Soil Carbon Pools Research Articles

Mapping organic layer thickness and fuel load of the boreal forest in Alberta, Canada

Forest organic layers are important soil carbon pools that can, in the absence of disturbance, accumulate to great depths, especially in lowland areas. Across the Canadian boreal forest, fire is the primary disturbance agent, often limiting organic layer accumulation through the direct consumption of these fuels. Organic layer thickness (OLT) and fuel load (OLFL) are common physical attributes used to characterize these layers, especially for wildland fire science. Understanding the drivers and spatial distribution of these attributes is important to improve predictions of fire behaviour, emissions and effects models. We developed maps of OLT and OLFL using machine learning approaches (weighted K-nearest neighbour and random forests) for the forested region of the province of Alberta, Canada (538, 058 km2). The random forests approach was found to be the best approach to model the spatial distribution of these forest floor attributes. A databased of 3, 237 OLT and 594 OLFL plots were used to train the models. The error in our final model, particularly for OLT (5 cm), was relatively close to the variability we would expect to find naturally (3 cm). The dominant tree species was the most important covariate in the models. Age, solar radiation, spatial location, climate variables and surficial geology were also important drivers, although their level of importance varied between tree species and depended on the modelling method that was used.

A dynamic local-scale vegetation model for lycopsids (LYCOm v1.0)

Abstract. Lycopsids represent a distinct lineage of vascular plants with a long evolutionary history including numerous extant and extinct species that started out as tiny herbaceous plants and later went on to grow into forests with tree-like structures. They enriched the soil carbon pool through newly developed root-like structures and promoted soil microbial activity by providing organic matter. These plants enhanced soil carbon dioxide (CO2) via root respiration and also modified soil hydrology. These effects potentially promoted the dissolution of silicate minerals, thus intensifying silicate weathering. The weathering of silicate rocks is considered one of the most significant geochemical regulators of atmospheric CO2 over a long (hundreds of thousands to millions of years) timescale. The motivation for this study is to achieve an increased understanding of the realized impacts of vascular plants, represented by modern relatives of the most basal plants with vascular tissues and shallow root systems, on silicate weathering and past climate. To this end, it is necessary to quantify physiological characteristics, spatial distribution, carbon balance, and the hydrological impacts of early lycopsids. These properties, however, cannot be easily derived from proxies such as fossil records. Hence, as a first step, a process-based model is developed to estimate net carbon uptake by these organisms at the local scale. The model includes key features such as the distribution of biomass above and below ground, along with a plausible root distribution in the soil affecting water uptake by plants. The stomatal regulation of water loss and its immediate implications for photosynthesis are considered. Moreover, root respiration plays a crucial role in the model by affecting soil carbon dioxide and weathering rates. The model features ranges of key physiological traits of lycopsids to predict the emerging characteristics of the Lycopsida class community under any given climate by implicitly simulating the process of selection. In this way, extinct plant communities can also be represented. In addition to physiological properties, the model also simulates weathering rates using a simple limit-based approach and estimates the biotic enhancement of weathering by these plants. We run the Lycopsid model, called LYCOm, at seven sites encompassing various climate zones under today's climatic conditions. LYCOm can simulate realistic properties of lycopsid communities at the respective locations and estimates values of net primary production (NPP) ranging from 126 to 245 g carbon m−2 yr−1. Our limit-based weathering model predicts a mean chemical weathering rate ranging from 5.3 to 45.1 cm ka−1 of rock with lycopsids varying between different sites, as opposed to 0.6–8.3 cm ka−1 of rock without these plants, thereby highlighting the potential importance of such vegetation at the local scale for enhancing chemical weathering. Our modeling study establishes a basis for assessing the biotic enhancement of weathering by lycopsids at the global scale and also for the geological past. Although our method is associated with limitations and uncertainties, it represents a novel, complementary approach towards estimating the impacts of lycopsids on biogeochemistry and climate.

