A STUDY OF CARBON-MONOXIDE AND NEUTRAL CARBON IN THE S106 MOLECULAR CORE

Maps are presented of J=2-1 and J=3-2 (CO)-O-18 emission from the molecular environment of the bipolar nebula S106, together with complementary observations of the P-3(1)-P-3(0), C I emission. Line splitting observed extensively over the E molecular cloud suggests that it is best explained as the expanding remnant of a thick toroid surrounding the optical lobes. The poor correlation between the observed molecular line emission and dust continuum emission in the E cloud is probably due to a large temperature gradient. Strong C I emission from the protostellar candidate S106 FIR suggests the nearby presence of a powerful source of far-UV radiation, whose energy supply is unlikely to arise from gravitational contraction of a protostar. It is probable that this source is the star S106 LR, which also heats S106 FIR. There is evidence, in both C I and (CO)-O-18, for a predominantly blueshifted outflow from S106 IR, best interpreted as a stellar wind-driven shock into the toroidal remnant. (CO)-O-18 and (CO)-C-13 appear to be depleted, relative to canonical values for their abundances, in S106 FIR, despite its high optical extinction, which should discourage selective photodissociation. Elsewhere in the cloud the C I line profiles show a resemblance to those of (CO)-O-18, with intensity equivalent to a few photodissociation regions (PDRs) along the line of sight.

Long-chain haloalkanes are incorporated into fatty-acids by Rhodococcus rhodochrous NCIMB-13064

The fatty acid composition of the cellular lipids of Rhodococcus rhodochrous NCIMB 13064 grown on various long-chain haloalkanes has been investigated and the influence of halogen substituents, carbon chain length and the position of halogen substitution in the growth substrate explored. Of the total fatty acids present in cells grown on 1-chloro-, 1-bromo- and 1-iodohexadecane, 75, 90 and 81%, respectively, were substituted in the omega-position by the corresponding halogen but only 1% of the fatty acids present after growth on 1-fluorotetradecane were fluorinated in this position. The extent of the halofatty acid incorporation with different halogen substituents in the growth substrate appears to reflect the degree to which oxygenase attack is restricted to the non-halogenated end of the haloalkane. Studies of the fatty acid composition of cells after growth on a series of 1-chloroalkanes containing an even number of carbon atoms between C-10 and C-18 indicated chlorofatty acid incorporation from C-12 to C-18 substrates at levels ranging from 21% with C-12 to 75% with C-16. The chlorofatty acids formed by initial oxidation of the chloroalkane were chain-lengthened or chain-shortened by from two to eight carbon atoms, with accompanying desaturation in some instances. Substantial quantities of a methyl-branched C-19:0 chlorofatty acid were also present with several chloroalkane substrates, When the fatty acid composition of cells after growth on 1-bromoalkanes containing an odd number of carbon atoms between C-11 and C-17 was examined, the incorporation of bromofatty acids was observed with C-13, C-15 and C-17 substrates; a maximum of 76% was recorded for the C-15 bromoalkane. As with even chain-length chloroalkanes, both chain-lengthening and -shortening occurred predominantly via two-carbon units so that most bromoacids present possessed an odd number of carbon atoms, When 1-bromododecane or 2-bromododecane were substrates, overall incorporations of bromofatty acids into the lipid fraction were very similar, demonstrating that the position of halogen substitution in the haloalkane was not critical in determining the extent of incorporation of the haloacids into cellular lipids. The results of the study indicate a mechanism by which degradation products of chlorinated paraffins could enter the biological food chain.

