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Negative relationships between dissolved organic carbon (DOC) concentration and fish productivity have been reported from correlative studies across lakes, but to date there have not been experimental tests of these relationships. We increased the DOC concentration in a lake by 3.4 mg x [L.sup.-1], using a before-after control-impact design, to quantify the effects on the productivity and population structure of largemouth bass (Micropterus salmoides). Greater DOC reduced the volume of the epilimnion, the preferred habitat of largemouth bass, resulting in increased bass density. The likelihood that adult bass had empty diets decreased despite this increase in bass density; diet composition also changed. There was no apparent change in bass growth or condition. Overall, there was no net change in largemouth bass productivity. However, changes in young of year and juvenile recruitment and feeding success suggest the possibility that future effects could occur. Our results are the first to examine the effects of an increase in DOC on fish productivity through a 5-year temporal lens, which demonstrates that the relationship between DOC and fish productivity is multidimensional and complex. Des etudes correlatives sur des lacs multiples ont fait etat de relations negatives entre la concentration de carbone organique dissous (COD) et la productivite de poissons, mais aucun test experimental permettant de valider ces relations n'a ete propose a ce jour. Nous avons accru la concentration de COD dans un lac de 3,4 mg x [L.sup.-1] et employe un schema avant-apres temoin-intervention pour quantifier les effets sur la productivite et la structure de la population d'achigans a grande bouche (Micropterus salmoides). Une plus grande concentration de COD s'est traduite par une reduction du volume de l'epilimnion, l'habitat privilegie des achigans a grande bouche, entrainant une augmentation de la densite d'achigans. La probabilite que des achigans adultes aient des regimes alimentaires vides a diminue malgre la densite accrue d'achigans; la composition des regimes alimentaires a egalement change. La croissance et l'embonpoint des achigans ne presentent pas de changement apparent. Globalement, il n'y a pas eu de changement net de la productivite des achigans a grande bouche. Cependant, des modifications du recrutement de jeunes de l'annee et de juveniles et du succes d'alimentation indiqueraient que des effets futurs sont possibles. Nos resultats sont les premiers a examiner les effets d'une augmentation du COD sur la productivite de poissons dans une optique quinquennale, qui demontre que la relation entre le COD et la productivite de poissons est complexe et multidimensionnelle. [Traduit par la Redaction], Introduction Dissolved organic carbon (DOC) concentrations vary widely across lake-rich landscapes, and many lakes in the Northern Hemisphere are increasing in DOC (Hanson et al. 2007; Monteith et al. 2007). [...]

Although abundant in organic molecules, carbon-hydrogen (C-H) bonds are typically considered unreactive and unavailable for chemical manipulation. Recent advances in C-H functionalization technology have begun to transform this logic, while emphasizing the importance of and challenges associated with selective alkylation at a sp.sup.3 carbon.sup.1,2. Here we describe iron-based catalysts for the enantio-, regio- and chemoselective intermolecular alkylation of sp.sup.3 C-H bonds through carbene C-H insertion. The catalysts, derived from a cytochrome P450 enzyme in which the native cysteine axial ligand has been substituted for serine (cytochrome P411), are fully genetically encoded and produced in bacteria, where they can be tuned by directed evolution for activity and selectivity. That these proteins activate iron, the most abundant transition metal, to perform this chemistry provides a desirable alternative to noble-metal catalysts, which have dominated the field of C-H functionalization.sup.1,2. The laboratory-evolved enzymes functionalize diverse substrates containing benzylic, allylic or [alpha]-amino C-H bonds with high turnover and excellent selectivity. Furthermore, they have enabled the development of concise routes to several natural products. The use of the native iron-haem cofactor of these enzymes to mediate sp.sup.3 C-H alkylation suggests that diverse haem proteins could serve as potential catalysts for this abiological transformation, and will facilitate the development of new enzymatic C-H functionalization reactions for applications in chemistry and synthetic biology.Evolved iron-containing enzymes based on cytochrome P450 achieve selective intermolecular alkylation of sp.sup.3 C-H bonds through a carbene C-H insertion strategy., Author(s): Ruijie K. Zhang [sup.1] , Kai Chen [sup.1] , Xiongyi Huang [sup.1] , Lena Wohlschlager [sup.1] [sup.2] , Hans Renata [sup.1] [sup.3] , Frances H. Arnold [sup.1] Author Affiliations:(1) [...]

Author(s): Rohan E. J. Beckwith The basis of organic chemistry is the study of carbon-containing compounds with the aim of manipulating carbon atoms to generate new molecules through the formation [...]

