Soil Organic Carbon Stocks Research Articles

Poplar plantations enhance biomass and soil organic carbon stocks in a Yangtze River-connected floodplain wetland, China

Abstract Floodplain wetlands have a significant capacity for carbon sequestration but are vulnerable to land use changes. Poplars are extensively planted in wetlands due to the increasing demand for wood products and bioenergy. Although the large biomass of poplar may increase the carbon stock in wetlands, a high transpiration rate may reduce soil moisture, thereby improving the aeration of wetland soils and facilitating the oxidation of organic materials. Therefore, the impact of poplars on wetland carbon stocks is undetermined and remains unexplored. Here, we investigated the effects of poplar plantations on biomass carbon stocks (BCS) and soil organic carbon (SOC) stocks in Dongting Lake wetlands, China, using native Miscanthus lutarioriparius vegetation as a control. Our results indicated that the BCS of middle-aged and near-mature poplar plantations (36.47–81.34 t ha−1) was higher than that of M. lutarioriparius (8.31 t ha−1), and it increased with stand age. The SOC stocks within the 0–60 cm depth in young, middle-aged, and near-mature poplar plantations (130.32–152.58 t ha−1) were higher than those in M. lutarioriparius (70.48 t ha−1), but it did not increase with stand age. The BCS was positively associated with soil bulk density, and the SOC stocks were negatively associated with soil sand content. Overall, our findings indicate that poplar plantations increase carbon stocks in the Dongting Lake wetlands. Nevertheless, the long-term effect of poplar plantation on carbon sequestration in floodplain wetlands should be further investigated.

Geospatial digital mapping of soil organic carbon using machine learning and geostatistical methods in different land uses

Improper management of soil resources leads to the destruction of soil organic carbon (SOC) stock and, as a result, the reduction of soil quality, as well as accelerating the process of climate change through the release of SOC into the atmosphere. This study was conducted to evaluate potential of different simulation models to map the spatial variability of SOC as affected by land use in a study area in Qarasu watershed in Kermanshah province, west of Iran. Map of sampling points was prepared using the Latin hypercube sampling method. A total of 168 observation points were selected and the soil profile was dug and described in these points. The soil samples were taken in different horizon to determine the SOC content in laboratory. SOC was mapped using kriging geostatistical method in the study area. The SOC changes were simulated using multivariate analysis and machine learning methods including generalized linear model (GLM), linear additive model (LAM), cubist, random forest (RF), and support vector machine (SVM) models. Comprehensive measurement data is utilized to develop and validate the predictive models. Predictor variables included 16 topographic variables as well as two vegetation, six parent material, and four climatic variables. In-depth statistical analyses are proposed to evaluate the proposed models performance. The results showed that the SOC content ranged from 0.19 to 8.44 percent in different land uses. The spherical variogram model with MAE = 0.41 best fits to interpolate and map SOC using ordinary kriging in different land uses. The LAM method was estimated wider range of the SOC change (SOC = 0.18–4.82%) among different simulation model. However, the RF model (R2 = 0.64 and RMSE = 0.58%) was the most accurate in predicting SOC quantity comparing the other simulation models. It can be used as a reliable simulation model to predict SOC variability in the study area and other similar semiarid regions of West Asia in different land uses. Among the different predictor variables, the parent material’s intrinsic soil properties and topography variables had the greatest effect in predicting soil organic carbon variability.

Depth dependence of soil organic carbon additional storage capacity in different soil types by the 2050 target for carbon neutrality

Abstract. Land planning projects aiming to maximize soil organic carbon (SOC) stocks are increasing in number and scope, often in line with the objective to reach carbon neutrality by 2050. In response, a rising number of studies assesses where additional SOC could be stored over regional to global spatial scales. In order to provide realistic values transferrable beyond the scientific community, studies providing targets of SOC accrual should consider the timescales needed to reach them, taking into consideration the effects of C inputs, soil type, and depth on soil C dynamics. This research was conducted in a 320 km2 territory in north-eastern France, where eight contrasted soil types have been identified, characterized, and mapped thanks to a high density of fully described soil profiles. Continuous profiles of SOC stocks were interpolated for each soil type and land use (cropland, grassland, or forest). We defined potential targets for SOC accrual using percentile boundary lines and used a linear model of depth-dependent C dynamics to explore the C inputs necessary to reach those targets within 25 years. We also used values from the literature to model C input scenarios and provided maps of SOC stocks, maximum SOC accrual, and realistic SOC accrual over 25 years. SOC stocks and maximum SOC accrual are highly heterogenous over the region of study. Median SOC stocks range from 78–333 tC ha−1. Maximum SOC accrual varies from 19 tC ha−1 in forested Leptosols to 197 tC ha−1 in grassland Gleysols. The simulated realistic SOC accrual over 25 years in the whole region of study was one-fifth of the the maximum SOC accrual. Further consideration of depth-dependent SOC dynamics in different soil types is therefore needed to provide targets of SOC storage over timescales relevant to public policies aiming to approach carbon neutrality by 2050.

