Gerd Gleixner

Max Planck Institute for Biogeochemistry Jena, Jena, Thuringia, Germany

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Publications (163)348.6 Total impact

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    ABSTRACT: Trees and shrubs in tropical Africa use the C3 cycle as a carbon fixation pathway during photosynthesis, while grasses and sedges mostly use the C4 cycle. Leaf-wax lipids from sedimentary archives such as the long-chain n -alkanes (e.g., n -C27 to n -C33) inherit carbon isotope ratios that are representative of the carbon fixation pathway. Therefore, n -alkane δ 13C values are often used to reconstruct past C3/C4 composition of vegetation, assuming that the relative proportions of C3 and C4 leaf waxes reflect the relative proportions of C3 and C4 plants. We have compared the δ 13C values of n -alkanes from modern C3 and C4 plants with previously published values from recent lake sediments and provide a framework for estimating the fractional contribution (areal-based) of C3 vegetation cover (fC3fC3) represented by these sedimentary archives. Samples were collected in Cameroon, across a latitudinal transect that accommodates a wide range of climate zones and vegetation types, as reflected in the progressive northward replacement of C3-dominated rain forest by C4-dominated savanna. The C3 plants analysed were characterised by substantially higher abundances of n -C29 alkanes and by substantially lower abundances of n -C33 alkanes than the C4 plants. Furthermore, the sedimentary δ 13C values of n -C29 and n -C31 alkanes from recent lake sediments in Cameroon (−37.4‰ to −26.5‰) were generally within the range of δ 13C values for C3 plants, even when from sites where C4 plants dominated the catchment vegetation. In such cases simple linear mixing models fail to accurately reconstruct the relative proportions of C3 and C4 vegetation cover when using the δ 13C values of sedimentary n -alkanes, overestimating the proportion of C3 vegetation, likely as a consequence of the differences in plant wax production, preservation, transport, and/or deposition between C3 and C4 plants. We therefore tested a set of non-linear binary mixing models using δ 13C values from both C3 and C4 vegetation as end-members. The non-linear models included a sigmoid function (sine-squared) that describes small variations in the fC3fC3 values as the minimum and maximum δ13C values are approached, and a hyperbolic function that takes into account the differences between C3 and C4 plants discussed above. Model fitting and the estimation of uncertainties were completed using the Monte Carlo algorithm and can be improved by future data addition. Models that provided the best fit with the observed δ13C values of sedimentary n-alkanes were either hyperbolic functions or a combination of hyperbolic and sine-squared functions. Such non-linear models may be used to convert δ13C measurements on sedimentary n-alkanes directly into reconstructions of C3 vegetation cover.
    Geochimica et Cosmochimica Acta 10/2014; 142:482–500. · 3.88 Impact Factor
  • ORCHEM 2014, Weimar; 09/2014
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    ABSTRACT: In general, a moderate drying trend is observed in mid-latitude arid Central Asia since the Mid-Holocene, attributed to the progressively weakening influence of the mid-latitude Westerlies on regional climate. However, as the spatio-temporal pattern of this development and the underlying climatic mechanisms are yet not fully understood, new high-resolution paleoclimate records from this region are needed. Within this study, a sediment core from Lake Son Kol (Central Kyrgyzstan) was investigated using sedimentological, (bio)geochemical, isotopic, and palynological analyses, aiming at reconstructing regional climate development during the last 6000 years. Biogeochemical data, mainly reflecting summer moisture conditions, indicate predominantly wet conditions until 4950 cal. yr BP, succeeded by a pronounced dry interval between 4950 and 3900 cal. yr BP. In the following, a return to wet conditions and a subsequent moderate drying trend until present times are observed. This is consistent with other regional paleoclimate records and likely reflects the gradual Late Holocene diminishment of the amount of summer moisture provided by the mid-latitude Westerlies. However, climate impact of the Westerlies was apparently not only restricted to the summer season but also significant during winter as indicated by recurrent episodes of enhanced allochthonous input through snowmelt, occurring before 6000 cal. yr BP and at 5100–4350, 3450–2850, and 1900–1500 cal. yr BP. The distinct ~1500-year periodicity of these episodes of increased winter precipitation in Central Kyrgyzstan resembles similar cyclicities observed in paleoclimate records around the North Atlantic, likely indicating a hemispheric-scale climatic teleconnection and an impact of North Atlantic Oscillation (NAO) variability in Central Asia.
    The Holocene 07/2014; 24(8):970-984. · 3.79 Impact Factor
  • Trends in Metabolomics - Analytics and Applications, Frankfurt a.M.; 06/2014