Effects of land use and land cover change on soil organic carbon storage in the Hexi regions, Northwest China

Soil organic carbon (SOC) storage in arid inland regions is significantly affected by land use and land cover change (LUCC) associated with climate change and agricultural activities. A systematic evaluation to the LUCC effects on SOC storage could enable us to better manage soil carbon pools in arid inland regions. Here, we evaluated the effects of LUCC on SOC storage in the Hexi Regions based on high-resolution SOC and LUCC maps derived from Landsat imagery and digital soil mapping using machine learning algorithm and environmental covariates. The results showed that SOC generally increased from northwest to southeast over the Hexi Regions with an average stock of 7.15 kg C m−2 at a soil depth of 100 cm and a total storage of 2783.05 Tg C. The SOC stock and storage in the Qilian Mountains (mountains) was about 3.90 and 4.55 times higher than that in the Hexi Corridor (plains), respectively. It was estimated that LUCC over the past four decades caused a net increase of 23.41 and 18.19 Tg C in total SOC storage for the Qilian Mountains and Hexi Corridor, respectively. Specifically, the development in grasslands quality as well as the land-use category conversion from the bare land to grassland mainly contributed to the increase in SOC storage of the Qilian Mountains, where the LUCC was mainly driven by climate change. By contrast, the SOC storage change in the Hexi Corridor was mainly associated with the conversion from sandy land and low-cover grassland to cropland as well as sandy land to grassland, being mainly affected by intense cropland expansion and desertification control. Our results highlighted the importance of climate change and cropland expansion in enhancing SOC storage of the Qilian Mountains and Hexi corridor, respectively.

The carbon and nitrogen stoichiometry in litter-soil-microbe continuum rather than plant diversity primarily shapes the changes in bacterial communities along a tropical forest restoration chronosequence

Soil bacteria play core roles in mediating the functional linkage between above- and belowground components during forest restoration. However, the pattern and mechanism through which plants and soils influence bacterial communities remain unclear. This study aimed to quantify the contributions of plant community and soil characteristics to shifts in bacterial composition and diversity along a tropical forest restoration chronosequence in the Xishuangbanna. We found a negative effect of forest restoration on bacterial composition and a positive impact on the diversity. Forest restoration changed bacterial communities from being oligotrophic Acidobacteria and Actinobacteria dominatedto copiotrophic Proteobacteria and Firmicutes dominated. Forest restoration also induced a 1.5–1.6 fold increase in OTU richness and diversity of bacterial communities. Soil variables, including plant litter, contributed 46.3–58.1% to the variations in bacterial composition and diversity, while the contribution of plant community was 6.4–13.8%. Furthermore, the increase in plant richness and diversity had minor contribution to variations in bacterial diversity and composition during forest restoration. Soil bacterial diversity was primarily explained by the elevated levels of carbon and nitrogen stoichiometry in the litter-soil-microbe continuum, but litter was explained by the increased plant diversity. In contrast, soil bacterial composition was negatively correlated with biomass, nitrogen, and carbon:nitrogen of the litter, as well as the level of soil carbon and nitrogen pools. Our data suggested that the carbon and nitrogen stoichiometry in litter-soil-microbe continuum rather than plant diversity primarily shaped the changes in bacterial composition and diversity along tropical forest restoration.

Agroforestry for controlling soil erosion and enhancing system productivity in ravine lands of Western India under climate change scenario.

