The priming potential of biochar products in relation to labile carbon contents and soil organic matter status
TL;DR: In this article, the priming potential of biochar in the context of its own labile fraction and procedures for their assessment were examined. But the results conclusively showed that while carbon mineralisation was often higher in biochar amended soil, this was probably due to rapid utilisation of a small labile component of Biochar and that biochar did not prime for the loss of native organic soil organic matter.
Abstract: Recognition of biochar as a potential tool for long-term carbon sequestration with additional agronomic benefits is growing However, the functionality of biochar in soil and the response of soils to biochar inputs are poorly understood It has been suggested, for example, that biochar additions to soils could prime for the loss of native organic carbon, undermining its sequestration potential This work examines the priming potential of biochar in the context of its own labile fraction and procedures for their assessment A systematic set of biochar samples produced from C4 plant biomass under a range of pyrolysis process conditions were incubated in a C3 soil at three discrete levels of organic matter status (a result of contrasting long-term land management on a single site) The biochar samples were characterised for labile carbon content ex-situ and then added to each soil Priming potential was determined by a comparison of CO2 flux rates and its isotopic analysis for attribution of source The results conclusively showed that while carbon mineralisation was often higher in biochar amended soil, this was due to rapid utilisation of a small labile component of biochar and that biochar did not prime for the loss of native organic soil organic matter Furthermore, in some cases negative priming occurred, with lower carbon mineralisation in biochar amended soil, probably as a result of the stabilisation of labile soil carbon
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TL;DR: The collective vision of the future of extracellular enzyme research is offered: one that will depend on imaginative thinking as well as technological advances, and be built upon synergies between diverse disciplines.
Abstract: This review focuses on some important and challenging aspects of soil extracellular enzyme research. We report on recent discoveries, identify key research needs and highlight the many opportunities offered by interactions with other microbial enzymologists. The biggest challenges are to understand how the chemical, physical and biological properties of soil affect enzyme production, diffusion, substrate turnover and the proportion of the product that is made available to the producer cells. Thus, the factors that regulate the synthesis and secretion of extracellular enzymes and their distribution after they are externalized are important topics, not only for soil enzymologists, but also in the broader context of microbial ecology. In addition, there are many uncertainties about the ways in which microbes and their extracellular enzymes overcome the generally destructive, inhibitory and competitive properties of the soil matrix, and the various strategies they adopt for effective substrate detection and utilization. The complexity of extracellular enzyme activities in depolymerising macromolecular organics is exemplified by lignocellulose degradation and how the many enzymes involved respond to structural diversity and changing nutrient availabilities. The impacts of climate change on microbes and their extracellular enzymes, although of profound importance, are not well understood but we suggest how they may be predicted, assessed and managed. We describe recent advances that allow for the manipulation of extracellular enzyme activities to facilitate bioremediation, carbon sequestration and plant growth promotion. We also contribute to the ongoing debate as to how to assay enzyme activities in soil and what the measurements tell us, in the context of both traditional methods and the newer techniques that are being developed and adopted. Finally, we offer our collective vision of the future of extracellular enzyme research: one that will depend on imaginative thinking as well as technological advances, and be built upon synergies between diverse disciplines.
1,475 citations
TL;DR: In this paper, a review of the preparation, characterization, modification, and especially environmental application of biochar, based on more than 200 papers published in recent 10 year, to provide an overview of Biochar with a particular on its environmental application.
1,017 citations
TL;DR: In this article, a meta-analysis of the biochar decomposition in soil was performed and the authors concluded that only a small part of biochar is bioavailable and that the remaining 97% contribute directly to long-term carbon sequestration in soil.
