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Soil organic matter (SOM) plays a central role for both the C cycle and soil functions. Plants provide the input and heterotrophic (micro)organisms are essential for the turnover. Microbial metabolism links matter and energy fluxes and generates the highest energy turnover dynamics in SOM because the organisms need both energy and matter for maintenance and growth. In this perspectives paper, we evaluate the knowledge on thermodynamic approaches potentially applicable to study the turnover of organic matter in the soil system. Thermodynamics is essential for understanding organic matter turnover in soil as turnover and storage are controlled by the energy supply to, and consumption by, microbes. Instead of just comparing the heat of combustion of compounds without considering microbial anabolism, we need to apply conventional thermodynamic state variables that can be either estimated using established thermodynamic equations, or measured empirically in soil. In particular, we can follow and quantify overall changes of enthalpies by calorimetry. Here, we suggest to apply a thermodynamic concept with the related experimental approaches of calo(respiro)metry and turnover mass balances including biomass formation. This enables us to better interpret and understand the highly variable carbon use efficiency (CUE) in a multi-substrate system such as soil and to relate this to energy use efficiency (EUE). Combining the experimental measurements of the thermodynamic state variables with mass turnover data allow prediction of whether compounds can be metabolized with energy delivery to microorganisms, or be thermodynamically stabilized under the respective redox and electron acceptor conditions. Energy balancing shows how much energy is actually used and retained in the soil, how much is emitted as heat, and how much may be stabilized due to endergonic turnover reactions. Thermodynamic stabilization should therefore be considered as basic stabilization process for organic compounds in soil. • Energy fluxes are essential to sustain active microbes contributing to soil organic matter (SOM). • Dynamic energy and matter fluxes in soil are tightly coupled. • Thermodynamics can describe microbial SOM formation and transformation. • Thermodynamic state variables allow balancing and interpreting of soil processes. • Gibbs energy gain for microbes is dominated by the electron acceptors half-reaction. [ABSTRACT FROM AUTHOR]

The climate change problem is caused by human-induced increases in the stock of greenhouse gases (GHGs) in the atmosphere. In Cambodia, forests provide many important ecosystem services to local people such as food production, natural medicine, water supply, and wind/storm protection. Additionally, Cambodian forests sequester a considerable amount of carbon, contributing to the mitigation of greenhouse gas-induced climate change on a global level. However, the amount of carbon stored in forests differs according to spatial and temporal factors such as forest type, size, age, stand structure, associated vegetation, and ecological zonation, among other things. The current research aimed to i) conduct forest inventory of upland forest area in the Koh Kong, Mondulkiri, Preah Viher, and Siem Reap provinces of Cambodia, and ii) assess carbon stock at the target sites across different provinces. The study applied the carbon stock assessment methodology as outlined in the National Forest Inventory and the Field Manual for the National Forestry Inventory of Cambodia issued by the Food and Agriculture Organization (FAO) in 2018, applied across different types of forest at several pilot project sites. In addition, the study conducted an assessment of carbon stock in soil and ground litter carbon pools. The research studied five carbon pools: aboveground biomass pool (AGB), belowground biomass pool (BGB), litter biomass pool, dead wood biomass pool, and soil organic carbon pool (SOC). The results indicated total carbon stock in Koh Kong Province at 200.04 tonnes C/ha for evergreen forest, in Mondulkiri Province at 246.18 tonnes C/ha for deciduous forest, in Preah Vihear Province at 185.06 tonnes C/ha for deciduous forest, and in Siem Reap Province at 207.67 tones C/ha for deciduous forest and 414.13 tones C/ha for evergreen forest [ABSTRACT FROM AUTHOR]

Evaluates the short- and intermediate-term effects of repeatedly amending sandy soil with paper mill residuals (PMR) and composted PMR in a vegetable rotation in Wisconsin's central sands. Effects of PMR and composted PMR on total soil carbon; Changes in water-holding capacity and plant-available water (PAW); Relationship between total soil carbon and PAW.

One of the most promising recycling procedures of some industrial organic wastes, as paper mill sludge (PMS), is soil amendment. In this field of application, PMS and natural soil are mixed together according to specific regulations to avoid potential environmental risks that can arise after land restoration, and hence, the mixture must be scrupulously characterized and evaluated, also by means of different analytical techniques. Proton nuclear magnetic resonance (H NMR) is a powerful, noninvasive and nondestructive technique to investigate natural and artificial porous media, and it is a promising tool to characterize amended soils as well, also in the light of the experimental difficulties that these materials generally entail. In this work, NMR micro- and macro-porosity were related to total organic carbon (TOC) content, and information on the behavior of organic matter (OM) contained inside the mineral matrix was obtained. In particular, a high presence of TOC shows that micropores are forbidden to the saturating water, giving evidence of OM interactions with soil microstructure. This kind of analysis has clear implications in the characterization of amended soil biological processes, such as biodegradation. [ABSTRACT FROM AUTHOR]

Assesses the effect of soil amendment by de-inking paper sludge (DPS) incorporation on organic matter and clay loam. Increase of soil carbon content with the addition of DPS; Formation of clusters of wood fibers by DPS encrusted with mineral particles; Proportion of residual carbon attributed to DPS.

Arbuscular mycorrhizal fungi (AMF) in the soil have many positive effects on growth, nutrient acquisition, and stress tolerance of host plants, as well as soil fertility, soil structure, and soil ecology. Glomalin-related soil proteins (GRSP) are a mixture of humic substances and heat-stable glycoproteins, primarily of AMF origin. GRSP are as an important component of soil organic carbon (C) pools, which can stabilize and sequestrate C, thus reducing soil C emissions for slowing down global warming. Based on the CiteSpace software and the core collection of Web of Science as the database, this study made a visual analysis of GRSP's literature in the C field published from 1999 to 2022, including the number of publications, countries, institutions, co-cited literature, keywords, top cited papers, etc. The study regarding the GRSP in the C field could be divided into the initial stage (1999–2009), the steady stage (2010–2018), and the explosive stage (2019–2022). The Chinese Academy of Sciences is the organization with the most publications, and the United States, China, and India are the three leading nations in the C field of GRSP. However, there was little collaboration among the participating countries and the study's institutions. The focus of the research has shifted from the composition and content of GRSP in C to the question of whether C in GRSP affects soil properties. Future research was also prospected. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Agrometeorology is the property of Editorial Board of Chinese Journal of Agrometeorology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The research papers assessing the content of soil organic carbon with the help of Vis-NIR spectroscopy approaches are systematically analyzed and subject to meta-analysis. This meta-analysis included 134 studies published in 1986–2022 with a total sample of 709 values of quantitative metrics. The papers have been searched for in databases of scientific periodicals (RSCI, Science Direct, Scopus, and Google Scholar) by the key word combination "Vis-NIR spectroscopy AND soil organic carbon". The meta-analysis using the nonparametric one-sided Kruskal–Wallis variance analysis in conjunction with nonparametric pairwise method shows the presence of a statistically significant difference between the median values of the accepted quantitative metrics of the predictive power of the models, namely, coefficient of determination (R2cv/val), root mean square error (RMSE), and the ratio of performance to deviation (RPD). The best performance of the preprocessing method for spectral curves is demonstrated and the estimates of soil organic carbon content obtained by laboratory and field spectroscopies are compared. [ABSTRACT FROM AUTHOR]

