Heavy Density Fractions Research Articles

Enhanced loss but limited mobility of pyrogenic and organic matter in continuous permafrost-affected forest soils

Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an important pool of soil organic carbon (SOC). The dynamics of PyOM and SOC in boreal and permafrost-affected soils are largely unknown, while storing large amounts of global carbon and being vulnerable to climate change. Here, we traced the vertical mobility, allocation in soil fractions and decomposition losses of highly 13C-labeled PyOM and its precursor ryegrass organic matter (grass OM) after two years of in-situ incubation in soil cores installed in the upper 10 cm of continuous (northern sites) and discontinuous to sporadic (southern sites) permafrost-affected forest soils in Northern Canada. At the northern sites, up to three times more PyOM was lost by decomposition (39% of initial) compared to the southern sites (11% of initial). Losses of grass OM were substantial (69–84% of initial) and larger in southern soils. The vertical incorporation was limited and >90% of recovered PyOM and grass OM were found at the applied depth (0–3 cm). The PyOM strongly interacted with mineral surfaces, as indicated by around 40% recovered in the mineral-associated heavy density fractions (<63 μm). Microscale analyses by SEM and NanoSIMS showed that PyOM was mainly allocated towards the fine fraction in a particulate and aggregated form, highlighting the importance of abiotic processes for the incorporation of PyOM in permafrost-affected soils. The grass OM was mainly recovered in the mineral fractions at southern soils with enhanced allocation towards mineral surfaces as well as increased distribution at the microscale after initial decomposition, while it remained as particulate OM in northern soils. Our results highlight that permafrost-affected boreal forest soils are sensitive to fresh PyOM and OM inputs with substantial losses. Especially PyOM persistence depended on site and soil specific properties and not solely on its physico-chemical persistence. The responses are decoupled for PyOM and non-pyrolyzed OM and require a better understanding to evaluate carbon feedbacks of high-latitude soils with global warming and associated shifts in vegetation and wildfire regimes.

Effects of sugarcane substrate inputs on microbial biomass and nitrogen availability in tropical sandy soils of northeast Thailand

ABSTRACT The increasing demand for sugarcane residue to produce industrial biofuels competes with organic-matter inputs to tropical soils for increasing fertility. Soil nitrogen (N) availability to plants and carbon (C) storage can be optimized by the selection of substrate types and quantities. We tested whether substrate-induced microbial growth increases soil N mineralization and C stabilization as substrate inputs increase. The effects of substrate additions (cane sugar, leaf litter, and humic acid extracted from filter cake) on microbial growth and N availability were studied using C3/C4 plant C isotopic signatures in a sandy soil of northeast Thailand. The initial growth of microbial biomass in cane sugar-amended soil caused a short-term flush of N derived from the native soil organic matter within 3 days, whereas in the soils amended with leaf litter or humic acid, N was retained in microbial biomass or dissolved organic matter, respectively. Net mineralization of the native soil organic N was maximized by sugar addition at a dosage corresponding to 10 folds of microbial biomass-C. The efficacy of substrates stabilized in the heavy density fraction (>1.6 g cm−3) followed the order: leaf litter > humic acid > sugar. Soil net N mineralization can be promoted by sugar inputs (e.g., bud node) at an early growth stage, while leaf litter and humic acid inputs can increase C storage efficiently in the sandy soil without increasing risks of N starvation and loss when they are applied at several tons of C per hectare at least 3 weeks before planting.

Lime and/or Phosphate Application Affects the Stability of Soil Organic Carbon: Evidence from Changes in Quantity and Chemistry of the Soil Water-Extractable Organic Matter.

The mechanisms by which lime and/or phosphate addition impacts the preservation of soil organic matter (OM) are poorly understood. We explored the changes in quantity and chemistry of water-extractable organic matter (WEOM) in the bulk soil and its heavy density fraction (>1.6 g/cm3) of an unmanaged C-rich volcanic soil caused by lime and/or phosphate application. The addition of lime or phosphate caused (i) a significant increase in the WEOM, along with a decrease in its C/N ratio and an increase in its aromaticity, and (ii) changes in the WEOM chemical composition, measured with pyrolysis-gas chromatography/mass spectrometry, this being most impacted by lime application. The combined effect of lime and phosphate addition on the quantity and chemistry of WEOM was larger than the effects of separate lime and phosphate additions. By comparing the response of the bulk soil and the heavy fraction, we infer that phosphate has a greater contribution to the destabilization of vulnerable particulate OM, while lime causes a comparable disruption in the particulate OM and that in the heavy fraction. These findings provide a mechanistic insight into the decreased OM stability after liming and/or P fertilizing Andosols. They have implications for designing climate-smart management practices for these soils.