Changes in Soil Properties, Organic Carbon, and Nutrient Stocks After Land‐Use Change From Forests to Grasslands in Kumaun Himalaya, India

ABSTRACTLand‐use changes are anticipated to be a substantial contributor to global change climate, substantially causing significant modifications in soil characteristics. This study addressed the impact of land‐use change from native forests to grasslands on the soil physico‐chemical properties in entirely replicated grasslands of three different forest zones (Oak, Pine and Cypress) in temperate region of Kumaun Himalaya. A total of 162 soil samples (6 sites × 3 plots × 3 seasons × 3 depths = 162 samples) were randomly collected from each site in triplicates from depths. The soil texture, bulk density (bD), porosity, water holding capacity, soil moisture content, pH, organic carbon (SOC), total nitrogen (TN), available phosphorus (P) and available potassium (K) were determined at different depths in forest and grassland sites. Results showed that soil bD, pH, SOC, TN, P and K significantly (p < 0.05) decreased with increasing depth. Moreover, conversion of forests into grassland reduced nutrient concentrations, physical qualities (bD and porosity), and pH levels. The decreasing trend of nutrient along the soil depth explains that the zone of nutrient accumulation is not well established in these grasslands because of the substantial leaching effect. Our findings indicate that conversion of natural forests into grasslands resulted in significant losses of SOC and TN stocks which can be attributed to the disturbance of natural forests. Therefore, while making land‐use change plans, the impact of these alterations on soil nutrients must be considered. These findings emphasize the value of establishing natural vegetation (forests) in these areas to retain nutrients and safeguard soil against runoff and erosion. However, anticipating the physico‐chemical impacts of land‐use alteration necessitates a better comprehension of its relations with other drivers of global change, such as changing climate and nitrogen deposition.

Predicting bulk density in Brazilian soils for carbon stocks calculation: a comparative study of multiple linear regression and Random Forest models using continuous and categorical variables

Soil bulk density (ρb) is vital for assessing soil organic carbon (SOC) and nutrient stocks, as well as for modeling soil processes. Although ρb can be measured using traditional methods, these are labor-intensive and time-consuming. Consequently, there is a growing interest in developing pedotransfer functions (PTFs) to predict ρb based on more easily measured soil properties. The vast Brazilian territory, with different climates and biomes, presents a challenge for development of national-scale PTFs, particularly for ρb. In this study, a comprehensive dataset was compiled from various sources to develop ρb PTFs across Brazil. The dataset includes particle size distribution (PSD), SOC, ρb, sampling depth, soil order, land use, and geographic coordinates, allowing for the incorporation of additional numerical and categorical variables. Rigorous data preprocessing ensured quality and reliability. PTFs were developed using multiple linear regression (MLR) and Random Forest (RF) models. Model accuracy was evaluated using mean absolute error, bias, root mean square error (RMSE), and coefficient of determination. Both MLR and RF models accurately predicted ρb, with log-transformed PSD and SOC emerging as key predictors. The RF model slightly outperformed the MLR model (RMSE = 0.12 vs. 0.13 g cm−3) on the test dataset, underscoring the importance of environmental and categorical variables in predicting ρb. The developed PTFs, along with other PTFs for Brazil, were applied to estimate SOC stocks across different biomes and land uses. Best estimations were obtained with the RF model, with an R2 of 0.97, emphasizing the value of categorical variables in improving SOC stock estimations.

