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Introduction: Vegetation fires lead to the formation of charred materials, often referred to as pyrogenic carbon (PyC), which are recalcitrant and have a high carbon densitymeaning they have the potential to act as a long-term carbon store. In the United Kingdom, peatlands are periodically subject to fire, both management burns and wildfires, which generate PyC. However, in the United Kingdom context, the characterisation of physical and chemical properties of PyC is limited. Methods: In this study, samples of peatland vegetation (Calluna vulgaris, Polytrichum juniperinum, Vaccinium myrtillus and Eriophorum vaginatum) were burnt in laboratory conditions across typical ranges of characteristics from United Kingdom peatland vegetation fires (250°C–800°C and 2–10 min burn duration). Four broad severity groupings were established (low, moderate, high, very high) corresponding to 60, 70, 80% and 90% mass loss respectively. The PyC samples were then analysed using Brunauer-Emmett-Teller (BET) surface area analysis, CHNO elemental analysis, and Fouriertransform infrared spectroscopy (FTIR) to gain a greater understanding of their physiochemical characteristics. Results: While there was a good degree of similarity between samples within each severity group, there were significant differences between severity groups. Low to high severity samples had relatively low surface areas compared to the very high severity samples, which exhibited the greatest surface areas and a high degree of variability. O/C and H/C ratios decreased with increasing severity. FTIR showed that distinct spectra were produced between severity groups, reflecting increased sample aromaticity with burn severity. Discussion: The findings of this study suggest that burn severity is a good predictor of PyC physiochemical characteristics. [ABSTRACT FROM AUTHOR]

Manganese oxide (MnO x) plays crucial roles in shaping various environmental and geochemistry processes, with their reactivity largely dependent on the structure of MnO x. Tunnel MnO x effectively hosts a substantial quantity of soil elements within its tunnel structure, exerting significant control over element turnover and pertinent geochemical processes, while the precise determinants regarding the layer-to-tunnel transformation of MnO x with electron transfer remain unclear. In this study, we delved into the transformation of layer-structured MnO x during the interaction with coexisting soil redox components (pyrogenic carbon and Tl with differing redox reactivity). Our findings revealed that the transformation from layer to tunnel structure only occurred in the presence of reductive pyrogenic carbon and oxidative Tl(III) rather than sole reductants/oxidants within a short incubation period of 6 weeks. The macro reducing environment created by the pyrogenic carbon and the micro oxidizing environment related to the Tl(III) chelation was pivotal in the cyclic valence change of Mn, resulting in the generation of Mn(III) and vacancies in the Mn structure, the prerequisite for the layer-to-tunnel transformation. Anchoring of oxidative Tl(III) on the surface or inside the tunnel structure of MnO x through Tl–O–Mn bonding was the key to building a micro oxidative environment under bulk-reducing conditions. During the transformation, Tl was integrated into the tunnel of high-crystallinity MnO x , and prolonged incubation resulted in the deeper embedding of Tl and the formation of atomic clusters. The embedding of Tl inside of the tunnel MnO x led to lower solubility and bioaccessibility, with only 0.05–0.26 mg Kg−1 being extracted with soil organic acids through reductive dissolution and 8.7–8.9 % by in vitro physiologically based extraction test. This study underscores the significant role of electron-donating and electron-accepting components in triggering interconnected geochemical processes with MnO x , carbon, and trace elements. [ABSTRACT FROM AUTHOR]

Maize is an important cereal in many developed and developing countries of the world. One of the primary challenges for maize cultivation is soil acidity. Acidic soil is a major constrain in achieving food security requiring sustainable solutions. Biochar, a pyrogenic carbon-rich material, carries reactive surfaces (i.e., high surface area and variable surface charges). Therefore, it facilitates nutrient retention in soil and gradual release to plants, thereby supporting crop growth. However, the combine effects of functionalized biochar with microbes on phosphorus (P) bioavailability and plant performance remain unclear. This study investigates the application of different oxidized biochars (i.e.,fresh rice husk biochar (RHB), pH adjusted oxidized RHB and control) and phosphate solubilizing bacteria (i.e., Pseudomonas aeruginosa, and control) on soil properties including phosphorus dynamics and the performance of maize grown in an acid soil. Biochar was oxidized using 10% hydrogen peroxide while the pH was adjusted to 8.5. Maize was grown in pots having 20 kg of soil or soil-biochar mixture. Overall, biochar and microbes treatments increased soil phosphorus bioavailability and maize yield with a greater effects in the oxidized biochar giving a significant biochar × microbes interactions. Specifically, oxidized biochar when applied with Pseudomonas aeruginosa increased P availability by 380 % which then contributed to yield increment (291%). We also observed a significant reduction in available aluminum (Al) concentration (40% ) compare to the control. These improvement in yield might have occurred due to an increase soil pH, P bioavailability (r2= 0.74), and a reduction in Al toxicity (r2= 0.36).Findings of this study could have significant implications for crop production in acidic soil.

Pyrogenic carbon (PyC) is a temperature forcing agent, air pollutant and dangerous to human health, but its functions in soils are still under discussion. There is a huge knowledge gap in Bulgaria on PyC distribution in soils especially in those located in mine-energy regions where the PyC major source are concentrated. Therefore, the present study aims to propose a method for determination of PyC content and to present its 3D-distribution in soils located in the oldest mine-energy regions of Bulgaria. The method described in this article is a modification of the method developed by Lim and Cachier and uses a dichromate mixture for isolation of PyC fraction. It is experimented with Vertisols which are considered PyC-containing soils. The method is also applicable to soils strongly enriched with coal fragments that are usually located in mine-energy regions of Bulgaria. According to the results obtained a strong variation of PyC content was established in studied soils from Maritsa-iztok and Pernik mine-energy regions (0.10% - 19.07%). A higher content (max 19.07%, average 4.30%) was registered in the region of Pernik, where weakly transformed organic artefacts (soot and coal) increased weather-resistant pyromorphic carbon forms. According to the developed evaluative scale, the medium content of PyC prevails in Bulgarian soils - from 0.29% to 0.51%. The factors influencing this distribution are: paleo- and present fires, the content of coal impurities, and deposition of PyC-enriched aerosols emitted from coal operating thermal-electric power plants, domestic heating with coal, coal mining and transport. [ABSTRACT FROM AUTHOR]

Fire exclusion is a key factor driving conifer expansion into temperate semi-arid grasslands. However, it remains unclear how reintroducing fire affects the aboveground storage of carbon (C) and nitrogen (N) in the expanding tree species and belowground in soils. To assess the impacts of fire reintroduction C and N pools and fluxes in areas of conifer expansion we targeted a region of the Northern Great Plains that has experienced extensive woody plant expansion (WPE) of two species: ponderosa pine (Pinus ponderosa) and juniper (Juniperus spp). We quantified tree mortality of both species to estimate the amount of dead biomass C and N produced by a recent prescribed fire, in addition to changes in soil C, pyrogenic C (PyC), and N concentrations across a woody-cover gradient using a before/after/control experimental design. Post-fire soil chemical analysis revealed a 2 year increase in mineral soil C, PyC and N, suggesting the return of fire led to the transfer of partially combusted plant organic matter back to the soil. Further, we found that functional trait differences between the two species influenced the distribution of living conifer biomass-N prior to fire. Despite junipers having 41% less total aboveground biomass than ponderosa, they contained two times more aboveground N. Prescribed fire resulted in 88% mortality of all mature juniper stems and increased fire severity correlated with greater pre-fire juniper cover. Ponderosa mortality varied by size class, with > 40 cm stem diameter class having only 28% mortality. High mortality and greater aboveground N storage in juniper biomass, compared to ponderosa, led to 77% of the total conifer biomass N lost. Consequently, the functional attributes of expanding trees differentially contribute to fluxes of C and N after the return of fire, with junipers acting as conduits for N movement due to their relatively higher N content in less fire-resistant tissues and ponderosa serving as important and more stable storage pools for C. Together, these findings highlight the importance of considering species-specific traits when planning WPE management strrategies at landscape-scales, particularly when goals include C storage or soil nutrient status. [ABSTRACT FROM AUTHOR]

