Soil Carbon Pools Research Articles

Shifts in C-degradation genes and microbial metabolic activity with vegetation types affected the surface soil organic carbon pool

The incorporation of plant-derived biomass by microorganisms into deceased microbial biomass, i.e., a “microbial carbon pump”, is essential for forming a soil carbon (C) pool. Therefore, microbial communities and associated functions could shape the formation of soil organic C (SOC) composition and persistence. However, the mechanism by which microorganisms mediate the degradation of various types of biomass (such as plant or microbial) and its impact on SOC formation under different vegetation types remains unclear. Herein, we analyzed microbial communities, carbohydrate-activated enzymes (CAZymes), absolute quantification of C-degradation genes, and extracellular enzyme activities to track microbial-mediated SOC formation under three vegetation types on the Loess Plateau. Changes in vegetation type influenced microbial community structure and distributions of certain bacterial groups. Specifically, dominant bacterial taxa shifted from oligotrophic Actinobacteria to eutrophic Proteobacteria from grass to forest soil. The proportion of microbial CAZymes responsible for decomposing plant-derived components (86–89%) exceeded that of microbial-derived components (11–14%), suggesting a greater capacity for the degradation of deceased plant biomass by microorganisms. There was a reduction of 14%–17% in the absolute abundance of specific C-degradation genes for hemicellulose and cellulose in forest soil compared to grass, while an increase of 20%–32% was observed in lignin and chitin degradation. This indicated a higher decomposition potential of lignin and chitin by microorganisms in forest soil. The number of CAZymes genes involved in the degradation of bacteria-derived biomass (peptidoglycan) was higher than fungi-derived biomass (chitin and glucans) and had a close correlation with the qCO2, microbial biomass C (MBC), and particulate organic C (POC). The abundance of C-degrading genes increased with the increase in the corresponding enzyme activity, indicating that enzyme activity is regulated by functional genes. In conclusion, shifts in CAZymes genes encoding for the degradation of diverse carbon sources could impact microbial metabolic activity through a microbial “carbon pump” regulation process. This mechanism could facilitate the formation of soil organic carbon and its fractions across different vegetation types.

The Seasonal Impact of Thinning Intensities on Soil Carbon Cycling in the Lesser Xing’an Range, Northeast China

Forest degradation, driven by human and natural factors, diminishes ecological functions and carbon storage. Understanding the complex dynamics of soil carbon pools is crucial for the global carbon cycle, although these dynamics are poorly understood. This study examines how different thinning intensities influence seasonal soil carbon cycling in degraded forests. ANOVA revealed significant differences in soil properties across treatments (p < 0.05). Redundancy analysis and random forest analyses were used to explore relationships among thinning intensities, soil properties, and carbon sequestration. Thinning significantly altered soil attributes, as revealed by field experiments and data analysis. Moderate thinning (20% intensity) significantly enhanced litter retention and soil nutrient levels year-round (p < 0.05). Seasonal variations affected soil carbon dynamics and lower thinning intensities improved carbon sequestration in spring and summer. Conversely, higher thinning intensities led to carbon loss in autumn and winter. Litter carbon, fine root carbon, and correction factor significantly respond to thinning intensities year-round as examined through redundancy analysis and random forest analyses. Findings indicate moderate thinning effectively enhances soil carbon sequestration in degraded forests. Strategically planned thinning could aid climate change mitigation by boosting forest soil carbon storage, influencing forest management and conservation.

Carbon stocks and effluxes in mangroves converted into aquaculture: a case study from Banten province, Indonesia