Copyright of Revista CIENCIA UNEMI is the property of Universidad Estatal de Milagro (UNEMI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper soil carbon, nitrogen and phosphorus concentrations and related elemental ratios, as well as and nitrogen and phosphorus stocks were investigated in 17 paired sites and in a regional survey encompassing more than 100 pasture soils in the Cerrado, Atlantic Forest, and Pampa, the three important biomes of Brazil. In the paired sites, elemental soil concentrations and stocks were determined in native vegetation, pastures and crop-livestock systems (CPS). Overall, there were significant differences in soil element concentrations and ratios between different land uses, especially in the surface soil layers. Carbon and nitrogen contents were lower, while phosphorus contents were higher in the pasture and CPS soils than in forest soils. Additionally, soil stoichiometry has changed with changes in land use. The soil C:N ratio was lower in the forest than in the pasture and CPS soils; and the carbon and nitrogen to available phosphorus ratio (PME) decreased from the forest to the pasture to the CPS soils. The average native vegetation soil nitrogen stocks at 0-10, 0-30 and 0- 60 cm soil depth layers were equal to approximately 2.3, 5.2, 7.3Mgha-1, respectively. 15 In the paired sites, nitrogen loss in the CPS systems and pasture soils were similar and equal to 0.6, 1.3 and 1.5Mgha-1 at 0-10, 0-30 and 0-60 cm soil depths, respectively. In the regional pasture soil survey, nitrogen soil stocks at 0-10 and 0-30 soil layers were equal to 1.6 and 3.9Mgha-1, respectively, and lower than the stocks found in the native vegetation of paired sites. On the other hand, the soil phosphorus stocks 20 were higher in the CPS and pasture of the paired sites than in the soil of the original vegetation. The original vegetation soil phosphorus stocks were equal to 11, 22, and 43 kg ha-1 in the three soil depths, respectively. The soil phosphorus stocks increased in the CPS systems to 30, 50, and 63 kg ha-, respectively, and in the pasture pair sites to 22, 47, and 68 kg ha-1, respectively. In the regional pasture survey, the soil phosphorus stocks were lower than in the native vegetation, and equal to 9 and 15 kg ha-1 at 0-10 and 0-30 depth layer. The findings of this paper illustrate that land-use changes that are currently common in Brazil alter soil concentrations, stocks and elemental ratios of carbon, nitrogen and phosphorus. These changes could have an impact on the subsequent vegetation, decreasing soil carbon, increasing nitrogen limitation, but alleviating soil phosphorus deficiency. [ABSTRACT FROM AUTHOR]

In this paper we calculated soil carbon stocks in Brazil using 17 paired sites where soil stocks were determined in native vegetation, pastures and crop-livestock systems (CPS), and in other regional samplings encompassing more than 100 pasture soils, from 6.58 °S to 31.53 °S, involving three major Brazilian biomes: Cerrado, Atlantic Forest, and the Pampa. The average native vegetation soil carbon stocks at 10 and 30cm soil depth were equal to approximately 33 and 65Mgha-1, respectively. In the paired sites, carbon losses of 7.5Mgha-1 and 11.9Mgha-1 in CPS systems were observed at 10 cm and 30 cm soil depth averages, respectively. In pasture soils, carbon losses were similar and equal to 8.3Mgha-1 and 12.2Mgha-1 at 10 cm and 30 cm soil depths, respectively. The average soil δ13C under native vegetation at 10 and 30 cm depth were equal to -25.4% and -24.0%, increasing to -19.6% and -17.7% in CPS, and to -18.9%, and -18.3% in pasture soils, respectively; indicating an increasing contribution of C4 carbon in these agrosystems. In the regional survey of pasture soils, the soil carbon stock at 30 cm was equal to approximately 51 Mg ha-1, with an average δ13C value of -19.6%. Key controllers of soil carbon stock at pasture sites were sand content and mean annual temperature. Collectively, both could explain approximately half of the variance of soil carbon stocks. When pasture soil carbon stocks were compared with the average soil carbon stocks of native vegetation estimated for Brazilian biomes and soil types by Bernoux et al. (2002) there was a carbon gain of 6.7Mgha-1, which is equivalent to a carbon gain of 15% compared to the carbon soil stock of the native vegetation. The findings of this study are consistent with differences found between regional comparisons like our pasture sites and local paired study sites in estimating soil carbon stocks changes due to land use changes. [ABSTRACT FROM AUTHOR]

The carbon sequestration potential in coastal soils is linked to aboveground and belowground plant productivity and biomass, which in turn, is directly and indirectly influenced by nutrient input. We evaluated the influence of long-term and near-term nutrient input on aboveground and belowground carbon accumulation in seagrass beds, using a nutrient enrichment (nitrogen and phosphorus) experiment embedded within a naturally occurring, long-term gradient of phosphorus availability within Florida Bay (USA). We measured organic carbon stocks in soils and above- and belowground seagrass biomass after 17 months of experimental nutrient addition. At the nutrient-limited sites, phosphorus addition increased the carbon stock in aboveground seagrass biomass by more than 300%; belowground seagrass carbon stock increased by 50-100%. Soil carbon content slightly decreased (~10%) in response to phosphorus addition. There was a strong but non-linear relationship between soil carbon and Thalassia testudinum leaf nitrogen: phosphorus (N : P) or belowground seagrass carbon stock. When sea grass leaf N: P exceeded a threshold of 75 : 1, or when belowground seagrass carbon stock was less than 100 gm-2, there was less than 3% organic carbon in the sediment. Despite the marked difference in soil carbon between phosphorus-limited and phosphorus-replete areas of Florida Bay, all areas of the bay had relatively high soil carbon stocks near or above the global median of 1.8% organic carbon. The relatively high carbon content in the soils indicates that seagrass beds have extremely high carbon storage potential, even in nutrient-limited areas with low biomass or productivity. [ABSTRACT FROM AUTHOR]

We modelled the carbon (C) cycle in Mexico with a process-based approach. We used different available products (satellite data, field measurements, models and flux towers) to estimate C stocks and fluxes in the country at three different time frames: present (defined as the period 2000-2005), the past century (1901-2000) and the remainder of this century (2010-2100). Our estimate of the gross primary productivity (GPP) for the country was 2137±1023 TgCyr-1 and a total C stock of 34 506±7483 TgC, with 20 347±4622 PgC in vegetation and 14 159±3861 in the soil. Contrary to other current estimates for recent decades, our results showed that Mexico was a C sink over the period 1990-2009 (+31 TgCyr-1) and that C accumulation over the last century amounted to 1210±1040 TgC. We attributed this sink to the CO2 fertilization effect on GPP, which led to an increase of 3408±1060 TgC, while both climate and land use reduced the country C stocks by -458±1001 and -1740±878 TgC, respectively. Under different future scenarios the C sink will likely continue over 21st century, with decreasing C uptake as the climate forcing becomes more extreme. Our work provides valuable insights on relevant driving processes of the C-cycle such as the role of drought in marginal lands (e.g. grasslands and shrublands) and the impact of climate change on the mean residence time of C in tropical ecosystems. [ABSTRACT FROM AUTHOR]

Alder-based shifting cultivation, particularly, has been identified for its unique ecological and socio-economic role. It is a distinctive agricultural practice in Nagaland, India, with significant implications for climate change. This study explores the interactions between alder-based shifting cultivation and climate change dynamics. The paper examines how integrating alders into the shifting cultivation system influences carbon sequestration and soil enrichment in this bio-diversity-rich but environmentally vulnerable region. The paper comprehensively analyses the carbon balance within this managed ecosystem. The findings emphasise alder trees' role in enhancing nitrogen levels in the soil and promoting carbon storage in the biomass and soil organic matter. This paper advocates that agroforestry systems can be effective strategies for climate-resilient development in Nagaland if adequately managed. The study concludes that recognising and reinforcing the role of indigenous practices is crucial in shaping effective and inclusive climate change responses in the region. The other hilly parts of the country can set this as a model. [ABSTRACT FROM AUTHOR]

Land use change is the most important driving factor of terrestrial carbon stock change. Soil is the largest carbon reservoir of terrestrial ecosystems, and the impact of land use change on soil carbon sequestration is related to major issues such as the global warming process and food security. The research can provide a basis for land managers and policy makers to develop appropriate planning strategies for soil carbon sequestration management. Despite the widespread attention of relevant studies, macro reviews are still lacking. In order to objectively reveal the current situation of the research field, firstly this paper conducted a bibliometric analysis based on relevant papers in the Web of Science Core Collection database from 1985 to 2021. Secondly, we conducted a review study of land use change on soil carbon sequestration. The research results showed that: (1) the overall amount of the published literature in related fields showed an upward trend, and the development could be divided into three stages, growing slowly from 1985 to 1999, steadily from 2000 to 2009, and rapidly from 2010 to 2021. (2) From the perspective of national distribution, the published papers were mainly from the United States and China, which were much higher than those in other countries. There was mutual cooperation between research institutions in different countries and on a certain scale. (3) Since 2000, soil carbon sequestration has been more frequently mentioned in articles on land use change. Related research was mostly focused on exploring the impact of different land use types and different farming methods on soil organic carbon content in the context of global warming. Land use change and management among agricultural land, woodland, and grassland are the focus of research. The conversion of woodland to agricultural land and grassland is an important reason for the decrease in soil carbon sequestration. Corresponding management measures can be taken to improve soil carbon sequestration. Future research should use multidisciplinary technical means and methods to further explore the interaction mechanism between climate change, land use change, and soil carbon sequestration, so as to carry out more accurate prediction and assessment of different climate scenarios. [ABSTRACT FROM AUTHOR]