Inferring the impact of earthworms on the stability of organo-mineral associations, by Rock-Eval thermal analysis and 13C NMR spectroscopy

Stabilization of organic matter (OM) against decomposition and its de-stabilization leading to mineralization, are important processes in the control of greenhouse gas emissions and carbon sequestration in soils. Soil organisms, particularly earthworms, may influence these processes greatly through their potential impacts on the interaction of OM with clay minerals, which is a mechanism which may protect OM for medium (years) to long (decades, centuries) time scales. The aim of this study was to use earthworms and pure minerals in order to investigate enhancement of carbon sequestration through the formation of aggregates containing particulate OM and organo-mineral associations, during a composting experiment. To this end we compared OM transformations in composting treatments with and without (i) clay minerals (montmorillonite) and (ii) epigeic earthworms (Eisenia andrei and Eisenia foetida). We used density fractionation of the end-products to quantify the amount of aggregates, including organo-mineral associations, formed during 196 days. Chemical composition and stability were examined by elemental analyses, Rock-Eval 6 thermal analysis and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy.The results indicated that the addition of minerals led to the formation of heavy fractions, most probably containing aggregates and organo-mineral associations, in treatments with and without earthworms. While OM showed higher oxidative transformation in all treatments, addition of earthworms changed organic carbon (OC) and nitrogen (N) concentrations in specific density fractions and increased the thermal stability of OM in heavy density fractions. These fractions contained higher proportions of aromatic and proteinaceous materials. We conclude that, earthworms under composting conditions, earthworms may be able to effectively to stabilize OM through the formation of aggregates and/or organo-mineral associations containing greater proportions of microbially-derived material.

Spatial variability of organic matter degradability in tidal Elbe sediments

PurposeThe microbial turnover of sediment organic matter (OM) in ports and waterways impacts water quality, sonic depth finding and presumably also rheological properties as well as greenhouse gas emissions, especially if organic carbon is released as methane. As a consequence, sediment management practices as a whole are affected. This study aimed to discern spatial OM degradability patterns in the Port of Hamburg and investigated correlations with standard analytical properties as a basis for future predictive modelling.Materials and methodsSediments in the Port of Hamburg were repeatedly sampled at nine locations along an east-west transect using a 1-m corer. In a stratified sampling approach, layers of suspended particulate matter (SPM), fluid mud (FM), pre-consolidated sediment (PS) and consolidated sediment (CS) were identified and individually analysed for long-term aerobic and anaerobic degradation of organic matter, DNA concentration, stable carbon isotope signature, density fractions and standard solids and pore water properties.Results and discussionThe investigation area was characterised by a distinct gradient with a 10-fold higher OM degradability in upstream areas and lower degradability in downstream areas. Concomitantly, upstream locations showed higher DNA concentrations and more negative δ13C values. The share of bulk sediment in the heavy density fraction as well as the proportion and absolute amount of organic carbon were significantly larger at downstream locations. A depth and hence age-related gradient was found at individual locations, showing higher degradability of the upper, younger material, concomitant with higher DNA concentration, and lower OM turnover in the deeper, older and more consolidated material. Deeper layers were also characterised by higher concentrations of pore water ammonium, indicative of anaerobic nitrogen mineralisation.ConclusionsOrganic matter lability is inversely linked to its stabilisation in organo-mineral complexes. The observed degradability gradient is likely due to the different OM quality in relation to its origin. Downstream OM enters the system with the tidal flood current from the direction of the North Sea whereas upstream locations receive OM originating from the catchment, containing more autochthonous, plankton-derived and more easily degradable components. At individual sampling points, depth-related degradability gradients reflect an age gradient, with easily degradable material in top layers and increasing stabilisation of OM in organo-mineral compounds with depth.