Vitamin B-6 deficiency in rats reduces hepatic serine hydroxymethyltransferase and cystathionine beta-synthase activities and rates of in vivo protein turnover, homocysteine remethylation and transsulfuration

Vitamin B-6 deficiency causes mild elevation in plasma homocysteine, but the mechanism has not been clearly established. Serine is a substrate in one-carbon metabolism and in the transsulfuration pathway of homocysteine catabolism, and pyridoxal phosphate (PLP) plays a key role as coenzyme for serine hydroxymethyltransferase (SHMT) and enzymes of transsulfuration. In this study we used [H-2(3)]serine as a primary tracer to examine the remethylation pathway in adequately nourished and vitamin B-6-deficient rats pi and 0.1 mg pyridoxine (PN)/kg diet]. [H-2(3)]Leucine and [1-C-13]methionine were also used to examine turnover of protein and methionine pools, respectively, All tracers were injected intraperitoneally as a bolus dose, and then rats were killed (n = 4/time point) after 30, 60 and 120 min. Rats fed the low-PN diet had significantly lower growth and plasma and liver PLP concentrations, reduced liver SHMT activity, greater plasma and liver total homocysteine concentration, and reduced liver S-adenosylmethionine concentration. Hepatic and whole body protein turnover were reduced in vitamin B-6-deficient rats as evidenced by greater isotopic enrichment of [H-2(3)]leucine. Hepatic [H-2(2)]methionine production from [H-2(3)]serine via cytosolic SHMT and the remethylation pathway was reduced by 80.6% in vitamin B-6 deficiency. The deficiency did not significantly reduce hepatic cystathionine-beta-synthase activity, and in vivo hepatic transsulfuration flux shown by production of [H-2(3)]cysteine from the [H-2(3)]serine increased over twofold. In contrast, plasma appearance of [H-2(3)]cysteine was decreased by 89% in vitamin B-6 deficiency. The rate of hepatic homocysteine production shown by the ratio of [1-C-13]homocysteine/[1-C-13]methionine areas under enrichment vs. time curves was not affected by vitamin B-6 deficiency. Overall, these results indicate that vitamin B-6 deficiency substantially affects one-carbon metabolism by impairing both methyl group production for homocysteine remethylation and flux through whole-body transsulfuration.

Stable isotope probing analysis of the influence of liming on root exudate utilization by soil microorganisms

Rhizosphere microorganisms play an important role in soil carbon flow, through turnover of root exudates, but there is little information on which organisms are actively involved or on the influence of environmental conditions on active communities. In this study, a (CO2)-C-13 pulse labelling field experiment was performed in an upland grassland soil, followed by RNA-stable isotope probing (SIP) analysis, to determine the effect of liming on the structure of the rhizosphere microbial community metabolizing root exudates. The lower limit of detection for SIP was determined in soil samples inoculated with a range of concentrations of C-13-labelled Pseudomonas fluorescens and was found to lie between 10(5) and 10(6) cells per gram of soil. The technique was capable of detecting microbial communities actively assimilating root exudates derived from recent photo-assimilate in the field. Denaturing gradient gel electrophoresis (DGGE) profiles of bacteria, archaea and fungi derived from fractions obtained from caesium trifluoroacetate (CsTFA) density gradient ultracentrifugation indicated that active communities in limed soils were more complex than those in unlimed soils and were more active in utilization of recently exuded C-13 compounds. In limed soils, the majority of the community detected by standard RNA-DGGE analysis appeared to be utilizing root exudates. In unlimed soils, DGGE profiles from C-12 and C-13 RNA fractions differed, suggesting that a proportion of the active community was utilizing other sources of organic carbon. These differences may reflect differences in the amount of root exudation under the different conditions.