Soil erosion in semi-arid climate leading to the development of ravine lands is the most severe form of land degradation. Ravine lands are formed when soil is not fully covered by the vegetation throughout the year and sporadic vegetation is not able to bind the soil particles from being washed away by rainfall. Throughout the globe, ravine lands have severe limitations for their rehabilitation and sustainable utilization as a consequence of its unique topographical features. Climatic and edaphic stresses make crop production extremely challenging in these lands. Practicing sole cropping promotes erosion, produces low crop yield, utilizes high energy, and emits greenhouse gasses (GHGs). Tree cultivation either sole or in combination with crops (agroforestry) has a strong potential to control erosion, produce sustainable economic yield, reduce energy consumption, and sequester greater amount of atmospheric carbon dioxide in biomass and soil carbon pools besides providing various ecosystem services. Therefore, practicing agroforestry could be a promising approach to obtain the greater environmental and economic benefits in the ravine lands. The present study was conducted on three systems, i.e., sole crop cultivation (cowpea + castor), agroforestry (sapota + cowpea + castor), and sole sapota plantation, to evaluate their impact on soil erosion, runoff, system productivity, profitability, energetics, and carbon sequestration during the 4-year period (2017-2020). The results revealed that agroforestry reduced the total soil loss and runoff by 37.7% and 19.1%, respectively, compared to the sole crop cultivation. Likewise, the highest system productivity as cowpea equivalent yield (CEY) was obtained under agroforestry system that increased the CEY by 162% and 81.9%, compared to sole crop and sole tree plantation, respectively. The climate change mitigation potential in terms of net carbon balance was observed highest in sole tree plantation (8.4 t/ha) followed by agroforestry system (5.9 t/ha) and lowest in sole cropping system (-2.8 t/ha). Therefore, an agroforestry system could be recommended for controlling soil erosion, improving system productivity and profitability, and reducing energy consumption as well as mitigating climate change in ravine lands.

Role of hydrological parameters in the uncertainty in modeled soil organic carbon using a coupled water-carbon cycle model

Soil organic carbon is the largest carbon pool in the terrestrial biosphere. Large uncertainties exist in the numerical simulations of soil organic carbon due to inaccuracies in their mathematical descriptions of hydrological processes. In this study, the upper limit of uncertainty in modeled soil organic carbon that is induced by hydrological parameter errors, which may stem from measurement or experiential errors, is estimated in China under four different arid and humid conditions. The study was conducted using a conditional nonlinear optimal perturbation related to parameters (CNOP-P) approach and a model of the coupled water-carbon cycle (the Lund-Potsdam-Jena Wetland Hydrology and Methane Dynamic Global Vegetation Model, LPJ-WHyMe). Uncertainties in hydrological processes resulted in the largest error (2.73 kg C m−2 yr−1, 20.2%) in the modeled soil organic carbon in the arid and semiarid regions of northern China, with errors of 1.20 kg C m−2 yr−1 (6.1%) in northeastern China, 0.45 kg C m−2 yr−1 (3.3%) in southern China, and -1.71 kg C m−2 yr−1 (13.7%) in the semihumid region of northern China. By analyzing the three components of soil organic carbon, the fast soil carbon pool was found to be the main cause of the uncertainties in modeled soil organic carbon in the four regions of China. Moreover, belowground litter was another cause of the uncertainties in the modeled soil organic carbon in northeastern China and in the semihumid region of northern China. Additional results indicated that the simulation and prediction abilities of soil organic carbon could be improved by reducing parameter errors in hydrological processes through observations or targeted observations. The parameter sensitivity test showed that the benefits to modeling soil organic carbon were similar when reducing the errors in the sensitive hydrological parameter subset, compared to the benefits of reducing the errors in all the hydrological parameters.

Impact of Land-Use Changes on Soil Properties and Carbon Pools in India: A Meta-analysis