Plant species richness has declined and composition shifted in response to elevated atmospheric deposition of biologically active nitrogen over much of the industrialized world. Litter thickness, litter nitrogen (N) content, and soil N mineralization rates often remain elevated long after inputs cease, clouding the prospects that plant community diversity and composition would recover should N inputs be reduced. Here we determined how N cycling, litter accumulation, and recruitment limitation influenced community recovery following cessation of long-term N inputs to prairie-like grasslands. We alleviated each of these potential inhibitors through a two-year full-factorial experiment involving organic carbon addition, litter removal, and seed addition. Seed addition had the largest effect on increasing seedling and species numbers and may be necessary to overcome long-term burial of seeds of target perennial grassland species. Litter removal increased light availability and bare sites for colonization, though it had little effect on reducing the biomass of competing neighbors or altering extractable soil N. Nonetheless, these positive influences were enough to lead to small increases in species richness within one year. We found that, although C addition quickly altered many factors assumed favorable for the target community (decreased N availability and biomass of nearby competitors, increased light and site availability), these changes were insufficient to positively impact species richness or seedling numbers over the experimental duration. However, only carbon addition had species-specific effects on the existing plant community, suggesting that its apparent limited utility may be more a result of slow recovery under ambient recruitment rather than from a lack of a restorative effect. There were dramatic interactions among treatments, with the positive effects of litter removal largely negated by carbon addition, and the positive effects of seed addition generally amplified by litter removal. It remains unclear whether each mechanism explored here will induce community recovery, but over different temporal scales. Long-term monitoring will help resolve these remaining questions. Regardless, our results suggest that reversal of species loss and compositional shifts from N deposition in prairies may be more inhibited by habitat fragmentation, recruitment limitation, and long-term suppression of fire than from continued effects of elevated N. Key words: carbon addition; diversity; grassland; invasion; litter inhibition, nitrogen deposition; prairie restoration; recovery; recruitment limitation.

Bacteriogenic iron oxides in natural environments are characterized by an abundance of ferrihydrite precipitates intermixed with bacterial structures that commonly resemble those produced by the lithoautotrophic microorganisms Gallionella ferruginea and Leptohtrix ochracea. These species have been inferred to play a causal role in the formation of bacteriogenic iron oxides, providing a pathway for the reduction of C[O.sub.2] and the depletion of [sup.13]C in the organic constituents of bacteriogenic iron oxides. In this study, stable carbon isotope fractionation was determined for bacteriogenic iron oxide samples collected from submarine hydrothermal vents (Axial Volcano, Juan de Fuca Ridge), subterranean (Aspo Hard Rock Laboratory, Sweden) and surficial (Chalk River, Canada) groundwater seeps, and cultures of G. ferruginea. Data were also collected from ferrihydrite samples lacking evidence of bacteria from Bounty Seamount in the vicinity of Pitcairn Island. The mean [delta][sup.13]C ([per thousand]) of ferrihydrite was determined to be -15.87 [per thousand] [+ or -] 4.96 [per thousand] for the samples from Axial Volcano, -24.97 [per thousand] [+ or -] 0.43 [per thousand] for Aspo, -27.80 [per thousand] [+ or -] 0.85 [per thousand] for Chalk River, -29.3 [per thousand] [+ or -] 0.2 [per thousand] for the microbial culture, and -8.43 [per thousand] [+ or -] 1.89 [per thousand] for the samples from Pitcairn. Samples with the highest concentration of organic carbon also had the lightest [delta][sup.13]C in a logarithmic relationship. The consistency of carbon isotope values in relation to the presence of iron-oxidizing bacteria from natural and laboratory samples is interpreted as the ability of these microorganisms to fractionate carbon. The potential of this fractionation to serve as a biosignature holds promise when the resistance of carbon and bacteriogenic ferrihydrite to diagenesis is taken into consideration. doi: 10.1130/G30986.1

[C.sub.4] plants are widely successful in the grass-dominated ecosystems of tropical, subtropical, and warm-temperate regions, largely as a result of their ability to limit photorespiration and improve water-use efficiency. A widely held paradigm is that low ( doi: 10.1130/G31117.1

Emissions of polycyclic aromatic hydrocarbons (PANs), elemental carbon (EC), organic carbon (OC), and size distributions of particulate matter from summer tire-concrete road interaction were studied. Based on particle size distribution, particles were categorized in three groups: (1) [PM.sub.10] (0.02%); (2) [PM.sub.10-100] (44.20%); and (3) [PM.sub.100-2,000] (55.78%). The emission factor for total of four PAHs [fluoranthene, phenenthrene, pyrene, and benzo(ghi)perylene] was estimated as 378 ng [tire.sup.-1] [km.sup.-1] for small cars (engine displacement volume [less than or equal to] 1,000 [cm.sup.3]; load [less than or equal to] 170 kg [tire.sup.-1]). Out of eight PAHS analyzed in particles (all sizes), the main PAH compounds were pyrene (54%) and benzo(ghi)perylene (21%). Emission factors for EC and OC were 1.46 and 2.37 mg [tire.sup.-1] [km.sup.-1]. DOI: 10.1061/(ASCE)EE.1943-7870.0000274 CE Database subject headings: Air pollution; Emissions; Hydrocarbons; Vehicles; Urban areas; Particle distribution. Author keywords: Air pollution; Emissions; Hydrocarbon; Vehicle impacts; Particle distribution.