Abstract: The stability and decomposition of biochar are fundamental to understand its persistence in soil, its contribution to carbon (C) sequestration, and thus its role in the global C cycle. Our current knowledge about the degradability of biochar, however, is limited. Using 128 observations of biochar-derived CO2 from 24 studies with stable (13C) and radioactive (14C) carbon isotopes, we meta-analyzed the biochar decomposition in soil and estimated its mean residence time (MRT). The decomposed amount of biochar increased logarithmically with experimental duration, and the decomposition rate decreased with time. The biochar decomposition rate varied significantly with experimental duration, feedstock, pyrolysis temperature, and soil clay content. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years with pool sizes of 3% and 97%, respectively. These results show that only a small part of biochar is bioavailable and that the remaining 97% contribute directly to long-term C sequestration in soil. The second database (116 observations from 21 studies) was used to evaluate the priming effects after biochar addition. Biochar slightly retarded the mineralization of soil organic matter (SOM; overall mean: −3.8%, 95% CI = −8.1–0.8%) compared to the soil without biochar addition. Significant negative priming was common for studies with a duration shorter than half a year (−8.6%), crop-derived biochar (−20.3%), fast pyrolysis (−18.9%), the lowest pyrolysis temperature (−18.5%), and small application amounts (−11.9%). In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This indicates that biochar stimulates microbial activities especially in soils with low fertility. Furthermore, abiotic and biotic processes, as well as the characteristics of biochar and soils, affecting biochar decomposition are discussed. We conclude that biochar can persist in soils on a centennial scale and that it has a positive effect on SOM dynamics and thus on C sequestration.
654 citations
Cites background from "The priming potential of biochar pr..."
...For SOC-rich soils, however, biochar can stimulate SOM mineralization (Cross & Sohi, 2011; Stewart et al., 2013)....
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...(5) A few studies were excluded that reported negative values of biochar decomposition because of high variation by application of 13C natural abundance or because isotopic fractionation was not considered (Cross & Sohi, 2011)....
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TL;DR: In this article, a fixed-bed slow pyrolysis from various feedstock biomasses under a range of process conditions was used to produce biochar, which was characterized by proximate analysis, CHN-elemental analysis, pH in solution, bomb calorimetry for higher heating value, N2 adsorption for BET surface area and two biological degradation assays (oxygen demand, carbon mineralization in soil).
Abstract: Biochar was produced by fixed-bed slow pyrolysis from various feedstock biomasses under a range of process conditions. Feedstocks used were pine wood, wheat straw, green waste and dried algae. Process conditions varied were the highest treatment temperature (HTT) and residence time. The produced chars were characterized by proximate analysis, CHN-elemental analysis, pH in solution, bomb calorimetry for higher heating value, N2 adsorption for BET surface area and two biological degradation assays (oxygen demand, carbon mineralization in soil). In proximate analysis, it was found that the fixed carbon content (expressed in wt% of dry and ash-free biochar) in the biochar samples strongly depended on the intensity of the thermal treatment (i.e. higher temperatures and longer residence times in the pyrolysis process). The actual yield in fixed carbon (i.e. the biochar fixed carbon content expressed as wt% of the dry and ash-free original feedstock biomass weight) was practically insensitive to the highest treatment temperature or residence time. The pH in solution, higher heating value and BET surface positively correlated with pyrolysis temperature. Finally, soil incubation tests showed that the addition of biochar to the soil initially marginally reduced the C-mineralization rate compared against the control soil samples, for which a possible explanation could be that the soil microbial community needs to adapt to the new conditions. This effect was more pronounced when adding chars with high fixed carbon content (resulting from more severe thermal treatment), as chars with low fixed carbon content (produced through mild thermal treatment) had a larger amount of volatile, more easily biodegradable, carbon compounds.
635 citations
Cites background or methods from "The priming potential of biochar pr..."
...However, this positive priming effect has not always been observed to significant extent (Cross & Sohi, 2011; Case et al., 2012) or a negative priming effect, a reduction in initial CO2 soil respiration in © 2012 Blackwell Publishing Ltd, GCB Bioenergy, 5, 104–115 biochar-amended soil samples could…...
