carbon (DOC) content was higher at the high-salinity sites compared to the low-salinity sites, while the soil microbial biomass carbon (MBC) content was higher at the low-salinity sites than at the high-salinity sites. The EOC/SOC and DOC/SOC ratios were greater at the high-salinity sites than at the low-salinity sites, whereas the MBC/SOC ratios were higher at the low-salinity sites than at the high-salinity sites. Iron (Fe) and aluminum (Al) mineral-associated organic carbon [Fe(Al)-OC] and calcium-associated organic carbon (Ca-OC) contents were higher at the high-salinity sites compared to the low-salinity sites, and at the low-flooding frequency sites compared to the high-flooding frequency sites.Meanwhile, Fe(Al)-OC was the dominant fraction among mineral-associated organic carbon at all sites. The dominant phyla of bacterial community included Proteobacteria (49.31 %–66.36 %), Firmicutes (2.67 %–28.44 %), Chloroflexi (3.81 %–9.54 %), and Acidobacteria (4.28 %–7.02 %). In addition, Desulfobacca, a sulfate-reducing bacterium, promoted the formation of mineral-associated organic carbon.Random forest analysis showed that SOC and DOC were key factors in promoting mineral-associated organic carbon formation. Partial least squares path modeling (PLS-PM) indicated that sea level rise affects DOC content by altering soil physicochemical properties, promoting the formation of mineral-associated organic carbon.In summary, while soil organic carbon activity increases, the chemical association of minerals with organic carbon is becoming increasingly crucial for the protection of organic carbon under rising salinity conditions driven by sea level rise.

Estimation of top soil properties by Sentinel-2 imaging

ABSTRACT This study evaluated the feasibility of using free multispectral remote sensing data from Sentinel-2A satellites to predict soil properties in Northern Karnataka, India. Sentinel-2A images were downloaded for selected sites, covering Vertisol, Ultisol, and Alfisol soils. Multiple linear regression (MLR) models incorporated four Sentinel-2 bands and six spectral indices (NDVI, GNDVI, SAVI, TVI, EVI, and BI) as independent variables, with soil properties as dependent variables. Surface samples (0–15 cm depth) were collected from March to May 2022. The analysis showed significant correlations between individual bands and soil properties, with variations in Organic Carbon (OC) compared to sand, silt, clay, and pH. Sand positively correlated with all spectral indices, while silt, clay, and pH were negatively correlated. The red and Near-Infrared (NIR) bands showed a non-significant relationship with OC. No significant correlation was found between EVI and the soil properties. Strong regression coefficients were observed between Sentinel-2 predictions and laboratory measurements: sand (r² = 0.63), silt (r² = 0.73), clay (r² = 0.59), and pH (r² = 0.59). These results demonstrate the potential of Sentinel-2 data for predicting soil properties, offering a valuable tool for managing unsampled agricultural fields.

Fate of soil organic carbon in estuarine mangroves: Evidences from stable isotopes and lignin biomarkers

Coastal wetlands are increasingly recognized for their role in climate change mitigation, particularly through the sequestration of soil organic carbon (SOC). Despite widespread acknowledgement of their importance, the variation in organic carbon (OC) sources among different estuarine mangrove wetlands, and how these sources interact with environmental factors, is not fully elucidated. This research focuses on the role of estuarine mangrove wetlands in climate change mitigation through SOC sequestration. It explores the distribution, sources, and decomposition of SOC in a wetland with four mangrove communities along a tidal gradient. These include a tidal flat, a Sonneratia apetala forest, a mixed S. apetala and Kandelia obovata forest, and a K. obovata forest. The study employs biogenic element analysis (C, N, lignin phenols) and natural stable carbon isotope ratios (δ13C and δ15N) to assess SOC. Key findings show a decrease in SOC and total nitrogen (TN) from the upstream K. obovata forest to the downstream tidal flat. A stable isotope mixing model reveals a diminishing mangrove-derived OC contribution in topsoil (0–40 cm), estimated at 62 % in the K. obovata forest, 45 % in the central region, and 24 % in tidal flats. Soil profiles suggest microbial decomposition as the main isotope fractionation mechanism, with lignin analysis indicating woody angiosperms as the primary OC source. These findings enhance understanding of OC origins and decomposition in coastal wetlands and inform “blue carbon” management, highlighting the terrestrial-estuary continuum's significance.

