Estimation of soil carbon pools in the forests of Khyber Pakhtunkhwa Province, Pakistan

In order to explore the effects of different forest types on active soil carbon pool, the amounts and density of soil organic carbon (SOC) were studied at different soil horizons under typical coniferous and broad-leaved forests in the mountainous area of Beijing. The results showed that the amount of total SOC, readily oxidizable carbon and particulate organic carbon decreased with increasing depths of soil horizons and the amounts at depths of 0–10 cm and 10–20 cm in broad-leaved forest was clearly higher than that in coniferous forests. The trend of a decrease in SOC density with increasing depth of the soil horizon was similar to that of the amount of SOC. However, no regular trend was found for SOC density at different depths between coniferous forest and broad-leaved forests. The ratio of readily oxidizable carbon to total amount of SOC ranged from 0.36–0.45 and the ratio of particulate organic carbon to total amount of SOC from 0.28–0.73; the ratios decreased with increasing depths of soil horizons. Active SOC was significantly correlated with total SOC; the relationship between readily oxidizable carbon and particulate organic carbon was significant. A broad-leaved forest may produce more SOC than a coniferous forest.

ABSTRACTMeasuring soil bulk density (as well as carbon content) is crucial for accurate soil carbon stock calculations. Given the growing interest in soil carbon sequestration on farmlands as a strategy for mitigating greenhouse gas emissions, effective large‐scale field monitoring has become more important than ever. However, traditional methods for measuring soil bulk density, such as the core (volumetric cylinder) and clod methods, require undisturbed samples, making them labour‐intensive, time‐consuming and costly—due to the high complexity of sample collection and preparation. To overcome these challenges, we developed a laser‐induced breakdown spectroscopy (LIBS)‐based method for efficient and cost‐effective bulk density estimation that does not require undisturbed samples. We trained and evaluated LIBS‐based models using a dataset of 880 diverse Brazilian soil samples, randomly split into 70% for training and 30% for testing. The LIBS‐based models, combining discrete wavelet transform (DWT), feature selection via F‐test for regression, and Ridge regression, achieved an R2 of 0.72 and a root mean square error (RMSE) of 0.12 g cm−3 on the test set for soil bulk density prediction. Furthermore, by combining LIBS‐predicted soil bulk density with measured soil carbon concentration, we estimated soil carbon stock, achieving an R2 of 0.93 and an RMSE of 2.2 Mg C ha−1 on the test set, indicating that the uncertainty in bulk density predictions has a minor impact on soil carbon stock estimations. To further streamline soil carbon stock estimation, we developed a model to directly predict soil carbon density—the product of soil carbon concentration and bulk density—using LIBS‐derived spectral features, eliminating the need for separate measurements or estimations. Although this approach resulted in a lower R2 of 0.78 and a higher RMSE of 4.1 Mg C ha−1, its performance was adequate for carbon stock prediction while simplifying the estimation process. These findings highlight the potential of LIBS as a rapid and effective tool for assessing soil bulk and carbon densities, contributing to sustainable soil management and climate change mitigation and adaptation.

Organic Carbon Sequestration and Ecosystem Service of Indian Tropical Soils

Grassland, as a key component of the carbon cycle in terrestrial ecosystems, is vital in confronting global climate change. Characterising the carbon density of grassland ecosystems in the Longzhong Loess Plateau is important for accurately assessing the contribution of grasslands to global climate change and achieving the goal of “peak carbon” and “carbon neutral”. In this study, the Longzhong Loess Plateau was used as the research object to explore changes in the plant–soil system carbon density in two grassland types by analysing the aboveground vegetation biomass carbon density, belowground vegetation biomass carbon density, 0–100 cm soil carbon density, and ecosystem carbon density of temperate steppe and temperate desert. The results showed that the vegetation biomass (standing and living, litter, and belowground biomass), soil, and ecosystem carbon densities of the temperate steppe were significantly higher than those of the temperate desert (p < 0.05). Their carbon densities were 700.51, 7612.95, and 8313.45 g·m−2, respectively. The vertical distribution of belowground biomass and soil carbon density in the temperate steppe was significantly higher than that in the temperate desert. The overall trend of belowground biomass carbon density in the temperate steppe and temperate desert showed a gradual decrease, whereas soil carbon density showed a steady increase. More than 91% and 96% of the carbon was stored in soil in the temperate steppe and temperate desert, respectively, and the belowground biomass carbon stock accounted for more than 84% of the total biomass carbon pools in both temperate steppe and temperate desert. Temperate steppe has a significant effect in improving the carbon stock of grassland ecosystems, so ecological protection and restoration of grassland should be strengthened in the future to enhance the capacity of grassland to sequester carbon and increase sinks.