Aquaculture is one of the main drivers of mangrove loss across Southeast Asian countries. The conversion of mangroves to aquaculture generates substantial loss of carbon stocks and reduces carbon storage capacity. Here, we present total ecosystem carbon stocks (TECS), carbon dioxide (CO2) and methane (CH4) effluxes obtained from mangrove forests (fringe and interior mangroves), silvofishery aquaculture ponds (dense and sparse mangroves), and non-silvofishery aquaculture ponds in Sawah Luhur, Banten, Indonesia. We found no significant difference in TECS across five land uses, ranging from 261 ± 14 Mg C ha-1 in non-silvofishery ponds to 574 ± 119 Mg C ha-1 in fringe mangroves. Most of these stocks were found in the soil carbon pool (87%) in fringe and interior mangroves. However, the conversion of mangroves to aquaculture ponds resulted in soil carbon loss from -6% to 60%. The highest soil CO2 effluxes during dry and wet seasons were observed in interior mangroves (151 ± 12 mg CO2 m-2 h-1). The highest soil CH4 effluxes were found in fringe mangroves with 0.13 ± 0.04 mg CH4 m-2 h-1. The highest aquatic CO2 and CH4 effluxes were found in dense silvofishery ponds, at 118 ± 7 mg CO2 m-2 h-1 and 0.38 ± 0.04 mg CH4 m-2 h-1, respectively. Our findings suggest that land use that includes mangroves (i.e., mangrove forest and/or silvofishery ponds) tends to have higher carbon stocks, soil, and aquatic CO2 and CH4 effluxes, compared to aquaculture ponds without mangroves. It is therefore crucial to maintain mangroves for natural carbon capture and storage through carbon stock enhancement.

Emergent temperature sensitivity of soil organic carbon driven by mineral associations

Soil organic matter decomposition and its interactions with climate depend on whether the organic matter is associated with soil minerals. However, data limitations have hindered global-scale analyses of mineral-associated and particulate soil organic carbon pools and their benchmarking in Earth system models used to estimate carbon cycle–climate feedbacks. Here we analyse observationally derived global estimates of soil carbon pools to quantify their relative proportions and compute their climatological temperature sensitivities as the decline in carbon with increasing temperature. We find that the climatological temperature sensitivity of particulate carbon is on average 28% higher than that of mineral-associated carbon, and up to 53% higher in cool climates. Moreover, the distribution of carbon between these underlying soil carbon pools drives the emergent climatological temperature sensitivity of bulk soil carbon stocks. However, global models vary widely in their predictions of soil carbon pool distributions. We show that the global proportion of model pools that are conceptually similar to mineral-protected carbon ranges from 16 to 85% across Earth system models from the Coupled Model Intercomparison Project Phase 6 and offline land models, with implications for bulk soil carbon ages and ecosystem responsiveness. To improve projections of carbon cycle–climate feedbacks, it is imperative to assess underlying soil carbon pools to accurately predict the distribution and vulnerability of soil carbon.

Characterization of an In-Situ Soil Organic Carbon (SOC) via a Smart-Electrochemical Sensing Approach.

Soil is a vital component of the ecosystem that drives the holistic homeostasis of the environment. Directly, soil quality and health by means of sufficient levels of soil nutrients are required for sustainable agricultural practices for ideal crop yield. Among these groups of nutrients, soil carbon is a factor which has a dominating effect on greenhouse carbon phenomena and thereby the climate change rate and its influence on the planet. It influences the fertility of soil and other conditions like enriched nutrient cycling and water retention that forms the basis for modern 'regenerative agriculture'. Implementation of soil sensors would be fundamentally beneficial to characterize the soil parameters in a local as well as global environmental impact standpoint, and electrochemistry as a transduction mode is very apt due to its feasibility and ease of applicability. Organic Matter present in soil (SOM) changes the electroanalytical behavior of moieties present that are carbon-derived. Hence, an electrochemical-based 'bottom-up' approach is evaluated in this study to track soil organic carbon (SOC). As part of this setup, soil as a solid-phase electrolyte as in a standard electrochemical cell and electrode probes functionalized with correlated ionic species on top of the metalized electrodes are utilized. The surficial interface is biased using a square pulsed charge, thereby studying the effect of the polar current as a function of the SOC profile. The sensor formulation composite used is such that materials have higher capacity to interact with organic carbon pools in soil. The proposed sensor platform is then compared against the standard combustion method for SOC analysis and its merit is evaluated as a potential in situ, on-demand electrochemical soil analysis platform.

Quantifying carbon pool in ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia.