Greater variation of soil organic carbon in limestone- than shale-based soil along soil depth in a subtropical coniferous forest within a karst faulted basin of China

Lithology strongly influences soil microbial traits and edaphic factors and in turn soil organic carbon (SOC) dynamics. However, the effect of lithology on microbial traits, edaphic factors and resulting SOC physical fractions variation along soil depth remains inadequately understood in karst faulted basin of China. This understanding is critical for improving SOC stability. By separating SOC into labile particulate organic carbon (POC) and stable mineral-associated organic carbon (MAOC) over karst limestone and non-karst shale soil in a subtropical coniferous forest, we aimed to assess potential regulatory mechanisms underlying lithology-associated SOC stability variations across soil depth by integrating soil nutrients, mineralogical characteristics, and microbial traits. We found that SOC and its fractions were higher in limestone than in shale soil, which implying vegetation restoration effects on SOC and its fractions partly depending on lithology. Additionally, we found that the effects of soil depth on SOC and its fractions were greater in limestone soils than shale soils, and the ratios of MAOC to SOC (MAOC:SOC) and MAOC to POC (MAOC:POC) show a opposite trend in response to soil depth between two the lithologies. Variation partitioning and random forest analyses revealed that among multiple factors, the variation of SOC stability assessed via MAOC:SOC was mainly explained by microbial traits than soil nutrients and mineral properties. Contrast to soil depth, structural equation modeling analyses showed that lithology was the primary factor controlling the SOC stability when microbial traits, soil nutrients and mineralogical characteristics were controlled as conditional variables. Overall, these results highlight the crucial role of lithology in regulating the SOC stability along soil depth, which improve our understanding and management of soil carbon (C) pool in karst faulted basin of southwest China.

Hydrology, vegetation, and soil properties as key drivers of soil organic carbon in coastal wetlands: A high-resolution study

Coastal wetlands are important blue carbon ecosystems that play a significant role in the global carbon cycle. However, there is insufficient understanding of the variations in soil organic carbon (SOC) stocks and the mechanisms driving these ecosystems. Here we analyze a comprehensive multi-source dataset of SOC in topsoil (0–20 cm) and subsoil (20–100 cm) across 31 coastal wetlands in China to identify the factors influencing their distribution. Structural equation models (SEMs) reveal that hydrology has the greatest overall effect on SOC in both soil layers, followed by vegetation, soil properties, and climate. Notably, the mechanisms driving SOC density differ between the two layers. In topsoil, vegetation type and productivity directly impact carbon density as primary sources of carbon input, while hydrology, primarily through seawater salinity, exerts the largest indirect influence. Conversely, in subsoil, hydrology has the strongest direct effect on SOC, with seawater salinity also influencing SOC indirectly through soil and vegetation mediation. Soil properties, particularly pH, negatively affect carbon accumulation, while climate influences SOC indirectly via its effects on vegetation and soil, with a diminishing impact at greater depths. Using Random Forest, we generate high-resolution maps (90 m × 90 m) of topsoil and subsoil carbon density (R2 of 0.53 and 0.62, respectively), providing the most detailed spatial distribution of SOC in Chinese coastal wetlands to date. Based on these maps, we estimate that SOC storage to a depth of 1 m in Chinese coastal wetlands totals 74.58 ± 3.85 Tg C, with subsoil carbon storage being 2.5 times greater than that in topsoil. These findings provide important insights into mechanism on driving spatial pattern of blue carbon and effective ways to assess carbon status on a national scale, thus contributing to the advancement of global blue carbon monitoring and management.