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...© 2012 Blackwell Publishing Ltd, GCB Bioenergy, 5, 104–115 produced from low-temperature pyrolysis processes have also been previously observed by Zimmerman (2010) and Cross & Sohi (2011)....
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TL;DR: In this review, multiple and multilevel structures of biochars are interpreted based on their elemental compositions, phase components, surface properties, and molecular structures to design a "smart" biochar for environmentally sustainable applications.
Abstract: Biochar is the carbon-rich product of the pyrolysis of biomass under oxygen-limited conditions, and it has received increasing attention due to its multiple functions in the fields of climate change mitigation, sustainable agriculture, environmental control, and novel materials. To design a “smart” biochar for environmentally sustainable applications, one must understand recent advances in biochar molecular structures and explore potential applications to generalize upon structure–application relationships. In this review, multiple and multilevel structures of biochars are interpreted based on their elemental compositions, phase components, surface properties, and molecular structures. Applications such as carbon fixators, fertilizers, sorbents, and carbon-based materials are highlighted based on the biochar multilevel structures as well as their structure-application relationships. Further studies are suggested for more detailed biochar structural analysis and separation and for the combination of macros...
520 citations
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TL;DR: In this article, the authors investigated the source of the higher surface charge of BC compared with non-BC by mapping crosssectional areas of BC particles with diameters of 10 to 50 mm for C forms.
Abstract: Black Carbon (BC) may significantly affect nutrient retention and play a key role in a wide range of biogeochemical processes in soils, especially for nutrient cycling. Anthrosols from the Brazilian Amazon (ages between 600 and 8700 yr BP) with high contents of biomassderived BC had greater potential cation exchange capacity (CEC measured at pH 7) per unit organic C than adjacent soils with low BC contents.Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) spectroscopy coupled with scanning transmission X-ray microscopy (STXM) techniques explained the source of the higher surface charge of BC compared with non-BC by mapping crosssectional areas of BC particles with diameters of 10 to 50 mm for C forms. The largest cross-sectional areas consisted of highly aromatic or only slightly oxidized organic C most likely originating from the BC itself with a characteristic peak at 286.1 eV, which could not be found in humic substance extracts, bacteria or fungi. Oxidation significantly increased from the core of BC particles to their surfaces as shown by the ratio of carboxyl-C/aromatic-C. Spotted and non-continuous distribution patterns of highly oxidized C functional groups with distinctly different chemical signatures on BC particle surfaces (peak shift at 286.1 eV to a higher energy of 286.7 eV) indicated that non-BC may be adsorbed on the surfaces of BC particles creating highly oxidized surface. As a consequence of both oxidation of the BC particles themselves and adsorption of organic matter to BC surfaces, the charge density (potential CEC per unit surface area) was greater in BC-rich Anthrosols than adjacent soils. Additionally, a high specific surface area was attributable to the presence of BC, which may contribute to the high CEC found in soils that are rich in BC.
1,932 citations
TL;DR: In this paper, a re-evaluation of our 10-year old paper on priming effects is presented, and the most important needs for future research are identified and evaluated.
Abstract: In this re-evaluation of our 10-year old paper on priming effects, I have considered the latest studies and tried to identify the most important needs for future research. Recent publications have shown that the increase or decrease in soil organic matter mineralization (measured as changes of CO 2 efflux and N mineralization) actually results from interactions between living (microbial biomass) and dead organic matter. The priming effect (PE) is not an artifact of incubation studies, as sometimes supposed, but is a natural process sequence in the rhizosphere and detritusphere that is induced by pulses or continuous inputs of fresh organics. The intensity of turnover processes in such hotspots is at least one order of magnitude higher than in the bulk soil. Various prerequisites for high-quality, informative PE studies are outlined: calculating the budget of labeled and total C; investigating the dynamics of released CO 2 and its sources; linking C and N dynamics with microbial biomass changes and enzyme activities; evaluating apparent and real PEs; and assessing PE sources as related to soil organic matter stabilization mechanisms. Different approaches for identifying priming, based on the assessment of more than two C sources in CO 2 and microbial biomass, are proposed and methodological and statistical uncertainties in PE estimation and approaches to eliminating them are discussed. Future studies should evaluate directions and magnitude of PEs according to expected climate and land-use changes and the increased rhizodeposition under elevated CO 2 as well as clarifying the ecological significance of PEs in natural and agricultural ecosystems. The conclusion is that PEs – the interactions between living and dead organic matter – should be incorporated in models of C and N dynamics, and that microbial biomass should regarded not only as a C pool but also as an active driver of C and N turnover.