Ex-mining lake-converted constructed wetlands play a significant role in the carbon cycle, offering a great potential to sequester carbon and mitigate climate change and global warming. Investigating the quantity of carbon storage capacity of ex-mining lake-converted constructed wetlands provides information and justification for restoration and conservation efforts. The present study aims to quantify the carbon pool of the ex-mining lake-converted constructed wetlands and characterise the physicochemical properties of the soil and sediment. Pearson's correlation and a one-way ANOVA were performed to compare the different sampling stations at Paya Indah Wetland, Selangor, Malaysia. An analysis of 23years of ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia, revealed that the estimated total carbon pool in soil and sediment accumulated to 1553.11 Mg C ha-1 (equivalent to 5700 Mg CO2 ha-1), which translates to an annual carbon sink capacity of around 67.5 Mg C ha-1 year-1. The characterisation showed that the texture of all soil samples was dominated by silt, whereas sediments exhibited texture heterogeneity. Although the pH of the soil and sediment was both acidic, the bulk density was still optimal for plant growth and did not affect root growth. FT-IR and WDXRF results supported that besides the accumulation and degradation of organic substances, which increase the soil and sediment carbon content, mineral carbonation is a mechanism by which soil and sediment can store carbon. Therefore, this study indicates that the ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia have a significant carbon storage potential.

Possible hazards from biodegradation of soil plastic mulch: Increases in microplastics and CO2 emissions

Biodegradable mulches are widely recognized as ecologically friendly substances. However, their degradation percentage upon entering soils may vary based on mulch type and soil microbial activities, raising concerns about potential increases in microplastics (MPs). The effects of using different types of mulch on soil carbon pools and its potential to accelerate their depletion have not yet well understood. Therefore, we conducted an 18-month experiment to investigate mulch biodegradation and its effects on CO2 emissions. The experiment included burying soil with biodegradable mulch made of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT), and control treatments with traditional mulch (PE) and no mulch (CK). The results indicated that PE did not degrade, and the degradation percentage of PLA and PBAT were 46.2% and 88.1%, and the MPs produced by the degradation were 6.7 × 104 and 37.2 × 104 items/m2, respectively. Biodegradable mulch, particularly PLA, can enhance soil microbial diversity and foster more intricate bacterial communities compared to PE. The CO2 emissions were 0.58, 0.74, 0.99, and 0.86 g C/kg in CK, PE, PLA, , PBAT, respectively. A positive correlation was observed between microbial abundance and diversity with CO2 emissions, while a negative correlation was observed with soil total organic carbon. Biodegradable mulch enhanced the transformation of soil organic C into CO2 by stimulating microbial activity.

Predicting organic carbon in European soils: Only in Southern Ukraine can we expect an increase in humus content

Soil organic carbon comprises the majority of the terrestrial soil carbon pool and plays an important role in the global carbon cycle and balance. Even minor changes in soil organic carbon (SOC) can have a significant impact, not only on climate but also on ecosystem stability, due to its key role in soil-atmosphere carbon exchange, plant growth, and food production. In order to assess the feedbacks between the terrestrial carbon cycle and climate change, and to maintain ecosystem functions, it is crucial to understand the spatial and temporal changes in SOC and the drivers of these changes. The role of soil as a source or sink of atmospheric CO2 is primarily influenced by changes in climate and soil water content. Climate change, particularly global warming, can have a direct or indirect impact on the decomposition of organic matter by regulating soil microbes and fauna, enzyme activity, and soil respiration. A warming climate may increase the loss of soil carbon to the atmosphere because warming has a stronger effect on respiration than on photosynthesis, resulting in a positive soil carbon-climate feedback. Climate warming can significantly affect soil organic matter stocks, with the magnitude of the effect largely dependent on the initial organic matter stock size. Soil carbon content is a crucial aspect of terrestrial ecosystems that affects their functional properties and the climate. Conversely, climate also has an impact on soil organic carbon content. The spatial variability of soil organic carbon content and the predictions made for the west-central European region are also important considerations. The study identified the spatial variation of soil organic carbon throughout Europe and forecast its dynamics in the next 50–70 years, considering global climate change. Digital soil mapping enables a more precise representation of soil properties in space, including the spatial quantification of prediction errors. The accuracy of these predictions increases as more local observations, such as soil profiles, are available to construct the prediction model. Digital soil mapping allows flexible spatial development of soil property maps. Soil properties, such as nutrient concentration and stocks, carbon, heavy metals, pH, cation exchange capacity, and physical properties like particle size and bulk density, can be modelled at different depths and spatial resolutions depending on the project's objectives and available input data. The r GSOCmap project used a 1 km grid to model soil organic matter content. In Europe, the range of soil organic carbon content is from 0 to 750 t/ha, with a mean of 78.1 t/ha and a standard deviation of 50.1 t/ha. Climatic factors were found to account for 29% of the variation in soil organic carbon based on regression analysis. The study revealed that an increase in air temperature leads to a decrease in soil organic carbon content, while an increase in precipitation results in an increase in this indicator. Additionally, the content of soil organic matter is negatively impacted by an increase in the seasonality of precipitation. According to the forecast, global climate change will cause an increase of 1.0–1.1 t/ha in the organic carbon content of 3.6% of the continent's area over the next 70 years. On 7.6% of the area, the changes will be insignificant. The soil organic carbon content is expected to decrease on 88.9% of the area. Of this, 35.1% will experience a slight decrease in carbon content by 0–1 t/ha, 28.4% will experience a moderate decrease in soil organic carbon content by 1.0–1.1 t/ha, and 25.3% will experience a significant decrease by 1.1–1.3 t/ha. The Baltic countries, Belarus, and the Black Earth zone of Russia are at the highest risk. The risk of Russia becoming highly dependent on food imports is increased by this fact. The prospects for Ukraine are quite optimistic. Even in the northern Azov region, we can expect an intensification of humus accumulation processes in the near future, mainly due to increased precipitation. Precipitation in southern Ukraine is a limiting factor that significantly affects agricultural productivity. Increased precipitation and organic matter growth in the soil present positive prospects for agriculture in southern Ukraine, including the northern Azov, Black Sea, and Crimea. It is possible that the occupation of these territories, which are promising for agricultural production, is one of the goals of Russian armed aggression against Ukraine.