Carbon flow in an upland grassland: effect of liming on the flux of recently photosynthesized carbon to rhizosphere soil

The effect of liming on the flow of recently photosynthesized carbon to rhizosphere soil was studied using (CO2)-C-13 pulse labelling, in an upland grassland ecosystem in Scotland. The use of C-13 enabled detection, in the field, of the effect of a 4-year liming period of selected soil plots on C allocation from plant biomass to soil, in comparison with unlimed plots. Photosynthetic rates and carbon turnover were higher in plants grown in limed soils than in those from unlimed plots. Higher delta(13)C% values were detected in shoots from limed plants than in those from unlimed plants in samples clipped within 15 days of the end of pulse labelling. Analysis of the aboveground plant production corresponding to the 4-year period of liming indicated that the standing biomass was higher in plots that received lime. Lower delta(13)C% values in limed roots compared with unlimed roots were found, whereas no significant difference was detected between soil samples. Extrapolation of our results indicated that more C has been lost through the soil than has been gained via photosynthetic assimilation because of pasture liming in Scotland during the period 1990-1998. However, the uncertainty associated with such extrapolation based on this single study is high and these estimates are provided only to set our findings in the broader context of national soil carbon emissions.

CO2 uptake by a soil microcosm

Sequestration of CO2 via biological sinks is a matter of great scientific importance due to the potential lowering of atmospheric CO2. In this study, a custom built incubation chamber was used to cultivate a soil microbial community to instigate chemoautotrophy of a temperate soil. Real-time atmospheric CO2 concentrations were monitored and estimations of total CO2 uptake were made. After careful background flux corrections, 4.52 +/- 0.05 g CO2 kg I dry soil was sequestered from the chamber atmosphere over 40 h. Using isotopically labelled (CO2)-C-13 and GCMS-IRMS, labelled fatty acids were identified after only a short incubation, hence confirming CO2 sequestration for soil. The results of this in vivo study provide the ground work for future studies intending to mimic the in situ environment by providing a reliable method for investigating CO2 uptake by soil microorganisms.(C) 2012 Elsevier Ltd. All rights reserved.

Holocene environmental changes in northeast Thailand as reconstructed from a tropical wetland

Geochemical variables (TOC, C/N, TS, delta C-13) and diatom assemblages were analyzed in a lake sediment sequence from Nong (Lake) Han Kumphawapi in northeast Thailand to reconstruct regional climatic and environmental history during the Holocene. By around c. 10,000-9400 cal yr BP, a large shallow freshwater lake had formed in the Kumphawapi basin. Oxygenated bottom waters and a well-mixed water column were characteristic of this early lake stage, which was probably initiated by higher effective moisture and a stronger summer monsoon. Decreased run-off after c. 6700 cal yr BP favored increased aquatic productivity in the shallow lake. Multiple proxies indicate a marked lowering of the lake level around 5900 cal yr BP, the development of an extensive wetland around 5400 cal yr BP, and the subsequent transition to a peatland. The shift from shallow lake to wetland and later to a peatland is interpreted as a response to lower effective moisture. A hiatus at the transition from wetland to peatland suggests very low accumulation rates, which may result from very dry climatic conditions. A rise in groundwater and lake level around 3200 cal yr BP allowed the re-establishment of a wetland in the Kumphawapi basin. However, the sediments deposited between c. 3200 and 1600 cal yr BP provide evidence for at least two hiatuses at c. 2700-2500 cal yr BP, and at c. 1900-1600 cal yr BP, which would suggest surface dryness and consequently periods of low effective moisture. Around 1600 cal yr BP a new shallow lake became re-established in the basin. Although the underlying causes for this new lake phase remain unclear, we hypothesize that higher effective moisture was the main driving force. This shallow lake phase continued up to the present but was interrupted by higher nutrient fluxes to the lake around 1000-600 cal yr BP. Whether this was caused by intensified human impact in the catchment or, whether this signals a lowering of the lake level due to reduced effective moisture, needs to be corroborated by further studies in the region. The multi-proxy study of Kumphawapi's sediment core CP3A clearly shows that Kumphawapi is a sensitive archive for recording past shifts in effective moisture, and as such in the intensity of the Asian summer monsoon. Many more continental paleorecords, however, will be needed to fully understand the spatial and temporal patterns of past changes in Asian monsoon intensity and its ecosystem impacts. (C) 2012 Elsevier B.V. All rights reserved.