Effect of Long Term Nutrient Management on Carbon Pools and Indices in Rice-Rice Cropping System in Lateritic Soils of Humid Tropics

ABSTRACT Soil organic carbon (SOC) serves a vital role in sustaining environmental quality and supporting agroecosystems. The study evaluated the effects of long-term manuring and fertilization on SOC pools in rice-rice cropping system in the lateritic soils of Central Plain, Kerala, India. Soil samples from the long term fertilizer plots were used to determine the SOC pools. Treatments were: 50% recommended dose of nitrogen (N), phosphorus (P), potassium (K) (50% NPK), 100% NPK, 150% NPK, 100% NPK + lime, 100% NP, 100% N, 100% NPK + farm yard manure (FYM) (100% NPK + FYM), 50% NPK + FYM, 100% NPK + Sesbania aculeata (SA), 50% NPK + SA and no fertilizers or manures (control). Integrated nutrient management (INM) treatments improved the Walkley and Black carbon (WBC) content. Water-soluble carbon (WSC) ranged from 0.009 to 0.012%, with the highest value found in INM. KMnO4-oxidizable carbon ranged from 0.092 to 0.158%. The management practices were found to greatly influence microbial biomass carbon (MBC) in the soil with values 195.55 to 298.19 µg g−1 soils. The treatments had a significant effect on fractions of SOC that are strongly connected to aggregate stability namely, total polysaccharides, and glomalin. Application of NPK from 50% to 150% improved WBC, WSC and MBC by 7.69%, 22.22% and 27.90%, respectively. The INM practices also improved the SOC stocks. The carbon management index (CMI) found to be superior in one receiving INM practices than one receiving prescribed levels of nutrition using only mineral fertilizers.

Experimental Soil Warming Impacts Soil Moisture and Plant Water Stress and Thereby Ecosystem Carbon Dynamics

AbstractExperimental soil heating experiments have found a consistent increase in soil‐surface CO2 emissions (Fs), but inconsistent soil organic carbon (SOC) responses. Interpretation of heating effects is complicated by spatial heterogeneity and soil moisture, nitrogen availability, and microbial and plant responses. Here we applied a mechanistic ecosystem model to interpret heating impacts on a California forest subjected to 1 m deep, 4°C heating. The model accurately simulated control‐plot CO2 fluxes, SOC stocks, fine root biomass, soil moisture, and soil temperature, and the observed increases in Fs and decreases in fine root biomass. We show that a complex suite of interactions can lead to a consistent increase in Fs (∼17%) over the 5‐year study period, with very small changes in SOC stocks (<1%). Modeled increases in leaf water stress from soil drying reduced GPP and NPP. The resulting reduction in leaf and fine root allocation increased fine root litter inputs to the soil and reduced root exudation. Soil heating led to about a 50% larger increase in root autotrophic respiration than in heterotrophic respiration, with the heating effect on both these fluxes decreasing over the simulation period. Increased heterotrophic respiration led to increased soil N availability and plant N uptake. These heating responses are mechanistically linked, of magnitudes that can affect ecosystem dynamics, and long‐term observations of them are rarely made. Therefore, we conclude that a coupled observational and mechanistic modeling framework is needed to interpret manipulation experiments, and to improve projections of climate change impacts on terrestrial ecosystem carbon dynamics.

Can environmental variables, high sampling density and machine learning deliver detailed maps of soil organic carbon and carbon stock in tropical regions?

Can environmental variables, high sampling density and machine learning deliver detailed maps of soil organic carbon and carbon stock in tropical regions?

A harmonized dataset relating alternative farmer management practices to crop yield, soil organic carbon stock, nitrous oxide emissions, and nitrate leaching generated using IPCC methodologies and meta-analyses.

Farming practices such as soil tillage, organic/mineral fertilization, irrigation, crop selection and residues management influence multiple ecosystem services provided by agricultural systems. These practices exhibit complex, non-linear interrelationships that affect crop productivity, water quality, and non-carbon dioxide greenhouse gases (GHG) emissions, possibly offsetting their benefits regarding soil organic carbon (SOC) sequestration. Current methodologies from the Intergovernmental Panel on Climate Change (IPCC) for assessing the impacts of alternative farming practices on GHG emissions rely on global or country-specific coefficients. However, these methods often do not explicitly account for the combined effects of management practices on carbon and nitrogen cycles or productivity, as this is not required for national GHG inventories. Here we present a new dataset featuring 1.8 Mln of agronomic case scenarios, i.e., unique combinations of farming practices and pedoclimatic conditions, which have been associated with values of SOC changes, nitrous oxide emissions, nitrate-nitrogen leaching, and crop yield. To synthesize trade-offs and synergies between farming practices, each case scenario has been ranked with a ∑ommit index (∑i) value, a fuzzy-based measure ranging from 0 (bad) to 1 (good). The four trade-off components have been estimated by combining available information from i) the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, ii) the guidelines for Green Water Footprint Accounting, iii) the Italian National Institute of Statistics, iv) and other international meta-analytic studies. The dataset presents four ∑i series, corresponding to alternative perceptions of sustainability from three potential stakeholder categories (young farmers' cooperative, agrochemical company, public agricultural policy agency) plus one equally weighted option. By providing a harmonized data source and an innovative metric, this dataset allows users to explore trade-offs associated with alternative management practices across four key agricultural components and assess their impact on perceived agroecosystem sustainability.