The composition of clay minerals in soils, and more particularly the presence of montmorillonite (as part of the smectite family), is a key factor in soil swell–shrinking as well as off–road vehicle mobility. Detecting these topsoil clay minerals and quantifying the montmorillonite abundance are a challenge since they are usually intimately mixed with other minerals, soil organic carbon and soil moisture content. Imaging spectroscopy coupled with unmixing methods can address these issues, but the quality of the estimation degrades the coarser the spatial resolution is due to pixel heterogeneity. With the advent of UAV-borne and proximal hyperspectral acquisitions, it is now possible to acquire images at a centimeter scale. Thus, the objective of this paper is to evaluate the accuracy and limitations of unmixing methods to retrieve montmorillonite abundance from very-high-resolution hyperspectral images (1.5 cm) acquired from a camera installed on top of a bucket truck over three different agricultural fields, in Loiret department, France. Two automatic endmember detection methods based on the assumption that materials are linearly mixed, namely the Simplex Identification via Split Augmented Lagrangian (SISAL) and the Minimum Volume Constrained Non-negative Matrix Factorization (MVC-NMF), were tested prior to unmixing. Then, two linear unmixing methods, the fully constrained least square method (FCLS) and the multiple endmember spectral mixture analysis (MESMA), and two nonlinear unmixing ones, the generalized bilinear method (GBM) and the multi-linear model (MLM), were performed on the images. In addition, several spectral preprocessings coupled with these unmixing methods were applied in order to improve the performances. Results showed that our selected automatic endmember detection methods were not suitable in this context. However, unmixing methods with endmembers taken from available spectral libraries performed successfully. The nonlinear method, MLM, without prior spectral preprocessing or with the application of the first Savitzky–Golay derivative, gave the best accuracies for montmorillonite abundance estimation using the USGS library (RMSE between 2.2–13.3% and 1.4–19.7%). Furthermore, a significant impact on the abundance estimations at this scale was in majority due to (i) the high variability of the soil composition, (ii) the soil roughness inducing large variations of the illumination conditions and multiple surface scatterings and (iii) multiple volume scatterings coming from the intimate mixture. Finally, these results offer a new opportunity for mapping expansive soils from imaging spectroscopy at very high spatial resolution. [ABSTRACT FROM AUTHOR]

Biotic and abiotic factors influence the accumulation of organic carbon (Corg) in seagrass ecosystems. We surveyed Posidonia sinuosa meadows growing in different water depths to assess the variability in the sources, stocks and accumulation rates of Corg. We show that over the last 500 years, P. sinuosa meadows closer to the upper limit of distribution (at 2-4m depth) accumulated 3 to 4-fold higher Corg stocks (averaging 6.3 kgCorg m-2) at 3 to 4-fold higher rates (12.8 gCorg m-2 yr-1) compared to meadows closer to the deep limits of distribution (at 6-8m depth; 1.8 kgCorg m-2 and 3.6 gCorg m-2 yr-1). In shallower meadows, Corg stores were mostly derived from sea-grass detritus (88% in average) compared to meadows closer to the deep limit of distribution (45%on average). Also, sediment accumulation rates and fine-grained sediment content (< 0.125 mm) in shallower meadows (2.0mmyr-1 and 9%, respectively) were approximately 2-fold higher than in deeper meadows (1.2mmyr-1 and 5%, respectively). The Corg stocks and accumulation rates accumulated over the last 500 years in bare sediments (0.6 kgCorg m-2 and 1.2 gCorg m-2 yr-1) were 3 to 11-fold lower than in P. sinuosa meadows, while fine-grained sediment content (1%) and seagrass detritus contribution to the Corg pool (20%) were 8 and 3-fold lower than in Posidonia meadows, respectively. The patterns found support the hypotheses that Corg storage in seagrass soils is influenced by interactions of biological (e.g. meadow productivity, cover and density), chemical (e.g. recalcitrance of Corg stocks) and physical (e.g. hydrodynamic energy and sediment accumulation rates) factors within the meadow. We conclude that there is a need to improve global estimates of seagrass carbon storage accounting for biogeochemical factors driving variability within habitats. [ABSTRACT FROM AUTHOR]

A number of nonlinear microbial models of soil carbon decomposition have been developed. Some of them have been applied globally but have yet to be shown to realistically represent soil carbon dynamics in the field. Therefore a thorough analysis of their key differences will be very useful for the future development of these models. Here we compare two nonlinear microbial models of soil carbon decomposition: one is based on reverse Michaelis-Menten kinetics (model A) and the other on regular Michaelis- Menten kinetics (model B). Using a combination of analytic solutions and numerical simulations, we find that the oscillatory responses of carbon pools model A to a small perturbation in the initial pool sizes have a higher frequency and damps faster than model B. In response to soil warming, soil carbon always decreases in model A; but likely decreases in cool regions and increases in warm regions in model B. Maximum CO2 efflux from soil carbon decomposition (Fmax) after an increased carbon addition decreases with an increase in soil temperature in both models, and the sensitivity of Fmax to the amount of carbon input increases with soil temperature in model A; but decreases monotonically with an increase in soil temperature in model B. These differences in the responses to soil warming and carbon input between the two nonlinear models can be used to differentiate which model is more realistic with field or laboratory experiments. This will lead to a better understanding of the significance of soil microbial processes in the responses of soil carbon to future climate change at regional or global scales. [ABSTRACT FROM AUTHOR]

Microbial metabolism plays a key role in regulating the biogeochemical cycle of forest ecosystems, but the mechanisms driving microbial growth are not well understood. Here, we synthesized 689 measurements on soil microbial biomass carbon (Cmic) and nitrogen (Nmic) and related parameters from 207 independent studies published during the past 15 years across China's forest ecosystems. Our objectives were to (1) examine patterns in Cmic, Nmic, and microbial quotient (i.e., Cmic /Csoil and Nmic =Nsoil rates) by climate zones and management regimes for these forests; and (2) identify the factors driving the variability in the Cmic, Nmic, and microbial quotient. There was a large variability in Cmic (390.2mg kg-1), Nmic (60.1mg kg-1), Cmic :Nmic ratio (8.25), Cmic =Csoil rate (1.92%), and Nmic =Nsoil rate (3.43%) across China's forests, with coeffcients of variation varying from 61.2 to 95.6%. The natural forests had significantly greater Cmic and Nmic than the planted forests, but had less Cmic :Nmic ratio and Cmic =Csoil rate. Soil resources and climate together explained 24.4-40.7% of these variations. The Cmic :Nmic ratio declined slightly with the Csoil :Nsoil ratio, and changed with latitude, mean annual temperature and precipitation, suggesting a plastic homeostasis of microbial carbon-nitrogen stoichiometry. The Cmic =Csoil and Nmic =Nsoil rates were responsive to soil resources and climate differently, suggesting that soil microbial assimilation of carbon and nitrogen be regulated by different mechanisms. We conclude that soil resources and climate jointly drive microbial growth and metabolism, and also emphasize the necessity of appropriate procedures for data compilation and standardization in cross-study syntheses. [ABSTRACT FROM AUTHOR]