Grassland ecosystems have evolved alongside fire, a fundamental element that shapes and sustains their ecological balance. Recent research indicates that carbon produced during pyrogenic events in fire-dependent ecosystems may occur in more recalcitrant forms within deeper soil horizons. Notably, refractory organic carbon (ROC) and black carbon (BC) fractions are globally recognised as highly stable components of soil carbon. Here, we examined the impact of prescribed fires on the accumulation of ROC and BC fractions within South African mesic grassland soils. Our findings revealed that while BC remains stable in the soil, exhibiting consistent levels across soil horizons, increased fire frequency led to breakdown of BC in the soil. Greater BC quantities were observed in burn exclusion and prescribed burns with a greater burn interval, suggested as primarily driven by a decline in soil pH. There were no significant differences in ROC within the burn treatments, but there was a notable decrease in ROC with increasing depth increments below 5 cm. The observed trend of ROC accumulation in the top layer of soil, influenced by [ABSTRACT FROM AUTHOR]

IntroductionVegetation fires lead to the formation of charred materials, often referred to as pyrogenic carbon (PyC), which are recalcitrant and have a high carbon densitymeaning they have the potential to act as a long-term carbon store. In the United Kingdom, peatlands are periodically subject to fire, both management burns and wildfires, which generate PyC. However, in the United Kingdom context, the characterisation of physical and chemical properties of PyC is limited.MethodsIn this study, samples of peatland vegetation (Calluna vulgaris, Polytrichum juniperinum, Vaccinium myrtillus and Eriophorum vaginatum) were burnt in laboratory conditions across typical ranges of characteristics from United Kingdom peatland vegetation fires (250°C–800°C and 2–10 min burn duration). Four broad severity groupings were established (low, moderate, high, very high) corresponding to 60, 70, 80% and 90% mass loss respectively. The PyC samples were then analysed using Brunauer-Emmett-Teller (BET) surface area analysis, CHNO elemental analysis, and Fouriertransform infrared spectroscopy (FTIR) to gain a greater understanding of their physiochemical characteristics.ResultsWhile there was a good degree of similarity between samples within each severity group, there were significant differences between severity groups. Low to high severity samples had relatively low surface areas compared to the very high severity samples, which exhibited the greatest surface areas and a high degree of variability. O/C and H/C ratios decreased with increasing severity. FTIR showed that distinct spectra were produced between severity groups, reflecting increased sample aromaticity with burn severity.DiscussionThe findings of this study suggest that burn severity is a good predictor of PyC physiochemical characteristics.

Background: Indigenous fire management in northern Australian savannas (beginning at least 11,000 years ago) involved frequent, small, cool, early dry season fires. This fire regime changed after European arrival in the late 1700s to unmanaged fires that burn larger areas, late in the dry season, detrimental to carbon stocks and biodiversity. Aims: Test the hypothesis that significant sequestration of pyrogenic carbon in soil accompanies the reimposition of an Indigenous fire regime. Methods: Savanna soils under the same vegetation, but with the number of fires varying from 0 to 13 (irrespective of the season) between 2000 and 2022 were sampled. Organic and pyrogenic carbon stocks as well as carbon isotope composition of the 0–5 cm soil layer were determined along sample transects with varying fire return intervals. Key results: An average increase of 0.25 MgC ha−1 was observed in soil pyrogenic carbon stocks in transects with ≥5 fires, compared to transects with 0–4 fires, with a small increase in soil organic carbon stocks that was not significant. Conclusions: A return to more frequent fires early in the dry season has the potential to sequester significant pyrogenic carbon in northern Australian savanna soils on decadal timescales. The reimposition of an Indigenous fire regime (frequent, small, cool, early dry season fires) has the potential to sequester significant pyrogenic carbon in northern Australian savanna soils on decadal timescales. We observed an increase of 0.25 MgC ha−1 in transects with ≥5 fires over a 22-year period. [ABSTRACT FROM AUTHOR]

Wildfires have the potential to dramatically alter the carbon (C) storage potential, ecological function, and the fundamental mechanisms that control the C balance of Pacific Northwest (PNW) forested ecosystems. In this study, we explored how wildfire influences processes that control soil C stabilization and the consequent soil C persistence, and the role of previous fire history in determining soil C fire response dynamics. We collected mineral soils at four depth increments from burned (low, moderate, and high soil burn severity classes) and unburned areas and surveyed coarse woody debris (CWD) in sites within the footprint of the 2020 Holiday Farm Fire and in surrounding Willamette National Forest and the H.J. Andrews Experimental Forest. We found few changes in overall soil C pools as a function of fire severity; we instead found that unburned sites contained high levels of pyrogenic C (PyC) that were commensurate with PyC concentrations in the high severity burn sites—pointing to the high background rate of fire in these ecosystems. An analysis of historical fire events lends additional support, where increasing fire count is loosely correlated with increasing PyC concentration. An unexpected finding was that PyC concentration was lower in low soil burn severity sites than in control sites, which we attribute to fundamental ecological differences in regions that repeatedly burn at high severity compared with those that burn at low severity. Our CWD analysis showed that high mean fire return interval (decades between fire events) was strongly correlated with low annual CWD accumulation rate; whereas areas that burn frequently had a high annual CWD accumulation rate. Within the first year postfire, trends in soil density fractions demonstrated no significant response to fire for the mineral-associated organic matter pool but slight increases in the particulate pool with increasing soil burn severity—likely a function of increased charcoal additions. Overall, our results suggest that these PNW forest soils display complex responses to wildfire with feedbacks between CWD pools that provide varying fuel loads and a mosaic fire regime across the landscape. Microclimate and historic fire events are likely important determinants of soil C persistence in these systems. [ABSTRACT FROM AUTHOR]

Dissolved black carbon (DBC) is the remobilized soluble fraction of black carbon (BC). DBC, present in all aquatic environments, is a heterogeneous mixture of various pyrogenic aromatics. For a long time, oceans were solely considered to be the largest pool of DBC. However, recent research indicates that lakes might also contain significant concentrations of DBC. Anthropogenic BC emissions and seasonal changes driven by climate change could increase DBC flux to glacial and fluvial lacustrine systems with unique effects. In this article, current knowledge concerning the formation, sources, transportation, fate, and environmental implications of DBC in lacustrine networks is presented. Furthermore, ambiguities pertaining to terminology and methodologies used in the separation and quantification of DBC are also reviewed, and research gaps that should be addressed in future studies are highlighted. Constraining DBC dynamics and residence times in lacustrine systems could provide valuable insights into anthropogenic perturbations of the global carbon cycle. [ABSTRACT FROM AUTHOR]

Wildfires directly emit 2.1 Pg carbon (C) to the atmosphere annually. The net effect of wildfires on the C cycle, however, involves many interacting source and sink processes beyond these emissions from combustion. Among those, the role of post‐fire enhanced soil organic carbon (SOC) erosion as a C sink mechanism remains essentially unquantified. Wildfires can greatly enhance soil erosion due to the loss of protective vegetation cover and changes to soil structure and wettability. Post‐fire SOC erosion acts as a C sink when off‐site burial and stabilization of C eroded after a fire, together with the on‐site recovery of SOC content, exceed the C losses during its post‐fire transport. Here we synthesize published data on post‐fire SOC erosion and evaluate its overall potential to act as longer‐term C sink. To explore its quantitative importance, we also model its magnitude at continental scale using the 2017 wildfire season in Europe. Our estimations show that the C sink ability of SOC water erosion during the first post‐fire year could account for around 13% of the C emissions produced by wildland fires. This indicates that post‐fire SOC erosion is a quantitatively important process in the overall C balance of fires and highlights the need for more field data to further validate this initial assessment. [ABSTRACT FROM AUTHOR]