Land-use changes (LUC), primarily due to deforestation and soil disturbance, are one of the major causes of soil quality degradation and greenhouse gas emissions. Effects of LUC on soil physicochemical properties and changes in soil quality and land use management strategies that can effectively restore soil carbon and microbial biomass levels have been reported from all over the world, but the impact analysis of such practices in the Indian context is limited. In this study, over 1,786 paired datasets (for meta-analysis) on land uses (LUs) were collected from Indian literature (1990–2019) to determine the magnitude of the influence of LUC on soil carbon, microbial biomass, and other physical and chemical properties at three soil depths. Meta-analysis results showed that grasslands (36.1%) lost the most soil organic carbon (SOC) compared to native forest lands, followed by plantation lands (35.5%), cultivated lands (31.1%), barren lands (27.3%), and horticulture lands (11.5%). Our findings also revealed that, when compared to forest land, the microbial quotient was lower in other LUs. Due to the depletion of SOC stock, carbon dioxide equivalent (CO2 eq) emissions were significantly higher in all LUs than in forest land. Results also showed that due to the conversion of forest land to cultivated land, total carbon, labile carbon, non-labile carbon, microbial biomass carbon, and SOC stocks were lost by 21%, 25%, 32%, 26%, and 41.2%, respectively. Changes in soil carbon pools and properties were more pronounced in surface (0–15 cm) soils than in subsurface soils (15–30 cm and 30–45 cm). Restoration of the SOC stocks from different LUs ranged from a minimum of 2% (grasslands) to a maximum of 48% (plantation lands). Overall, this study showed that soil carbon pools decreased as LUC transitioned from native forestland to other LUs, and it is suggested that adopting crop-production systems that can reduce CO2 emissions from the intensive LUs such as the ones evaluated here could contribute to improvements in soil quality and mitigation of climate change impacts, particularly under Indian agro-climatic conditions.

Disturbance alters relationships between soil carbon pools and aboveground vegetation attributes in an anthropogenic peatland in Patagonia.

Anthropogenic‐based disturbances may alter peatland soil–plant causal associations and their ability to sequester carbon. Likewise, it is unclear how the vegetation attributes are linked with different soil C decomposition‐based pools (i.e., live moss, debris, and poorly‐ to highly‐decomposed peat) under grassing and harvesting conditions. Therefore, we aimed to assess the relationships between aboveground vegetation attributes and belowground C pools in a Northern Patagonian peatland of Sphagnum magellanicum with disturbed and undisturbed areas. We used ordination to depict the main C pool and floristic gradients and structural equation modeling (SEM) to explore the direct and indirect relationships among these variables. In addition, we evaluated whether attributes derived from plant functional types (PFTs) are better suited to predict soil C pools than attributes derived from species gradients. We found that the floristic composition of the peatland can be classified into three categories that follow the C pool gradient. These categories correspond to (1) woody species, such as Baccharis patagonica, (2) water‐logged species like Juncus procerus, and (3) grasslands. We depicted that these classes are reliable indicators of soil C decomposition stages. However, the relationships change between management. We found a clear statistical trend showing a decrease of live moss, debris, and poorly‐decomposed C pools in the disturbed area. We also depicted that plant diversity, plant height, and PFT composition were reliable indicators of C decomposition only under undisturbed conditions, while the species‐based attributes consistently yielded better overall results predicting soil C pools than PFT‐based attributes. Our results imply that managed peatlands of Northern Patagonia with active grassing and harvesting activities, even if small‐scaled, will significantly alter their future C sequestration capacities by decreasing their live and poorly‐decomposed components. Finally, aboveground vegetation attributes cannot be used as proxies of soil C decomposition in disturbed peatlands as they no longer relate to decomposition stages.

Determining Carbon Dioxide Emission Response in Soil Microcosms from a Shallow Mid-Atlantic Peatland: The Influence of Water Table Restoration

Johnson, A.M.; Atkinson, R.B.; Steven, J.C.; Whiting, G.; Napora, K.; Sharrett, L., and Mirda, C., 2022. Determining carbon dioxide emission response in soil microcosms from a shallow mid-Atlantic peatland: The influence of water table restoration. Journal of Coastal Research, 38(2), 261–268. Coconut Creek (Florida), ISSN 0749-0208. Determining carbon dioxide emission response in shallow microcosms from a shallow mid-Atlantic peatland: The influence of water table restoration. Peatlands provide ecosystem services such as pollution filtration, flood control, and carbon storage as these ecosystems contain 33% to 50% of the global soil carbon pool. Reestablishing soil saturation in degraded peatlands can limit microbial oxidation of organic matter; however, drainage history may alter soil saturation patterns and challenge restoration efforts. The purpose of this study was to investigate carbon emission response to water table restoration for two shallow peatlands including a Histosol and an Ultisol with divergent drainage histories. Soil cores were gathered from the top 22.5 cm of organic-rich surface horizons within Cavalier Wildlife Management Area in Chesapeake, Virginia. Cores were randomly assigned to four water level treatments that simulated restoration conditions, and carbon dioxide emissions were measured using an LI-6400XT portable open-flow photosynthesis system twice a week for 4 weeks. Despite higher organic matter content in the long-drained site, emissions (2.1 to 3.9 µmol CO2 m–2 s–1) were higher than at the historically less drained site (1.5 to 2.3 µmol CO2 m–2 s–1). Volumetric water content trends revealed that longer-drained soils retained lower water content within restoration treatments and were associated with higher carbon emissions. Restoration of long-drained peats in the mid-Atlantic region may require higher water tables than otherwise predicted to overcome a resistance to rewetting where limiting microbial soil respiration is a management objective.