Long-term human interactions with landscape and nature produced a plethora of trends and patterns of environmental disturbances in time and space. Nitrogen deposition, closely tracking energy and land use, is known to be among the main pollution drivers, affecting both freshwater as terrestrial ecosystems. We investigated the geographical 5 distribution of nitrogen deposition and the impacts of accumulation on recent soil carbon to nitrogen ratios over Europe. After the Second Industrial Revolution (1880-2010), large landscape stretches characterized by different atmospheric deposition caused either by industrialized areas or by intensive agriculture emerged. Nitrogen deposition affects in a still recognizable way recent soil C:N ratios despite the 10 emission abatement of oxidized and reduced nitrogen during the last two decades. Given the seemingly disparate land-use history, we focused on ~10 000 unmanaged ecosystems, providing evidence for a rapid response of nature to chronic nitrogen supply by atmospheric deposition. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays a crucial role in the global carbon cycle as a potential sink or source. Land management influences SOC storage, so the European Parliament decided in 2013 that changes in carbon stocks within a certain land use type, including arable land, must be reported by all member countries in their national inven- tory reports for greenhouse gas emissions. Here we show the temporal dynamics of SOC during the past two decades in Swedish agricultural soils, based on soil inventories conducted in 1988-1997 (Inventory I), 2001-2007 (Inventory II) and from 2010 onwards (Inventory III), and link SOC changes with trends in agricultural management. From Inventory I to Inventory II, SOC increased in 16 out of 21 Swedish counties, while from Inventory I to Inventory III it increased in 18 out of 21 counties. Mean topsoil (0- 20 cm) SOC concentration for the entire country increased from 2.48 to 2.67%C (a relative increase of 7.7 %, or 0.38%yr-1) over the whole period. We attributed this to a substantial increase in ley as a proportion of total agricultural area in all counties. The horse population in Sweden has more than doubled since 1981 and was identified as the main driver for this management change (R² = 0.72). Due to subsidies introduced in the early 1990s, the area of long-term set-aside (mostly old leys) also contributed to the increase in area of ley. The carbon sink function of Swedish agricultural soils demonstrated in this study differs from trends found in neighbouring countries. This indicates that country-specific or local socio-economic drivers for land management must be accounted for in larger-scale predictions. [ABSTRACT FROM AUTHOR]

A warming climate is altering land-atmosphere exchanges of carbon, with a potential for increased vegetation productivity as well as the mobilization of permafrost soil carbon stores. Here we investigate land-atmosphere carbon dioxide (CO2) dynamics through analysis of net ecosystem productivity (NEP) and its component fluxes of gross primary productivity (GPP) and ecosystem respiration (ER) and soil carbon residence time, simulated by a set of land surface models (LSMs) over a region spanning the drainage basin of northern Eurasia. The retrospective simulations were conducted over the 1960-2009 record and at 0.5° resolution, which is a scale common among many global carbon and climate model simulations. Model performance benchmarks were drawn from comparisons against both observed CO2 fluxes derived from sitebased eddy covariance measurements as well as regional-scale GPP estimates based on satellite remote sensing data. The site-based comparisons show the timing of peak GPP to be well simulated. Modest overestimates in model GPP and ER are also found, which are relatively higher for two boreal forest validation sites than the two tundra sites. Across the suite of model simulations, NEP increases by as little as 0.01 to as much as 0.79 gCm in future model development and intercomparison studies. Resulting improvements in parameterizations and processes driving productivity and soil respiration rates will increase confidence in model estimates of net CO2 exchange, component carbon fluxes, and underlying drivers of change across the northern high latitudes. [ABSTRACT FROM AUTHOR]

Temperature sensitivity of SOC mineralization (Q10) determines how strong the feedback from global warming may be on the atmospheric CO2 concentration, thus understanding the factors influencing the interannual variation in Q10 is important to accurately estimate the local soil carbon cycle. In situ SOC mineralization was measured using an automated CO2 flux system (Li-8100) in long-term bare fallow soil in the Loess Plateau (35° 12' N, 107° 40' E) in Changwu, Shaanxi, China form 2008 to 2013. The results showed that the annual cumulative SOC mineralization ranged from 226 to 298 gCm-2 y-1 (mean= 253 gCm-2 y-1; CV= 13 %), annual Q10 ranged from 1.48 to 1.94 (mean= 1.70; CV= 10 %), and annual soil moisture content ranged from 38.6 to 50.7% WFPS (mean= 43.8% WFPS; CV= 11 %), which were mainly affected by the frequency and distribution of precipitation. Annual Q10 showed a negative quadratic correlation with soil moisture. In conclusion, understanding of the relationships between interannual variation in Q10 of SOC mineralization, soil moisture and precipitation is important to accurately estimate the local carbon cycle, especially under the changing climate. [ABSTRACT FROM AUTHOR]

Large amount of organic carbon is stored in high latitude soils. A substantial proportion of this carbon stock is vulnerable and may decompose rapidly due to temperature increases that are already greater than the global average. It is therefore crucial to quantify and understand carbon exchange between the atmosphere and subarctic/arctic ecosystems. In this paper, we combine an arctic-enabled version of the process-based dynamic ecosystem model, LPJ-GUESS (version LPJG-WHyMe-TFM) with comprehensive observations of terrestrial and aquatic carbon fluxes to simulate long-term carbon exchange in a subarctic catchment comprising both mineral and peatland soils. The model is applied at 50m resolution and is shown to be able to capture the seasonality and magnitudes of observed fluxes at this fine scale. The modelled magnitudes of CO2 uptake generally follow the descending sequence: birch forest, non-permafrost Eriophorum, Sphagnum and then tundra heath during the observation periods. The catchment-level carbon fluxes from aquatic systems are dominated by CO2 emissions from streams. Integrated across the whole catchment, we estimate that the area is a carbon sink at present, and will become an even stronger carbon sink by 2080, which is mainly a result of a projected densification of birch forest and its encroachment into tundra heath. However, the magnitudes of the modelled sinks are very dependent on future atmospheric CO2 concentrations. Furthermore, comparisons of global warming potentials between two simulations with and without CO2 increase since 1960 reveal that the increased methane emission from the peatland could double the warming effects of the whole catchment by 2080 in the absence of CO2 fertilization of the vegetation. This is the first process-based model study of the temporal evolution of a catchment-level carbon budget at high spatial resolution, integrating comprehensive and diverse fluxes including both terrestrial and aquatic carbon. Though this study also highlights some limitations in modelling subarctic ecosystem responses to climate change including aquatic system flux dynamics, nutrient limitation, herbivory and other disturbances and peatland expansion, our application provides a mechanism to resolve the complexity of carbon cycling in subarctic ecosystems while simultaneously pointing out the key model developments for capturing complex subarctic processes. [ABSTRACT FROM AUTHOR]

We used a process-based model to examine the roles of spatial heterogeneity of surface and sub-surface water on the carbon budget of the wetlands of the West Siberian Lowland over the period 1948-2010. We found that, while surface heterogeneity (fractional saturated area) had little overall effect on estimates of the region's carbon fluxes, sub-surface heterogeneity (spatial variations in water table depth) played an important role in both the overall magnitude and spatial distribution of estimates of the region's carbon fluxes. In particular, to reproduce the spatial pattern of CH4 emissions recorded by intensive in situ observations across the domain, in which very little CH4 is emitted north of 60°N, it was necessary to (a) account for CH4 emissions from unsaturated wetlands and (b) use a methane model parameter set that reduced estimated CH4 emissions in the northern half of the domain. Our results suggest that previous estimates of the response of these wetlands to thawing permafrost may have overestimated future increases in methane emissions in the permafrost zone. [ABSTRACT FROM AUTHOR]

Climate change and land management practices are projected to significantly affect soil organic carbon (SOC) dynamics and dissolved organic carbon (DOC) leaching from soils. In this modelling study, we adopted the Century model to simulate past (1906-2012), present, and future (2013-2100) SOC and DOC levels for sandy and loamy soils typical for Northwestern European conditions under three land use types (forest, grassland and arable land) and several future scenarios addressing climate change and land management change. To our knowledge, this is the first time that the Century model has been applied to assess the effects of climate change and land management on DOC concentrations and leaching rates, which, in combination with SOC, play a major role in metal transport through soil. The simulated current SOC levels were generally in line with the observed values for the different kinds of soil and land use types. The climate change scenarios result in a decrease in both SOC and DOC for the agricultural systems, whereas for the forest systems, SOC is projected to slightly increase and DOC to decrease. An analysis of the sole effects of changes in temperature and changes in precipitation showed that, for SOC, the temperature effect predominates over the precipitation effect, whereas for DOC, the precipitation effect is more prominent. A reduction in the application rates of fertilizers under the land management scenario leads to a decrease in the SOC stocks and the DOC leaching rates for the arable land systems, but has a negligible effect on SOC and DOC levels for the grassland systems. Our study demonstrated the ability of the Century model to simulate climate change and agricultural management effects on SOC dynamics and DOC leaching, providing a robust tool for the assessment of carbon sequestration and the implications for contaminant transport in soils. [ABSTRACT FROM AUTHOR]