Extracellular enzymes play a key role in mediating organic matter decomposition in soils and the mobility of enzymes is largely controlled by their interaction with soil surfaces. The introduction of pyrogenic products, including biochar produced for the purpose of carbon sequestration or soil health management, may alter the ecological functioning of soil. In this work, we studied the adsorption of four representative soil extracellular enzymes (urease, invertase, α-amylase and protease) to biochar (derived from wood biomass and wheat straw produced at different pyrolysis temperatures, and a wildfire pine char) and soil mixed with biochar. A pH-edge adsorption experiment showed that, for all biochar/enzyme combinations, adsorption of all extracellular enzymes decreased as pH increased from 4 to 9. This pH dependency suggests that electrostatic interaction was the primary adsorption mechanism. Equilibrium enzyme adsorption data was best fit by the Langmuir isotherm and adsorption capacity varied significantly with enzyme type, ranging from 67 to 232 mg·g−1 for urease and 0 to 11 mg·g−1 for the others at pH 5.0. Enzyme adsorption also differed among biochars with or without surface oxidation treatment. Correlations between enzyme adsorption data and biochar properties demonstrated the relevance of enzyme sizes, biochar surface porous structure, and surface chemical functionality in determining biochar adsorption capacity and affinity for enzymes. Soil adsorption experiment showed that biochar addition can enhance or reduce soil adsorption of enzymes, depending on the relative enzyme affinity between the soil and biochar. These findings indicate that pyrogenic organic matter has varying impacts on the mobility of soil extracellular enzymes through direct adsorption and potentially affect the activity and stability of enzymes, and ultimately soil carbon and nutrient cycling.

Abstract Although addition of pyrolyzed organic materials (biochars) to soil generally results in increased growth and physiological performance of plants, neutral and negative responses have also commonly been detected. Toxicity of organic compounds generated during pyrolysis, sorbed by biochars, and then released into the soil solution, has been implicated as a possible mechanism for such negative effects. Conversely, water-soluble biochar constituents have also been suggested to have “hormetic” effects (positive effects on plants at low concentrations); however, no specific compounds responsible have been identified. We investigated the relative phytotoxicity—and possible hormetic effects—of 14 organic compounds common in aqueous extracts of freshly produced lignocellulosic biochars, using seed germination bioassays. Of the compounds examined, volatile fatty acids (VFAs: acetic, propionic, butyric, valeric, caproic, and 2-ethylbutyric acids) and phenol, showed acute phytotoxicity, with germination-based ED50 values of 1–30 mmol L−1, and 2-ethylbutyric acid showed ED50 values of 0.1–1.0 mmol L−1. Other compounds (benzene, benzoic acid, butanone, methyl salicylate, toluene, and 2,4-di-tert-butylphenol) showed toxic effects only at high concentrations close to solubility limits. Although phytotoxic at high concentrations, valeric and caproic acid also showed detectable hormetic effects on seedlings, increasing radicle extension by 5–15% at concentrations of ~ 0.01–0.1 mmol L−1. These data support the hypothesis that VFAs are the main agents responsible for phytotoxic effects of lignocellulosic biochar leachates, but that certain VFAs also have hormetic effects at low concentrations and may contribute to positive effects of biochar leachates on early plant development in some cases. Graphical Abstract

Abstract Background Black carbon (BC) encompasses a range of carbonaceous materials––including soot, char, and charcoal––derived from the incomplete combustion of fossil fuels and biomass. Urban soils can become enriched in BC due to proximity to these combustion sources. We conducted a literature review of BC in urban soils globally and found 26 studies reporting BC and total organic carbon (TOC) content collected to a maximum of 578 cm depth in urban soils across 35 cities and 10 countries. We recorded data on city, climate, and land use/land cover characteristics to examine drivers of BC content and contribution to TOC in soil. Results All studies were conducted in the northern hemisphere, with 68% of the data points collected in China and the United States. Surface samples (0–20 cm) accounted for 62% of samples in the dataset. Therefore, we focused our analysis on 0–10 cm and 10–20 cm depths. Urban soil BC content ranged from 0–124 mg/g (median = 3 mg/g) at 0–10 cm and from 0–53 mg/g (median = 2.8 mg/g) at 10–20 cm depth. The median proportional contribution of BC to TOC was 23% and 15% at 0–10 cm and 10–20 cm, respectively. Surface soils sampled in industrial land use and near roads had the highest BC contents and proportions, whereas samples from residential sites had among the lowest. Soil BC content decreased with mean annual soil temperature. Conclusions Our review indicates that BC comprises a major fraction (nearly one quarter) of the TOC in urban surface soils, yet sampling bias towards the surface could hide the potential for BC storage at depth. Land use emerged as an importer driver of soil BC contents and proportions, whereas land cover effects remain uncertain. Warmer and wetter soils were found to have lower soil BC than cooler and drier soils, differences that likely reflect soil BC loss mechanisms. Additional research on urban soil BC at depth and from diverse climates is critical to better understand the role of cities in the global carbon cycle.

Although addition of pyrolyzed organic materials (biochars) to soil generally results in increased growth and physiological performance of plants, neutral and negative responses have also commonly been detected. Toxicity of organic compounds generated during pyrolysis, sorbed by biochars, and then released into the soil solution, has been implicated as a possible mechanism for such negative effects. Conversely, water-soluble biochar constituents have also been suggested to have "hormetic" effects (positive effects on plants at low concentrations); however, no specific compounds responsible have been identified. We investigated the relative phytotoxicity—and possible hormetic effects—of 14 organic compounds common in aqueous extracts of freshly produced lignocellulosic biochars, using seed germination bioassays. Of the compounds examined, volatile fatty acids (VFAs: acetic, propionic, butyric, valeric, caproic, and 2-ethylbutyric acids) and phenol, showed acute phytotoxicity, with germination-based ED50 values of 1–30 mmol L−1, and 2-ethylbutyric acid showed ED50 values of 0.1–1.0 mmol L−1. Other compounds (benzene, benzoic acid, butanone, methyl salicylate, toluene, and 2,4-di-tert-butylphenol) showed toxic effects only at high concentrations close to solubility limits. Although phytotoxic at high concentrations, valeric and caproic acid also showed detectable hormetic effects on seedlings, increasing radicle extension by 5–15% at concentrations of ~ 0.01–0.1 mmol L−1. These data support the hypothesis that VFAs are the main agents responsible for phytotoxic effects of lignocellulosic biochar leachates, but that certain VFAs also have hormetic effects at low concentrations and may contribute to positive effects of biochar leachates on early plant development in some cases. Highlights: 151 compounds were identified in leachates from 13 biochars. Among common compounds, volatile fatty acids (VFAs) and phenol showed the most pronounced phytotoxic effects. Some VFAs also had hormetic effects, enhancing radicle extension growth at low concentrations. Effects were consistent among test plant species but the smallest-seeded species showed the highest sensitivity. [ABSTRACT FROM AUTHOR]

The slash-and-burn cultivation system is a millenarian practice still used in many countries today, with significant environmental impacts. However, identifying evidence of this agricultural method in soil records is challenging due to natural and human factors that can obscure or alter fire signals. This challenge is particularly evident in the Yucatán Peninsula, where the ancient Maya practiced slash-andburn agriculture in a dynamic tropical karst environment, making it difficult to pinpoint the origins and consequences of this practice. In this study, we use a recent agricultural burning in a karstic landscape in Chiapas as a model to understand alterations in soil properties. We then apply these insights to identify similar features at a Maya site on the Yucatán Peninsula, specifically at Coyote Quarry. For both cases, we conducted micromorphological analysis, soil physical-chemical characterization, thermogravimetry and differential scanning calorimetry analysis, and radiocarbon dating of mollusk shells, soil organic carbon, and charcoal fragments (the latter exclusively at Coyote Quarry). Our findings reveal significant effects on the soils from the Chiapas site post-burning, including changes in grain size distribution, pH, and total organic and inorganic carbon. These results were compared to those obtained from the Coyote Quarry soils and pedosediments. Key findings include micromorphological features, the presence of charcoal and other burned materials, and pyrogenic carbon identified through thermal analyses. The preservation of these burned features was facilitated by the typical karstic vertical soil erosion and redeposition as pedosediments in karstic depressions. The intrinsic association of the fire signals found in these karstic sinkholes and their radiocarbon dates enables us to link this evidence to the initiation of slash-and-burn agriculture by the Maya in the Yucatán Peninsula during the transition between the Archaic and Early Pre-Classic periods. [ABSTRACT FROM AUTHOR]