The paradigm that carbon export is derived almost exclusively from the primary production of large phytoplankton has been challenged by inverse ecosystem modeling studies that suggest that most carbon export in the open ocean is fueled by picophytoplankton. To readdress this hypothesis, we use an inverse model to synthesize the planktonic rate measurements from a pair of recent cruises in the equatorial Pacific. The analysis based on this new experimental data, which crucially include vertically integrated taxon-specific production and grazing estimates, largely resolve the unexpected results of the previous inverse studies, including unbalanced growth and grazing processes and the dominance of production by picophytoplankton. While this very small size class does not produce the majority of phytoplankton carbon that is eventually exported to depth (only 23%, vs. 73% from a previous analysis of Joint Global Ocean Flux Study Equatorial Pacific data), our base model supports the conclusion that the role of picophytoplankton in vertical carbon flux is largely proportional to their contribution to net primary productivity (though neither is proportional to biomass). We show, however, that export-production proportionality is sensitive to the model representation of the detrital pool such that the relative export role of picophytoplankton declines substantially for an alternate model with size-structured detritus. A definitive assessment of the role of picoplankton in vertical carbon flux will thus require detailed experimental examination of the origin, composition, and fate of euphotic zone detrital material. doi: 10.4319/lo.2010.55.6.2669

Whole-lake carbon (C) mass-balance budgets were constructed for a chain of six hard-water lakes to quantify the relative importance of organic carbon (OC) and inorganic carbon (IC) exchanges between atmosphere, water column, sediments, and rivers. Mean summer C fluxes were calculated for each lake during the ice-free periods (May to September) of 1995-2007 by measuring deposition of IC and OC in lake sediments, export of C to outflow rivers, lotic C influxes, and atmospheric exchange of C[O.sub.2]. Unlike soft-water lakes, IC in rivers accounted for 68.2-85.6% of total C (TC) influx to these hard-water lakes, C[O.sub.2] efflux accounted for 044.5% of total C export (median 2.8%), and sedimentation buried similar amounts of OC and IC. Deposition of C in sediments accounted for 1.8-61.7% of total export and was correlated to water residence time, while C efflux through rivers accounted for 32.6-8.2% of total export, mainly as IC (69.6-85.1% of TC). Unexpectedly, estimates of net ecosystem production based on OC mass balances suggested that all lakes were autotrophic (production > respiration) during summer, despite elevated dissolved organic carbon content (5.6-16.1 mg C [L.sup.-1]), pC[O.sub.2] values, and net C[O.sub.2] emissions to the atmosphere from three lakes. We conclude that C fluxes within and among these hard-water lakes are regulated by hydrologic inputs of dissolved IC rather than by lake metabolism, IC and OC pathways are only loosely coupled, and future climate variability will alter C fluxes in similar lakes mainly through regulation of mass transfer from land. doi: 10.4319/10.2010.55.4.1551

This study focuses on the retrieval of the normalized mass absorption cross section (MAC) of soot using theoretical calculations that incorporate new measurements of the optical properties of organic carbon (OC) intrinsic to fresh diesel soot. Intrinsic OC was extracted by water and an organic solvent, and the complex refractive index of the extracted OC was derived at 532 and 355-nm wavelengths using cavity ring-down aerosol spectrometry. The extracted OC was found to absorb weakly in the visible wavelengths and moderately at blue wavelengths. The mass ratio of OC and elemental carbon (EC) in the collected particles was evaluated using a thermo-optical method. The measured EC/OC ratio in the soot exhibited substantial variability from measurement to measurement, ranging between 2 and 5. To test the sensitivity of the MAC to this variability, three different EC/OC ratios (2:1, 1:1, and 1:2) were chosen as representative. Particle size and spherule morphology were estimated using scanning electron microscopy, and the soot was found to be primarily in the form of aggregates with a dominant aggregate diameter mode in the range 200-250 nm. The measured refractive index of the extracted OC was used with a variety of theoretical models to calculate the MAC of internally mixed diesel soot at 532 and 355 nm. We conclude that Rayleigh-Debye--Gans theory on clusters of coated spherules and T-matrix of a solid EC spheroid coated by intrinsic OC are both consistent with 'previous measurements; however, Rayleigh-Debye--Gans theory provides a more realistic physical model for the calculation black carbon | cavity ring-down | coated particles | mass absorption cross section doi/ 10.1073/pnas.0903311106

Radiocarbon ([sup.14]C) is a radioactive isotope that is useful for determining the age and cycling of carbon-based materials in the Earth system. Compound specific radiocarbon analysis (CSRA) provides powerful insight into the turnover of individual components that make up the carbon cycle. Extraneous or nonspecific background carbon ([C.sub.ex]) is added during sample processing and subsequent isolation of CSRA samples. Here, we evaluate the quantity and radiocarbon signature of [C.sub.ex] added from two sources: preparative capillary gas chromatography (PCGC, [C.sub.PCGC] and chemical preparation of CSRA of black carbon samples ([C.sub.chemistry]). We evaluated the blank directly using process blanks and indirectly by quantifying the difference in the isotopic composition between processed and unprocessed samples for a range of sample sizes. The direct and indirect assessment of [C.sub.chemistry+PCGC] agree, both in magnitude and radiocarbon value (1.1 [+ or -] 0.5 [micro]g of C, fraction modern = 0.2). Half of the [C.sub.ex] is introduced before PCGC isolation, likely from coeluting compounds in solvents used in the extraction method. The magnitude of propagated uncertainties of CSRA samples are a function of sample size and collection duration. Small samples collected for a brief amount of time have a smaller propagated [sup.14]C uncertainty than larger samples collected for a longer period of time. CSRA users are cautioned to consider the magnitude of uncertainty they require for their system of interest, to frequently evaluate the magnitude of [C.sub.ex] added during sampling processing, and to avoid isolating samples [less than or equal to] 5 [micro]g of carbon. 10.1021/ac901922s

Stratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian--Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive [delta][sup.13]C fluctuations for the Cenomanian--Turonian boundary, the Middle Turonian, the upper Turonian--lower Coniacian, and the Santonian. A biostratigraphic framework of the age-diagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these [delta][sup.13]C fluctuation events are comparable with those recorded in [delta][sup.13]C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these [delta][sup.13]C events in terms of global chemostratigraphy. In particular, the [delta][sup.13]C patterns within the overall positive interval of the Cenomanian--Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of [delta][sup.13]C fluctuation patterns demonstrates that the terrestrial organic [delta][sup.13]C data mirror the global-scale [delta][sup.13]C patterns in the carbon reservoir of ocean--atmosphere--terrestrial biosphere during the Cenomanian--Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic [delta][sup.13]C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic [delta][sup.13]C events appears more amplified than that of coeval marine carbonate [delta][sup.13]C events. This correlation is interpreted to mean that the effects of local C[O.sub.2] emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global [delta][sup.13]C trend and resulted in the terrestrial organic [delta][sup.13]C records of the Yezo Group. Keywords: carbon isotope stratigraphy, Hokkaido, Japan, terrestrial organic matter, Upper Cretaceous.

Methylated metal(loid) compounds are formed in the environment by abiotic as well as enzymatically catalyzed transfer of a methyl group. Due to the increased mobility and toxicity in comparison to the inorganic precursors, the investigation of the formation process is of high relevance. Though the natural abundance carbon isotope ratio can give important insights toward their origin as well as the biochemical methyl transfer process, so far, these species have not been investigated by carbon isotope ratio mass spectrometry (IRMS). This is due to the analytical challenge to precisely determine the natural isotope distribution of trace amounts of metal(loid)-bound carbon in complex organic matrixes. To overcome this problem, we tested the concept of selective derivatization of non-volatile organometal(loid)s by hydride generation (HG) followed by purge and trap (P-T) enrichment, heart-cut gas chromatography (hcGC), and subsequent analysis by GC/IRMS. Parameter optimization of HG/P-T/hcGC was conducted using online coupling to element-sensitive ICPMS (inductively coupled plasma mass spectrometry) detection. The purity of the HG/P-T/hcGC fraction was verified by GC/MS. For the model substance trimethylarsine oxide (TMAsO), an excellent agreement of the [[delta].sup.13]C-value analyzed by HG/P-T/hcGC-GC/IRMS was achieved in comparison to the bulk [[delta].sup.13]C-value, which shows that no significant isotope fractionation occurred during hydride generation and subsequent separation. The optimized method showed good reproducibility and a satisfying absolute detection limit of 4.5 [micro]g TMAsO (1.2 [micro][g.sub.carbon]). This method was applied to the analysis of TMAsO in compost. The low [delta][sup.13]C value of this compound (-48.38 [+ or -] 0.41%[per thousand]) indicates that biomethylation leads to significant carbon fractionation. HG/P-T/hcGC-GC/IRMS is a promising tool for investigation of the biomethylation process in the environment.

The 260-million-year-old Emeishan volcanic province of southwest China overlies and is interbedded with Middle Permian carbonates that contain a record of the Guadalupian mass extinction. Sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations. These show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae. The temporal coincidence of these two phenomena supports the idea of a cause-and-effect relationship. The crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean-atmosphere carbon cycle.

Carbon atoms self-assemble into the famous soccer-ball shaped Buckminsterfullerene ([C.sub.60]), the smallest fullerene cage that obeys the isolated-pentagon rule (IPR). Carbon atoms self-assemble into larger (n > 60 vertices) empty cages as well--but only the few that obey the IPR--and at least 1 small fullerene (n [less than or equal to] 60) with adjacent pentagons. Clathrin protein also self-assembles into small fullerene cages with adjacent pentagons, but just a few of those. We asked why carbon atoms and clathrin proteins self-assembled into just those IPR and small cage isomers. In answer, we described a geometric constraint--the head-to-tail exclusion rule--that permits self-assembly of just the following fullerene cages: among the 5,769 possible small cages (n [less than or equal to] 60 vertices) with adjacent pentagons, only 15; the soccer ball (n = 60); and among the 216,739 large cages with 60 < n [less than or equal to] 84 vertices, only the 50 IPR ones. The last finding was a complete surprise. Here, by showing that the largest permitted fullerene with adjacent pentagons is one with 60 vertices and a ring of interleaved hexagons and pentagon pairs, we prove that for all n > 60, the head-to-tail exclusion rule permits only (and all) fullerene cages and nanotubes that obey the IPR. We therefore suggest that self-assembly that obeys the IPR may be explained by the head-to-tail exclusion rule, a geometric constraint. Buckminsterfullerene | buckyball | self assembly | clathrin

BACKGROUND: Although a number of studies have documented the relationship between lung function and traffic-related pollution among children, few have focused on adult lung function or examined community-based populations. OBJECTIVE: [...]

Interior Alaska around the summer solstice belies any descriptions of America's far north as desolate or inhospitable. In late June, the tundra explodes with life. Mosses and lichens cushion the [...]