Hyperfine interaction in the ground state of the negatively charged nitrogen vacancy center in diamond

The N-14, N-15, and C-13 hyperfine interactions in the ground state of the negatively charged nitrogen vacancy (NV-) center have been investigated using electron-paramagnetic-resonance spectroscopy. The previously published parameters for the N-14 hyperfine interaction do not produce a satisfactory fit to the experimental NV- electron-paramagnetic-resonance data. The small anisotropic component of the NV- hyperfine interaction can be explained from dipolar interaction between the nitrogen nucleus and the unpaired-electron probability density localized on the three carbon atoms neighboring the vacancy. Optical spin polarization of the NV- ground state was used to enhance the electron-paramagnetic-resonance sensitivity enabling detailed study of the hyperfine interaction with C-13 neighbors. The data confirmed the identification of three equivalent carbon nearest neighbors but indicated the next largest C-13 interaction is with six, rather than as previously assumed three, equivalent neighboring carbon atoms.

Dietary switching of collembola in grassland soil food webs

Soil food webs are characterised by complex direct and indirect effects among the organisms. Consumption of microorganisms by soil animals is considered as an important factor that contributes to the stability of communities, though cascading effects within the food web can be difficult to detect. In a greenhouse experiment, an addition of a high number the fungal feeding collembola Folsomia quadrioculata was applied to grassland soil food webs in monocultures of three plant species: Plantago lanceolato (forb), Lotus corniculatus (legume) and Holcus lanatus (grass). The abundance of microorganisms, determined as the abundances of phospholipid fatty acids (PLFAs) and the abundances of resident invertebrates, nematodes and collembolans, did not change due to the addition of E quadrioculata. Trophic positions of collembolans were determined by analyses of natural abundances of N-15 stable isotopes. The use of food resources by microorganisms and collembolans was determined by C-13 analysis of microbial PLFAs and solid samples of collembolans. delta C-13 values of the resident collembola Folsomia fimetaria were lower in the presence of E quadrioculata than in the control food webs indicating a use of more depleted C-13 food resources by E fimetaria. The delta N-15 values of E fimetaria did not change at the addition of E quadrioculata thus no change of trophic levels was detected. The switch of E fimetaria to a different food resource could be due to indirect interactions in the food web as the two collembolan species were positioned on different trophic positions, according to different delta N-15 values. (c) 2008 Elsevier Ltd. All rights reserved.

Ethylene oxidation over platinum: In situ electrochemically controlled promotion using Na-beta'' alumina and studies with a Pt(111)/Na model catalyst

Electrochemically modified ethylene oxidation over a PI film supported on the Na+ ion conductor beta '' alumina has been studied over a range of conditions encompassing both promotion and poisoning, The system exhibits reversible behavior, and the data are interpreted in terms of (i) Na-enhanced oxygen chemisorption and (ii) poisoning of the surface by accumulation of Na compounds. At low Na coverages the first effect results in increased competitive adsorption of oxygen at the expense of ethylene, resulting in an increased rate, At very negative catalyst potentials (high Na coverage) both effects operate to poison the system: the increased strength of the Pt-O bond and coverage of the catalytic surface by compounds of Na strongly suppress the rate, Kinetic and spectroscopic results for ethylene oxidation over a Pt(111)-Na model catalyst shed light on important aspects of the electrochemically controlled system, Low levels of Na promote the reaction and high levels poison it, mirroring the behavior observed under electrochemical control and strongly suggesting that sodium pumped from the solid electrolyte is the key species, XP and Auger spectra show that under reaction conditions, the sodium exists as a surface carbonate. Post-reaction TPD spectra and the use of (CO)-C-13 demonstrate that CO is formed as a stable reaction intermediate, The observed activation energy (56 +/- 3 kJ/mol) is similar to that measured for CO oxidation under comparable conditions, suggesting that the rate limiting step is CO oxidation. (C) 1996 Academic Press, Inc.