Background: Black carbon (BC) encompasses a range of carbonaceous materials––including soot, char, and charcoal––derived from the incomplete combustion of fossil fuels and biomass. Urban soils can become enriched in BC due to proximity to these combustion sources. We conducted a literature review of BC in urban soils globally and found 26 studies reporting BC and total organic carbon (TOC) content collected to a maximum of 578 cm depth in urban soils across 35 cities and 10 countries. We recorded data on city, climate, and land use/land cover characteristics to examine drivers of BC content and contribution to TOC in soil. Results: All studies were conducted in the northern hemisphere, with 68% of the data points collected in China and the United States. Surface samples (0–20 cm) accounted for 62% of samples in the dataset. Therefore, we focused our analysis on 0–10 cm and 10–20 cm depths. Urban soil BC content ranged from 0–124 mg/g (median = 3 mg/g) at 0–10 cm and from 0–53 mg/g (median = 2.8 mg/g) at 10–20 cm depth. The median proportional contribution of BC to TOC was 23% and 15% at 0–10 cm and 10–20 cm, respectively. Surface soils sampled in industrial land use and near roads had the highest BC contents and proportions, whereas samples from residential sites had among the lowest. Soil BC content decreased with mean annual soil temperature. Conclusions: Our review indicates that BC comprises a major fraction (nearly one quarter) of the TOC in urban surface soils, yet sampling bias towards the surface could hide the potential for BC storage at depth. Land use emerged as an importer driver of soil BC contents and proportions, whereas land cover effects remain uncertain. Warmer and wetter soils were found to have lower soil BC than cooler and drier soils, differences that likely reflect soil BC loss mechanisms. Additional research on urban soil BC at depth and from diverse climates is critical to better understand the role of cities in the global carbon cycle. [ABSTRACT FROM AUTHOR]

BACKGROUND: Despite the optimal characteristics of peat, more environmental‐friendly materials are needed in the nursery sector, although these must guarantee specific quantitative and qualitative commercial standards. In the present study, we evaluated the influence of biochar and compost as peat surrogates on yield and essential oil profile of two different varieties of basil (Ocimum basilicum var. Italiano and Ocimum basilicum var. minimum). In two 50‐day pot experiments, we checked the performances of biochar from pruning of urban trees and composted kitchen scraps, both mixed in different proportions with commercial peat (first experiment), and under different nitrogen (N) fertilization regimes (second experiment), in terms of plant growth and volatile compounds profile of basil. RESULTS: Total or high substitution of peat with biochar (100% and 50% v.v.) or compost (100%) resulted in seedling death a few days from transplantation, probably because the pH and electrical conductivity of the growing media were too high. Substrates with lower substitution rates (10–20%) were underperforming in terms of plant growth and color compared to pure commercial peat during the first experiment, whereas better performances were obtained by the nitrogen‐fertilized mixed substrates in the second experiment, at least for one variety. We identified a total of 12 and 16 aroma compounds of basil (mainly terpenes) in the two experiments. Partial replacement of peat did not affect basil volatile organic compounds content and composition, whereas N fertilization overall decreased the concentration of these compounds. CONCLUSION: Our results support a moderate use of charred or composted materials as peat surrogates. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Background. Charcoal increases in reflectance with increased intensity and/or duration of heating, and this has been proposed as a potential quantitative metric for fire severity. Because fuel properties also influence reflectance, relationships between heat exposure and reflectance must currently be considered fuel-specific, limiting the application of the method. Aims. We assessed the effect of wood density on charcoal reflectance, to test whether it could be used as a proxy for overall variation in wood properties. Methods. Wood samples from 25 tree species were charred under constant conditions in a microcalorimeter, and reflectance measured by microphotometry. Key results. A positive linear relationship was found between wood density and charcoal reflectance (r = 0.53). Wood density was highly correlated with total heat release per unit volume (r = 0.94). Conclusions. Wood density accounts for a substantial component of the variation in charcoal reflectance under constant heat exposure. Implications. The relationship of density to reflectance shown here is relevant to the assessment of charcoals formed anaerobically, where endogenous heating (combustion of the sample itself) does not occur. In fire-produced chars, an additional increase in reflectance from endogenous heating should produce a stronger correlation, and density might account for a large component of the variation in reflectance under such conditions. [ABSTRACT FROM AUTHOR]

Abstract Carbon materials (e.g., pyrogenic carbon (PyC)) are widely used in agricultural soils and can participate in various biogeochemical processes, including iron (Fe) cycling. In soils, Fe(II) species have been proposed as the main active contributor to produce reactive oxygen species (ROS), which are involved in various biogeochemical processes. However, the effects of PyC on the transformation of different Fe species in soils and the associated production of ROS are rarely investigated. This study examined the influence of PyC (pyrolyzed at 300–700 °C) on Fe(II)/Fe(III) cycling and hydroxyl radical (·OH) production during redox fluctuations of paddy soils. Results showed that the reduction of Fe(III) in soils was facilitated by PyC during anoxic incubation, which was ascribed to the increased abundance of dissimilatory Fe(III)-reducing microorganisms (biotic reduction) and the electron exchange capacity of PyC (abiotic reduction). During oxygenation, PyC and higher soil pH promoted the oxidation of active Fe(II) species (e.g., exchangeable and low-crystalline Fe(II)), which consequently induced higher yield of ·OH and further led to degradation of imidacloprid and inactivation of soil microorganisms. Our results demonstrated that PyC accelerated Fe(II)/Fe(III) cycling and ·OH production during redox fluctuations of paddy soils (especially those with low content of soil organic carbon), providing a new insight for remediation strategies in agricultural fields contaminated with organic pollutants. Graphical Abstract

Natural or anthropogenic‐induced biomass burning produces large amounts of charcoals, which enter riverine or lacustrine systems mostly via surface runoff processes. Charcoal storage and cycling within large riverine systems can play a crucial role in mediating long‐term carbon sink across transient reservoirs, thereby influencing the global carbon budget. However, natural processes governing the transport and storage of charcoal particles in large terrestrial reservoirs such as the Indo‐Gangetic region still remain unknown. To understand charcoal movement and accumulation across upland and lowland transient reservoirs, we characterized spatial distribution and morphology of different charcoal forms (>125 μm and <125 μm) from bedload and floodplain sediments of the Yamuna sub‐basin (YSB), India. Both >125 μm and <125 μm charcoal forms in bedload and floodplain sediments did not exhibit similar spatial distribution patterns, indicating the segregation of charcoal particles influenced by variable flow regimes. Attrition with sediments breaks down fragile charcoals (leaves) quickly compared to the woody forms, resulting in dominant woody microforms in transient deposits. Higher stream power and limited stable bedform development in upland mountainous regions restrict charcoal storage. During lowland riverine transits, reduced stream power conditions allow increased floodwater inundation and finer clay substrate availability, facilitating an exponential increase in charcoal storage. However, increased discharge from peninsular rivers into the YSB leads to erosion and redistribution of sediment, including charcoal particles, and reduced charcoal storage in lowland transient areas. Such diverse dispersal pathways and fate of charcoal particles across riverine transits highlight the influence of regional hydrogeomorphic processes on the overall carbon cycle within transient reservoirs. Plain Language Summary: Rivers and wind carry a lot of charcoal, which comes from burned plants, to temporary storage places. Rivers play an essential role in charcoal distribution across mountain and lowland regions before it ends up to the ocean. Impact of river in charcoal movement is an important component of nature that helps in the recycling of carbon globally and this process still remains poorly understood. This study attempts to understand the natural response of charcoal particles across the Yamuna River (India) and its tributaries. It is observed that the river flow influences the spatial distribution of smaller charcoals (<125 μm) more than bigger (>125 μm) charcoal. Higher river flow provided less time to settle charcoals in the mountain areas, allowing limited charcoal accumulation. In lowland areas, charcoal tends to gather where there is more sand and dirt piling up. But when lots of water rushes in from rivers, it can wash away the charcoal, making it harder for charcoals to stay in one place. Such responses of charcoal particles to complex river actions, such as sediment types, river flow, and landscape, impact the storage of charcoal particles and can contribute to variation in the carbon recycling across Earth surface. Key Points: Regional geomorphic and hydrodynamic processes influence charcoal segregation in large river complexesSusceptibility of charcoals to different flow regimes impacts distribution of carbon fluxes in transient areasTransient lowlands favored more charcoal storage than upland areas due to higher availability of finer substrate in lowland floodplains [ABSTRACT FROM AUTHOR]