Afforestation of loess soils: Old and new organic carbon in aggregates and density fractions

Afforestation is an important strategy to increase soil organic carbon (SOC) stocks and stabilize soils against degradation and erosion. While the area under afforestation has increased globally during the last 20 years, the dynamics of SOC accumulation due to afforestation are still poorly known, as it cannot be directly compared to that in cropland. The goals of this study were: i) to investigate the dynamics of SOC accumulation after afforestation on the Loess Plateau; ii) to determine SOC contents and distribution in density fractions and aggregates most strongly affected by afforestation; and iii) to analyze the relationships between old and new SOC in relation with afforestation periods. A chronosequence of forest plots aged 1, 5, 12 (with Chinese pine, Pinus tabulaeformis Carr.) and 30 years (with white poplar, Populus alba L.) were selected within the large scale “Grain for Green” project. A maize field nearby was chosen as a control, which represents the land use prior to afforestation. At each location, soils were sampled at depths of 0–10 and 10–30 cm, respectively and aggregates were fractionated into <250, 250–2000 and > 2000 μm sizes, which were subsequently separated into light (ρ < 1.85 g cm−3) and heavy (ρ > 1.85 g cm−3) density fractions. SOC content was generally higher in afforested soils than in cropland and increased with stand age. The mean SOC accumulation rate was 0.11 g C kg−1 year−1 for the 0–10 cm layer of the 30-year-old forests, whereas the maximum rate was found for 5-year-old forest at 0.24 g C kg−1 year−1. For each period of afforestation, the maximum SOC content was recorded in the macroaggregates. The C turnover of the light fraction (calculated based on δ13C of SOC) peaked in the large macroaggregates and ranged from 21 to 23 years). Whereas SOC turnover in the heavy fraction, peaked in the microaggregates at a relatively longer period of 46 to 70 years. We conclude that the initial SOC accumulation under afforestation occurs mainly in the macroaggregates, with a faster turnover compared with microaggregates. During the first 30 years of afforestation, the SOC accumulation and stabilization is ongoing mainly in the upper 10 cm, while the C sequestration in 10 to 30 cm depth needs much longer time.

Comparative carbon stability in surface soils and subsoils under submerged rice and upland non-rice crop ecologies: A physical fractionation study

The role of subsoil to store stable carbon (C) has become an important research topic in recent decades. In doing so, pools of subsoil C are compared to surface soil. The present study identified differences in mineral associated C (as separated by density fractionation) and aggregate occluded C in surface and subsurface soils. It also considered the impact of submerged rice as well as upland non-rice ecology on soil C stability. Results indicated that subsoil had a significantly greater amount of soil microaggregates as well as microaggregates within macroaggregates compared to surface soils. Subsequently, subsoil also had higher microaggregate occluded C, inaccessible to microorganisms. The higher ‘ratio of C present in the heavy density fraction with C present in bulk soils’ suggested that more C was strongly associated with the subsoil mineral fraction. Besides, spectroscopic analysis of functional groups indicated higher stability of subsoil aggregate occluded C than the aggregate C of surface soils. Summarily, results indicated that subsoil is a potential niche for recalcitrant C storage. Contrariwise, submerged rice ecology resulted in marginally higher soil aggregation compared to upland non-rice soils. Crop ecology did not influence aggregate occluded C dynamics and mineral-C association. As soil physical and aggregation dynamics differ substantively in puddled rice soils and upland non-rice soils, more research is warranted before making a strong conclusion.