Long-term warming offsets the beneficial effect of elevated CO2 on mineral associated organic carbon in Mollisols.

The stability of soil organic carbon (SOC) is fundamentally important to the carbon-climate feedback because soils act as a major carbon source or sink under climate change. The uncertainty of SOC stability in farming soils in response to climate change necessitates mechanistic studies on microbial attributes to the change of SOC. Here, we used open-top chambers to simulate elevated CO2 (eCO2) and warming for 12years in a soybean-grown Mollisol. We did not find the change of SOC stock under eCO2 or warming. Although eCO2 resulted in the accumulation of mineral-associated organic carbon, this effect diminished under warming. The amplicon sequencing of 16S gene indicated a significant change in microbial community composition under warming or eCO2. The metagenomic sequencing demonstrated that warming increased the abundances of microbial genes related to decomposition of labile carbon such as hemicellulose and pectin. The warming-induced stimulation of microbial catabolic metabolisms on organic carbon decomposition might have accelerated SOC turnover, which may offset the increased mineral-associated organic carbon of the Mollisol under eCO2. Long-term eCO2 and warming might not significantly alter the SOC stock or stability but accelerate carbon cycling in farming Mollisols.

Identifying bacterial fixation pathway of mediating soil carbon stock changes along tropical forest restoration

The mechanism mediating carbon accumulation changes along ropical forest restoration remains unclear. Here, we identified how functional bacteria, litter input, and abiotic variables control soil organic carbon stock changes along an age-chronosequence of tropical forest restoration. Over 51-yr recovery, significant increases in total organic carbon stocks (∼1.7 fold) were strongly associated with increases in copy number of carbon fixation bacterial genes (cbbL) (∼2.6 fold). The direct pathways of cbbL abundance, microbial and mineral-associated organic carbon explained 76 % of carbon stock variation. In contrast, litter carbon, soil water, and bulk density indirectly regulated carbon stocks through affecting cbbL abundance (68 %) and microbial carbon level (29 %). Furthermore, cbbL abundance had a higher contribution (71 %) to carbon fraction transformation than microbial carbon level (19 %). We suggest that tropical forest restoration controls carbon stocks primarily via direct bacterial fixation pathway mediated by litter carbon and physical soil variables. Our results are helpful to further understand the mechanism of tropical forest restoration regulating carbon transformation and accumulation.

Comprehensive assessment of straw returning with organic fertilizer on paddy ecosystems: A study based on greenhouse gas emissions, C/N sequestration, and risk health.

High greenhouse gas emissions and soil deterioration are caused by the overuse of chemical fertilizers. To improve soil quality and crop productivity, it is necessary to utilize fewer chemical fertilizers to achieve sustainable agriculture. Organic substitution is a scientific fertilization strategy that will benefit future agricultural productivity development, little is known about how it affects the heavy metal content and trace gas emissions in rice grains. A field experiment using straw return to the field (SRF), organic fertilizer application (OFA), and their combination (SRF/OFA) fertilization strategies. The results demonstrated that SRF, OFA, and SRF/OFA increased the yield by 19.40%, 22.39%, and 28.36% than the natural growth control group (NG). The OFA has the highest STN stock and SRF/OFA has the highest STN sequestration rate, while SRF achieved the highest SOC stock and sequestration rate. The OFA reduced CO2, CH4, and N2O emissions by 17.73%, 71.87%, and 86.06%, resulting in a minimum global warming potential and greenhouse gas intensity yield among these strategies. Cumulative seasonal CO2 and CH4 emissions were negatively correlated with soil paddy soil C/N and C/P (P<0.05). Moreover, Cu, Cd, and Pb contents in grain were reduced by 66.18%-70.31%, 35.45%-40.91%, and 76.62%-77.92%, respectively. The health risk evaluation revealed that all metals had a target hazard quotient of <1, except for NG. The hazard index (0.42-0.53), which measures the additive effects of contaminants, exceeded the threshold. The implementation of the organic alternative strategy can reduce the trend of increasing surface pollution, slow down the excessive utilization intensity of agricultural resources, and encourage the development of a greener, more sustainable agricultural way.