Carbon Storage Potential of Agroforestry System near Brick Kilns in Irrigated Agro-Ecosystem

The current study was conducted to estimate the carbon (C) storage status of agroforestry systems, via a non-destructive strategy. A total of 75 plots (0.405 ha each) were selected by adopting a lottery method of random sampling for C stock estimations for soil, trees and crops in the Mandi-Bahauddin district, Punjab, Pakistan. Results revealed that the existing number of trees in selected farm plots varied from 25 to 30 trees/ha. Total mean tree carbon stock ranged from 9.97 to 133 Mg C ha−1, between 5–10 km away from the brick kilns in the study area. The decreasing order in terms of carbon storage potential of trees was Eucalyptus camaldulensis > Syzygium cumin > Popolus ciliata > Acacia nilotica > Ziziphus manritiana > Citrus sinensis > Azadirachtta Indica > Delbergia sisso > Bambusa vulgaris > Melia azadarach > Morus alba. Average soil carbon pools ranged from 10.3–12.5 Mg C ha−1 in the study area. Meanwhile, maximum C stock for wheat (2.08 × 106 Mg C) and rice (1.97 × 106 Mg C) was recorded in the cultivated area of Tehsil Mandi-Bahauddin. The entire ecosystem of the study area had an estimated woody vegetation carbon stock of 68.5 Mg C ha−1 and a soil carbon stock of 10.7 Mg C ha−1. These results highlight that climate-smart agriculture has great potential to lock up more carbon and help in the reduction of CO2 emissions to the atmosphere, and can be further used in planning policies for executing tree planting agendas on cultivated lands and for planning future carbon sequestration ventures in Pakistan.

Diverging patterns at the forest edge: Soil respiration dynamics of fragmented forests in urban and rural areas.

As urbanization and forest fragmentation increase around the globe, it is critical to understand how rates of respiration and carbon losses from soil carbon pools are affected by these processes. This study characterizes soils in fragmented forests along an urban to rural gradient, evaluating the sensitivity of soil respiration to changes in soil temperature and moisture near the forest edge. While previous studies found elevated rates of soil respiration at temperate forest edges in rural areas compared to the forest interior, we find that soil respiration is suppressed at the forest edge in urban areas. At urban sites, respiration rates are 25% lower at the forest edge relative to the interior, likely due to high temperature and aridity conditions near urban edges. While rural soils continue to respire with increasing temperatures, urban soil respiration rates asymptote as temperatures climb and soils dry. Soil temperature- and moisture-sensitivity modeling shows that respiration rates in urban soils are less sensitive to rising temperatures than those in rural soils. Scaling these results to Massachusetts (MA), which encompasses 0.25Mha of the urban forest, we find that failure to account for decreases in soil respiration rates near urban forest edges leads to an overestimate of growing-season soil carbon fluxes of >350,000Mg C. This difference is almost 2.5 times that for rural soils in the analogous comparison (underestimate of <143,000Mg C), even though rural forest area is more than four times greater than urban forest area in MA. While a changing climate may stimulate carbon losses from rural forest edge soils, urban forests may experience enhanced soil carbon sequestration near the forest edge. These findings highlight the need to capture the effects of forest fragmentation and land use context when making projections about soil behavior and carbon cycling in a warming and increasingly urbanized world.