Windthrows change forest structure and species composition in Central Amazon forests. However, the effects of widespread tree mortality associated with wind-disturbances on soil properties have not yet been described. In this study, we investigated short-term effects (seven years after disturbance) of a windthrow event on soil carbon stocks and concentrations in a Central Amazon terra firme forest. The soil carbon stock (averaged over a 0-30 cm depth profile) in disturbed plots (61.4 ± 4.18 Mg ha−1, mean ± standard error) was marginally higher (p = 0.009) than that from undisturbed plots (47.7 ± 6.95 Mg ha−1). The soil organic carbon concentration in disturbed plots (2.0 ± 0.08%) was significantly higher (p < 0.001) than that from undisturbed plots (1.36 ± 0.12%). Moreover, soil carbon stocks were positively correlated with soil clay content (r = 0.575 and p = 0.019) and with tree mortality intensity (r = 0.493 and p = 0.045). Our results indicate that large inputs of plant litter associated with large windthrow events cause a short-term increase in soil carbon content, and the degree of increase is related to soil clay content and tree mortality intensity. Higher nutrient availability in soils from large canopy gaps created by wind disturbance may increase vegetation resilience and favor forest recovery. [ABSTRACT FROM AUTHOR]

Approximately a third of all annual greenhouse gas emissions globally are directly or indirectly associated with the food system, and over a half of these are linked to livestock production. In temperate oceanic regions, such as the UK, most meat and dairy is produced in extensive systems based on pasture. There is much interest in the extent to which such grassland may be able to sequester and store more carbon to partially or completely mitigate other greenhouse gas emissions in the system. However, answering this question is difficult due to context-specificity and a complex and sometimes inconsistent evidence base. This paper describes a project that set out to summarize the natural science evidence base relevant to grassland management, grazing livestock and soil carbon storage potential in as policy-neutral terms as possible. It is based on expert appraisal of a systematically assembled evidence base, followed by a wide stakeholders engagement. A series of evidence statements (in the appendix of this paper) are listed and categorized according to the nature of the underlying information, and an annotated bibliography is provided in the electronic supplementary material. [ABSTRACT FROM AUTHOR]

The author reflects on the study which investigates the global status of soil carbon contents conducted by Niels Batjes. The author discusses the importance of the study associated with land use and policies on greenhouse gas emission control. He also mentions various persons who commented on the study such as Peter Loveland, Franz Conen and Bas van Wesemael.

This paper explores the application and advantages of remote sensing, machine learning, and mid-infrared spectroscopy (MIR) as a popular proximal sensing spectroscopy tool in the estimation of soil organic carbon (SOC). It underscores the practical implications and benefits of the integrated approach combining machine learning, remote sensing, and proximal sensing for SOC estimation and prediction across a range of applications, including comprehensive soil health mapping and carbon credit assessment. These advanced technologies offer a promising pathway, reducing costs and resource utilization while improving the precision of SOC estimation. We conducted a comparative analysis between MIR-predicted SOC values and laboratory-measured SOC values using 36 soil samples. The results demonstrate a strong fit (R² = 0.83), underscoring the potential of this integrated approach. While acknowledging that our analysis is based on a limited sample size, these initial findings offer promise and serve as a foundation for future research. We will be providing updates when we obtain more data. Furthermore, this paper explores the potential for commercialising these technologies in Australia, with the aim of helping farmers harness the advantages of carbon markets. Based on our study's findings, coupled with insights from the existing literature, we suggest that adopting this integrated SOC measurement approach could significantly benefit local economies, enhance farmers' ability to monitor changes in soil health, and promote sustainable agricultural practices. These outcomes align with global climate change mitigation efforts. Furthermore, our study's approach, supported by other research, offers a potential template for regions worldwide seeking similar solutions. [ABSTRACT FROM AUTHOR]

Both modelling and experimental approaches have been applied to assess C exchange fluxes at large spatial scales. Yet, these approaches are subjected to substantial limitations and uncertainties. Here, we aim to highlight two key mechanisms able to improve the estimation of the hillslope aggregated CO2 fluxes: (i) the persistence of soil organic carbon (OC) in deep colluvium deposits; and (ii) the physical controls on CO2 fluxes along soil profiles. This study focuses on a sloping cropland in the central loess belt of Belgium. On two contrasted soil types along the studied hillslope, we recorded time-series of CO2 concentration, water content and temperature along 1 m long soil profiles during two periods of 6 months. Then, we calculated profiles of CO2 fluxes using the gradient method. To extrapolate these fluxes to entire yearly periods (2011-2013), we performed simulation using the SOILCO2RothC model. The vertical partitioning of the soil CO2 fluxes shows that ca. 90 to ca. 95% of the surface CO2 fluxes originates from the 10 first centimeters of the soil profile at the foot-slope. We show that high water filled pore space at this slope position disables the transfer of biotic CO2 along the soil profile. However, the total annual flux averaged along 3 years of simulation show that the top soil layer (0-10 cm) of the footslope generates CO2 fluxes (870 ± 64 CO2-C m-2 year-1) which exceed those observed at the summit position (583 ± 61 CO2-C m-2 year-1). Hence, our results reconcile two seemingly contradictory hypotheses, i.e. (i) these support that soil OC at such a footslope is stored along the main part of the soil profile and submitted to a long-term stabilization, and (ii) at the same time these support that the depositional footslope profile emits more CO2 than the summit, due to its high amount and quality of OC. Our results support the need to consider slopes when modeling soil-atmosphere C exchanges. If landscapes dynamic processes are not accounted for, we pointed out a risk to underestimate annual soil-atmosphere CO2 exchanges by ca. 20 %. [ABSTRACT FROM AUTHOR]

Carbon (C) saturation theory suggests that soils have a limited capacity to stabilize organic C and that this capacity may be regulated by intrinsic soil properties such as clay content and mineralogy. While C saturation theory has advanced our ability to predict soil C stabilization, we only have a weak understanding of how C saturation affects N cycling. In biogeochemical models, C and N cycling are tightly coupled, with C decomposition and respiration driving N mineralization. Thus, changing model structures from non-saturation to C saturation dynamics can change simulated N dynamics. Carbon saturation models proposed in the literature calculate a theoretical maximum C storage capacity of saturating pools based on intrinsic soil properties, such as clay content. The extent to which current C stocks fill the storage capacity of the pool is termed the C saturation ratio, and this ratio is used to regulate either the efficiency or the rate of C transfer from donor to receiving pools. In this study, we evaluated how the method of implementing C saturation and the number of pools in a model affected net N mineralization from decomposing plant residues. In models that use the C saturation ratio to regulate transfer efficiency, C saturation affected N mineralization, while in those in which the C saturation ratio regulates transfer rates, N mineralization was independent of C saturation. When C saturation ratio regulates transfer efficiency, as the saturation ratio increases, the threshold C:N ratio at which positive net N mineralization occurs also increases because more of the C in the residue is respired. In a single-pool model where C saturation ratio regulated the transfer efficiency, predictions of N mineralization from residue inputs were unrealistically high, missing the cycle of N immobilization and mineralization typically seen after the addition of high C:N inputs to soils. A more realistic simulation of N mineralization was achieved simply by adding a second pool to the model to represent short-term storage and turnover of C and N in microbial biomass. These findings increase our understanding of how to couple C saturation and N mineralization models, while offering new hypotheses about the relationship between C saturation and N mineralization that can be tested empirically. [ABSTRACT FROM AUTHOR]