Response of soil organic carbon stocks and soil microbial biomass carbon to natural grassland conversion: A global meta-analysis.

Natural grasslands worldwide are increasingly being converted into other land-use types, such as cropland and forest, thereby impacting soil carbon cycles and stocks. Soil organic carbon (SOC) is essential for regulating soil properties and microbial communities, while microbial biomass carbon (MBC) is the most active fraction of the SOC pool, both of which play pivotal roles in the global carbon cycle. Here, we performed a meta-analysis on 623 and 85 individual observations from 85 peer-reviewed articles to quantitatively evaluate the effect of grassland conversion on SOCS and MBC. Overall, conversions significantly reduced SOCS and MBC by 10.11% and 30.63%, respectively. Notably, the impact varied by conversion type: converting grassland to forest, cropland, and plantation reduced SOCS by 7.69%, 16.47%, and 20.55%, respectively. Meanwhile, converting grassland to cropland and abandoned land decreased MBC by 47.80% and 38.74%, respectively. Environmental factors such as mean annual temperature (MAT), mean annual precipitation (MAP), soil total nitrogen (TN), and soil carbon-to‑nitrogen ratio (C/N) influenced these changes. SOCS and MBC were positively correlated with MAT, soil C/N and TN. Specifically, when the C/N or TN of the converted soil exceeded 1.21 or 1.11 times that of the original grassland, SOCS would exhibit a trend of carbon sequestration. Our findings provide valuable insights for global soil carbon sequestration and land use management policies.

Effects of land use/land cover change on soil physicochemical properties and soil carbon stock in Kochore district, southern Ethiopia

Land use changes from year to year due to natural and human-made factors are a serious cause of the degradation of soil properties. Therefore, this study aimed to investigate the impact of land use land cover changes on selected soil physicochemical properties and soil organic carbon stocks in Kochore district, Southern Ethiopia. Satellite images (2000, 2010, and 2020) were used as sources of information for land use and land cover analysis using ArcGIS 10.3 and ERDAS Imagine 2014 software. Three land use types (cultivated, agroforestry, and grazing land) were identified through field surveys and satellite image analysis. Soil samples were collected at different depths (0–20 cm and 20–40 cm), and selected soil properties were analyzed. The results indicate that geospatial data of the land cover of agroforestry continuously increased and a decrease in grazing and cultivated in the given periods of 2000, 2010, and 2020, and soil properties revealed such as sand, bulk density, organic carbon, total nitrogen, pH, cation exchange capacity, and exchangeable bases were significantly (P < 0.001) affected by land use and soil depth. The highest content of OC (2.37), Av.P. (3.36), and TN (0.13) was observed on agroforestry land, and the lowest 1.43 and 0.08 was OC and TN respectively. The highest value of soil organic carbon stock (60.2 mg ha−1) was observed in AFL. The study suggests the deterioration of soil properties under cultivated and grazing land, emphasizing the importance of sustainable integrated soil fertility management to optimize and maintain favorable soil physicochemical properties.

Soil Aggregation, Aggregate Stability, and Associated Soil Organic Carbon in Huron Mountains Forests, Michigan, USA