Optimizing nitrogen and phosphorus application to improve soil organic carbon and alfalfa hay yield in alfalfa fields.

Soil organic carbon (SOC) is the principal factor contributing to enhanced soil fertility and also functions as the major carbon sink within terrestrial ecosystems. Applying fertilizer is a crucial agricultural practice that enhances SOC and promotes crop yields. Nevertheless, the response of SOC, active organic carbon fraction and hay yield to nitrogen and phosphorus application is still unclear. The objective of this study was to investigate the impact of nitrogen-phosphorus interactions on SOC, active organic carbon fractions and hay yield in alfalfa fields. A two-factor randomized group design was employed in this study, with two nitrogen levels of 0 kg·ha-1 (N0) and 120 kg·ha-1 (N1) and four phosphorus levels of 0 kg·ha-1 (P0), 50 kg·ha-1 (P1), 100 kg·ha-1 (P2) and 150 kg·ha-1 (P3). The results showed that the nitrogen and phosphorus treatments increased SOC, easily oxidized organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC), microbial biomass carbon (MBC) and hay yield in alfalfa fields, and increased with the duration of fertilizer application, reaching a maximum under N1P2 or N1P3 treatments. The increases in SOC, EOC, DOC, POC, MBC content and hay yield in the 0-60 cm soil layer of the alfalfa field were 9.11%-21.85%, 1.07%-25.01%, 6.94%-22.03%, 10.36%-44.15%, 26.46%-62.61% and 5.51%-23.25% for the nitrogen and phosphorus treatments, respectively. The vertical distribution of SOC, EOC, DOC and POC contents under all nitrogen and phosphorus treatments was highest in the 0-20 cm soil layer and tended to decrease with increasing depth of the soil layer. The MBC content was highest in the 10-30 cm soil layer. DOC/SOC, MBC/SOC (excluding N0P1 treatment) and POC/SOC were all higher in the 0-40 cm soil layer of the alfalfa field compared to the N0P0 treatment, indicating that the nitrogen and phosphorus treatments effectively improved soil fertility, while EOC/SOC and DOC/SOC were both lower in the 40-60 cm soil layer than in the N0P0 treatment, indicating that the nitrogen and phosphorus treatments improved soil carbon sequestration potential. The soil layer between 0-30 cm exhibited the highest sensitivity index for MBC, whereas the soil layer between 30-60 cm had the highest sensitivity index for POC. This suggests that the indication for changes in SOC due to nitrogen and phosphorus treatment shifted from MBC to POC as the soil depth increased. Meanwhile, except the 20-30 cm layer of soil in the N0P1 treatment and the 20-50 cm layer in the N1P0 treatment, all fertilizers enhanced the soil Carbon management index (CMI) to varying degrees. Structural equation modeling shows that nitrogen and phosphorus indirectly affect SOC content by changing the content of the active organic carbon fraction, and that SOC is primarily impacted by POC and MBC. The comprehensive assessment indicated that the N1P2 treatment was the optimal fertilizer application pattern. In summary, the nitrogen and phosphorus treatments improved soil fertility in the 0-40 cm soil layer and soil carbon sequestration potential in the 40-60 cm soil layer of alfalfa fields. In agroecosystems, a recommended application rate of 120 kg·ha-1 for nitrogen and 100 kg·ha-1 for phosphorus is the most effective in increasing SOC content, soil carbon pool potential and alfalfa hay yield.