Gas production from dredged sediment

The anaerobic degradation of sediment organic matter leads to considerable gas production in constructions made from sediments and in landfills where contaminated sediments are disposed of, inducing problems with the mechanical stability of constructions or necessitating extraction and treatment of gas. However, little is known about the magnitude of gas generation from dredged sediment, hence validated input parameters for gas production modelling are missing. On the occasion of drillings performed for the installation of inclinometers on a mono-landfill for contaminated dredged sediment, eleven waste layers of known were sampled. Samples were analysed for gas generation in a long-term laboratory incubation experiment carried out for 757 days. It was found that the residual gas potential of the deposited dredged material ranged between 2 and 12 m3 MgDW−1, relating to 3–11% of the organic matter being degraded. Correlation analyses with material properties suggest a strong role of nitrogen, either directly or as indicative parameter, with the gas potential increasing with total nitrogen content and the share of degradable carbon decreasing with increasing TOC/TN ratio. The by far greatest share of organic matter was bound in the heavy density fraction >1.4 g cm−3, suggesting that the readily available light organic matter pool had already been depleted during pre-treatment of the dredged sediment in dewatering fields and the subsequent years of landfilling. Consequently, the correlation of the remaining gas potential with heavy fraction nitrogen was even stronger than for bulk nitrogen. The gas potential as revealed from the long-term test correlated well with short-term values, but outreached the commonly applied potential measured for 21 days by the factor of four. The data improve the state of knowledge on gas production from the large mineral waste stream of dredged material and serve to improve gas production modelling for these types of wastes. The strong correlation of gas potential to TN suggests that TN may serve as a proxy to estimate total gas potential.

Different responses of soil organic carbon fractions to additions of nitrogen

SummaryCarbon–nitrogen (C–N) interactions in terrestrial ecosystems regulate climate–C cycle feedbacks. How additions of N affect soil C sequestration and then regulate climate change, however, are not fully understood. Previous studies have assessed effects of N on bulk soil organic C (SOC) but have not yet carefully examined its effects on different SOC fractions, which determine how fast the N‐regulated C cycle feeds back to climate. Here we synthesized data from 36 studies with 296 observations by a meta‐analysis to evaluate the responses of SOC fractions to N additions. We hypothesized that additions of N might increase both labile and non‐labile C fractions. The SOC that was separated by density fractionation increased by 18.3% for free light fractions and by 3.0% for heavy density fractions without change in the occluded light fraction under N addition compared with the control. The SOC that was separated by aggregate fractionation increased by 4.4% for macroaggregate‐associated fractions and by 6.5% for aggregate mineral‐associated fractions without change in the microaggregate‐associated fraction under N additions. When bulk SOC was separated by chemical permanganate oxidation, the oxidizable fraction increased by 10.4%, whereas the unoxidizable fraction increased by 4.5%. The changes in different soil C fractions were related to the mechanisms of SOC stabilization. Because of the significant increases in non‐labile SOC fractions, our findings suggest that on a global scale, increased additions of N might promote SOC accumulation and slow down climate change in the long term. Our results will be useful in model development for better prediction of SOC sequestration under additions of N.HighlightsEffects of N deposition on soil C fractions were addressed using meta‐analysis. Nitrogen additions significantly increased labile SOC fractions. Non‐labile SOC fractions were also increased under N additions. Nitrogen additions might promote SOC accumulation in the long term.

Distribution of soil organic carbon in the light and heavy fractions for six shelterbelt species and their adjacent agricultural fields in Saskatchewan.

Agroforestry systems play an important role in the sequestration of carbon (C) to reduce atmospheric carbon dioxide (CO2) levels. However, the extent of long-term C sequestration will depend on physical stabilization of the sequestered C. This study determined the influence of six major shelterbelt species on soil organic carbon (SOC) distribution in the light- and heavy-density fractions of bulk soil compared with adjacent agricultural fields. Soil samples were collected from the shelterbelts and adjacent agricultural fields and were separated into light and heavy fractions using sodium iodide solution (NaI, density = 1.6 g cm−3) and analyzed for their organic C stocks. Both the light and heavy fractions to a 50 cm soil depth contained higher SOC stocks for the shelterbelts (21 and 91 Mg C ha−1, respectively) compared with the adjacent agricultural fields (14 and 81 Mg C ha−1, respectively). Most SOC added at the 0–10 cm soil depth was in the form of labile light fraction (92%), whereas heavy fraction co...