The purpose of this study was to determine the fractional recovery rate of labeled C[O.sub.2] in the breath of severely burned children. This information is needed to perform tracer studies of substrate oxidation using carbon-labeled fatty acids. Nine children, ages 4-14 yr with massive burns participated in the study. All experiments were performed 7 days post burn after an overnight fast. A primed (60 [micro]mol/kg), constant (2.0 [micro]mol x [kg.sup.-1] x [min.sup.-1]) infusion of [[1,2-.sup.13]C]acetate was given during a 4-h basal period and during a 4-h hyperinsulinemic euglycemic clamp. A priming dose (150 [micro]mol/kg) of Na[H.sup.13]C[O.sub.3] was given at the beginning of the study. Breath samples were collected every 10 min during the last 40 min of each period. Indirect calorimetry was performed during the last 30 min of each period. The isotopic enrichment of [sup.13]C[O.sub.2] was determined by isotope ratio-mass spectrometry, and total C[O.sub.2] excretion was measured by indirect calorimetry. The fractional recovery of acetate label was 0.89 [+ or -] 0.05 and 0.88 [+ or -] 0.04 during the basal state and clamp, respectively. We conclude that the fractional recovery of labeled acetate in severely burned children is approximately three times the recovery of a nonburned adult and similar to the value in exercising adults. The high recovery rate reflects the rapid turnover of the TCA cycle in burned children relative to the rate of exchange reactions. Minimal correction of expired C[O.sub.2] data is needed in this circumstance to quantify fatty acid oxidation using [sup.13]C-labeled fatty acids. acetate correction factor; fatty acid oxidation

Although the Earth's environment is constantly changing, there have been a few unusual episodes over the last c. 200 Ma when change was extreme in terms of its rapidity, severity, long-lasting consequences and unpredictability. The geochemical and biotic records for two of these episodes, the Palaeocene--Eocene thermal maximum and the Toarcian Oceanic Anoxic Event (Early Jurassic), possess many significant similarities. Each event was associated with a major carbon isotope excursion, significant levels of biotic extinctions, severe global warming, an enhanced hydrological cycle, and evidence for widespread seawater anoxia. Both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations; based on a detailed comparison, the Palaeocene Eocene thermal maximum may have been an incipient Oceanic Anoxic Event. The geochemical and biotic changes during these two events are most readily explained by the abrupt, large-scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province. Carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere, indicating that ancient events such as these may usefully serve as analogues for present-day environmental change.

Determination of compound-specific carbon isotope values by continuous flow isotope ratio mass spectrometry is impacted by variation in several routine operating parameters of which one of the most important is signal size, or linearity. Experiments were carried out to evaluate the implications of these operating parameters on both reproducibility and accuracy of [delta][sup.13]C measurements. A new method is described for assessing total instrumental uncertainty of routine compound-specific [delta][sup.13]C analysis, incorporating both accuracy and reproducibility. These findings have important implications for application of compound-specific isotope analysis in environmental geochemistry and in particular for the rapidly developing field of isotopic investigation of biodegradation and remediation of organic chemicals in contaminant hydrogeology.

The factors controlling spatial and temporal patterns in soil solution and streamwater chemistry are highly uncertain in northern hardwood forest ecosystems in the northeastern United States, where concentrations of reactive nitrogen (Nr) in streams have surprisingly declined over recent decades in the face of persistent high rates of atmospheric Nr deposition and aging forests. Reactive nitrogen includes inorganic species (e.g., ammonium [N[H.sub.4.sup.+]], nitrate [N[O.sub.3.sup.-]]) and some organic forms (e.g., amino acids) available to support the growth of plants and microbes. The objective of this study was to examine controls on the spatial and temporal patterns in the concentrations and fluxes of nitrogen (N) species and dissolved organic carbon (DOC) in a 12-year record of soil solutions and streamwater along an elevational gradient (540-800 m) of a forested watershed at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire, USA. Dissolved organic N and DOC concentrations were elevated in the high-elevation spruce--fir--white birch (SFB) zone of the watershed, while N[O.sub.3.sup.-] was the dominant N species in the lower elevation hardwood portion of the watershed. Within the soil profile, N retention was centered in the mineral horizon, and significant amounts of N were retained between the lower mineral soil and the stream, supporting the idea that near- and in-stream processes are significant sinks for N at the HBEF. Temporal analysis suggested that hydrologic flow paths can override both abiotic and biotic retention mechanisms (i.e., during the non-growing season when most hydrologic export occurs, or during years with high rainfall), there appears to be direct flushing of N from the organic horizons into the stream via horizontal flow. Significant correlations between soil N[O.sub.3.sup.-] concentrations, nitrification rates and streamwater N[O.sub.3.sup.-] exports show the importance of biological production as a regulator of inorganic N export. The lack of internal production response (e.g., mineralization, nitrification) to a severe ice storm in 1998 reinforces the idea that plant uptake is the dominant regulator of export response to disturbance. Key words: dissolved organic carbon; dissolved organic nitrogen; Hubbard Brook Experimental Forest; nitrate; nitrogen; soil solution; streamwater.