Effects of Straw Return Duration on Soil Carbon Fractions and Wheat Yield in Rice–Wheat Cropping System

In China’s subtropical rice–wheat cropping system, the changes in the soil organic carbon (SOC) pool due to long-term straw return and its connection with crop yield remain unclear. This study aims to provide insights into establishing a sensible straw return system by evaluating the differences in the distribution and variation rates of SOC, light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) in the 0–20 cm soil layer under different durations of straw return. Additionally, the study analyzes the relationship between the changes in SOC and its fractions and wheat yield. The experiment was conducted in 2019 in a rice–wheat rotation field with ten years of straw return treatments: no straw return (NR) or 1, 2, 3, 4, 5, 6, 7, 8, 9 year(s) of straw return (SR1–9), and an additional treatment in 2020 (10 years of straw return, SR10). The results revealed that with an increase in the duration of straw return, the contents of SOC, LFOC, HFOC, and POC gradually increased, showing the highest increments of 45.88%, 187.22%, 41.55%, 97.89%, and 28.21%, respectively, compared to the NR treatment. However, after eight years of straw return, the compound annual increase in soil organic carbon and its components was lower than in years 1–8, indicating a trend of diminishing increments. The SOC content and its variation were significantly correlated with the content and variation of LFOC, HFOC, POC, and MOC, with the highest sensitivity observed for the variation in LFOC, indicating the strong influence of the duration of straw return. The SOC and its fraction contents showed significant positive correlations with wheat yield, with the highest contribution to wheat yield increase attributed to an increase in LFOC content. In summary, straw return enhances the 0–20 cm deep soil carbon pool, with LFOC being the most sensitive indicator, reflecting the influence of the duration of straw return on soil carbon pools.

Soil Carbon and Nitrogen Pools and Their Storage Characteristics under Different Vegetation Restoration Types on the Loess Plateau of Longzhong, China

Soil carbon and nitrogen pools are crucial for maintaining the balance of carbon and nitrogen cycling in ecosystems and also for reducing the impacts of global climate change. However, current research lacks an understanding of the effects of long-term vegetation restoration on soil carbon and nitrogen pools and their storage in vulnerable ecosystems. Therefore, we studied the characteristics of soil carbon (soil organic carbon, microbial biomass carbon, dissolved organic carbon) and nitrogen pools (total nitrogen, ammonium nitrogen, nitrate nitrogen) and their storage under four types of vegetation restoration (Stipa bungeana Trin., SB; Caragana korshinskii Kom., CK; Xanthoceras sorbifolia Bunge., XS; Picea asperata Mast., PA) in the Longzhong Loess Plateau area. We found that the carbon and nitrogen pools in the 0–40 cm soil layer under the XS and PA vegetation restoration types were higher compared to those under the SB and CK vegetation, and the values of soil ammonium–nitrogen ratios ranged from 0.72 to 0.83 under different vegetation types. Carbon and nitrogen interactions were stronger in the 0–40 cm soil under PA vegetation, which had significantly higher soil carbon (49.06 t·ha−1) and nitrogen (1.78 t·ha−1) storage than did the other vegetation types. We also found that soil carbon and nitrogen stores differed among different types of vegetation restoration. These elements were mainly distributed in soils from 0 to 20 cm depth, where the carbon and nitrogen pools in soils from 0 to 10 cm exceeded those in the lower layers. Furthermore, we discovered that redundancy analysis (RDA) supported by soil enzyme activity and physical properties significantly explained the variation in soil carbon and nitrogen triggered by vegetation restoration. According to this research, the stability and transformation of soil carbon and nitrogen pools in the region can be influenced by various forms of vegetation restoration. Additionally, the findings highlight that forest vegetation restoration can be a successful strategy for effectively sequestering soil carbon and nitrogen within the Longzhong Loess Plateau area.