Significance of antifouling paint flakes to the distribution of dichlorodiphenyltrichloroethanes (DDTs) in estuarine sediment

Recently published literature indicated that dichlorodiphenyltrichloroethane (DDT)-containing antifouling paint flakes were heterogeneously distributed within estuarine sediments. However, the significance of antifouling paint flakes in the fate and transport of DDT compounds and other organic pollutants in estuarine sediment is yet to be adequately addressed. To fill this knowledge gap, estuarine sediment and paint flakes from cabin and boat surfaces were collected from a fishery base in Guangdong Province of South China and analyzed for DDT compounds. Coarse fractioned samples collected from the vicinity of boat maintenance facilities contained appreciable amounts of colorful particles, which were identified as paint flakes by Fourier transform infrared spectroscopy. The highest concentrations of DDXs (sum of DDTs and its metabolites) occurred in the heavy-density (>1.7 g cm−3) fraction of coarse-size (200–2000 μm) sediments from near the boat maintenance facilities, suggesting the importance of paint flakes in the distribution pattern of “hot spots” in estuarine sediment. Moreover, the desorption rates of DDT compounds from paint flakes and the heavy-density fraction of coarse-size sediment were both extremely slow. Apparently, unevenly distributed paint flakes in sediment can artificially inflate the sorption capacity of heavy-density sediment for DDT compounds, and therefore can substantially change the environmental fate and behavior of hydrophobic organic chemicals in estuarine sediment. Finally, commonly used source diagnostic indices of DDT compounds were mostly grain-size and density dependent in sediment, as a result of the occurrence of paint flakes, which may strongly compromise the outcome of any source diagnostics efforts.

Nickel in a serpentine-enriched Fluvisol: Redox affected dynamics and binding forms

We determined redox-induced (im)mobilization of geogenic nickel (Ni) as well as binding forms of Ni in a Fluvisol at the River Velika Morava valley (Serbia), enriched with serpentine minerals. The selected site is representative for intensive agricultural land use in the area and susceptible to dynamic redox conditions due to periodical flooding. A seven-step sequential extraction, grain-size and light-liquid separation as well as mineralogical analyses were used, first, to assess binding forms of Ni and second, to determine relationships between grain-size fractions, abundance of heavy density minerals, and Ni concentration in the bulk soil. The sequential extraction revealed that the majority of Ni was in the residual fraction, followed by organic matter and Fe oxides. Fine grain-size fraction (<63μm) was the major location of accumulation of Ni in the soil. Minerals which are characteristic for serpentine soils such as serpentine, spinels, hematite, and magnetite were found in silt and in the heavy density fraction (>2.9gml−1) of the medium and fine sand. However, the light minerals quartz, chlorite, micas, and secondary clay minerals dominate the soil mineral composition. Thus, total Ni concentration in the soil is derived from the content of Ni-bearing minerals and diluted by the minerals which are low in Ni.We simulated flooding using an automated biogeochemical microcosm system and determined the release dynamics of Ni at controlled redox potentials (EH) in soil slurries. Pre-defined redox-windows were systematically created in steps of approximately 100mV from reducing to oxidizing conditions while EH and pH were continuously monitored. In parallel, the release dynamics of soluble nickel (Ni), iron (Fe), magnesium (Mg), manganese (Mn), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and sulfate (SO42−) were measured at each EH-window. Our results highlighted that geogenic Ni can be mobilized to a considerable amount during low EH, while elevating EH from reducing to oxidizing conditions generated an immobilization Ni. We suggested that mobilization of Ni has been primarily affected by formation of Ni–DOC complexes at low EH, whereas Ni seems to be immobilized as a result of formation of Fe/Mn (hydro)oxides and the linked co-precipitation of Ni during oxidation. Factor analysis (FA) as multivariate statistical method explained 85.08% of the variance (67.89% and 17.19% component Nos. 1 and 2, respectively). The FA reveals that soluble Ni, Fe, DOC, Mn, and Mg were clustered in one group which indicate that the combined effect of DOC together with the chemistry of Fe, Mn, and Mg might be linked to the redox-induced release dynamics of Ni. The practical perspective of the study was to draw attention to dynamics of soluble Ni in fluctuating conditions for a better ecological risk assessment of floodplain sites under agricultural use. Nevertheless, similar studies should be conducted with further serpentine soils from various sites world-wide to verify the detected dynamics and processes.