Carbon Sequestration in Soils of Latin America

Reduced carbon assimilation by trees is often considered to lower the overall carbon sink function of drought-stressed forests. However, soil organic carbon (SOC) stocks may respond differently to drought than ecosystem carbon flux dynamics, leading to imprecise predictions of soil carbon sequestration when one value is inferred from the other. As a major component of soil organic matter, SOC is the largest actively cycling terrestrial carbon reservoir, and thus fulfills various important ecosystem services. Yet, there is uncertainty about how SOC quantity and quality respond to drought in temperate forests. This study addressed the depth distribution of SOC stocks and soil organic matter stability in a forest exposed to artificial drought for five consecutive growing seasons below clusters of temperate mature deciduous beech (Fagus sylvatica L.) and coniferous spruce (Picea abies (L.) Karst.). In addition to SOC stock determination, we measured concentrations of water-extractable organic carbon (WEOC), performed density fractionation, and determined beta values of SOC (slopes of linear regressions between δ13C of soil and log-transformed SOC content throughout soil depth profiles). Following drought, SOC stocks down to 30 cm depth increased by a factor of 1.5 under P. abies while they did not change with drought under F. sylvatica. Under both species, SOC stocks in the mineral topsoil (0–5 cm soil depth) increased by >80 % with drought, increasing the relative contribution of this thin depth section to total SOC from 5 % to >30 %. At 5–15 cm soil depth, SOC stocks decreased with drought under F. sylvatica but not under P. abies. With drought, carbon in the free light fraction (fLF) increased under F. sylvatica but declined marginally under P. abies. Results from density fractionation and beta values suggest decreased soil organic matter stability under F. sylvatica and increased stability under P. abies. Greater SOC accumulation suggests that the belowground carbon sink strength of drought-stressed forests increases, which contrasts with reduced ecosystem carbon uptake under drought.

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

The additional mineralized soil organic carbon (SOC) after soil crushing is considered to be the amount of SOC protected within aggregates (>200 μm). This study investigated the effect of soil moisture in crushed and uncrushed soil samples on the calculated amounts of protected SOC in five tropical soils (Arenosol, two Ferralsols, Nitisol, and Vertisol). No differences in soil moisture optimum were observed between crushed and uncrushed soil samples, except in clayey soils with high SOC contents and high SOC mineralization rates (Nitisol and Vertisol). Crushing the soil increased soil respiration by 0.9 to 2.4 times. Soil moisture seemed to be a confounding factor in estimation of the SOC-protected amount only in soil with a high amount of protected SOC or with a low macroaggregate stability (Ferralsol and Vertisol). In these soils, the amount of protected SOC could be influenced by the method used to estimate it.