Biochar effects are strongly dependent on its properties. Biochar improves physical soil properties by decreasing bulk density and increasing medium and large aggregates, leading to faster and deeper water infiltration and root growth. Improvement of the chemical properties of soil is connected with pH neutralization of acidic soils, increase of cation exchange capacity and base saturation, providing a larger surface for sorption of toxicants and exchange of cations. Biochar increases the stocks of macro- and micronutrients in soil and remains sufficient for decades. Biochar effects on (micro)biological properties are mainly indirect, based on the improvements of habitat conditions for organisms, deeper root growth providing available C for larger soil volume, higher crop yield leading to more residues on and in the topsoil, better and deeper soil moisture, supply of all nutrients, and better aeration. Along with positive, negative effects of biochar while used as a soil conditioner are discussed in the review: presence of PAH, excessive amounts of K, Ca and Mg, declination of soil pH. In conclusion, despite the removal of C from the biological cycle by feedstock pyrolysis, the subsequent application of biochar into soil increases fertility and improves physical and chemical properties for root and microbial growth is a good amendment for low fertility soils. Proper use of biochar leads not only to an increase in crop yield but also to effective sequestration of carbon in the soil, which is important to consider when economically assessing its production. Further research should be aimed at assessing and developing methods for increasing the sequestration potential of biochar as fertilizer. [ABSTRACT FROM AUTHOR]

Soil acidity is a major problem of agriculture in many parts of the world. Soil acidity causes multiple problems such as nutrient deficiency, elemental toxicity and adverse effects on biological characteristics of soil, resulting in decreased crop yields and productivity. Although a number of conventional strategies including liming and use of organic and inorganic fertilizers are suggested for managing soil acidity but cost-effective and sustainable amendments are not available to address this problem. Currently, there is increasing interest in using biochar, a form of biomass derived pyrogenic carbon, for managing acidity while improving soil health and fertility. However, biochar varies in properties due to the use of wide diversity of biomass, variable production conditions and, therefore, its application to different soils can result in positive, neutral and or negative effects requiring an in-depth understanding of biochar-acid soil interactions to achieve the best possible outcomes. Here, we present a comprehensive synthesis of the current literature on soil acidity management using biochar. Synthesis of literature showed that biochars, enriched with minerals (i.e., usually produced at higher temperatures), are the most effective at increasing soil pH, basic cation retention and promoting plant growth and yield. Moreover, the mechanism of soil acidity amelioration with biochar amendments varies biochar types, i.e., high temperature biochars with liming effects and low temperature biochars with proton consumption on their functional groups. We also provide the mechanistic interactions between biochar, plant and soils. Altogether, this comprehensive review will provide guidelines to agricultural practitioners on the selection of suitable biochar for the reclamation of soil acidity. [ABSTRACT FROM AUTHOR]

Biomass‐derived pyrogenic carbon is attractive for advanced oxidation processes (AOPs); however, its amorphous structure limits its activation efficiency. Graphene with highly conjugated π structure possesses superior electron transport ability and thus high usefulness. However, bygone strategies are scarcely effective for reforming pyrogenic carbon to graphene. Herein, for the first time, a state‐of‐the‐art flash Joule heating (FJH) technique is showcased for reforming pyrogenic carbon to 2–5‐layer graphene. FJH current‐induced ultrahigh temperature and stress field realize instantaneous (≈10 s) regeneration of pyrogenic carbon via synchronization actions of carbonization, graphitization, and exfoliation. Meanwhile, volatilization of doped N atoms accelerates graphitization but has less of an effect on graphene configuration. Accordingly, tuned oxygen groups at the graphene edge boost peroxydisulfate (PDS) adsorption for finer initiating activation. Subsequently, 2D graphene with excellent electron utilization rate strengthens hydroxyl radical and direct electron transfer pathways in activating PDS for sulfamethoxazole (SMX) degradation. Impressively, the SMX degradation efficiency by fabricated graphene raises ≈8.9‐fold as compared with pristine pyrogenic carbon. Additionally, fabricated graphene is more efficient in PDS activation than commercial metal catalysts. Undoubtedly, this study realizes effective transformation of pyrogenic carbon to graphene for highly efficient metal‐free carbocatalyst. [ABSTRACT FROM AUTHOR]

Fires cause significant changes in morphological soil properties. Examples of soils of lichen and lingonberry–green-moss pine forests and green-moss spruce forests subjected to ground fires at different times are given. The preservation of pyrogenic features in soil morphology within different periods after fires is discussed. Soils of recently burnt areas are characterized by a lower acidity and lower content of water-soluble organic matter and an increase in the content of aromatic structures and polycyclic aromatic hydrocarbons (PAHs) in the soil organic matter. The composition of densimetric fractions of soils of post-pyrogenic forests is analyzed. The content of PAHs increases in the composition of light densimetric fractions. Examples of increasing hydrophobicity of the upper mineral horizons of post-pyrogenic soils are given. [ABSTRACT FROM AUTHOR]

Background. Strongly varying timescales of pyrogenic carbon (PyC) degradation have been observed across depositional settings. To date, PyC degradation in UK peatlands has had limited investigation. Aims. This study aims to evaluate how PyC recalcitrance relates to differing production characteristics, fuels and duration of exposure in UK peatlands. Methods. PyC samples produced from key peatland vegetation types were exposed on a peatland surface to assess molecular (by Fourier-transform infrared), leachable carbon (water-extractable organic carbon) and elemental (C, H, N, O) changes occurring over a year. Key results. PyC degradation phases were observed: (1) very rapid (=1 month) loss of leachable carbon; (2) longer-term (1-12 months) changes to PyC characteristics indicative of soil interactions. 'Severity' had a significant effect on all measured variables. Conclusions. This study indicates that PyC is susceptible to changes within short timescales in UK peatlands, particularly low-temperature PyC, but that stabilisation through soil matrix interactions may occur over longer periods (>1 year). Implications. The findings indicate that UK peatland wildfire carbon cycling research should consider early pulses of carbon to the wider environment, as well as longer-term C storage in PyC. [ABSTRACT FROM AUTHOR]

Carbon materials (e.g., pyrogenic carbon (PyC)) are widely used in agricultural soils and can participate in various biogeochemical processes, including iron (Fe) cycling. In soils, Fe(II) species have been proposed as the main active contributor to produce reactive oxygen species (ROS), which are involved in various biogeochemical processes. However, the effects of PyC on the transformation of different Fe species in soils and the associated production of ROS are rarely investigated. This study examined the influence of PyC (pyrolyzed at 300–700 °C) on Fe(II)/Fe(III) cycling and hydroxyl radical (·OH) production during redox fluctuations of paddy soils. Results showed that the reduction of Fe(III) in soils was facilitated by PyC during anoxic incubation, which was ascribed to the increased abundance of dissimilatory Fe(III)-reducing microorganisms (biotic reduction) and the electron exchange capacity of PyC (abiotic reduction). During oxygenation, PyC and higher soil pH promoted the oxidation of active Fe(II) species (e.g., exchangeable and low-crystalline Fe(II)), which consequently induced higher yield of ·OH and further led to degradation of imidacloprid and inactivation of soil microorganisms. Our results demonstrated that PyC accelerated Fe(II)/Fe(III) cycling and ·OH production during redox fluctuations of paddy soils (especially those with low content of soil organic carbon), providing a new insight for remediation strategies in agricultural fields contaminated with organic pollutants. Highlights: Pyrogenic carbon (PyC) with high EEC promoted active Fe(II) formation in anoxic paddy soils through abiotic and biotic mechanisms. Pyrolysis temperature affected the physiochemical properties of PyC, which regulated Fe cycling and ·OH production in soils. The enhanced production of ·OH led to microbial inactivation and organic pollutant degradation. [ABSTRACT FROM AUTHOR]