Understanding how carbon dioxide (CO2) flux from soils feeds back to climate warming depends in part on our ability to quantify the efficiency with which microorganisms convert soil organic carbon (C) into either biomass or CO2. Quantifying ecosystem-level respiratory CO2 losses often also requires assumptions about stable C isotope fractionations associated with the microbial transformation of soil organic substrates. However, the diversity of organic substrates' δ13C and the challenges of measuring microbial C use efficiency (CUE) in soils fundamentally limit our ability to project soil, and thus ecosystem, C budgets in a warming climate. Here, we quantify the effect of temperature on C fluxes during metabolic transformations of cellobiose, a common microbial substrate, by a cosmopolitan soil microorganism growing at a constant rate. Specific respiration rate increased by 250% between 13 and 26.5 °C, decreasing CUE from 77 to 56%. Specific respiration rate was positively correlated with an increase in respiratory 13C discrimination from 4.4 to 6.7 ‰ across the same temperature range. This first demonstration of a direct link between temperature, microbial CUE and associated isotope fluxes provides a critical step towards understanding δ13C of respired CO2 at multiple scales, and towards a framework for predicting future soil C fluxes. [ABSTRACT FROM AUTHOR]

Increasing soil organic carbon (SOC) in agricultural soils can mitigate atmospheric CO2 concentration and also contribute to increase soil fertility and ecosystem resilience. The role of major nutrients on SOC dynamics is complex, due to simultaneous effects on net primary productivity (NPP) that influence crop residue carbon inputs and on the rate of heterotrophic respiration (carbon outputs). This study investigated the effect on SOC stocks of three different levels of phosphorus and potassium (PK) fertilisation rates in the absence of nitrogen fertilisation and of three different levels of nitrogen in the absence of PK. This was done by analysing data from 10 meta-replicated Swedish long-term field experiments (> 45 years).With N fertilisation, SOC stocks followed yield increases. However, for all PK levels, we found average SOC losses ranging from -0.04±0.09Mgha-1 yr-1 (ns) for the lowest to -0.09±0.07Mgha-1 yr-1 (p = 0.008) for the highest application rate, while crop yields as a proxy for carbon input increased significantly with PK fertilization by 1, 10 and 15%. We conclude that SOC dynamics are mainly output-driven in the PK fertilised regime but mostly input-driven in the N fertilised regime, due to the much more pronounced response of NPP to N than to PK fertilisation. It has been established that P rather than K is the element affecting ecosystem carbon fluxes, where P fertilisation has been shown to: (i) stimulate heterotrophic respiration, (ii) reduce the abundance of arbuscular mycorrhizal fungi and (iii) decrease crop root : shoot ratio, leading to lower root-derived carbon input. The higher export of N in the PK fertilised plots in this study could (iv) have led to increased N mining and thus mineralisation of organic matter. More integrated experiments are needed to gain a better understanding of the relative importance of each of the abovementioned mechanisms leading to SOC losses after P addition. [ABSTRACT FROM AUTHOR]

Priming of soil carbon decomposition encompasses different processes through which the decomposition of native (already present) soil organic matter is amplified through the addition of new organic matter, with new inputs typically being more labile than the native soil organic matter. Evidence for priming comes from laboratory and field experiments, but to date there is no estimate of its impact at global scale and under the current anthropogenic perturbation of the carbon cycle. Current soil carbon decomposition models do not include priming mechanisms, thereby introducing uncertainty when extrapolating short-term local observations to ecosystem and regional to global scale. In this study we present a simple conceptual model of decomposition priming, called PRIM, able to reproduce laboratory (incubation) and field (litter manipulation) priming experiments. Parameters for this model were first optimized against data from 20 soil incubation experiments using a Bayesian framework. The optimized parameter values were evaluated against another set of soil incubation data independent from the ones used for calibration and the PRIM model reproduced the soil incubations data better than the original, CENTURY-type soil decomposition model, whose decomposition equations are based only on first order kinetics. We then compared the PRIM model and the standard first order decay model incorporated into the global land biosphere model ORCHIDEE. A test of both models was performed at ecosystem scale using litter manipulation experiments from 5 sites. Although both versions were equally able to reproduce observed decay rates of litter, only ORCHIDEE-PRIM could simulate the observed priming (R² = 0.54) in cases where litter was added or removed. This result suggests that a conceptually simple and numerically tractable representation of priming adapted to global models is able to capture the sign and magnitude of the priming of litter and soil organic matter. [ABSTRACT FROM AUTHOR]

Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from grasslands play a significant role in atmospheric CO2 sequestration. However, anomalous phytC radiocarbon (14C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14C and δ13C) of phytC, plant tissues, atmospheric CO2, and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemical-thermal decomposability properties of phytC. Although photosynthesis is the main source of carbon in plant tissue, it is found that phytC is partially derived from soil carbon that can be several thousand years old. The accumulation of old soil organic matter derived carbon in plant biosilica suggests that Si absorption and phytolith production promote old soil organic carbon mobilization. Although the magnitude of this mechanism still needs to be properly assessed at plant and ecosystem scales, its confirmation alone argues against attempts to use phytC as a proxy of plant carbon and call for the reexamination of phytolith atmospheric CO2 biosequestration estimates. [ABSTRACT FROM AUTHOR]

Northern Hemisphere permafrost affected land areas contain about twice as much carbon as the global atmosphere. This vast carbon pool is vulnerable to accelerated losses through mobilization and decomposition under projected global warming. Satel- lite data records spanning the past 3 decades indicate widespread reductions (~ 0.8- 1.3 daysdecade-1) in the mean annual snow cover extent and frozen season duration across the pan-Arctic domain, coincident with regional climate warming trends. How the soil carbon pool responds to these changes will have a large impact on regional and global climate. Here, we developed a coupled terrestrial carbon and hydrology model framework with detailed 1-D soil heat transfer representation to investigate the sensitivity of soil organic carbon stocks and soil decomposition to changes in snow cover and soil freeze/thaw processes in the Pan-Arctic region over the past three decades (1982-2010). Our results indicate widespread soil active layer deepening across the pan-Arctic, with a mean decadal trend of 6.6-12.0 (SD) cm, corresponding with widespread warming and lengthening non-frozen season. Warming promotes vegetation growth and soil heterotrophic respiration, particularly within surface soil layers (≤ 0.2 m). The model simulations also show that seasonal snow cover has a large impact on soil temperatures, whereby increases in snow cover promote deeper (≥ 0.5 m) soil layer warming and soil respiration, while inhibiting soil decomposition from sur face (≤ 0.2m) soil layers, especially in colder climate zones (mean annual T ≤ -10 °C). Our results demonstrate the important control of snow cover in affecting northern soil freeze/thaw and soil carbon decomposition processes, and the necessity of considering both warming, and changing precipitation and snow cover regimes in characterizing permafrost soil carbon dynamics. [ABSTRACT FROM AUTHOR]

Soil carbon models are important tool to understand soil carbon balance and project carbon stocks in terrestrial ecosystems, particularly under global change. The initialization and/or parameterization of soil carbon models can vary among studies even when the same model and dataset are used, causing potential uncertainties in projections. Although a few studies have assessed such uncertainties, it is yet unclear what these uncertainties are correlated with and how they change across varying environmental and management conditions. Here, applying a process-based biogeochemical model to 90 individual field experiments (ranging from 5 to 82 years of experimental duration) across the Australian cereal-growing regions, we demonstrated that well-designed calibration procedures enabled the model to accurately simulate changes in measured carbon stocks, but did not guarantee convergent forward projections (100 years). Major causes of the projection uncertainty were due to insufficient understanding of how microbial processes and soil carbon composition change to modulate carbon turnover. For a given site, the uncertainty significantly increased with the magnitude of future carbon input and years of the projection. Across sites, the uncertainty correlated positively with temperature, but negatively with rainfall. On average, a 331% uncertainty in projected carbon sequestration ability can be inferred in Australian agricultural soils. This uncertainty would increase further if projections were made for future warming and drying conditions. Future improvement in soil carbon modeling should focus on how microbial community and its carbon use efficiency change in response to environmental changes, better quantification of composition of soil carbon and its change, and how the soil carbon composition will affect its turnover time. [ABSTRACT FROM AUTHOR]