Evaluation of no-tillage impacts on soil respiration by 13C-isotopic signature in North China Plain

It is a challenge to characterize soil respiration of crop residue return systems in the North China Plain (NCP) under no-tillage (NT) and conventional tillage (CT) practices. In this study, we addressed the “hot spot” research challenge of impacts of tillage practices on soil carbon storage and soil CO2 emissions in the NCP by 13C-isotopic signature. A short-term (2018–2020) field experiment was conducted with two tillage practices: NT and CT. The results showed that in the tested area, NT had advantages of lower CO2 emissions compared to CT with average reduced CO2 emissions by 10.82%–19.14%. The results of this study suggested that the NT facilitated enhanced soil carbon storage by 2.80%, which was evidenced by the δ13C data. Based on the path analysis model, the main line of soil respiration reduced by NT was attributed to the increased of soil microbial carbon and nitrogen as well as soil moisture in NT, which further increased δ13C and eventually inhibited soil respiration. Overall, adopting NT in NCP is an effective means to improve soil carbon pool and decrease soil CO2 emissions in agriculture practices.

The accumulation of microbial residues and plant lignin phenols are more influenced by fertilization in young than mature subtropical forests

Soil microbial residues and plant-derived compounds are important components of the stable carbon (C) pool in forest soil. It is not well understood how microbial residues and plant lignin phenols respond to nutrient inputs in subtropical forests of different ages, especially in mature forest stands. Here, a 5-year nitrogen (N) and phosphorus (P) fertilization (addition) management experiment was conducted in two stages of subtropical forests (<40- and > 80-year). We found that the concentrations of amino sugars (i.e., microbial residues) and plant lignin phenols and their contributions to soil organic carbon (SOC) were significantly higher in the > 80-year forests than in the < 40-year forests. In the < 40-year forests, N addition increased amino sugars and lignin phenols and their contributions to SOC, whereas P addition decreased muramic acid (bacterial-derived) and its contribution to SOC. In the > 80-year forests, however, N and P addition had no significant effect on amino sugars and lignin phenols and their contributions to SOC. Overall, soil total amino sugars and lignin phenols could be directly and indirectly affected by forest age and N addition, and could be only indirectly impacted by P addition. Our results suggest that microbial residues and plant lignin phenols are sensitive to the nutrient additions in the young forests, which have a greater potential for the soil stable C sequestration in comparison with the mature forests.

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

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

Rhizosphere enzyme activities and microorganisms drive the transformation of organic and inorganic carbon in saline\u2013alkali soil region

Western Jilin Province is one of the world's three major saline–alkali land distribution areas, and is also an important area of global climate change and carbon cycle research. Rhizosphere soil microorganisms and enzymes are the most active components in soil, which are closely related to soil carbon cycle and can reflect soil organic carbon (SOC) dynamics sensitively. Soil inorganic carbon (SIC) is the main existing form of soil carbon pool in arid saline–alkali land, and its quantity distribution affects the pattern of soil carbon accumulation and storage. Previous studies mostly focus on SOC, and pay little attention to SIC. Illumina Miseq high-throughput sequencing technology was used to reveal the changes of community structure in three maize fields (M1, M2 and M3) and three rice fields (R1, R2 and R3), which were affected by different levels of salinization during soil development. It is a new research topic of soil carbon cycle in saline–alkali soil region to investigate the effects of soil microorganisms and soil enzymes on the transformation of SOC and SIC in the rhizosphere. The results showed that the root—soil—microorganism interaction was changed by saline–alkali stress. The activities of catalase, invertase, amylase and β-glucosidase decreased with increasing salinity. At the phylum level, most bacterial abundance decreases with increasing salinity. However, the relative abundance of Proteobacteria and Firmicutes in maize field and Firmicutes, Proteobacteria and Nitrospirae in rice field increased sharply under saline–alkali stress. The results of redundancy analysis showed that the differences of rhizosphere soil between the three maize and three rice fields were mainly affected by ESP, pH and soil salt content. In saline–alkali soil region, β-glucosidase activity and amylase were significantly positively correlated with SOC content in maize fields, while catalase and β-glucosidase were significantly positively correlated with SOC content in rice fields. Actinobacteria, Bacteroidetes and Verrucomicrobia had significant positive effects on SOC content of maize and rice fields. Proteobacteria, Gemmatimonadetes and Nitrospirae were positively correlated with SIC content. These enzymes and microorganisms are beneficial to soil carbon sequestration in saline–alkali soils.