Functional and Microbiological Responses of Iron–Carbon Galvanic Cell-Supported Autotrophic Denitrification to Organic Carbon Variation and Dissolved Oxygen Shaking

Iron–carbon galvanic-cell-supported autotrophic denitrification (IC-ADN) is a burgeoning efficient and cost-effective process for low-carbon wastewater treatment. This study revealed the influence of organic carbon (OC) and dissolved oxygen (DO) on IC-ADN in terms of functional and microbiological characteristics. The nitrogen removal efficiency increased to 91.6% and 94.7% with partial organic carbon source addition to COD/TN of 1 and 3, respectively. The results of 16S rRNA high-throughput sequencing with nirS and cbbL clone libraries showed that Thiobacillus was the predominant autotrophic denitrifying bacteria (ADB) in the micro-electrolysis-based autotrophic denitrification, which obtained nitrogen removal efficiency of 80.9% after 96 h. The ADBs shifted gradually to heterotrophic denitrifying bacteria Thauera with increasing COD/TN ratio. DO concentration of 0.8 rarely affected the denitrification efficiency and the denitrifying communities. When the DO concentration increased to 2.8 mg/L, the nitrogen removal efficiency decreased to 69.1%. These results demonstrated that autotrophic denitrification was notably affected by COD/TN and high DO concentration, which could be used to acquire optimum conditions for nitrogen removal. These results provided an in-depth understanding of the influential factors for galvanic-cell-based denitrification and helped us construct a stable and highly efficient treatment process for insufficient carbon source wastewater.

Estimating spatiotemporal variations of cropland soil organic carbon and its sequestration potential in central China from 1984 to 2019

Assessing spatial and temporal changes in soil organic carbon (SOC) over time is crucial for understanding soil fertility and its impact on the global carbon cycle. This study analyzed the spatiotemporal changes of SOC in a typical agricultural region of the North China Plain from 1984 to 2019 and explored the potential for SOC sequestration. A total of 411 soil samples were collected in 1984, with subsequent sampling in 2009 (411 samples) and 2019 (181 samples). Geostatistical Sequential Gaussian Simulation (SGS) was utilized to quantify the spatiotemporal trends of SOC changes from 1984 to 2019. The SOC sequestration potential (SOCp) was estimated using the Levenberg-Marquardt and Universal Global Optimization algorithms. The results revealed a significant elevation in mean SOC from 5.84 g kg−1 in 1984 to 10.64 g kg−1 in 2019, with an increasing trend observed from the northwest towards the southeast. The SOC increase rate during 2009–2019 (0.48 t/ha yr−1) surpassed that of 1984–2009 (0.32 t/ha yr−1). The fine-textured soil in the north showed a faster increase in SOC compared to coarse-textured soils in the south. Estimated SOCp ranged from 2.81 to 24.34 t C/ha, with a mean of 12.43 t C/ha across the area. Loam clay, silt clay, clay loam and loam in the north exhibited lower SOCp (0–10 t C/ha) compared to sandy loam in the south. The time required to reach SOC saturation (Ts) was high (>20 years) in the south, an area dominated by sandy loam, compared to the north, with a low Ts (0–20 years) covered by fine-textured soil. These findings suggest croplands might be a potential carbon sink to be developed through sustainable and efficient agricultural management in this typical agricultural region of the North China Plain, particularly in the sandy loam of the region’s southern area.

High-resolution organic and black carbon records in the South Yellow Sea over the last century

The mud depositional area ("mud area") of the South Yellow Sea serves as a prominent carbon sink within the Eastern Continental Shelf of China, offering crucial insights into human activities and climate fluctuations and its relationship with carbon cycle. This study investigates variations in total organic carbon (TOC) and black carbon (BC) concentrations in South Yellow Sea sediments. By combining 210Pb isotope analysis with grain-size profiling, the study distinguishes organic carbon origins, revealing the complex interplay between human activities and environmental shifts since the Industrial Revolution. The reasons for discrepancies between TOC and BC contents are analyzed, yielding the following results: (1) Sediment core QY-2 predominantly contains terrestrial-sourced organic carbon, primarily derived from the Yellow River and the Yangtze River. (2) Temporal fluctuations of BC in core QY-2 show distinct trends, periodic responses to human activities, particularly peaks in 1937 and 1945, linked to large-scale wars in China. (3) Relaxed carbon emission regulations in China, coupled with industrial growth spurred by the “reform and opening up” policy, led to a continuous rise in BC content from the mid-1960s to the 1980s, peaking in 1980. Subsequently, reduced BC values during the 1990s correlated with emission control policies and the shift from highly polluting domestic coal stoves to cleaner alternatives like liquefied petroleum gas or natural gas stoves. (4) BC content was influenced by the East Asian monsoon and Pacific Decadal Oscillation (PDO), with higher BC accumulation rates occurring in summer and depletion in winter. (5) Interestingly, changes in BC and TOC content exhibited a negative correlation. While grain size and material sources minimally influenced these discrepancies, the primary driver lay in the water's redox environment, impacting other TOC components and thereby causing variations in both TOC and BC content. This study of black carbon sources to sinks in the South Yellow Sea Mud Area holds significant implications for the broader Yellow Sea sedimentary system and provides support for understanding carbon cycle and marine environments.

