Carbon Isotope Signature (carbon + isotope_signature)

Distribution by Scientific Domains

Kinds of Carbon Isotope Signature

  • stable carbon isotope signature


  • Selected Abstracts


    Quantifying root lateral distribution and turnover using pine trees with a distinct stable carbon isotope signature

    FUNCTIONAL ECOLOGY, Issue 1 2005
    K. JOHNSEN
    Summary 1In order to help assess spatial competition for below-ground resources, we quantified the effects of fertilization on root biomass quantity and lateral root distribution of mid-rotation Pinus taeda trees. Open-top chambers exposed trees to ambient or ambient plus 200 µmol mol,1 atmospheric CO2 for 31 months. 2Tank CO2 was depleted in atmospheric 13C; foliage of elevated CO2 trees had ,13C of ,42·9, compared with ,29·1 for ambient CO2 trees. 3Roots 1 m from the base of elevated CO2 -grown trees had more negative ,13C relative to control trees, and this difference was detected, on average, up to 5·8, 3·7 and 3·7 m away from the trees for 0,2, 2,5 and >5 mm root-size classes, respectively. Non-fertilized tree roots extended as far as fertilized trees despite the fact that their above-ground biomass was less than half that of fertilized trees. 4These results are informative with respect to root sampling intensity and protocol, and the distances required between experimental manipulations to evaluate below-ground processes of independent treatments. 5Fine-root turnover has usually been estimated to range from weeks to 3 years, representing a major avenue of carbon flux. Using a mixing model we calculated that 0,2 mm roots had a mean residence time of 4·5 years indicating relatively slow fine-root turnover, a result that has major implications in modelling C cycling. [source]


    Stable carbon isotope signature of ancient maize agriculture in the soils of Motul de San José, Guatemala

    GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 3 2007
    Elizabeth A. Webb
    Soil profiles collected from a 2.5-km transect radiating from the Maya center of Motul de San José were analyzed for the stable carbon-isotope composition of their soil organic matter. The residues of maize (Zea mays), the only C4 plant known to have been cultivated in this area by the ancient Maya, impart a carbon-isotope signature to the underlying soil organic matter reservoir that is distinct from that produced by the native C3 forest vegetation. The varying turnover rates of the humic acid and humin fractions of the soil organic matter allowed us to distinguish between the presence of modern and ancient maize residues in these soils, and to delineate the lateral extent of maize cultivation at this ancient Maya site. The strongest isotopic evidence of maize residues is preserved in the soils surrounding the peripheral settlement of Chäkokot and at one locality within the urban center of Motul de San José. © 2007 Wiley Periodicals, Inc. [source]


    Associations between carbon isotope ratios of ecosystem respiration, water availability and canopy conductance

    GLOBAL CHANGE BIOLOGY, Issue 10 2004
    N. G. McDowell
    Abstract We tested the hypothesis that the stable carbon isotope signature of ecosystem respiration (,13CR) was regulated by canopy conductance (Gc) using weekly Keeling plots (n=51) from a semiarid old-growth ponderosa pine (Pinus ponderosa) forest in Oregon, USA. For a comparison of forests in two contrasting climates we also evaluated trends in ,13CR from a wet 20-year-old Douglas-fir (Pseudotsuga menziesii) plantation located near the Pacific Ocean. Intraannual variability in ,13CR was greater than 8.0, at both sites, was highest during autumn, winter, and spring when rainfall was abundant, and lowest during summer drought. The ,13CR of the dry pine forest was consistently more positive than the wetter Douglas-fir forest (mean annual ,13CR: ,25.41, vs. ,26.23,, respectively, P=0.07). At the Douglas-fir forest, ,13CR,climate relationships were consistent with predictions based on stomatal regulation of carbon isotope discrimination (,). Soil water content (SWC) and vapor pressure deficit (vpd) were the most important factors governing ,13CR in this forest throughout the year. In contrast, ,13CR at the pine forest was relatively insensitive to SWC or vpd, and exhibited a smaller drought-related enrichment (,2,) than the enrichment observed during drought at the Douglas-fir forest (,5,). Groundwater access at the pine forest may buffer canopy,gas exchange from drought. Despite this potential buffering, ,13CR at the pine forest was significantly but weakly related to canopy conductance (Gc), suggesting that ,13CR remains coupled to canopy,gas exchange despite groundwater access. During drought, ,13CR was strongly correlated with soil temperature at both forests. The hypothesis that canopy-level physiology is a critical regulator of ,13CR was supported; however, belowground respiration may become more important during rain-free periods. [source]