Marine or estuarine radiocarbon reservoir corrections for mollusks? A case study from a medieval site in the south of England

Mollusk shells are frequently radiocarbon dated and provide reliable calibrated age ranges when the regional marine reservoir correction is well-established. For mollusks from an estuarine environment the reservoir correction may be significantly different than the regional marine reservoir correction due to the input of bedrock or soil derived carbonates. Some mollusk species such as oysters are tolerant of a significant range of salinities which makes it difficult to determine which reservoir correction is appropriate. A case study is presented of an anomalous radiocarbon age for an oyster shell paint dish found in the fabric of the ruined nave walls of St Mary's Church, Shoreham-by-Sea, West Sussex, England. Stable isotopes (delta O-18 and delta C-13) were used to establish the type of environment in which the oyster had lived. Paired marine and terrestrial samples from a nearby medieval site were radiocarbon dated to provide an appropriate reservoir correction.

Not all jellyfish are equal: isotopic evidence for inter- and intraspecific variation in jellyfish trophic ecology

Jellyfish are highly topical within studies of pelagic food-webs and there is a growing realisation that their role is more complex than once thought. Efforts being made to include jellyfish within fisheries and ecosystem models are an important step forward, but our present understanding of their underlying trophic ecology can lead to their oversimplification in these models. Gelatinous zooplankton represent a polyphyletic assemblage spanning >2,000 species that inhabit coastal seas to the deep-ocean and employ a wide variety of foraging strategies. Despite this diversity, many contemporary modelling approaches include jellyfish as a single functional group feeding at one or two trophic levels at most. Recent reviews have drawn attention to this issue and highlighted the need for improved communication between biologists and theoreticians if this problem is to be overcome. We used stable isotopes to investigate the trophic ecology of three co-occurring scyphozoan jellyfish species (Aurelia aurita, Cyanea lamarckii and C. capillata) within a temperate, coastal food-web in the NE Atlantic. Using information on individual size, time of year and ;delta C-13 and delta N-15 stable isotope values, we examined: (1) whether all jellyfish could be considered as a single functional group, or showed distinct inter-specific differences in trophic ecology; (2) Were size-based shifts in trophic position, found previously in A. aurita, a common trait across species?; (3) When considered collectively, did the trophic position of three sympatric species remain constant over time? Differences in delta N-15 (trophic position) were evident between all three species, with size-based and temporal shifts in delta N-15 apparent in A. aurita and C. capillata. The isotopic niche width for all species combined increased throughout the season, reflecting temporal shifts in trophic position and seasonal succession in these gelatinous species. Taken together, these findings support previous assertions that jellyfish require more robust inclusion in marine fisheries or ecosystem models.

Determining adsorbate configuration on alumina surfaces with 13C nuclear magnetic resonance relaxation time analysis

Relative strengths of surface interaction for individual carbon atoms in acyclic and cyclic hydrocarbons adsorbed on alumina surfaces are determined using chemically resolved 13C nuclear magnetic resonance (NMR) T1 relaxation times. The ratio of relaxation times for the adsorbed atoms T1,ads to the bulk liquid relaxation time T1,bulk provides an indication of the mobility of the atom. Hence a low T1,ads/T1,bulk ratio indicates a stronger surface interaction. The carbon atoms associated with unsaturated bonds in the molecules are seen to exhibit a larger reduction in T1 on adsorption relative to the aliphatic carbons, consistent with adsorption occurring through the carbon-carbon multiple bonds. The relaxation data are interpreted in terms of proximity of individual carbon atoms to the alumina surface and adsorption conformations are inferred. Furthermore, variations of interaction strength and molecular configuration have been explored as a function of adsorbate coverage, temperature, surface pre-treatment, and in the presence of co-adsorbates. This relaxation time analysis is appropriate for studying the behaviour of hydrocarbons adsorbed on a wide range of catalyst support and supported-metal catalyst surfaces, and offers the potential to explore such systems under realistic operating conditions when multiple chemical components are present at the surface.