Matching soil grid unit resolution with polygon unit map scale is important to minimize uncertainty of regional soil organic carbon (SOC) pool simulation as their strong influences on the uncertainty. A series of soil grid units at varying cell sizes were derived from soil polygon units at the six map scales of 1 : 50 000 (C5), 1 : 200 000 (D2), 1 : 500 000 (P5), 1 : 1 000 000 (N1), 1 : 4 000 000 (N4) and 1 : 14 000 000 (N14), respectively, in the Tai lake region of China. Both format soil units were used for regional SOC pool simulation with DeNitrification-DeComposition (DNDC) process-based model, which runs span the time period 1982 to 2000 at the six map scales, respectively. Four indices, soil type number (STN) and area (AREA), average SOC density (ASOCD) and total SOC stocks (SOCS) of surface paddy soils simulated with the DNDC, were attributed from all these soil polygon and grid units, respectively. Subjecting to the four index values (IV) from the parent polygon units, the variation of an index value (VIV, %) from the grid units was used to assess its dataset accuracy and redundancy, which reflects uncertainty in the simulation of SOC. Optimal soil grid unit resolutions were generated and suggested for the DNDC simulation of regional SOC pool, matching with soil polygon units map scales, respectively. With the optimal raster resolution the soil grid units dataset can hold the same accuracy as its parent polygon units dataset without any redundancy, when VIV< 1% of all the four indices was assumed as criteria to the assessment. An quadratic curve regression model y = -8.0×10-6x²+0.228x+0.211 (R² = 0.9994, p < 0.05) was revealed, which describes the relationship between optimal soil grid unit resolution (y, km) and soil polygon unit map scale (1 : x). The knowledge may serve for grid partitioning of regions focused on the investigation and simulation of SOC pool dynamics at certain 25 map scale. [ABSTRACT FROM AUTHOR]

Rice production is increasingly challenged by irrigation water scarcity, however covering paddy rice soils with films (ground cover rice production system: GCRPS) can significantly reduce water demand as well as overcome temperature limitations at the beginning of the vegetation period resulting in increased grain yields in colder regions of rice production with seasonal water shortages. It has been speculated that the increased soil aeration and temperature under GCRPS may result in losses of soil organic carbon and nitrogen stocks. Here we report on a regional scale experiment, conducted by sampling paired adjacent Paddy and GCRPS fields at 49 representative sites in the Shiyan region, which is typical for many mountainous areas across China. Parameters evaluated included soil C and N stocks, soil physical and chemical properties, potential carbon mineralization rates, fractions of soil organic carbon and stable carbon isotopic composition of plant leaves. Furthermore, root biomass was quantified at maximum tillering stage at one of our paired sites. Against expectations the study showed that: (1) GCRPS significantly increased soil organic C and N stocks 5-20 years following conversion of production systems, (2) there were no differences between GCRPS and Paddy in soil physical and chemical properties for the various soil depths with the exception of soil bulk density, (3) GCRPS had lower mineralization potential for soil organic C compared with Paddy over the incubation period, (4) GCRPS showed lower δ15N in the soils and plant leafs indicating less NH3 volatilization in GCRPS than in Paddy; and (5) GCRPS increased yields and root biomass in all soil layers down to 40 cm depth. Our results suggest that GCRPS is an innovative rice production technique that not only increases yields using less irrigation water, but that it also is environmentally beneficial due to increased soil C and N stocks at regional scale. [ABSTRACT FROM AUTHOR]

Soil erosion plays important roles in organic matter (OM) storage and persistence in dynamic landscapes. The biogeochemical implication of soil erosion has been a focus of a growing number of studies over the last two decades. However, most of the available studies are conducted in agricultural systems or grasslands, and hence very little information is available on rate and nature of soil organic matter (SOM) eroded from forested upland ecosystems. In the southern parts of the Sierra Nevada Mountains in California, we determined the rate of carbon (C) and nitrogen (N) eroded from two sets of catchments under different climatic conditions to determine how the amount and distribution of precipitation affects lateral distribution of topsoil and associated SOM. We quantified sediment and SOM exported annually (for water years 2005-2011) from four low-order, snow-dominated catchments, and four low-order catchments that receive a mix of rain, and snow and compared it to soil at three different landform positions from the source slopes to determine if there is selective transport of some soil OM components.We found that the amount of sediment exported varied from 0.4 to 177 kgNha-1, while export of particulate C was between 0.025 and 4.2 kgCha-1, compared to export of particulate N that was between 0.001 and 0.04 kgha-1. Sediment yield and composition showed high interannual variation, with higher C and N concentrations in sediment collected in drier years. In our study catchments, erosion laterally mobilized OM-rich topsoil and litter material, some of which readily enters streams owing to the topography in these catchments that includes steep slopes adjacent to stream channels. Annual lateral sediment mass, C, and N fluxes were positively and strongly correlated with stream flows. Our results suggest that variability in climate, represented by stream discharge, is a primary factor controlling the magnitude of C and N eroded from upland temperature forest catchments. [ABSTRACT FROM AUTHOR]

The spatial heterogeneity of land surfaces affects energy, moisture, and greenhouse gas exchanges with the atmosphere. However, representing heterogeneity of terrestrial hydrological and biogeochemical processes in earth system models (ESMs) remains a critical scientific challenge. We report the impact of spatial scaling on environmental controls, spatial structure, and statistical properties of soil organic carbon (SOC) stocks across the US state of Alaska. We used soil profile observations and environmental factors such as topography, climate, land cover types, and surficial geology to predict the SOC stocks at a 50m spatial scale. These spatially heterogeneous estimates provide a dataset with reasonable fidelity to the observations at a sufficiently high resolution to examine the environmental controls on the spatial structure of SOC stocks. We upscaled both the predicted SOC stocks and environmental variables from finer to coarser spatial scales (s = 100, 200, 500 m, 1, 2, 5, 10 km) and generated various statistical properties of SOC stock estimates. We found different environmental factors to be statistically significant predictors at different spatial scales. Only elevation, temperature, potential evapotranspiration, and scrub land cover types were significant predictors at all scales. The strengths of control (the median value of geographically weighted regression coefficients) of these four environmental variables on SOC stocks decreased with increasing scale and were accurately represented using mathematical functions (R² = 0.83-0.97). The spatial structure of SOC stocks across Alaska changed with spatial scale. Although the variance (sill) and unstructured variability (nugget) of the calculated variograms of SOC stocks decreased exponentially with scale, the correlation length (range) remained relatively constant across scale. The variance of predicted SOC stocks decreased with spatial scale over the range of 50 to ~ 500 m, and remained constant beyond this scale. The fitted exponential function accounted for 98% of variability in the variance of SOC stocks. We found moderately-accurate linear relationships between mean and higher-order moments of predicted SOC stocks (R² ~ 0.55-0.63). Current ESMs operate at coarse spatial scales (50-100 km), and are therefore unable to represent environmental controllers and spatial heterogeneity of high-latitude SOC stocks consistent with observations. We conclude that improved understanding of the scaling behavior of environmental controls and statistical properties of SOC stocks can improve ESM land model benchmarking and perhaps allow 5 representation of spatial heterogeneity of biogeochemistry at scales finer than those currently resolved by ESMs. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of using circularity indicators is to show the effect of changes from linear to more circular systems. This paper contributes to highlighting the importance of methodological aspects of circularity indicators in the agricultural sector when using a life cycle thinking approach. Selected circularity indicators have been explored and compared with LCA impact categories by using them to evaluate the circularity of a livestock system. Methods: Circularity indicators were tested on a theoretical pig production system where several circularity strategies and associated mitigation actions were applied. The strategies and mitigation actions were as follows: anaerobic digestion of manure (closing resource loops), anaerobic digestion of bread waste (closing resource loops), precision fertilization (narrowing resource loops), use of cover crops in feed production (regenerating resource flows), and use of bread waste as feed (slowing resource loops). The functional unit was 1 kg pork as carcass weight, and the treatment of 1.1 kg bread waste for all impact categories and indicators. For each mitigation action, relevant circularity indicators were tested. Based on this, the functionality and suitability of these indicators were discussed. Results and discussion: Four of the circularity indicators were based on nitrogen (N) or phosphorus (P) substances: N recycling index, partial N balance, consumption of fossil-P fertilizers, and emissions to water bodies (P). Even if the indicators do not capture the impact of emissions of N and P as the eutrophication impact categories, they provide a useful indication of the circularity of a system. The other three circularity indicators tested were as follows: renewable energy production, soil organic carbon, and land use ratio. The renewable energy production indicator is easy to understand and communicate and provides unique information. Soil organic carbon presents a potential for soil carbon sequestration. Land use ratio is based on the same data as land occupation but provides an assessment of whether feed production competes for the suitable area for food production by including production of human-digestible protein. Conclusions: Circularity indicators provide valuable information about the circularity of an agricultural product system. The circularity indicators and LCA impact categories can be used either separately or together, or to complement each other. The choice of indicators depends on the questions raised, i.e., goals and scope, and it is therefore important to have a number of circular indicators to choose from in order to achieve a comprehensive assessment. [ABSTRACT FROM AUTHOR]