    Variability in the carbon isotope signature of Prochilodus lineatus (Prochilodontidae, Characiformes) a bottom-feeding fish of the Neotropical region

    JOURNAL OF FISH BIOLOGY, Issue 6 2007
    C. A. Lopes
    The spatial and seasonal variability of stable carbon isotopes in detritivorous Prochilodus lineatus, primary producers and particulate organic carbon (POC) were examined to promote a better understanding of the trophic dynamics of food webs in Neotropical ecosystems. Spatial variability in carbon isotope composition in the species showed a decreasing gradient in the Upper Paraná River system, from the Paraná River and Itaipu Reservoir subsystems to the Baía and Ivinheima subsystems. Fish ,13C followed the isotopic trend of POC along the Paraná River and Baía subsystem. Seasonal differences were not observed in fish. The analysis of percentile contribution of C3 and C4 sources in the species diet revealed the predominance of C3 plants (phytoplanktonic and periphytic algae and riparian vegetation) in most of the analysed subsystems and seasons. Nevertheless, the considerable participation of riparian vegetation was verified, especially in the Ivinheima subsystem in the dry season. C4 macrophytes presented a maximum contribution along the Upper Paraná River. These results demonstrate the existence of specific variability for the consumer and their food sources in different environments of the same ecosystem. [source]


    Digestion and Assimilation of the Free-living Nematode Panagrellus redivivus Fed to First Feeding Coregonid Larvae: Evidence from Histological and Isotopic Studies

    JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 1 2005
    Christian Schlechtriem
    The free-living nematode Panagrellus redivivus is a potential source of live food for first feeding fish. The digestion and assimilation of nematodes by larval fish were investigated with the aid of a histological and stable isotope approach. Larvae of whitefish Coregonus lavaretus were reared for 8 d with nematodes and compared with an unfed control. Nematodes were readily ingested by 3-d-old larvae. Different stages of nematode digestion could be observed in transverse sections of fish larvae sampled on Day 6 at regular intervals after feeding. Nematodes were produced on corn medium. In this way nematodes with a stable carbon isotope signature clearly different from the isotopic pattern of the fish larvae could be obtained. Stable carbon isotope signatures for lipids and lipid-free matter of fish larvae sampled on Days 2 and 8 after first feeding were clearly influenced by the stable isotopic pattern of the nematodes. The high acceptance of the nematodes by Coregonus lavaretus larvae and the early onset of digestion and nutrient retention positively confirm the potential of PanagreUus redivivus as a live food for first feeding fish larvae. [source]


    Determination of isotope fractionation factors and quantification of carbon flow by stable carbon isotope signatures in a methanogenic rice root model system

    GEOBIOLOGY, Issue 2 2006
    H. PENNING
    ABSTRACT Methanogenic processes can be quantified by stable carbon isotopes, if necessary modeling parameters, especially fractionation factors, are known. Anoxically incubated rice roots are a model system with a dynamic microbial community and thus suitable to investigate principal geochemical processes in anoxic natural systems. Here we applied an inhibitor of acetoclastic methanogenesis (methyl fluoride), calculated the thermodynamics of the involved processes, and analyzed the carbon stable isotope signatures of CO2, CH4, propionate, acetate and the methyl carbon of acetate to characterize the carbon flow during anaerobic degradation of rice roots to the final products CO2 and CH4. Methyl fluoride inhibited acetoclastic methanogenesis and thus allowed to quantify the fractionation factor of CH4 production from H2/CO2. Since our model system was not affected by H2 gradients, the fractionation factor could alternatively be determined from the Gibbs free energies of hydrogenotrophic methanogenesis. The fractionation factor of acetoclastic methanogenesis was also experimentally determined. The data were used for successfully modeling the carbon flow. The model results were in agreement with the measured process data, but were sensitive to even small changes in the fractionation factor of hydrogenotrophic methanogenesis. Our study demonstrates that stable carbon isotope signatures are a proper tool to quantify carbon flow, if fractionation factors are determined precisely. [source]


    Digestion and Assimilation of the Free-living Nematode Panagrellus redivivus Fed to First Feeding Coregonid Larvae: Evidence from Histological and Isotopic Studies

    JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 1 2005
    Christian Schlechtriem
    The free-living nematode Panagrellus redivivus is a potential source of live food for first feeding fish. The digestion and assimilation of nematodes by larval fish were investigated with the aid of a histological and stable isotope approach. Larvae of whitefish Coregonus lavaretus were reared for 8 d with nematodes and compared with an unfed control. Nematodes were readily ingested by 3-d-old larvae. Different stages of nematode digestion could be observed in transverse sections of fish larvae sampled on Day 6 at regular intervals after feeding. Nematodes were produced on corn medium. In this way nematodes with a stable carbon isotope signature clearly different from the isotopic pattern of the fish larvae could be obtained. Stable carbon isotope signatures for lipids and lipid-free matter of fish larvae sampled on Days 2 and 8 after first feeding were clearly influenced by the stable isotopic pattern of the nematodes. The high acceptance of the nematodes by Coregonus lavaretus larvae and the early onset of digestion and nutrient retention positively confirm the potential of PanagreUus redivivus as a live food for first feeding fish larvae. [source]


    Preparation of starch and soluble sugars of plant material for the analysis of carbon isotope composition: a comparison of methods,

    RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2009
    Andreas Richter
    Starch and soluble sugars are the major photosynthetic products, and their carbon isotope signatures reflect external versus internal limitations of CO2 fixation. There has been recent renewed interest in the isotope composition of carbohydrates, mainly for use in CO2 flux partitioning studies at the ecosystem level. The major obstacle to the use of carbohydrates in such studies has been the lack of an acknowledged method to isolate starch and soluble sugars for isotopic measurements. We here report on the comparison and evaluation of existing methods (acid and enzymatic hydrolysis for starch; ion-exchange purification and compound-specific analysis for sugars). The selectivity and reproducibility of the methods were tested using three approaches: (i) an artificial leaf composed of a mixture of isotopically defined compounds, (ii) a C4 leaf spiked with C3 starch, and (iii) two natural plant samples (root, leaf). Starch preparation methods based on enzymatic or acid hydrolysis did not yield similar results and exhibited contaminations by non-starch compounds. The specificity of the acidic hydrolysis method was especially low, and we therefore suggest terming these preparations as HCl-hydrolysable carbon, rather than starch. Despite being more specific, enzyme-based methods to isolate starch also need to be further optimized to increase specificity. The analysis of sugars by ion-exchange methods (bulk preparations) was fast but produced more variable isotope compositions than compound-specific methods. Compound-specific approaches did not in all cases correctly reproduce the target values, mainly due to unsatisfactory separation of sugars and background contamination. Our study demonstrates that, despite their wide application, methods for the preparation of starch and soluble sugars for the analysis of carbon isotope composition are not (yet) reliable enough to be routinely applied and further research is urgently needed to resolve the identified problems. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    Stable carbon isotopes as an indicator for soil degradation in an alpine environment (Urseren Valley, Switzerland)

    RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2009
    Monika Schaub
    Analyses of soil organic carbon (SOC) content and stable carbon isotope signatures (,13C) of soils were assessed for their suitability to detect early stage soil erosion. We investigated the soils in the alpine Urseren Valley (southern central Switzerland) which are highly impacted by soil erosion. Hill slope transects from uplands (cambisols) to adjacent wetlands (histosols and histic to mollic gleysols) differing in their intensity of visible soil erosion, and reference wetlands without erosion influence were sampled. Carbon isotopic signature and SOC content of soil depth profiles were determined. A close correlation of ,13C and carbon content (r,>,0.80) is found for upland soils not affected by soil erosion, indicating that depth profiles of ,13C of these upland soils mainly reflect decomposition of SOC. Long-term disturbance of an upland soil is indicated by decreasing correlation of ,13C and SOC (r,,,0.80) which goes in parallel with increasing (visible) damage at the site. Early stage soil erosion in hill slope transects from uplands to adjacent wetlands is documented as an intermediate ,13C value (,27.5,) for affected wetland soil horizons (0,12,cm) between upland (aerobic metabolism, relatively heavier ,13C of ,26.6,) and wetland isotopic signatures (anaerobic metabolism, relatively lighter ,13C of ,28.6,). Carbon isotopic signature and SOC content are found to be sensitive indicators of short- and long-term soil erosion processes. Copyright © 2009 John Wiley & Sons, Ltd. [source]