Pyrolyzed waste biomass, or biochar, has been suggested as a means to increase plant growth and mitigate soil salinization, which is a widespread agricultural issue and can reach extreme levels in urban soils impacted by de-icing salts. Soil mixing is enhanced by reduced biochar particle size; however, biochar properties vary with particle size, and recent studies have suggested that plant growth responses may be maximized at intermediate particle sizes. We examined the responses of two plant species (cowpea (Vigna unguiculata) and velvetleaf (Abutilon theophrasti)) to biochar amendments that spanned a wide range of particle sizes obtained by sieving, with and without de-icing salt additions. The smallest size fractions of biochar reduced plant growth relative to unamended controls. Plant biomass production was generally maximized at intermediate biochar particle size treatments, with particle sizes of 0.5–2.0 mm showing the best response. Mitigation of salt effects was also improved at intermediate biochar particle sizes in this particle size range. Our results emphasize the importance of optimizing biochar particle size to best enhance plant responses to biochar, with particular reference to saline soils. [ABSTRACT FROM AUTHOR]

Information about smoke cues for seed germination is fundamental to understanding fire adaptation. Recently, lignin-derived syringaldehyde (SAL) was identified as a new smoke cue for seed germination, which challenges the assumption that cellulose-derived karrikins are the primary smoke cues. We highlight the overlooked association between lignin and the fire adaptation of plants. [ABSTRACT FROM AUTHOR]

Efficient hydrogen production through methane pyrolysis is hindered by high temperature required and frequent catalyst deactivation due to carbon deposition. This study proposes a novel use of variable-frequency microwave heating to enhance the efficiency and stability of methane pyrolysis by leveraging the resonance effects between microwave frequencies and dielectric properties of activated charcoal (AC). A solid-state variable-frequency microwave reactor was employed to modulate microwave frequencies to match the dielectric properties of AC, with a peak tanδ of 0.19 at 4600 MHz. Experimental results showed that at a resonance frequency of 4650 MHz and a microwave power of 100 W, the reaction temperature of AC reached 960 °C within 2 min, achieving a 100% methane conversion rate. However, carbon deposition reduced the conversion rate to 35.1% after 150 min. By cyclically adjusting the microwave frequencies between 4650 MHz and 4640 MHz, the catalyst was successfully reactivated, restoring the conversion rate to 100%. This frequency modulation method enabled continuous methane pyrolysis for 1300 min, highlighting the potential of variable-frequency microwave heating as a novel and efficient approach for a sustainable production of green hydrogen. [Display omitted] • Developed a novel variable-frequency microwave reactor for methane pyrolysis. • Achieved 100% methane conversion at optimized 4650 MHz frequency. • Demonstrated 5-fold increase in heating efficiency over traditional methods. • Enabled cyclic reactivation of catalyst by switching microwave frequencies. • Significantly reduced energy consumption and environmental impact. [ABSTRACT FROM AUTHOR]

Purpose: The increase in human activities and climate change has caused more pyrogenic carbon (PyC), which is produced by fossil fuels or incomplete biomass consumption, to accumulate in natural ecosystems in the past hundred years and has caused serious effects on soil carbon pools. Although the peatland soil carbon pool represents 25–30% of the terrestrial soil carbon pool, the long-term effects of PyC on this pool are still unknown. Material and method: We identified the historical accumulation rates of PyC from fossil fuel and biomass sources through δ13C-PyC values in four typical peat cores in the Changbai Mountains (China) and evaluated the effects of PyC accumulation on peatland carbon pools. Results and discussion: The average δ13C-PyC values in the four peat cores of Changbai Mountains ranged from − 29.73 ± 0.66 to − 29.15 ± 1.46‰, and higher δ13C-PyC values in high-altitude peatlands than those in the low-altitude region indicated a higher proportion of fossil fuel-derived PyC deposited in high-altitude peatlands. Compared to local pollution history, fossil fuel-derived PyC in the high-altitude region was mainly produced from local industrial sources, and in the low-altitude region, it was mainly produced from several different anthropogenic sources (e.g., wars and transportation). Biomass-derived PyC in Changbai Mountains was caused by local fires, which were mainly influenced by climatic conditions and local government policies. Conclusion: The effects of these two sources of PyC on the carbon content and carbon accumulation rates were overall positive. Because local fires directly affect the peatland carbon pool, the impact of biomass-derived PyC on the peatland carbon pool is more complex than that of fossil fuel-derived PyC. [ABSTRACT FROM AUTHOR]

Fluorescence lifetimes and quantum yields featuring polycyclic aromatic hydrocarbons (PAHs) and other organics constituting pyrogenic carbon particulate matter (PM) are seldom measured. In this work, PM sampled in a fuel-rich ethylene flame was firstly separated in organic carbon (OC), soluble in dichloromethane, and refractory organic carbon (ROC), soluble in N -methyl pyrrolidinone, and then analyzed by size exclusion chromatography (SEC) coupled with online UV and fluorescence detection, and by offline fluorescence spectroscopy and mass spectrometry. It was found that three classes of differently light emitting carbon dots (CDs) could be bottom-up synthesized in the same flame system by selecting appropriately the residence time. Actually, OC presented blue fluorescence regardless the residence time, whereas ROC sampled at low and high residence time emitted fluorescence in the green (green CDs) and in the yellow (yellow CDs) region, respectively. The SEC molecular weight of all CDs presented similar trimodal distributions, centered around 300, 1000 and 10,000 u. For the first time fluorescence lifetimes and quantum yields of pyrogenic CD fractions were measured as additional parameters useful for discriminating the fluorescent components and inferring their structural properties, with the support of mass spectrometry. The different spectroscopic features of CDs could be associated to different compositional characteristics as the polydispersity of molecular components featuring blue CDs, opposed to the oligomer-like nature of green and yellow CDs. Pyrogenic CDs showed different fluorescence emission ranges, quantum yield and lifetimes, appealing for their possible applications in the fields of imaging, electronics and sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

Context: Organic amendments including biochar can improve crop production under salt stress. However, it is still not clear whether biochar enriched compost would enhance legume performance under salt stress after fresh application and in succeeding crops. Aim: The aim of the study was to examine the effect of biochar enriched compost in reducing the salinity stress after fresh application at increasing rates and in the succeeding crop. Methods: In a pot trial, biochar–compost was applied at four different rates (0, 1, 2, and 3%) while mungbean was grown under five different salt stress conditions (0, 2, 4, 8, and 12 dS m−1). In the field trial, the residual effect of different organic amendments (control, compost, cow urine, compost with cow urine, biochar–compost, and biochar–compost with cow urine) was evaluated under three different salt stress conditions (0, 3, and 6 dS m−1). Soil properties, plant performance, and nutrient uptake were determined. Key Results: Results revealed a significant biochar × salt treatment interaction in our pot culture. Biochar–compost application can minimise salt effects at a higher application rate resulting in better plant performance; however, these effects are minimal when salt was added at higher rates. We also observed a significant residual effect of biochar compost on biomass production (51.03%), seed yield (79.48%), and K+ uptake (77.95%) than the control treatment. We believe that biochar–compost buffered Na+ while improved plant water, and nutrient availability and uptake. In addition, biochar–compost might have increased nitrogen acquisition through enhanced biological nitrogen fixation. Conclusions: Biochar enriched compost enhances the yield of legume grown under salt stress. Implications: Our results suggest that biochar–compost can be one of the sustainable means for alleviating soil salinity. The application of co-composted biochar is an emerging mean of increasing agricultural productivity while sustaining soil health. However, it is unknown whether co-composted biochar applied in the previous season or its fresh application at increasing rates could promote the performance of a legume when grown under different levels of salinity. Co-composted biochar, applied in or previous season, increased mungbean yield through alleviating salt stress suggesting that it could be one of the sustainable means for legume production in saline-prone areas. [ABSTRACT FROM AUTHOR]