Vertical Distribution and Controlling Factors of Soil Inorganic Carbon in Poplar Plantations of Coastal Eastern China

Afforestation is a strategy to protect croplands and to sequestrate carbon in coastal areas. In addition, inorganic carbon is a considerable constitute of the coastal soil carbon pool. However, the vertical distribution and controlling factors of soil inorganic carbon (SIC) in plantations of coastal areas have been rarely studied. We analyzed the SIC content as well as physiochemical properties along soil profiles (0–100 cm) in young (YP) and mature (MP) poplar plantations in coastal eastern China. The soil profile was divided into six layers (0–10, 11–20, 21–40, 41–60, 61–80 and 81–100 cm) and a total of 36 soil samples were formed. The SIC content first increased from 0–10 cm (0.74%) to 11–20 cm (0.92%) and then fluctuated in the YP. In contrast, the SIC content increased with increasing soil depth until 40 cm and then leveled off, and the minimum and maximum appeared at 0–10 cm (0.54%) and 81–100 cm (0.98%) respectively in the MP. The soil inorganic carbon density was 12.05 and 12.93 kg m−2 within 0–100 cm in the YP and MP, respectively. Contrary to SIC, soil organic carbon (SOC) first decreased then levelled off within the soil profiles. Compared with the YP, the SIC content decreased 27.8% at 0–10 cm but increased 13.2% at 21–40 cm, meanwhile the SOC content in MP decreased 70.6% and 46.7% at 21–40 cm and 61–80 cm, respectively. The water-soluble Ca2+ and Mg2+ gradually decreased and increased, respectively within the soil profiles. The soil water-soluble Ca2+ increased 18.3% within 41–100 cm; however, the soil water-soluble Mg2+ decreased 32.7% within 21–100 cm in the MP when compared to the YP. Correlation analysis showed that SIC was negatively correlated with SOC, but positively correlated with soil pH and water-soluble Mg2+. Furthermore, structural equation modeling (SEM) indicated that SOC was the most important factor influencing the SIC content in the studied poplar plantations, indicating SOC sequestration promoted the dissolution of SIC. Therefore, our study highlights the trade-off between SIC and SOC in poplar plantations of coastal Eastern China.

Influence of Different Nutrient Management Practices and Cropping Systems on Organic Carbon Pools in Typic Ustochrept Soil of Indo-Gangetic Plains in India

Influence of Different Nutrient Management Practices and Cropping Systems on Organic Carbon Pools in Typic Ustochrept Soil of Indo-Gangetic Plains in India

Impact of long-term manures and balanced fertilization on soil carbon pools in mollisols under rice-wheat cropping system