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

Soil erosion has become an increasingly serious issue, drawing global attention. As one of the countries facing severe soil erosion in the world, China confronts significant ecological challenges. Against this backdrop, the country places great emphasis on soil conservation efforts, considering them a crucial component of ecological civilization construction. This study focuses on the carbon sink benefits of comprehensive soil conservation management in the loess hilly region and sandy slopes, using the Xiaonanshan Mountain small watershed in Youyu County, Shanxi Province, as a typical case for in-depth analysis. In terms of research methodology, an integrated monitoring approach combining fundamental data, measured data, and remote sensing data was developed. A comprehensive survey of the Xiaonanshan Mountain small watershed was conducted to categorize plant carbon pools and soil carbon pools, establish baseline scenarios, and utilize methods such as inverse distance spatial interpolation, sample calculation, and feature extraction to estimate forest carbon storage across different years and determine changes in soil and vegetation carbon storage. Simultaneously, data collection and preprocessing were carried out, including the gathering of fundamental data, field data collection, and internal data preprocessing. On this basis, a vegetation carbon storage model was constructed, and an assessment of soil carbon pool storage was conducted. The research results indicate that from 2002 to 2024, the continuous implementation of various soil conservation measures over 22 years has led to a significant increase in carbon storage within the Xiaonanshan Mountain small watershed. The vegetation carbon density of the entire small watershed increased from 14.66 t C/ha to 27.02 t C/ha, and the soil carbon density rose from 28.92 t C/ha to 32.48 t C/ha. The net carbon sink amount was 18,422.20 t C (corresponding to 67,548.08 t CO2e in terms of carbon dioxide equivalent). Populus simonii and Pinus sylvestris var. mongholica significantly contribute to the carbon sink; however, due to partial degradation of Populus simonii, its net carbon sink amount is less than that of Pinus sylvestris var. mongholica. Additionally, the carbon sink capacity of the small watershed exhibits spatial differences influenced by conservation measures, with high carbon density areas primarily concentrated within the range of Populus simonii, while low carbon density areas are mainly found in shrub zones. The increase in carbon storage within the small watershed is primarily attributed to the contributions of vegetation and soil carbon storage, indicating that comprehensive soil erosion management has a significant carbon accumulation effect; moreover, the annual growth rate of vegetation carbon storage exceeds that of soil carbon storage, with the proportion of soil carbon storage increasing year by year. Furthermore, the vegetation carbon sink, soil carbon sink, and total carbon sink of the small watershed were separately calculated. In terms of benefit analysis, the Xiaonanshan Mountain small watershed offers ecological benefits such as increased forest coverage, carbon fixation and oxygen release, and biodiversity conservation; from an economic perspective, the value of carbon trading is substantial, promoting soil conservation and rural revitalization, with the total value of timber reaching 7.6 million yuan, of which the value of standing timber constitutes the largest proportion; social benefits include the improvement of environmental landscapes, stimulation of ecological tourism, and attraction of investment, with the Xiaonanshan Mountain Ecological Park receiving numerous visitors and generating significant tourism revenue. This research provides a theoretical basis and data foundation for comprehensive soil conservation management in project areas or small watersheds within the loess hilly and sandy slope regions, offering technical and methodological support for other soil conservation carbon sink projects in the area.

Located at the foothills of the Himalayan Mountains, subtropical and moist temperate forests of Pakistan are very rich in flora and fauna. However, due to increased illegal and uncontrolled harvesting of wood, agricultural activities, and urbanization, these forests are fast disappearing. The recent expansion of human activities resulting illegal and uncontrolled harvesting, agricultural activities, and urbanization is a cause for concern. Using Landsat imagery, Markov Chain and Cellular Automata, this study focused on the quantitative assessment of spatiotemporal land use and land cover changes during 1998, 2008, 2018 and a simulation of 2028. In addition, a forest inventory survey of biomass and carbon sink were respectively calculated for these subtropical broad-leaved evergreen, subtropical chirpine and moist temperate forests. Results showed biomass was 560.56 ± 104.33 Mg ha−1, 350.95 ± 104.33 Mg ha−1 and 153.63 ± 104.33 Mg ha−1 in moist temperate, subtropical chirpine and subtropical broad-leaved forests respectively. Meanwhile, carbon was 313.94 ± 44.78 Mg C ha−1, 221.34 ± 44.78 Mg C ha−1 and 131.77 ± 44.78 Mg C ha−1 in moist temperate, subtropical chirpine and subtropical broad-leaved forests respectively. During the study period, land-use and land cover changes showed forest land changed from 40936.77 ha to 36709.23 ha, agricultural land from 4220.46 to 10374.64 ha, and built-up area from 1497.60 to 5395.12 ha. The average annual biomass and carbon loss were respectively 50.34 Gg ha−1yr−1 and 31.33 Gg C ha−1 yr−1. The information derived from this study could assist in the development of appropriate sustainable forest management policies in Pakistan.