Carbonado diamonds from the Central African Republic were investigated using spectroscopic observations and C-isotopic analysis. Based on photoluminescence (PL) spectra, carbonado samples were classified into two groups: Group-A, which exhibits an intense PL band at 504 nm; and Group-B, which exhibits PL bands at 504, 575, and 638 nm at room temperature. PL spectra measured at 120 K gave well-resolved side-band structures of 504 nm bands. Consequently, the 504 nm band of Group-A can be assigned to the 3H center attributable to self interstitials in diamond, whereas the 504 nm band from Group-B can be assigned to the H3 center attributable to a vacancy ([??]) trapped at nearest-neighbor substitutional nitrogen (N) pairs. The PL band at 575 nm, which is attributable to neutral N-[??] pairs, is known to increase its width with increasing residual stress in diamond aggregates. The average FWHM of the 575 nm band and the standard deviations were 3.80 and 0.54 nm for Group-A carbonado, and 2.80 and 0.38 nm for Group-B carbonado. These values suggest that Group-A carbonado samples have higher residual stress than the Group-B samples. The presence of an H3 center and the lower residual stress in Group-B carbonado both suggest that they originated from higher temperatures compared to Group-A. Radiation halos were observed in cathodoluminescence (CL) images of both Group-A and Group-B samples. The CL halos are traces of radiation damage from radioactive nuclides. The texture of the haloes suggests that the radiation damage was a secondary event after formation of the carbonado diamonds. The average C-isotopic composition of Group-A is -23.6 [+ or -] 0.52 [per thousand] in [[delta].sup.13][C.sub.PDB] and that of Group-B is -26.3 [+ or -] 0.65 [per thousand]. Group-A carbonado was enriched systematically in [sup.13]C compared with Group-B carbonado. Isotopic fractionation might occur as a result of the different thermal history of carbonado. Keywords: Carbonado, cathodoluminescence, photoluminescence, carbon isotope, diamond, radiation damage

Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from [approximately equal to] 0.2 to 2 [g*m.sup.-2]*[yr.sup.-1]. We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (C[O.sub.2]) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks. decomposition | global change | litter peat | C[O.sub.2]

Model composites of DNA-wrapped single-wall carbon nanotubes in poly(acrylic acid) are used to measure the metrics of single-wall carbon nanotube (SWNT) dispersion. The results have represented the first controlled comparison of the metrics for evaluating SWNT dispersion.

The microwave technique is found to be very applicable for the preparation of a-cellulose from wood samples and can be recommended for analyzing the stable carbon isotopes in tree rings. At a reaction temperature of 80 [degrees]C, the extraction time can be decreased from 36 h to 15 min. Microwave-supported prepared cellulose contains more amorphous constituents, resulting in a relatively higher reactivity and amenability for a following nitration with regard to determination of nonexchangeable hydrogen. The [delta][sup.18]O values of microwave-enhanced extracted cellulose remain significantly lighter than reference values, possibly as a result of an increased oxygen isotope exchange between bleaching solution and cellulose under conditions of high energy input. Therefore, this technique cannot be recommended for oxygen isotope analyses in wood cellulose.

Quantification of sources and sinks of carbon at global and regional scales requires not only a good description of the land sources and sinks of carbon, but also of the synoptic and mesoscale meteorology. An experiment was performed in Les Landes, southwest France, during May-June 2005, to determine the variability in concentration gradients and fluxes of C[O.sub.2]. The CarboEurope Regional Experiment Strategy (CERES; see also http://carboregional.mediasfrance.org/index) aimed to produce aggregated estimates of the carbon balance of a region that can be meaningfully compared to those obtained from the smallest downscaled information of atmospheric measurements and continental-scale inversions. We deployed several aircraft to sample the C[O.sub.2] concentration and fluxes over the whole area, while fixed stations observed the fluxes and concentrations at high accuracy. Several (mesoscale) meteorological modeling tools were used to plan the experiment and flight patterns. Results show that at regional scale the relation between profiles and fluxes is not obvious, and is strongly influenced by airmass history and mesoscale flow patterns. In particular, we show from an analysis of data for a single day that taking either the concentration at several locations as representative of local fluxes or taking the flux measurements at those sites as representative of larger regions would lead to incorrect conclusions about the distribution of sources and sinks of carbon. Joint consideration of the synoptic and regional flow, fluxes, and land surface is required for a correct interpretation. This calls for an experimental and modeling strategy that takes into account the large spatial gradients in concentrations and the variability in sources and sinks that arise from different land use types. We briefly describe how such an analysis can be performed and evaluate the usefulness of the data for planning of future networks or longer campaigns with reduced experimental efforts.

A study was conducted to characterize in detail microbially diverse communities in permeable shelf sands that have a large role in global biogeochemical cycles. Predominant phylotypes that could catalyze carbon and nitrogen cycling in marine sands were revealed.

The most prominent of the two major global [[delta].sup.13]C excursions in the Ordovician, the Hirnantian [[delta].sup.13]C excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated [[delta].sup.13]C values of +4 [per thousand] to +5 [per thousand]. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes. Keywords: carbon isotope excursion, Hirnantian, Upper Ordovician, Missouri-Illinois, Gondwana glaciation, sea-level changes.