Variations in iron-bound organic carbon in soils along an altitude gradient and influencing factors in a subtropical mountain ecosystem of southern China

Variations in iron-bound organic carbon in soils along an altitude gradient and influencing factors in a subtropical mountain ecosystem of southern China

Spatial–Temporal Variations in Soil Organic Carbon and Driving Factors in Guangdong, China (2009–2023)

Spatial–temporal variation in soil organic carbon is an important factor for national targets to mitigate climate change and land degradation impacts. In this research, we took Guangdong Province of China as the study area, evaluated the spatial–temporal distributions of soil organic carbon using data from three China Geochemical Baseline projects (conducted in 2009, 2016, and 2023, respectively), and quantified the main driving factors of spatial–temporal variations in soil organic carbon using the random forest algorithm, further predicting the density and inventories of soil organic carbon. The results demonstrate that the mean value of SOC in Guangdong in 2009 was 0.81%; in 2016 it was 1.13%; and in 2023 it was 1.02%. The inventories of soil organic carbon (0–30 cm) in Guangdong Province were 0.61 Pg in 2009, 0.74 Pg in 2016, and 0.62 Pg in 2023. Soil in Guangdong acted as a carbon sink from 2009 to 2023 as a whole, and the most important driving force behind spatial–temporal variations in soil organic carbon was temperature, followed by precipitation and vegetation cover.

Responses of soil organic carbon compounds to phosphorus addition between tropical monoculture and multispecies forests

Tropical forests are sensitive to nitrogen (N) and phosphorus (P) availability, and under nutrient application the variation of soil organic carbon (SOC) preserving mechanism remains to be explored. To reveal the forest-specific SOC preservation via biochemical selection in response to nutrient application, we investigated a monoculture (Acacia plantation) and a multispecies forest both with chronic fertilization in subtropical regions, and measured specific fingerprints of plant- and microbial-derived C compounds. In addition, to quantify the effect of P application on SOC content among tropical forests, we conducted a meta-analysis by compiling 125 paired measurements in field experiments from 62 studies. In our field experiment, microbial community composition and activity mediated forest-specific responses of SOC compounds to P addition. The shift of community composition from fungi towards Gram-positive bacteria in the Acacia plantation by P addition led to the consumption of microbial residual C (MRC) as C source; in comparison, P addition increased plant species with less complex lignin substrates and induced microbial acquisition for N sources, thus stimulated the decomposition of both plant- and microbial-derived C. Same with our field experiment, bulk SOC content had neutral response to P addition among tropical forests in the meta-analysis, although divergences could happen among experimental durations and secondary tree species. Close associations among SOC compounds with biotic origins and mineral associated organic C (MAOC) in the multispecies forest suggested contributions of both plant- and microbial-derive C to SOC stability. Regarding that fungal MRC closely associated with MAOC and consisted of soil N pool which tightly coupled to SOC pool, the reduce of fungal MRC by chronic P addition was detrimental to SOC accumulation and stability in tropical forests.