Grey alder at the regeneration stage: Long-term effects on soil nitrogen and carbon pools and Norway spruce growth

Increasing soil N availability is an effective way to enhance soil organic carbon (SOC) sequestration and biomass production in N-limited ecosystems such as boreal Norway spruce forests. Alder has a root nodule symbiosis with Frankia, an N2-fixing bacterium, and can thus add considerable amounts of N to soil mainly through its N-rich leaf litter. The objective of this study was to determine whether the presence of grey alder at the regeneration stage had any long-term effects on soil C and N cycling and stocks and spruce growth. The study sites were two relatively fertile 40-year-old Norway spruce stands (Luhdansuo and Porkkola) in Southern Finland. At both study sites, half the spruce stand had an admixture of grey alders for approximately 10–15 years after regeneration (alder treatment), but no alder had been present in the other half (control treatment). Alders were cut from the alder treatment 25 (Luhdansuo) or 30 (Porkkola) years before the measurements. At Porkkola, alder treatment received ash fertilisation 13 years ago. We observed no significant differences in the plant-available N fluxes, measured with a microdialysis technique, or SOC stocks between treatments. The total N stock (organic horizon + 0–30 cm mineral soil) and organic horizon thickness were larger, while the microbial biomass C:N and C mineralisation rate were lower in the alder versus the control treatment at Luhdansuo. The annual ring widths of spruces were larger in the alder versus the control treatment for up to six years after alder removal at both sites, but no differences were observed in the current tree diameters or diameter increments. In conclusion, most of the current soil or tree properties did not differ significantly between treatments, possibly because the effect of alder had faded out over the 25–30 years since its removal, and because the sites were initially relatively fertile.

Effects of long-term afforestation on soil water and carbon in the Alxa Plateau.

Plantations in dry and semi-arid areas significantly affect the soil's ability to store carbon and maintain a stable water balance. It is yet unclear, though, how planted trees in these regions might impact the soil's carbon and water levels. As a forest ages, it is unknown how soil water and soil carbon interact with one another. In order to conduct this study, four Saxaul plantations in the Alxa Plateau were chosen, with the neighboring mobile sandy (MS) ground serving as a control. The ages of the plantations ranged from 5 to 46 years. The major topics of the study included the relationship between soil water and soil carbon, changes in the 0-300 cm soil layer's soil water content (SWC), soil organic carbon (SOC), and soil inorganic carbon (SIC) following afforestation. The findings demonstrated that, in comparison to MS, afforestation considerably increased SOC and SIC stocks. In comparison to MS, the SIC grew by 4.02 kg m-2, 4.12 kg m-2, 5.12 kg m-2, and 6.52 kg m-2 throughout periods of 5 years, 11 years, 22 years, and 46 years, respectively. SOC increased relative to MS by 2.55 kg m-2, 2.91 kg m-2, 3.53 kg m-2, and 4.05 kg m-2. Afforestation, however, also contributed to a considerable decline in deep SWC and an increase in the soil water deficit (SWD). In comparison to MS, the mean SWC values were lower at 5 years, 11 years, 22 years, and 46 years, respectively, by 0.48%, 1.37%, 1.56%, and 4.00%. The increase in soil carbon pool caused by sand afforestation actually came at the expense of a reduction in soil water due to a large negative association between deep SWC, SOC, and SIC. To limit SWC losses and encourage sustainable forest land development, we advocate suitable harvest management practices on forest land.