Study relevance. Russian forests have the largest pool of carbon C among terrestrial ecosystems, and they are subject to periodic fires. Combustion products remain in soils for thousands of years and are now the longest term pool of carbon. However, the size of this pool in soils is still not understood very well in terms of knowledge about the C reserve structure in Russian forests. Study objectives. Our objectives are to determine the content and structure of pools of total and highly stable forms of pyrogenic carbon (PyC), estimate the proportions of various PyC forms within the soil C, and study the relationship between the PyC and the stand characteristics and soil properties of periodically burning larch forests of the Upper Amur region. Study objects and methods. This paper presents data from the first field assessment of the total and highly stable forms of pyrogenic C pools in the soils of regularly burning larch forests of the Upper Amur region along a 500-km transect from north to south. Total and stable forms of pyrogenic carbon have been studied; the reserves and thickness of litter, as well as soil density, moisture, pH, and content of Corg and N, have been determined. Study results. In the upper soil layer, the total concentration of PyC varies from 1 to 2.2%, and the stock reaches 3.3 t/ha. The proportion of total PyC in the soil organic C pool reaches 21%, while the proportion of highly resistant PyC forms does not exceed 4%. A principal component analysis revealed that the concentration and stock of total PyC in soils do not depend on soil properties, but tend to increase towards the north. At the same time, the content and reserves of highly stable PyC, which mirrored the high-intensity fires, positively and significantly correlate with the proportion of larch in the forest stand. Conclusions. Our results indicate the predominance of low-intensity surface fires, which do not result in the formation of a large number of highly stable forms of PyC. The fire strength is likely to correlate positively with the larch regeneration. [ABSTRACT FROM AUTHOR]

Climate change and human activity are increasing the frequency of wildfires in peatlands and threatening permafrost peatland carbon pools. In Northeast China, low-severity prescribed fires are conducted annually on permafrost peatlands to reduce the risk of wildfires. These fires typically do not burn surface peat but lead to the loss of surface vegetation and introduction of pyrogenic carbon. However, the long-term effects of repeated low-severity fires on soil carbon stability in these ecosystems remain unclear. Thus, we conducted low-severity prescribed fire experiments over 3 years in the permafrost peatlands of the Great Khingan Mountains. Our findings showed a gradual decline in the total carbon content, primarily due to the reduction in free particulate organic matter (fPOM). Initially, fPOM was higher in the burned sites but decreased with repeated burning. Chemical analyses revealed a 32% increase in the aromaticity of the fPOM at the burned sites, which diminished the thermal stability of the soil. Furthermore, both prescribed fires and the addition of pyrogenic carbon reduced biological stability while increasing enzyme activity and CO 2 production, which was attributed to the introduction of post-fire pyrogenic carbon. These results suggest that low-severity fires compromise the stability of permafrost peatlands, particularly because the pyrogenic carbon input alters the chemical composition of the soil carbon fraction.

Gases and dissolved black carbon (DBC) formed during pyrolysis of nitrogen-rich feedstock would affect atmospheric and aquatic environments. Yet, the mechanisms driving biomass gas evolution and DBC formation are poorly understood. Using thermogravimetric-Fourier transform infrared spectrometry and two-dimensional correlation spectroscopy, we correlated the temperature-dependent primary noncondensable gas release sequence (H 2 O → CO 2 → HCN, NH 3 → CH 4 → CO) with specific defunctionalization stages in the order: dehydration, decarboxylation, denitrogenation, demethylation, and decarbonylation. Our results revealed that proteins in feedstock mainly contributed to gas releases, and low-volatile pyrolytic products contributed to DBC. Combining mass difference analysis with Fourier transform ion cyclotron resonance mass spectrometry, we showed that 44-60% of DBC molecular compositions were correlated with primary gas-releasing reactions. Dehydration (-H 2 O), with lower reaction energy barrier, contributed to DBC formation most at 350 and 450 °C, whereas decarboxylation (-CO 2 ) and deamidization (-HCNO) prevailed in contributing to DBC formation at 550 °C. The aromaticity changes of DBC products formed via gas emissions were deduced. Compared to their precursors, dehydration increased DBC aromaticity, while deamidization reduced the aromaticity of DBC products. These insights on pyrolytic byproducts help predict and tune DBC properties via changing gas formed during biochar production, minimizing their negative environmental impacts.

Biochar effects are strongly dependent on its properties. Biochar improves physical soil properties by decreasing bulk density and increasing medium and large aggregates, leading to faster and deeper water infiltration and root growth. Improvement of the chemical properties of soil is connected with pH neutralization of acidic soils, increase of cation exchange capacity and base saturation, providing a larger surface for sorption of toxicants and exchange of cations. Biochar increases the stocks of macro- and micronutrients in soil and remains sufficient for decades. Biochar effects on (micro)biological properties are mainly indirect, based on the improvements of habitat conditions for organisms, deeper root growth providing available C for larger soil volume, higher crop yield leading to more residues on and in the topsoil, better and deeper soil moisture, supply of all nutrients, and better aeration. Along with positive, negative effects of biochar while used as a soil conditioner are discussed in the review: presence of PAH, excessive amounts of K, Ca and Mg, declination of soil pH. In conclusion, despite the removal of C from the biological cycle by feedstock pyrolysis, the subsequent application of biochar into soil increases fertility and improves physical and chemical properties for root and microbial growth is a good amendment for low fertility soils. Proper use of biochar leads not only to an increase in crop yield but also to effective sequestration of carbon in the soil, which is important to consider when economically assessing its production. Further research should be aimed at assessing and developing methods for increasing the sequestration potential of biochar as fertilizer.

Approximately 40% of earth's carbon (C) stored in land vegetation and soil is within the boreal region. This large C pool is subjected to substantial removals and transformations during periodic wildfire. Fire‐altered C, commonly known as pyrogenic carbon (PyC), plays a significant role in forest ecosystem functioning and composes a considerable fraction of C transport to limnic and oceanic sediments. While PyC stores are beginning to be quantified globally, knowledge is lacking regarding the drivers of their production and transport across ecosystems. This study used the chemo‐thermal oxidation at 375°C (CTO‐375) method to isolate a particularly refractory subset of PyC compounds, here called black carbon (BC), finding an average increase of 11.6 g BC m−2 at 1 year postfire in 50 separate wildfires occurring in Sweden during 2018. These increases could not be linked to proposed drivers, however BC storage in 50 additional nearby unburnt soils related strongly to soil mass while its proportion of the larger C pool related negatively to soil C:N. Fire approximately doubled BC stocks in the mineral layer but had no significant effect on BC in the organic layer where it was likely produced. Suppressed decomposition rates and low heating during fire in mineral subsoil relative to upper layers suggests potential removals of the doubled mineral layer BC are more likely transported out of the soil system than degraded in situ. Therefore, mineral soils are suggested to be an important storage pool for BC that can buffer short‐term (production in fire) and long‐term (cross‐ecosystem transport) BC cycling. Plain Language Summary: Northern forests store a substantial fraction of the earth's carbon. Monitoring these stores is crucial for understanding forest contribution to atmospheric CO2 levels as well as their health under a changing climate. Wildfire has a major impact on shifting forest carbon stores to the atmosphere via emissions due to burning. However, a fraction of burnt material is left in forests as pyrogenic carbon (PyC). PyC is known to have positive effects on forest health and is thought to have increased resistance to being emitted to the atmosphere. Little predictive knowledge exists regarding how much PyC is produced during wildfire and even less is known about how that PyC is transported into the larger environment. This study utilized a large area wildfire field sampling campaign to study PyC in northern forests. It found that the amount of PyC produced could not be predicted by forest or fire properties. However, it was discovered that a large fraction of wildfire produced PyC quickly moves downward in the soil profile where it will be protected from decomposition and future burning. This novel finding suggests that one of the first steps of PyC transport is also a protective one, conserving carbon and mitigating climate change. Key Points: Fifty separate summer 2018 boreal wildfires were sampled 1 year postfire for black carbon (BC) across the 57–67° latitudinal range within SwedenFire had an insignificant effect on total BC stocks in organic layers but approximately doubled stocks in mineral layersMineral soil may function to buffer short‐term (production) and long‐term (cross‐ecosystem transport) BC processes [ABSTRACT FROM AUTHOR]