This paper assesses the impact of long-term (30 years) application of balanced fertilizers with or without farmyard manure (FYM) on soil carbon pools after harvest of rice under intensively cultivated rice-wheat cropping system. Soil organic carbon (SOC) and its fractions were evaluated in soil (Aquic Hapludoll with silty loam) during 2014–15 from an ongoing long-term field experiment (LTFE) initiated in 1984 at Crop Research Centre of Govind Ballabh Pant University of Agriculture and Technology, Pantnagar. Fourteen fertilization treatments with different levels of nitrogen (N), phosphorus (P), potassium (K), with or without FYM and zinc (Zn) were arranged in a randomized block design. Findings of investigation revealed that application of 100% NPK (N120+P40+K40) and super optimal NPK (N180+P80+K40) along with FYM and Zn increased SOC by 51.5 and 58.7 per cent, particulate organic C by 41.4 and 45.4 per cent, water soluble C by 77.9 and 86.4 per cent, hot water extractable C by 91.2 and 97.1 per cent, water soluble carbohydrates by 187.3 and 204.9 per cent, potentially mineralizable C by 107.6 and 114.5 per cent, KMnO4 oxidizable C by 43.1 and 47.0 per cent and microbial biomass C by 66.3 and 64.4% over control in entire 0–60 cm soil profile, respectively. It was also found that rice grain yield was increased by 222.2 per cent over control with the application of 100% NPK (N120+P40+K40) along with FYM and Zn. Therefore, from this experiment it is concluded that application of balanced optimal and super optimal NPK along with FYM and Zn (N120+P40+K40+Zn+FYM and N180+P80+K40+Zn+FYM) in intensively cultivated cropping system is a sustainable management practice to sustain soil fertility by accumulating and sequestering sizable carbon in soil and enhanced production of rice-wheat cropping system.

Carbon Materials Advancing Microorganisms in Driving Soil Organic Carbon Regulation.

Carbon emission from soil is not only one of the major sources of greenhouse gases but also threatens biological diversity, agricultural productivity, and food security. Regulation and control of the soil carbon pool are political practices in many countries around the globe. Carbon pool management in engineering sense is much bigger and beyond laws and monitoring, as it has to contain proactive elements to restore active carbon. Biogeochemistry teaches us that soil microorganisms are crucial to manage the carbon content effectively. Adding carbon materials to soil is thereby not directly sequestration, as interaction of appropriately designed materials with the soil microbiome can result in both: metabolization and thereby nonsustainable use of the added carbon, or—more favorably—a biological amplification of human efforts and sequestration of extra CO2 by microbial growth. We review here potential approaches to govern soil carbon, with a special focus set on the emerging practice of adding manufactured carbon materials to control soil carbon and its biological dynamics. Notably, research on so-called “biochar” is already relatively mature, while the role of artificial humic substance (A-HS) in microbial carbon sequestration is still in the developing stage. However, it is shown that the preparation and application of A-HS are large biological levers, as they directly interact with the environment and community building of the biological soil system. We believe that A-HS can play a central role in stabilizing carbon pools in soil.

Impact of litter quality on the stability and storage of soil carbon in flooded wetlands

Context High inputs of plant litters and slow decomposition of soil organic carbon (SOC) influence the biogeochemical cycling of soil carbon in flooded wetlands. Aims To investigate the effects of different quality litter inputs on SOC stability and storage in flooded wetlands. Methods A 180-day microcosmic experiment to investigated the decomposition of litters of two dominant plants (Carex cinerascens Kukenth., CC; Cyperaceae family) and Triarrhena lutarioriparia L. Liu, TL; Poaceae family), in Poyang Lake Wetlands. Key results CC litters (high-quality, low lignin/N mass ratio) reduced gross content of SOC, but increased labile carbon and labile index (LI) of soils. In contrast, inputs of TL litters (low-quality, high lignin/N mass ratio) increased SOC gross content and recalcitrant carbon fractions of soils, but reduced soil labile carbons and LI. Significant effects of litters on SOC were not observed until ∼30 days indicating that the effects of litter inputs on soil carbon pools in flooded wetlands need time to be activated. CC and TL litters both increased the soil microbial biomass carbon (MBC) content. Soil MBC in CC treatments was significantly affected by the litter ash-free dry mass, while that in TL treatments was significantly affected by mass loss. Conclusions Litter quality may regulate the growth of soil MBC via different microbial growth strategies. Implications Our results suggest that inputs of high-quality litters can yield a high amount of labile carbon through stimulated microbial decomposition, leading to an overall loss of carbon. In contrast, inputs of low-quality litters can promote the microbial production of more recalcitrant carbons and increase soil carbon stability and carbon sequestration.