The effect of organic matter manipulations on site productivity, soil nutrients, and soil carbon on a southern loblolly pine plantation

Forest harvesting intrinsically removes organic matter and associated nutrients; these exports may impact soil productivity and soil carbon stores of managed forests. This study examined the effect of manipulating forest floor and harvest residue inputs on nutrient availability and carbon content in the context of intensive forest management. Treatments were applied 15years prior to this study and included removal and addition of forest floor and harvest residues, and a reference. We examined stand volume, litterfall, root biomass and foliar N and P at year 14 or 15. Soil moisture and temperature (0–10cm) and available N and P in the O and 0–20cm depths were measured once per month during year 15. Soil carbon and nitrogen were measured on whole soils as well as two density fractions in the O-horizon, 0–20, 20–40, and 40–60cm soil depths at year 15. In general, many of the initial responses found by an earlier study (age 10) have dissipated. Standing volume in the added treatment was 31% higher than the removed, but no significant difference was found between the removed and reference treatments. The added treatment resulted in higher concentrations of N in the light and heavy density fractions of the 0–20cm depth, which led to higher mass of N in both of these fractions. The added treatment had the greatest whole soil heavy fraction N mass. There were no differences in available N in the O-horizon or 0–20cm depth as tested using ion exchange membranes; however available P was significantly lower in the O-horizon of the removed treatment (37% lower than the reference). Bole volume was correlated with some measures of total and available N and P in the O and 0–20cm soil horizons, suggesting that increases in growth found in the added treatment were a result of additional nutrients. There were no significant differences between C concentration or mass of the 0–20cm or 20–40cm soil depths between the treatments; however the added treatment had significantly more (51% more than the reference) carbon at the 40–60cm soil depth. The added treatment had a significantly higher C:N relative to the reference in the 20–40cm (21.0 and 14.5, respectively) and 40–60cm (18.0 and 11.4, respectively) depths, suggesting that relatively fresh, undegraded organic matter had enriched this depth. This additional carbon sequestered at depth could contribute to a long-term soil carbon pool. The results of this study suggest that higher intensity use, such as forest floor removal and whole tree harvest, of these forests may not impact long term productivity at this site with typical soil nutrient status; however, more research is necessary to determine the mechanism(s) of this resilience.

Sorptive fractionation of organic matter and formation of organo-hydroxy-aluminum complexes during litter biodegradation in the presence of gibbsite

Solid and aqueous phase Al species are recognized to affect organic matter (OM) stabilization in forest soils. However, little is known about the dynamics of formation, composition and dissolution of organo-Al hydroxide complexes in microbially-active soil systems, where plant litter is subject to microbial decomposition in close proximity to mineral weathering reactions. We incubated gibbsite–quartz mineral mixtures in the presence of forest floor material inoculated with a native microbial consortium for periods of 5, 60 and 154days. At each time step, samples were density separated into light (<1.6gcm−3), intermediate (1.6–2.0gcm−3), and heavy (>2.0gcm−3) fractions. The light fraction was mainly comprised of particulate organic matter, while the intermediate and heavy density fractions contained moderate and large amounts of Al-minerals, respectively. Multi-method interrogation of the fractions indicated the intermediate and heavy fractions differed both in mineral structure and organic compound composition. X-ray diffraction analysis and SEM/EDS of the mineral component of the intermediate fractions indicated some alteration of the original gibbsite structure into less crystalline Al hydroxide and possibly proto-imogolite species, whereas alteration of the gibbsite structure was not evident in the heavy fraction. DRIFT, Py–GC/MS and STXM/NEXAFS results all showed that intermediate fractions were composed mostly of lignin-derived compounds, phenolics, and polysaccharides. Heavy fraction organics were dominated by polysaccharides, and were enriched in proteins, N-bearing compounds, and lipids. The source of organics appeared to differ between the intermediate and heavy fractions. Heavy fractions were enriched in 13C with lower C/N ratios relative to intermediate fractions, suggesting a microbial origin. The observed differential fractionation of organics among hydroxy-Al mineral types suggests that microbial activity superimposed with abiotic mineral-surface-mediated fractionation leads to strong density differentiation of organo-mineral complex composition even over the short time scales probed in these incubation experiments. The data highlight the strong interdependency of mineral transformation, microbial community activity, and organic matter stabilization during biodegradation.