• Biochar/Fe(III)/persulfate effectively degrades N,N ‑diethyl- m -toluamide (DEET). • SO 4 •− are the dominant reactive species in the biochar/Fe(III)/persulfate system. • Chloride shifts the reactive species from SO 4 •− to •OH and to chlorine species. • PMSO is not a selective indicator for Fe(IV) in persulfate-based oxidation systems. • PMSO 2 is formed via the reaction of PMSO with SO 4 •−. Fenton-like processes using persulfate for oxidative water treatment and contaminant removal can be enhanced by the addition of redox-active biochar, which accelerates the reduction of Fe(III) to Fe(II) and increases the yield of reactive species that react with organic contaminants. However, available data on the formation of non-radical or radical species in the biochar/Fe(III)/persulfate system are inconsistent, which limits the evaluation of treatment efficiency and applicability in different water matrices. Based on competition kinetics calculations, we employed different scavengers and probe compounds to systematically evaluate the effect of chloride in presence of organic matter on the formation of major reactive species in the biochar/Fe(III)/persulfate system for the transformation of the model compound N,N ‑diethyl- m -toluamide (DEET) at pH 2.5. We show that the transformation of methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO 2) cannot serve as a reliable indicator for Fe(IV), as previously suggested, because sulfate radicals also induce PMSO 2 formation. Although the formation of Fe(IV) cannot be completely excluded, sulfate radicals were identified as the major reactive species in the biochar/Fe(III)/persulfate system in pure water. In the presence of dissolved organic matter, low chloride concentrations (0.1 mM) shifted the major reactive species likely to hydroxyl radicals. Higher chloride concentrations (1 mM), as present in a mining-impacted acidic surface water, resulted in the formation of another reactive species, possibly Cl 2 •−, and efficient DEET degradation. To tailor the application of this oxidation process, the water matrix must be considered as a decisive factor for reactive species formation and contaminant removal. [Display omitted] [ABSTRACT FROM AUTHOR]

We report carbon isotopic values in total organic carbon (TOC) and pyrogenic carbon (PyC) preserved in two sediment cores from the Ross Sea, Antarctica. The δ13C values of PyC ranged from −10.9‰ to −17.2‰, with distinct differences from the δ13C values of TOC (−24.1‰ to −26.1‰) in the sediments. The radiocarbon ages of PyC were 9,128 and 8,410 years old on average in the two cores but were thousands of years younger than the ages of TOC at the same core depth. These isotopic records provide strong evidence indicating that the PyC was produced from ancient wildfires predominantly in C4 vegetation and transported to Antarctica in the atmosphere. We suggest that ancient wildfires in predominantly C4 grasslands likely frequently occurred on a large scale and at a high intensity in the Southern Hemisphere during the last deglaciation to mid‐Holocene period of 14,800–4,200 years ago. Plain Language Summary: A large fraction of pyrogenic carbon (PyC) is produced from incomplete combustion of biomass fires on Earth and is widely distributed on land and in the oceans. This study presents the first evidence of both radiocarbon and stable carbon isotopes in the PyC preserved in the slope sediments of the Ross Sea in Antarctica. The results revealed that PyC accounted for a significant fraction (10.0%–28.0%) of the sedimentary total organic carbon (TOC) buried in the sediments, and both the Δ14C and δ13C values of PyC showed distinctive differences compared with those of TOC. The well‐defined δ13C (−10.9‰ to −17.2‰) and Δ14C (−415‰ to −843‰) values of PyC in the sediments revealed that in ancient times, PyC was produced from wildfires of C4 vegetation in the Southern Hemisphere and was transported in the atmosphere to Antarctica. The isotopic records of PyC preserved in the Ross Sea sediments provide meaningful evidence for environmental changes. Key Points: Pyrogenic carbon (PyC) constitutes a significant fraction of total organic carbon (TOC) preserved in sediment of the Ross Sea, AntarcticaDistinctive differences in both radiocarbon and stable carbon isotope values exist between PyC and TOC in the Ross Sea sedimentThe isotopic records indicated that the PyC was produced from ancient wildfires in C4 grasslands and transported to Antarctica in atmosphere [ABSTRACT FROM AUTHOR]

Charcoal‐rich Technosols on century‐old relict charcoal hearths (RCHs) are the subject of ongoing research regarding potential legacy effects that result from historic charcoal production and subsequent charcoal amendments on forest soil properties and forest ecosystems today. RCHs consist mostly of Auh horizons that are substantially enriched in soil organic carbon (SOC), of which the largest part seems to be of pyrogenic origin (PyC). However, the reported range of SOC and PyC contents in RCH soil also suggests that they are enriched in nonpyrogenic SOC. RCH soils are discussed as potential benchmarks for the long‐term influence of biochar amendment and the post‐wildfire influences on soil properties. In this study, we utilised a large soil sample dataset (n = 1245) from 52 RCH sites in north‐western Connecticut, USA, to quantify SOC contents by total element analysis. The contents of condensed highly aromatic carbon as a proxy for black carbon (BC) were predicted by using a modified benzene polycarboxylated acid (BPCA) marker method in combination with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy‐based partial least square regression (r2 = 0.89). A high vertical spatial sampling resolution allowed the identification of soil organic matter (SOM) enrichment and translocation processes. The results show an average 75% and 1862% increase in TOC and BPCA‐derived carbon, respectively, for technogenic Auh horizons compared to reference soils. In addition to an increase in aromatic properties, increased carboxylic properties of the RCH SOC suggest self‐humification effects of degrading charcoal and thereby the continuing formation of leachable aromatic carbon compounds, which could have effects on pedogenic processes in buried soils. Indeed, we show BPCA‐derived carbon concentrations in intermediate technogenic Cu horizons and buried top/subsoils that suggest vertical translocation of highly aromatic carbon originating in RCH Auh horizons. Topmost Auh horizons showed a gradual decrease in total organic carbon (TOC) contents with increasing depth, suggesting accumulation of recent, non‐pyrogenic SOM. Lower aliphatic absorptions in RCH soil spectra suggest different SOM turnover dynamics compared to reference soils. Furthermore, studied RCH soils featured additional TOC enrichment, which cannot be fully explained now. Highlights: BC to TOC ratio and high resolution vertical SOC distribution in 52 RCH sites were studied.RCH soils non‐BC pool was potentially different to reference soils.RCH soils feature TOC accumulation in the topmost horizon.There is BC translocation into buried soils on RCH sites. [ABSTRACT FROM AUTHOR]

Seeking to evaluate the hypothesis that biochar optimises the composting and vermicomposting processes as well as their product quality, we carried out field and greenhouse experiments. Four grass clipping composting treatments (only grass, grass + single superphosphate (SSP), grass + biochar and grass + SSP + biochar) were evaluated. At the end of the maturation period (150 days), the composts were submitted to vermicomposting (Eisenia fetida earthworm) for an additional 90 days. Ordinary fine charcoal was selected due to its low cost (a by-product of charcoal production) and great availability; this is important since the obtained product presents low commercial value. A greater maturity of the organic matter (humification) was observed in the vermicompost treatments compared with the compost-only treatments. The addition of phosphate significantly reduced the pH (from 6.7 to 4.8), doubled the electrical conductivity and inhibited biological activity, resulting in less than 2% of the number of earthworms found in the treatment without phosphate. The addition of soluble phosphate inhibited the humification process, resulting in a less-stable compound with the preservation of labile structures, primarily cellulose. The P species found corroborate these findings because the pyrophosphate conversion from SSP in the absence of biochar may explain the strong acidification and increased electric conductivity. Biochar appears to prevent this conversion, thus mitigating the deleterious effects of SSP and favouring the formation of organic P species from SSP (78.5% of P in organic form with biochar compared to only 12.8% in the treatments without biochar). In short, biochar decreases pyrophosphate formation from SSP, avoiding acidification and salinity; therefore, biochar improves the whole composting and vermicomposting process and product quality. Vermicompost with SSP and biochar should be tested as a soil conditioner on account of its greater proportion of stabilized C and organic P. [ABSTRACT FROM AUTHOR]