Carbon stable-isotope variation through the Cenomanian-Santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven Chalk successions in England. The sections show consistent stratigraphic trends and [[delta].sup.13]C values that provide a basis for high-resolution correlation. Positive and negative [[delta].sup.13]C excursions and inflection points on the isotope profiles are used to define 72 isotope events. Key markers are provided by positive [[delta].sup.13]C excursions of up to + 2 [per thousand]: the Albian/Cenomanian Boundary Event; Mid-Cenomanian Event I; the Cenomanian/Turonian Boundary Event; the Bridgewick, Hitch Wood and Navigation events of Late Turonian age; and the Santonian/Campanian Boundary Event. Isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons. An age-calibrated composite [[delta].sup.13]C reference curve and an isotope event stratigraphy are constructed using data from the English Chalk. The isotope stratigraphy is applied to successions in Germany, France, Spain and Italy. Correlation with pelagic sections at Gubbio, central Italy, demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the Cenomanian-Turonian stages, confirming established relationships between Tethyan planktonic foraminiferal and Boreal macrofossil biozonations. Correlation of the Coniacian-Santonian stages is less clear cut: magnetostratigraphic evidence for placing the base of Chron 33r near the base of the Upper Santonian is in good agreement with the carbon-isotope correlation, but generates significant anomalies regarding the placement of the Santonian and Campanian stage boundaries with respect to Tethyan planktonic foraminiferal and nannofossil zones. Isotope stratigraphy offers a more reliable criterion for detailed correlation of Cenomanian--Santonian strata than biostratigraphy. With the addition of Campanian [[delta].sup.13]C data from one of the English sections, a composite Cenomanian-Campanian age-calibrated reference curve is presented that can be utilized in future chemostratigraphic studies. The Cenomanian-Campanian carbon-isotope curve is remarkably similar in shape to supposedly eustatic sea-level curves: increasing [[delta].sup.13]C values accompanying sea-level rise associated with transgression, and falling [[delta].sup.13]C values characterizing sea-level fall and regression. The correlation between carbon isotopes and sea-level is explained by variations in epicontinental sea area affecting organic-matter burial fluxes: increasing shallow sea-floor area and increased accommodation space accompanying sea-level rise allowed more efficient burial of marine organic matter, with the preferential removal of [sup.12]C from the marine carbon reservoir. During sea-level fall, reduced seafloor area, marine erosion of previously deposited sediments, and exposure of basin margins led to reduced organic-carbon burial fluxes and oxidation of previously deposited organic matter, causing falling [[delta].sup.13]C values. Additionally, drowning of carbonate platforms during periods of rapid sea-level rise may have reduced the global inorganic relative to the organic carbon flux, further enhancing [[delta].sup.13]C values, while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition. Variations in nutrient supply, changing rates of oceanic turnover, and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon-isotope ratios. Keywords: Cretaceous, carbon isotopes, Chalk, chemostratigraphy, sea-level change.

Herbivore attack elicits costly defenses that are known to decrease plant fitness by using resources that are normally slated for growth and reproduction. Additionally, plants have evolved mechanisms for tolerating attack, which are not understood on a molecular level. Using [sup.11]C-photosynthate labeling as well as sugar and enzyme measurements, we found rapid changes in sink-source relations in the annual Nicotiana attenuata after simulated herbivore attacks, which increased the allocation of sugars to roots. This herbivore-induced response is regulated by the [beta]-subunit of an SnRK1 (SNF1-related kinase) protein kinase, GAL83, transcripts of which are rapidly down-regulated in source leaves after herbivore attack and, when silenced, increase assimilate transport to roots. This C diversion response is activated by herbivore-specific elicitors and is independent of jasmonate signaling, which regulates most of the plant's defense responses. Herbivore attack during early stages of development increases root reserves, which, in turn, delays senescence and prolongs flowering. That attacked GAL83-silenced plants use their enhanced root reserves to prolong reproduction demonstrates that SnRK1 alters resource allocation so that plants better tolerate herbivory. This tolerance mechanism complements the likely defensive value of diverting resources to a less vulnerable location within the plant. carbon-11 | defense | plant-herbivore interactions | tolerance

Soluble, ultra-short (length < 60nm), carboxylated, single-walled carbon nanotubes (SWNTs) were prepared by a scalable process. The solubility of these ultra-short SWNTs (US-SWNTs) in organic solvents, superacid and water is about 2 wt %.

Shunting arc discharge is a pulsed plasma source of metals and semimetal materials and is ignited without any trigger sources at a wide range of gas pressures, from vacuum to atmospheric pressure under identical discharge conditions. In this paper, an ion extraction from magnetically driven carbon shunting arc discharge and a criterion of the arc ignition are described. A carbon rod with a diameter of 2 mm and a length of 40 mm was employed for arc ignition. The carbon rod was set in the vacuum and was initially heated up with a pulsed current supplied by a charged capacitor with a capacitance of 20 [micro]F, followed by self-ignition. The heating energy is almost independent of the charging voltage of the capacitor and changes with the rod position on the rail. The ions are extracted from the arc plasma by applying a negative pulse voltage to a target. The target current has a sharp peak at the initial stage, followed by a stationary state. The stationary current decreases with increasing the distance to the target from a muzzle of the shunting arc plasma gun. Under the assumption of a collisionless ion sheath, the ion density at a 20-mm target-muzzle distance is estimated as 1 x [10.sup.8] and 2 x [l0.sup.7] [cm.sup.-3] for the delay times of 250 and 1000 [micro]s, respectively. The density at a 250-[micro]s delay time decreases from 1 x [10.sup.8] to 0.8 x 108 [cm.sup.-3] by increasing the distance from 20 to 140 mm. The ion density increases as the charging voltage of the capacitor for arc generation is increased. Index Terms--Carbon, ion current, ion extraction, magnetically driven, plasma-based ion implantation (PBII), shunting arc.