Improving model performance in mapping cropland soil organic matter using time-series remote sensing data

Faced with increasing global soil degradation, spatially explicit data on cropland soil organic matter (SOM) provides crucial data for soil carbon pool accounting, cropland quality assessment and the formulation of effective management policies. As a spatial information prediction technique, digital soil mapping (DSM) has been widely used to spatially map soil information at different scales. However, the accuracy of digital SOM maps for cropland is typically lower than for other land cover types due to the inherent difficulty in precisely quantifying human disturbance. To overcome this limitation, this study systematically assessed a framework of “information extraction-feature selection-model averaging” for improving model performance in mapping cropland SOM using 462 cropland soil samples collected in Guangzhou, China in 2021. The results showed that using the framework of dynamic information extraction, feature selection and model averaging could efficiently improve the accuracy of the final predictions (R2: 0.48 to 0.53) without having obviously negative impacts on uncertainty. Quantifying the dynamic information of the environment was an efficient way to generate covariates that are linearly and nonlinearly related to SOM, which improved the R2 of random forest from 0.44 to 0.48 and the R2 of extreme gradient boosting from 0.37 to 0.43. Forward recursive feature selection (FRFS) is recommended when there are relatively few environmental covariates (<200), whereas Boruta is recommended when there are many environmental covariates (>500). The Granger-Ramanathan model averaging approach could improve the prediction accuracy and average uncertainty. When the structures of initial prediction models are similar, increasing in the number of averaging models did not have significantly positive effects on the final predictions. Given the advantages of these selected strategies over information extraction, feature selection and model averaging have a great potential for high-accuracy soil mapping at any scales, so this approach can provide more reliable references for soil conservation policy-making.

Soil Carbon Pool Allocation Dynamics During Soil Development in the Lower Yangtze River Alluvial Plain

The allocation dynamics of soil carbon pools during soil development and land use are the key to revealing the carbon cycle process. To clarify the distribution of the soil carbon pool and its change trend, a soil reclamation chronosequence (0 a, 60 a, 160 a, 280 a, 1 000 a, and 1 500 a reclamation) was established in a typical alluvial plain in the Lower Yangtze River, and the content and density of soil organic carbon (SOC), soil inorganic carbon (SIC), particulate organic carbon (POC), and mineral-associated organic carbon (MAOC), along with carbon sequestration potential (CSP) indicators of topsoil under different land use types were measured and analyzed. The results showed that after approximately 1 500 a reclamation, the SOC content developed from the Yangtze River alluvial deposits generally increased by 4.9% after the initial decline, whereas the SIC content decreased to 0.2% from 25.8% of the total carbon content due to its rapid leaching. The MAOC content was normally higher than that of POC, and MAOC was contributing 48.0%-79.7% of the SOC accumulation. In this region, the soil organic carbon density (SOCD) accounted for 57.4%-100% of the total carbon density, the soil carbon sequestration levels (CSL) ranged from 18.6% to 56.1%, and CSP under paddy-dryland rotation increased by 20.8% compared to that under dryland. The C/N ratio and total nitrogen content are key factors in explaining soil carbon accumulation processes, and the reclamation year plays an important role in evaluating soil carbon sequestration levels. After long-term utilization, the cultivated soil in the Yangtze River floodplain must be carefully managed through balanced fertilization to maintain soil productivity, promote the accumulation of SOC, and avoid the decline in soil carbon sequestration capacity.

Factors controlling the spatial heterogeneity of soil organic carbon concentrations and stocks in a boreal forest

Boreal soils play a crucial role in the global terrestrial carbon cycle, serving as significant carbon reservoirs. However, this region is experiencing rapid climate change which poses a threat to the stability of the soil carbon pool. To understand the carbon balance in the boreal region, it is essential to obtain accurate estimates of soil organic carbon (SOC) stocks. The objective of this study was to investigate factors controlling the spatial heterogeneity of SOC concentrations and stocks in a boreal forested catchment and to quantify spatial variability of SOC concentrations and stocks using a random forest-based regression kriging approach. Soil carbon content, gravel content and bulk density were obtained from the surface soil layer (0–30 cm) of 106 samples across a 390 ha catchment in northwestern Ontario, Canada. Spatial attributes including elevation, wetness index, distance to nearest ridge, relative position index, plan curvature, profile curvature and normalized difference vegetation index were used in the random forest-based regression kriging to estimate spatial heterogeneity of SOC stocks and concentrations across the catchment. Our results showed that shallow soils in well-drained upland areas contained low to moderate SOC concentrations (1.2–16.2%) while depressional wetlands had high concentrations (19.2–54.0%). Topographic variables, including wetness index were the strongest predictors of SOC concentrations, but SOC stocks were very heterogeneous across the study site (12.9–139.0 Mg ha−1) and were not well explained by topographic or vegetation variables. The gravel content was highly variable (0–29.0%), and without accounting for this fraction, SOC stocks were overestimated by 52.5% in this landscape. These results emphasize the substantial catchment scale variability in SOC stocks in boreal landscapes and underscore the significance of considering both landscape-scale drivers and intrinsic soil properties when estimating soil carbon in this region. By understanding these factors, we can better manage and protect the important carbon stores in boreal soils.