Soil organic carbon (SOC) plays a critical role in regulating the global carbon (C) cycle, with forest soils serving as significant C sinks. Soil aggregate stability and the distribution of SOC in different aggregate fractions would be affected by different forest types. In this study, we investigate the distribution and dynamics of SOC within different soil aggregate fractions across three main forest types in the Huron Mountains, Michigan, USA: white birch–eastern hemlock mixed forest, eastern-hemlock-dominated forest, and sugar maple forest. We hypothesize that variations in species composition and soil depth influence SOC storage and aggregate stability through mechanisms such as root interactions, microbial activity, and soil structure development. Soil samples were collected from three depth intervals (0–20 cm, 20–40 cm, and 40–60 cm) and analyzed for aggregate size distribution and SOC content. The results showed that aggregate size distribution and SOC stocks differ significantly across forest types, with the white birch–eastern hemlock mixed forest exhibiting the highest proportion of large aggregates (&gt;1.0 mm), which contribute to more stable soil structures. This forest type also had the highest total aggregate mass and mean weight diameter, indicating enhanced soil stability. In contrast, sugar maple forest displayed a greater proportion of smaller aggregates and a lower macroaggregate-to-microaggregate ratio, suggesting fewer stable soils. SOC stocks were closely linked to aggregate size, with macroaggregates containing the highest proportion of SOC. These differences in SOC distribution and soil aggregate stability can be attributed to several underlying mechanisms, including variations in plant root interactions, microbial activity, and the physical properties of the soil. Forests with diverse species compositions, such as the white birch–eastern hemlock mixed forest, tend to support more complex root systems and microbial communities, leading to improved soil aggregation and greater SOC storage. Additionally, forest management practices such as selective thinning and mixed-species planting contribute to these processes by enhancing soil structure, increasing root biomass, and promoting soil microbial health. These interactions play a crucial role in enhancing C sequestration and improving soil health. Our findings emphasized the importance of forest composition in influencing SOC dynamics and soil stability, offering insights into the role of forest management in C sequestration and soil health. This study provided a reference to a deeper understanding of SOC storage potential in forest ecosystems and supports the development of sustainable forest management strategies to mitigate climate change.

Long-Term Grazing and Nitrogen Management Impacted Methane Emission Potential and Soil Microbial Community in Grazing Pastures.

Achieving sustainable development in livestock agriculture by balancing livestock production, reduction of greenhouse gas (GHG) emissions, and effective utilization of nitrogen nutrient has indeed been challenging. This study investigated the long-term effects of continuous cattle grazing, stocking rates, and fertilization regimens on methane (CH4) emissions, soil microbial communities, and soil organic carbon (SOC) stocks in Bermudagrass pastures in East Texas, USA. Pastures were subjected to high or low stocking rates for over 50 years, with further subdivision based on fertilization: nitrogen-based fertilizer application or no fertilizer but with the growth of annual clover. Seasonal soil cores (0-60 cm) were collected, and laboratory microcosm incubation studies revealed unexpectedly high in vitro CH4 emissions in surface soils, particularly in the top 0-5 cm soil layer, reaching up to 300 nmol of CH4 mL-1. Higher CH4 emissions and methanogen abundance, along with lower SOC stocks, were observed in pastures subjected to high stocking rates compared to those with low stocking rates and in clover pastures compared to those with N-fertilized ryegrass. On the contrary, in low-stocked, N-fertilized annual ryegrass pastures, methanogen abundance was lowest, CH4 emissions were negligible, and SOC stocks were highest. Furthermore, animal excreta deposition significantly contributed to increased CH4 emissions. Prokaryotic and potential methanotrophic taxa, as compared to fungi, exhibited greater responsiveness to N-fertilization than to cattle stocking treatments with higher levels of methanotrophs observed in pastures subjected to high stocking rates and clover growth. This study suggests that strategic management practices such as optimal grazing and nitrogen management could effectively mitigate CH4 emissions in grazing lands.

Impact of short-term pasture development on soil aggregation, temperature sensitivity of soil organic carbon, and functional diversity in semi-arid ecosystem

Pasture development could be a viable option to restore degraded land in semi-arid region. New knowledge on soil functional diversity, aggregation, and temperature sensitivity (Q 10) of soil organic carbon (SOC) after pasture development would assist to accomplish the scope of global pastureland management for climate change mitigation and land restoration. To understand the impact of pasture development on soil aggregation, SOC stock, and its Q 10, research was undertaken at three development sites (RS1, RS2, RS3) in India with seeding of Cenchrus ciliaris, Megathyrus maximus, and Stylosanthes seabrana (at a line-ratio of 2:2:1). After three years, biomass productivity and for SOC, aggregation, enzyme activities, etc. at 0–20 and 21–40 cm depths were estimated. Pasture development improved biomass productivity from 0.68 mg ha−1 in undeveloped site to 3.62–4.64 mg ha−1. Pasture development enhanced SOC stock from 5.85 to 7.31 mg C ha−1 at the surface layer with an annual accumulation rate of 28–112 kg SOC ha−1 year−1. Greater activities of extracellular enzymes were observed at the surface soil layer in pasture development sites over undeveloped control. The mean weight diameter was ∼23–38% higher at pasture development sites over undeveloped sites. The Q 10 being controlled by the labile carbon was significantly higher (13–29%) at the pasture development sites over undeveloped site. Hence, short-term pasture development could improve the SOC stocks at the surface layer only, but the stocks were vulnerable to C loss at higher temperature. However, long-term pasture development could have a great potential to accrue C to mitigate climate change.