Forest soils are considered the largest carbon and nitrogen pools in soil organic matter among terrestrial ecosystems, and soil carbon and nitrogen dynamics and greenhouse gas (GHG) emissions are normally affected by climate change and human activity. The collection of recent research on this scientific theme would provide a basis for understanding the responses of soil carbon and nitrogen dynamics and GHG fluxes in forest ecosystems to climate change and human activity. A Special Issue was, thus, organized to discuss recent research achievements, including a total of nine research articles and one review. This Special Issue includes the effects of climate changes such as changes in throughfall, snow cover, and permafrost degradation; human activities such as nitrogen and/or phosphorus addition and the use of biochar; and soil–plant interactions on soil carbon and nitrogen dynamics and GHG fluxes in forest ecosystems. Although this collection of papers reflects only a small part of this scientific theme, it can, to some extent, provide a basis for understanding some important research aspects related to the future of forest soil carbon and nitrogen dynamics and GHG fluxes in a changing world, thereby enabling sustainable development and the mitigation of climate change. [ABSTRACT FROM AUTHOR]

[Objective] Soil organic carbon (SOC) is not only an indicator of soil health but also plays a crucial role in feedback interaction between global warming and carbon stock in terrestrial ecosystems. Its dynamics is modulated by a multitude of interactive abiotic and biotic factors. In this paper, we analyze the spatial distribution of SOC in the plough layer and its correlation with soil texture and other geochemical properties in the region of Zhengzhou in Henan province. [Method] Soil samples were taken from a grid network in the region. SOC, bulk density, soil texture and other geochemical properties in each soil sample were measured. The correlation between SOC and soil nutrients, including nitrogen, phosphorus, potassium and micronutrients in the soil, was analyzed using the GeoChemStudio software. [Result] The calcareous skeletol soil in the region has the highest SOC, reaching 2.307%. The SOC content varied from 0.1%-11.6% across the region, and was normally distributed with a mean of 1.134%. The SOC was positively correlated with N, P2O5, Fe, Mn, Zn, Cu, Mo and B, and their associated correlation coefficients were 0.804 5, 0.223 0, 0.156 3, 0.119 1, 0.223 8, 0.263 4, 0.162 8 and 0.191 1, respectively. Negative correlations were found between SOC and K2O and pH, and their associated correlation coefficients were -0.088 8 and -0.195 7, respectively. The average SOC content in the plough layer in the region was 1.09%. Spatially, SOC was rich in Xinmi, Dengfeng and Gongyi in the southwest of the region. In terms of soil texture, SOC is higher in skeletol soil and calcareous cinnamon soil than in other soils. SOC stored in the topsoil in the whole region was 1 012.87x104 t, with 523.13x104 t stored in the cinnamon soils and calcareous cinnamon soils, accounting for 51.64% of the total topsoil SOC in the region. [ABSTRACT FROM AUTHOR]

Achieving climate targets requires mitigation against climate change but also understanding of the response of land and ocean carbon systems. In this context, global soil carbon stocks and their response to environmental changes are key. This paper quantifies the global soil carbon feedbacks due to changes in atmospheric CO 2 , and the associated climate changes, for Earth system models (ESMs) in CMIP6. A standard approach is used to calculate carbon cycle feedbacks, defined here as soil carbon-concentration (βs) and carbon-climate (γs) feedback parameters, which are also broken down into processes which drive soil carbon change. The sensitivity to CO 2 is shown to dominate soil carbon changes at least up to a doubling of atmospheric CO 2. However, the sensitivity of soil carbon to climate change is found to become an increasingly important source of uncertainty under higher atmospheric CO 2 concentrations. [ABSTRACT FROM AUTHOR]

Colluvial soils are enriched in soil organic carbon (SOC) in comparison to the soils of upslope areas due to the deposition and subsurface burial of SOC. It has been suggested that the burial of SOC has important implications for the global carbon cycle, but the long-term dynamics of buried SOC remains poorly constrained. We address this issue by determining the SOC burial efficiency (i.e., the fraction of originally deposited SOC that is preserved in colluvial deposits) of buried SOC as well as the SOC stability in colluvial soils. We quantify the turnover rate of deposited SOC by establishing sediment and SOC burial chronologies. The SOC stability is derived from soil incubation experiments and the δ13C values of SOC. The C burial efficiency was found to decrease exponentially with time reaching a constant ratio of approximately 17%. This exponential decrease is attributed to the increasing recalcitrance of buried SOC with time and a less favourable environment for SOC decomposition with increasing depth. Buried SOC is found to be more stable and degraded in comparison to SOC sampled at the same depth at a stable site. This is due to preferential mineralization of the labile fraction of deposited SOC resulting in enrichment of more degraded and recalcitrant SOC in colluvial soils. In order to better understand the long-term effects of soil erosion for the global C cycle, the temporal variation of deposited SOC and its controlling factors need to be characterized and quantified. [ABSTRACT FROM AUTHOR]

Drained organic soils are anthropogenic emission hotspots of greenhouse gases (GHGs). Most studies have focused on deep peat soils and on peats with high organic carbon content. In contrast, Histic gleysols are characterized by shallow peat layers, which are left over from peat cutting activities, or by peat mixed with mineral soil. It is unknown whether they emit less GHGs than deep Histosols when drained. We present the annual carbon and GHG balance of grasslands for six sites on nutrient-poor histic gleysols with a shallow (30 cm) histic horizon or mixed with mineral soil in Northern Germany (soil organic carbon concentration (Corg) from 9 to 52%). The net GHG balance, corrected for carbon export by harvest, was around 4t CO2-C-eq. ha-1yr-1 on soils with peat layer and little drainage (mean annual water table < 20 cm below surface). The net GHG balance reached 7-91 CO2-C-eq. ha-1 yr-1 on soils with peat layer and deeper drainage (mean annual water table > 20 cm below surface) and on soils with sand mixed into the histic horizon, independent of water table level. GHG emissions from drained histic gleysols (i) were as high as those from deep histosols, (ii) linearly related to water table, (iii) but not affected by Corg content of the histic horizon. Ecosystem respiration (Reco) was linearly correlated with water table level even if it was below the histic horizon. The Reco : GPP ratio was 1.5 at all sites, so that we ruled out a major influence of the inter-site variability in vegetation composition on annual net ecosystem exchange (NEE). The IPCC definition of organic soils includes shallow histic topsoil, unlike most national and international definitions of histosols. Our study confirms that this broader definition is appropriate considering anthropogenic GHG emissions from drained organic soils. Countries currently apply soil maps in national GHG inventories which are likely not to include histic gleysols. The land area with GHG emission hotspots due to drainage is likely to be much higher than anticipated. Deeply drained histic gleysols are GHG hotspots which have so far been neglected or underestimated. Peat mixing with sand does not mitigate GHG emissions. Our study implies that rewetting organic soils, including histic gleysols, has a much higher relevance for GHG mitigation strategies than currently recognized. [ABSTRACT FROM AUTHOR]