Effect of different sources of biochar incubated with FYM on soil carbon pools and yield of fodder maize

Effect of different sources of biochar incubated with FYM on soil carbon pools and yield of fodder maize

Soil Carbon Pool as Influenced by Soil Microbial Activity&amp;#8212;An Overview

Soil Carbon Pool as Influenced by Soil Microbial Activity&amp;#8212;An Overview

Regulation of Precipitation on Soil Dissolved Organic Matter in Perturbed Mangrove Ecosystems

Carbon sinks in mangrove soils play a critical role in climate change mitigation globally. Soil dissolved organic matter (DOM) is a major form of labile organic matter and influences carbon cycling in wetland ecosystems. However, the factors regulating DOM pools in mangrove soils on a regional scale are not well understood. Here, we used a novel approach to assess soil DOM dynamics and its environmental drivers in mangrove wetlands on a national scale in China. Soil samples were collected from 43 sampling sites and distributed in mangroves across the coastline of China. DOM extracted from mangrove soils was characterized by fluorescence spectroscopy. We estimated that dissolved organic carbon (DOC) content ranged from 0.20 ± 0.02 g/kg to 3.85 ± 0.09 g/kg and nationally averaged 0.73 ± 0.07 g/kg in mangrove soils. Soil DOM was composed of humic-like substances, including humic acid-like (53.46 ± 8.74%) and fulvic acid-like (46.54 ± 8.74%). DOM pools in mangrove soils were identified to be perturbed by terrestrial inputs. Besides, the coupling interactions of environmental controls on the soil DOM pool were validated by establishing the structural equation modeling (SEM). We found that precipitation is the most important driver, which controlled directly the inputs and outputs of DOM pools. It also indirectly influenced DOM pools by regulating soil parameters through the cascade reactions. Cu, salinity, and clay are key mediators among soil parameters for precipitation affecting DOM pools. Precipitation influences soil DOC negatively and CDOM and FDOM positively markedly. The results provide novel insights into the labile carbon pool in mangrove soils and are beneficial for improving the assessment frameworks in the blue carbon ecosystems.

Effects of planting basins and farmyard manure addition on soil carbon and nitrogen pools under on‐farm conditions in Makueni county of Kenya

AbstractClimate change, land degradation and inadequate soil nutrients pose significant threats to food security and agricultural sustainability. This study aims to examine the effects of planting basins with farmyard manure on soil total carbon (C), nitrogen (N), isotopic C (δ13C) and N (δ15N) compositions within smallholder‐managed farms in Makueni County, Kenya. The study involved two management practices: planting basins with manure (PM) and conventional farming practices (FP) in 12 experimental sites. Soil samples were taken at three depths (0–10, 10–20 and 20–40 cm), with three replicates for each treatment. Significant interactions were observed between land management practices and sites as well as land management practices and soil depth on soil total C and N. At each of the 12 sites, soil total C was higher under PM (ranging from 0.44% to 1.86%, p &lt; .05) than FP management (ranging from 0.35% to 1.37%), across all soil depths. Soil total N concentrations ranged from 0.027% to 0.100% under FP and (0.060% to 0.190%, p &lt; .05) under PM management. Across soil depths, higher (less negative) soil δ13C values were observed under conventional farmer practice (range − 22.5‰ to −17.1‰) compared with PM management range (−24.3‰ to −18.1‰). Soil δ15N was significantly enriched under PM management (range: 7.4‰ to 12.6‰, p &lt; .05) compared with the conventional farmer practices (range: 6.1‰ to 9.8‰, p &lt; .05). The findings show that planting basins with farmyard manure offers both climate mitigation and adaptation benefits by increasing soil C contents and improving soil fertility. The study provides insights into the real‐world implications of these practices, emphasizing the potential of planting basins with manure in enhancing soil quality and climate resilience.