Soil organic carbon in tropical shade coffee agroforestry following land‐use changes in Mozambique

AbstractCoffee (Coffea L.) agroforestry systems (CAFS) and wooded grasslands (WG) have been pointed out as having high soil organic carbon (SOC) storage potential compared to monoculture systems. Studies analyzing the response of soil bulk density (BD) and SOC to the conversion of WG to slash‐and‐burn agriculture (SBA) and to CAFS are lacking in southern Africa. This study was conducted in the buffer zone of Gorongosa National Park (Mozambique), where depth profiles of BD and SOC were estimated to 0‐ to 100‐cm soil depth in WG, SBA, and CAFS sites, with coffee shrubs aged 3, 5, and 8 years after planting. The stratification ratio (SR) was used as an indicator of soil quality and recovery from disturbance. BD and SOC stocks varied significantly among land use systems and coffee ages only in the surface soil layer (0–20 cm). SOC stocks of the surface soil and SR increased with increasing coffee age. Compared to SBA, significant increases in SOC stocks were only observed 5 years after implementation of CAFS. WG conversion to SBA did not alter SOC stocks in any soil layer; however, it led to decreased SR. Surface SOC stocks were 25.6 and 33.7 Mg ha−1 in WG and SBA, and 28.0, 41.9, and 61.1 Mg ha−1 in 3‐ and 5‐ and 8‐year‐old CAFS (mean SOC accumulation of 6.65 Mg ha−1 year−1). This study reveals that CAFS have the potential to increase belowground carbon sequestration when compared to SBA and WG over comparable soils, making it a practical option for climate change mitigation.

Motor-manual release changes carbon distribution in soil and tree biomass pools in the short term

Despite offering multiple ecosystem services, such as their ability to sequester carbon (C), regenerating mixedwood boreal forests are often only managed to increase their coniferous part by controlling their competition, impacting the ecosystem C stocks. The aim of this study was to compare the short-term effect of motor-manual release treatments of variable intensities: broadcast brushing (brushing), release-from-below (RFB) and crop-tree release (CTR) on carbon stocks in soil (SOC) and live biomass (aboveground and root C stocks). The stands treated by brushing had twice as much SOC stocks than in the other stands, at the 5- to 10 cm depth. RFB treatment kept the largest aspen stems in the stands and retained enough total live biomass to compensate for the initial loss. Despite being similar in intensity, stands treated with RFB had more than twice the amount of live biomass than stands treated by brushing. Overall, total C stocks (SOC and live biomass) did not change between the stands but the distribution among the different C pools did, with the live biomass being the most impacted by the treatments. The design of the RFB treatment seemed promising to mitigate C loss during early forest operations while still controlling fast-growing competitors.

Increased but not pristine soil organic carbon stocks in restored ecosystems

Ecosystem restoration can contribute to climate change mitigation, as recovering ecosystems sequester atmospheric CO2 in biomass and soils. It is, however, unclear how much soil organic carbon (SOC) stocks recover across different restored ecosystems. Here, we show SOC recovery in different contexts globally by consolidating 41 meta-analyses into a second-order meta-analysis. We find that restoration projects have, since their inception, led to significant SOC increases compared to the degraded state in 12 out of 16 ecosystem-previous land-use combinations, with mean SOC increases thus far that range from 25% (grasslands; 10–39%, 95% CI) to 79% (shrublands; 38–120% CI). Yet, we observe a SOC deficit in restored ecosystems compared to pristine sites, ranging from 14% (forests; 12–16% CI) to 50% (wetlands; 14–87% CI). While restoration does increase carbon sequestration in SOC, it should not be viewed as a way to fully offset carbon losses in natural ecosystems, whose conservation has priority.