Wetland ecosystems contain large amounts of soil organic carbon. Their natural environment is often both at the junction of land and water with good conditions for carbon sequestration. Therefore, the study of accurate prediction of soil organic carbon (SOC) density in coastal wetland ecosystems of flat terrain areas is the key to understanding their carbon cycling. This study used remote sensing data to study SOC density potentials of coastal wetland ecosystems in Northeast China. Eleven environmental variables including normalized difference vegetation index (NDVI), difference vegetation index (DVI), soil adjusted vegetation index (SAVI), renormalization difference vegetation index (RDVI), ratio vegetation index (RVI), topographic wetness index (TWI), elevation, slope aspect (SA), slope gradient (SG), mean annual temperature (MAT), and mean annual precipitation (MAP) were selected to predict SOC density. A total of 193 soil samples (0–30 cm) were divided into two parts, 70% of the sampling sites data were used to construct the boosted regression tree (BRT) model containing three different combinations of environmental variables, and the remaining 30% were used to test the predictive performance of the model. The results show that the full variable model is better than the other two models. Adding remote sensing-related variables significantly improved the model prediction. This study revealed that SAVI, NDVI and DVI were the main environmental factors affecting the spatial variation of topsoil SOC density of coastal wetlands in flat terrain areas. The mean (±SD) SOC density of full variable models was 18.78 (±1.95) kg m−2, which gradually decreased from northeast to southwest. We suggest that remote sensing-related environmental variables should be selected as the main environmental variables when predicting topsoil SOC density of coastal wetland ecosystems in flat terrain areas. Accurate prediction of topsoil SOC density distribution will help to formulate soil management policies and enhance soil carbon sequestration.

Kohlenstoffumsatz in aggregierten Böden bestimmt mit Hilfe der natürlichen 13C Abundanz

Afforestation has been implemented on a large scale in the Loess Plateau of China since 1999. This paper aimed to judge the influence of plantation tree types on soil aggregate stability and carbon stocks. The results showed that : (1)the content of soil organic matter and macro-aggregates, the water stability of aggregates were significantly higher in P. tabuliformis plantation compared with R. pseudoacacia and M. pumila plantations, conversely, the content of soil calcium carbonate in P. tabuliformis plantation was the lowest; (2) the content of soil organic matter and organic carbon density were significantly negatively correlated with soil depth, while soil carbonate calcium and in-organic carbon density fluctuated with the increasing of soil depth; (3) compared with topsoil, subsoil was important carbon sink because there were more in-organic carbon; (4) Aggregate organic carbon increased while inorganic carbon decreased with the increasing of aggregate size respectively. We concluded that: (1) R. pseudoacacia played a more important role in soil carbon sequestration compared with P. tabuliformis; while P. tabuliformis was more beneficial to improve soil organic matter and soil structure; (2) subsoil and in-organic carbon were important carbon sinks compared with topsoil and organic carbon; (3) the bigger water stable aggregates having the higher content of soil organic matter and the lower carbonate calcium.

There is a growing interest in understanding soil organic carbon (SOC) and total nitrogen (TN) of various ecosystems worldwide, because they are important indicators of soil quality and soil fertility, especially on the availability of essential nutrients for plant growth; and climate change mitigation. We tested the hypothesis that the amount and vertical distribution of SOC and TN in 0-30cm and 30-100cm depths differ significantly in miombo woodland ecosystems. Soil samples were collected from 15m-radius circular plots (n=33). SOC was determined by Mid-Infrared (MIR) spectroscopy (ICRAF approach) and the Walkley and Black method (NAFORMA approach). The mean amount of SOC and TN at 30-100cm depth were significantly higher (<i>p</i>=0.003 and <i>p</i>=0.0001, respectively) than that within the 0-30cm depth. The amount of SOC at 20-40cm (39tCha^-1) was found to be significantly (<i>p</i>=0.0007) higher than at 0-20cm (32tCha^-1) followed by decreasing pattern to 100cm. On the other hand, TN decreased substantially from 0-20cm to 100cm depth. SOC was significantly (<i>p</i><0.05) and positively correlated with TN. The NAFORMA approach estimated significantly (<I>P</I><<i>0.05</i>) higher SOC than ICRAF approach. Clearing of forests for sesame cultivation invariably resulted in increased nitrogen in the top soil due to addition of ammonium fertilizers, but loss of SOC is due to removal of biomass (including slash burning) and a reduction in the quantity and quality of organic inputs added to the soil. Accurate estimation of SOC at national and regional scales should use the modern methods complimented by the standard methods in different ecosystems.