The distribution of [delta][sup.13]C values from human remains recovered in the eastern Chihuahuan Desert and central Texas demonstrates the existence of at least two distinct coeval dietary populations during the Early and Late Archaic. We employed a novel statistical technique, normal probability plots, to identify distinct dietary populations. [delta][sup.13]C values from one population in the Lower Pecos and Trans-Pecos regions of Texas reflect the long-term use of Chihuahuan Desert [C.sub.4] and CAM plants. A second group, consisting of all the central Texas individuals and some individuals from the Lower Pecos, depended heavily on [C.sub.3] plants more common in the Edwards Plateau or in the oak-pine forests in Mexico. The wide range of stable carbon isotope ratios from the Lower Pecos region of the eastern Chihuahuan Desert forces a reconsideration of hunter-gatherer settlement and social organization models proposed for that region. This study highlights the need to conduct more research on hunter-gatherer prehistoric diets and social organization. Keywords: Texas, Archaic, diet, Lower Pecos, stable isotopes

Climate change predictions derived from coupled carbon-climate models are highly dependent on assumptions about feedbacks between the biosphere and atmosphere. One critical feedback occurs if C uptake by the biosphere increases in response to the fossil-fuel driven increase in atmospheric [C[O.sub.2]] ('C[O.sub.2] fertilization'), thereby slowing the rate of increase in atmospheric [C[O.sub.2]]. Carbon exchanges between the terrestrial biosphere and atmosphere are often first represented in models as net primary productivity (NPP). However, the contribution of C[O.sub.2] fertilization to the future global C cycle has been uncertain, especially in forest ecosystems that dominate global NPP, and models that include a feedback between terrestrial biosphere metabolism and atmospheric [C[O.sub.2]] are poorly constrained by experimental evidence. We analyzed the response of NPP to elevated C[O.sub.2] ([approximately equal to] 550 ppm) in four free-air C[O.sub.2] enrichment experiments in forest stands. We show that the response of forest NPP to elevated [C[O.sub.2]] is highly conserved across a broad range of productivity, with a stimulation at the median of 23 [+ or -] 2%. At low leaf area indices, a large portion of the response was attributable to increased light absorption, but as leaf area indices increased, the response to elevated [C[O.sub.2]] was wholly caused by increased light-use efficiency. The surprising consistency of response across diverse sites provides a benchmark to evaluate predictions of ecosystem and global models and allows us now to focus on unresolved questions about carbon partitioning and retention, and spatial variation in NPP response caused by availability of other growth limiting resources. C[O.sub.2] fertilization | global change | leaf area index | net primary productivity

Open savannah grasslands (dominated by [C.sub.4] plants) became a significant component of northeast African vegetation during the late Neogene. We present molecule-specific carbon isotopic measurements of terrestrial plant biomarkers preserved in marine sediments off northeast Africa that allow reconstruction of orbital-scale vegetation changes in short time windows over the past 9.4 m.y. The biomarker data show large-amplitude vegetation variability as early as 3.8 Ma, with the greatest [C.sub.4] expansion occurring after 3.4 Ma. We sampled orbital-scale oscillations of up to 5% [per thousand], almost as large as the observed late Neogene range of 7 [per thousand], suggesting that large and repeated oscillations between more open and more closed landscapes were an important aspect of northeast African vegetation change during the past 4 m.y. Keywords: [[delta].sup.13]C, carbon isotopes, biomarker, Africa, vegetation, [C.sub.4].

A new approach for the carbon-specific determination of humic-like substances (HULIS) in atmospheric aerosols is presented. The method is based on a two-step isolation procedure of HULIS and the determination of HULIS carbon with a dissolved organic carbon analyzer. In the first step, a C18 solid-phase extraction is performed to separate HULIS from inorganic and hydrophilic organic sample constituents in aqueous sample solutions. The second isolation step is conducted on a strong anion exchanger to separate HULIS from remaining carbonaceous compounds. This ion chromatographic separation step including the subsequent on-line detection of HULIS carbon was performed fully automated to avoid the risk of sample contamination and to enhance the reproducibility of the method. With a 5-mL sample volume, a limit of detection of 1.0 mg C/L was obtained; this corresponds to an absolute amount of 5 [micro]g of HULIS carbon. The reproducibility of the method given as the relative standard deviation was 4.3% (n = 10). The method was applied for the determination of water-soluble HULIS in airborne particulate matter. PM10 concentrations at an urban site in Vienna, Austria, ranged from around 0.1 to 1.8 [micro]g of C/[m.sup.3] (n = 49); the fraction of water-soluble HULIS in OC was 12.1 [+ or -] 7.2% (n = 49).

Clarification of the factors involved in the formation of unusual ancient organic carbon--rich deposits (like eastern Mediterranean sapropels) is central in understanding oceanic carbon cycling. The role of oxygenation remains a subject of controversy primarily due to two major uncertainties: (1) it is unknown if ancient organic-rich deposits reflect an accumulation of refractory organic matter (OM) or oxygenation-related aberrant sediment OM recycling, and (2) although marine OM degradation may be slower under anoxic conditions, its ultimate impact on organic carbon ([C.sub.org]) preservation over geological time remains unclear. Here we provide direct experimental evidence that the [C.sub.org] in eastern Mediterranean S1 sapropeis (deposited >5 ka) is still highly reactive and that a shutdown in labile organic matter degradation under anoxic conditions played a key role in the formation of these deposits. Keywords: organic carbon, preservation, remineralization, nitrogen isotopes, carbon isotopes, sapropel.