1,470 citations
TL;DR: In this article, a conceptual model of the processes by which plant leaf and root litter is transformed to soil organic C and CO 2 is presented, which is viewed as resulting from three general sets of characteristics.
1,409 citations
TL;DR: In this article, the authors summarize the knowledge of the production and properties of charcoal that has been accumulated over the past 38 millenia and summarize the potential of charcoal as a renewable fuel.
Abstract: In this review, we summarize the knowledge of the production and properties of charcoal that has been accumulated over the past 38 millenia. The manipulation of pressure, moisture content, and gas flow enables biomass carbonization with fixed-carbon yields that approachor attainthe theoretical limit after reaction times of a few tens of minutes. Much of the heat needed to carbonize the feed is released by vigorous, exothermic secondary reactions that reduce the formation of unwanted tars by augmenting the charcoal yield in a well-designed carbonizer. As a renewable fuel, charcoal has many attractive features: it contains virtually no sulfur or mercury and is low in nitrogen and ash; it is highly reactive yet easy to store and handle. Carbonized charcoal can be a good adsorbent with a large surface area and a semimetal with an electrical resistivity comparable to that of graphite. Recent advances in knowledge about the production and properties of charcoal presage its expanded use as a renewable fuel, red...
1,402 citations
TL;DR: In an effort to better understand the interaction of pyrogenic C and soil organic matter (OM), a range of Florida soils were incubated with a variety of laboratory-produced biochars and CO 2 evolution was measured over more than one year as discussed by the authors.
Abstract: Pyrogenic carbon (biochar) amendment is increasingly discussed as a method to increase soil fertility while sequestering atmospheric carbon (C). However, both increased and decreased C mineralization has been observed following biochar additions to soils. In an effort to better understand the interaction of pyrogenic C and soil organic matter (OM), a range of Florida soils were incubated with a range of laboratory-produced biochars and CO 2 evolution was measured over more than one year. More C was released from biochar-amended than from non-amended soils and cumulative mineralized C generally increased with decreasing biomass combustion temperature and from hardwood to grass biochars, similar to the pattern of biochar lability previously determined from separate incubations of biochar alone. The interactive effects of biochar addition to soil on CO 2 evolution (priming) were evaluated by comparing the additive CO 2 release expected from separate incubations of soil and biochar with that actually measured from corresponding biochar and soil mixtures. Priming direction (positive or negative for C mineralization stimulation or suppression, respectively) and magnitude varied with soil and biochar type, ranging from −52 to 89% at the end of 1 year. In general, C mineralization was greater than expected (positive priming) for soils combined with biochars produced at low temperatures (250 and 400 °C) and from grasses, particularly during the early incubation stage (first 90 d) and in soils of lower organic C content. It contrast, C mineralization was generally less than expected (negative priming) for soils combined with biochars produced at high temperatures (525 and 650 °C) and from hard woods, particularly during the later incubation stage (250–500 d). Measurements of the stable isotopic signature of respired CO 2 indicated that, for grass biochars at least, it was predominantly pyrogenic C mineralization that was stimulated during early incubation and soil C mineralization that was suppressed during later incubation stages. It is hypothesized that the presence of soil OM stimulated the co-mineralization of the more labile components of biochar over the short term. The data strongly suggests, however, that over the long term, biochar–soil interaction will enhance soil C storage via the processes of OM sorption to biochar and physical protection.
1,125 citations