Characterization of Size and Density Separated Fractions of a Bituminous Coal as a Feedstock for Entrained Slagging Gasification

Coal is one of the main sources of energy in many parts of the world and has one of the largest reserves/production ratios amongst all the non-renewable energy sources. Gasification of coal is one among the advanced technologies that has potential to be used in a carbon constrained economy. However, gasification availability at several commercial demonstrations had run into problems associated with fouling of syngas coolers due to unpredictable flyash formation and unburnt carbon losses. Computer models of gasifiers are emerging as a powerful tool to predict gasifier performance and reliability, without expensive testing. Most computer models used to simulate gasifiers tend to model coal as a homogenous entity based on bulk properties. However, coal is a heterogeneous material and comminution during feedstock preparation produces particle classes with different physical and chemical properties. It is crucial to characterize the heterogeneity of the feedstocks used by entrained flow gasifiers. To this end, a low ash US bituminous coal that could be used as a gasifier feedstock was segregated into density and size fractions to represent the major mineral matter distributions in the coal. Float and sink method and sieving were employed to partition the ground coal. The organic and inorganic content of all density fractions was characterized for particle size distribution, heating value, ultimate analysis, proximate analysis, mineral matter composition, ash composition, and petrographic components, while size fractions were characterized for heating value, ash composition, ultimate and proximate analysis. The proximate, ultimate and high heating value analysis showed that variation in these values is limited across the range of size fractions, while the heterogeneity is significant over the range of density fractions. With respect to inorganics, the mineral matter in the heavy density fractions contribute significantly to the ash yield in the coal while contributing very little to its heating value. The ash yield across the size fractions exhibits a bimodal distribution. The heterogeneity is also significant with respect to the base-to-acid ratio across the size and density fractions. The results indicate that the variations in organic and inorganic content over a range of density and size classes are significant, even in the low ash, vitrinite rich coal sample characterized here. Incorporating this information appropriately into particle population models used in gasifier simulations will significantly enhance their accuracy of performance predictions.

Lipid Rafts Determine Clustering of STIM1 in Endoplasmic Reticulum-Plasma Membrane Junctions and Regulation of Store-operated Ca2+ Entry (SOCE)

Store depletion induces STIM1 to aggregate and relocate into clusters at ER-plasma membrane junctions where it functionally interacts with and activates plasma membrane channels that mediate store-operated Ca(2+) entry (SOCE). Thus, the site of peripheral STIM1 clusters is critical for the regulation of SOCE. However, what determines the location of the STIM1 clusters in the ER-PM junctional regions, and whether these represent specific sites in the cell is not yet known. Here we report that clustering of STIM1 in the subplasma membrane region of the cell and activation of TRPC1-dependent SOCE are determined by lipid raft domains (LRD). We show that store depletion increased partitioning of TRPC1 and STIM1 into plasma membrane LRD. TRPC1 and STIM1 associated with each other within the LRD, and this association was dynamically regulated by the status of the ER Ca(2+) store. Peripheral STIM1 clustering was independent of TRPC1. However, sequestration of membrane cholesterol attenuated thapsigargin-induced clustering of STIM1 as well as SOCE in HSG and HEK293 cells. Recruitment and association of STIM1 and TRPC1 in LRD was also decreased. Additionally STIM1(D76A), which is peripherally localized and constitutively activates SOCE in unstimulated cells, displayed a relatively higher partitioning into LRD and interaction with TRPC1, as compared with STIM1. Disruption of membrane rafts decreased peripheral STIM1(D76A) puncta, its association with TRPC1 and the constitutive SOCE. Together, these data demonstrate that intact LRD determine targeting of STIM1 clusters to ER-plasma membrane junctions following store depletion. This facilitates the functional interaction of STIM1 with TRPC1 and activation of SOCE.

Surface soil carbon size–density fractions altered by loblolly pine families and forest management intensity for a Spodosol in the southeastern US

The effects of genotypic differences on soil organic carbon (SOC) cycling and their interactions with forest management systems are poorly understood. This study was undertaken to examine the effects of family and family × management interactions on SOC and to evaluate the distribution of SOC across different size–density fractions in a forested Spodosol. The study site consisted of a 6-year-old loblolly pine plantation that was managed under two intensities (high and low level of fertilization and chemical understory control) and included three full-sib families (fast, medium and slow growers, designated a priori based on above ground growth). The fast growing family exhibited 59% higher C (p = 0.04) than the slow growing family in the 2,000 to 250-μm light density fraction. The medium grower exhibited 8% higher aggregate C than the fast grower in the 250 to 150-μm medium density (p = 0.05) and 2,000 to 250-μm heavy density (p = 0.06) fractions. Family and management effects were detected among all three density fractions. The 2,000 to 250-μm medium density fraction contained the most C. A modified size–density fractionation and sonication procedure proved sensitive for detecting significant family and management effects in as few as 6 years. These results highlight the potential of genotypic deployment as a factor influencing C sequestration and the need to fully understand the long-term effects of genotypic differences and forest management activities on SOC pools.