Effect of Paleoenvironmental Conditions on the Distribution of Lower Carboniferous Shale in Yaziluo Rift Trough, South China: Insights from Major/Trace Elements and Shale Composition

Paleoenvironmental conditions significantly influence the distribution patterns and organic matter enrichment of shale. This study investigated the vertical variations of major elements, trace elements, and total organic carbon (TOC) in the Lower Carboniferous marine shale from the Yaziluo Rift Trough, South China, to understand the paleoenvironmental conditions, including redox conditions, terrigenous detrital input, paleoproductivity, and paleo-seawater depth. The Lower Carboniferous formation consists of three sedimentary facies: basin facies, lower slope facies, and upper slope facies. From the basin to the lower slope and then to the upper slope facies, TOC, quartz, and pyrite contents gradually decrease, whereas the carbonate mineral content shows an increasing trend. A continuous decline in paleo-seawater depth transformed a deep-water anoxic environment with high paleoproductivity and low detrital input in the basin facies into a semi-deep-water environment with dysoxic-oxic conditions and moderate detrital influx in the lower slope facies, evolving further into a suboxic environment with high detrital flux in the upper slope facies. The geochemistry results suggest that anoxic conditions and high paleoproductivity were the primary controls on organic matter enrichment in the siliceous shale of the basin facies. In contrast, redox conditions significantly influenced organic matter accumulation in the mixed shale of the lower slope facies, attributed to relatively low paleoproductivity in a more restricted marine setting. Additionally, the adsorption of carbon components by clay minerals facilitated the preservation of organic matter in the calcareous shale of the upper slope facies.

Variation in soil organic carbon with structural composition of mangrove species in the Sundarbans

The world's biggest continual mangrove swampy land is the Sundarbans Mangrove Forest, which is crucial to both the terrestrial and marine carbon cycles. While numerous studies have focused on organic carbon variations within this ecosystem, few have explored the interaction between carbon stocks and the structural composition of mangrove species. This study sought to investigate the connection between soil organic carbon accumulation and functional attributes of vegetation (DBH, basal area). This study was carried out on four vegetative and two non-vegetative plots in three different sites within the oligohaline zone. Based on species Iv, the Karamjol area was prevalent by Heritiera fomes (Iv =139.3). In contrast, the Ghagramari area was predominated by Avicennia officinalis (IV =105.1). Accumulation of TBC, Avicennia officinalis presented the highest, despite having a smaller number of individuals within the study area. 1 m soil core was pulled out from each subplot of each main plot by using a one-meter-long open face peat auger. The forest areas exhibited maximum soil organic carbon accumulation, which was significantly (p < 0.01) higher than non-vegetative areas. Moreover, the mean soil C/N ratios in the Karamjol area (13.4±0.2) and Ghagramari area (13.2± 0.2) were significantly (p < 0.01) greater than those in the non-vegetative area (12.3±0.1). These findings suggest that regardless of the dominant species, species richness, or size (tall or dwarf) of the mangroves, a particular quantity of organic carbon is captured within the mangrove soil. Thus, when making future decisions, it is crucial to repute the role of the Sundarbans mangrove in the accumulation of organic and biomass carbon, which can directly affect mitigating global warming.

Variation of root traits and its influences on soil organic carbon stability in response to altered precipitation in an alpine meadow

Soil organic carbon (SOC) dynamics are strongly controlled by plant roots. Yet, how variation of root traits under precipitation change influences SOC stability remains unclear. As part of a 5-year field experiment manipulating precipitation including 90 % (0.1P), 50 % (0.5P), 30 % (0.7P) decrease, and 50 % increase (1.5P), this study was designed to assess the effects of changing precipitation on root traits and production dynamics by minirhizotron and examine how such influences regulate SOC stability in an alpine meadow on the Qinghai-Tibetan Plateau. We found that root length density (RLD), specific root length (SRL), root branching intensity (RBI), and root residue carbon input (RC input) exhibited no significant response, whereas root turnover (RT), root carbon (C), nitrogen (N) concentrations and C/N ratio were altered by precipitation change with nonlinear trends. Absorptive root RT positively correlated to manipulated precipitation within the interannual precipitation range in topsoil, but it showed no significant change under extreme drought treatment. Alpine meadows can maintain the SOC content and density under varied precipitation. However, it showed significant variation in aggregate stability and organic carbon (OC) distribution in aggregates in topsoil, which were mainly due to the strong direct effects of soil moisture and partly related to RLD and RC input of transport roots. Although subsurface soil aggregate stability and OC associated with aggregates were not modified, our results indicated a risk of SOC stability variation in subsurface soil if absorptive root RT and SRL changed. These findings provide vital information to predict responses of SOC dynamics of alpine meadow to future climate change.