Do nitrogen isotope patterns reflect microbial colonization of soil organic matter fractions?

Different theories have been brought forward to explain the commonly observed δ15N enrichment with depth in soil profiles, including the discrimination against 15N during N decomposition and the buildup of 15N-enriched microbial residues. A combination of soil organic matter (SOM) size and density fractionations, 15N determinations, and phospholipid fatty acid (PLFA) analyses was conducted on soils from a pristine N-limited Nothofagus forest in southern Chile. The purpose of this study was to investigate which SOM fractions mostly reflect the 15N-enrichment pattern and to link 15N SOM enrichment with microbial community composition. Nitrogen-15 enrichments were greater for the microaggregate ( 150 μm) size fraction, with Rayleigh isotope enrichment factors averaging −8.5‰ and −3.7‰, respectively. The macro-organic matter density fractions (>150 μm) showed intermediate enrichment factors of −5.1‰ and −7.3‰ for the light ( 1.37 g cm−3) fraction, respectively. The abundance of fungal and bacterial PLFAs was significantly higher in the microaggregate compared to the macroaggregate size fraction, but their relative abundance did not change between aggregate size fractions. Our data link differential 15N enrichment of SOM fractions to “total” microbial abundance and, as such, corroborates existing theories of microbial-induced 15N enrichment. Isotopic fractionation during microbial N decomposition processes alone could not explain the large 15N enrichment in the microaggregate size fraction (−8.5‰) and the heavy density fraction (−7.3‰). We therefore suggest that microbial turnover and accretion of 15N-enriched microbial (especially fungal) compounds was an additional driver for 15N enrichment of this soil profile.

Distribution and Occurrence of Arsenic in Two Typical Chinese Coals

Two complementary methods, float-sink experiment and sequential chemical leaching were used to probe into the occurrence of arsenic in two Chinese coals: Yima (YM) and Datong (DT). Flow injection-hydride generation atomic fluorescence spectrometry was employed to measure the arsenic content in parent coals as well as the size and density-fraction samples. Float-sink experiment indicated that the heavy density fractions were enriched mineral containing arsenic in two bituminous coals studied, as confirmed by the sequential chemical leaching method. Sequential chemical leaching revealed that sulfide arsenic was the primary mode of occurrence (> 50%), stable form also abounded in coal with content between 30 and 40%, and a small amount of arsenic took the occurrence of organic form.

Membrane Organization of the Serotonin 1A Receptor Monitored by a Detergent-Free Approach

: 1. Insolubility of membrane constituents in nonionic detergents such as Triton X-100 has been a widely used biochemical criterion to indicate their localization in membrane domains. However, concerns on the possibility of membrane perturbation in the presence of detergents have led to the development of detergent-free approaches.2. We have explored the organization of the serotonin(1A) receptor, an important G-protein coupled receptor, from bovine hippocampus and CHO cells using a detergent-free approach in order to address the points of agreement with our previous results using Triton X-100.3. A significant fraction of the serotonin(1A) receptor has been found to be localized in a heavy density fraction obtained using a detergent-free approach to isolate membrane domains. In addition, we have characterized the membrane fractions isolated in terms of their lipid composition and membrane physical properties.4. The results obtained on the membrane localization of the serotonin(1A) receptor from the present experiments using a detergent-free approach correlate well with our earlier findings obtained using a detergent-based method (Kalipatnapu, S., and Chattopadhyay, A., FEBS Lett. 576:455-460, 2004). These results provide important information on the membrane organization of the hippocampal serotonin(1A) receptor and are relevant in view of the concerns on the use of detergent in determination of membrane organization of constituent proteins and lipids.