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    ABSTRACT: Current carbon cycle-climate models predict that future soil carbon storage will be determined by the balance between CO2 fertilization and warming. However, it is uncertain whether greater carbon inputs to soils with elevated CO2 will be sequestered, particularly since warming hastens soil carbon decomposition rates, and may alter the response of soils to new plant inputs. We studied the effects of elevated CO2 and warming on microbial soil carbon decomposition processes using laboratory manipulations of carbon inputs and soil temperature. We incubated soils from the Aspen Free Air CO2 Enrichment experiment, where no accumulation of soil carbon has been observed despite a decade of increased carbon inputs to soils under elevated CO2. We added isotopically-labeled sucrose to these soils in the laboratory to mimic and trace the effects of increased carbon inputs on soil organic carbon decomposition and its temperature sensitivity. Sucrose additions caused a positive priming of soil organic carbon decomposition, demonstrated by increased respiration derived from soil carbon, increased microbial abundance, and a shift in the microbial community towards faster growing microorganisms. Similar patterns were observed for elevated CO2 soils, suggesting that the priming effect was responsible for reductions in soil carbon accumulation at the site. Laboratory warming accelerated the rate of the priming effect, but the magnitude of the priming effect was not different amongst temperatures, suggesting that the priming effect was limited by substrate availability, not soil temperature. No changes in substrate use efficiency were observed with elevated CO2 or warming. The stimulatory effects of warming on the priming effect suggest that increased belowground carbon inputs from CO2 fertilization are not likely to be stored in mineral soils.
    05/2014;
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    ABSTRACT: Ostracod shells, belonging to three taxa (Leucocytherella sinensis Huang, 1982, ?Leucocythere dorsotuberosa Huang, 1982 and ?Leucocythere dorsotuberosa f. postilirata sensu Pang, 1985), were collected from two sediment cores from Lake Nam Co, on the central Tibetan Plateau. Two variants of LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry), spot and line-scan analyses, were used to investigate trace element concentrations (Mg, Sr, Ba, U and rare earth elements [REEs]) in single ostracod shells. The results suggest that the line-scan method can provide better precision than the spot analysis and is therefore preferred. No significant difference in trace element composition between taxa was detected in our study. Fluctuations of Mg/Ca and Sr/Ca in the shells show good agreement with the reported lake level changes during the Holocene, indicating that ostracod Mg and Sr can be related to paleohydrochemical processes in this area. A high correlation between Ba/Ca and Sr/Ca was detected in our study, perhaps implying that both metals were controlled by the same mechanisms. A possible relationship between ostracod U/Ca and the past redox conditions on the lake bottom is discussed. Relatively low and constant La/Ca was observed, which could be due to the REE characteristics in the lake water, or ostracod biological processes, or even the associated Fe-Mn and/or organic contaminants. Future studies on more specimens from this area, especially shells from living ostracods, are essential to investigate the potential of ostracod Ba, U and REEs for use as paleoenvironmental indicators.
    Palaeogeography Palaeoclimatology Palaeoecology 04/2014; · 2.75 Impact Factor
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    ABSTRACT: Large amounts of carbon are required for plant growth, but young, growing tissues often also have high concentrations of defensive secondary metabolites. Plants' capacity to allocate resources to growth and defense is addressed by the growth-differentiation balance hypothesis and the optimal defense hypothesis, which make contrasting predictions. Isotope labeling can demonstrate whether defense compounds are synthesized from stored or newly fixed carbon, allowing a detailed examination of these hypotheses.Populus trichocarpa saplings were pulse-labeled with 13CO2 at the beginning and end of a growing season, and the 13C signatures of phenolic glycosides (salicinoids), sugars, bulk tissue, and respired CO2 were traced over time. Half of the saplings were also subjected to mechanical damage.Populus trichocarpa followed an optimal defense strategy, investing 13C in salicinoids in expanding leaves directly after labeling. Salicinoids turned over quickly, and their production continued throughout the season. Salicin was induced by early-season damage, further demonstrating optimal defense.Salicinoids appear to be of great value to P. trichocarpa, as they command new C both early and late in the growing season, but their fitness benefits require further study. Export of salicinoids between tissues and biochemical pathways enabling induction also needs research. Nonetheless, the investigation of defense production afforded by isotope labeling lends new insights into plants' ability to grow and defend simultaneously.
    New Phytologist 04/2014; · 6.74 Impact Factor
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    ABSTRACT: Little is known about the role of plant functional diversity for ecosystem-level carbon (C) fluxes. To fill this knowledge gap, we translocated monoliths hosting communities with four and 16 sown species from a long-term grassland biodiversity experiment (‘The Jena Experiment’) into a controlled environment facility for ecosystem research (Ecotron). This allowed quantifying the effects of plant diversity on ecosystem C fluxes as well as three parameters of C uptake efficiency (water and nitrogen use efficiencies and apparent quantum yield). By combining data on ecosystem C fluxes with vegetation structure and functional trait-based predictors, we found that increasing plant species and functional diversity led to higher gross and net ecosystem C uptake rates. Path analyses and light response curves unravelled the diversity of leaf nitrogen concentration in the canopy as a key functional predictor of C fluxes, either directly or indirectly via LAI and aboveground biomass.
    Ecology Letters 01/2014; · 17.95 Impact Factor
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    ABSTRACT: Plant diversity drives changes in the soil microbial community which may result in alterations in ecosystem functions. However, the governing factors between the composition of soil microbial communities and plant diversity are not well understood. We investigated the impact of plant diversity (plant species richness and functional group richness) and plant functional group identity on soil microbial biomass and soil microbial community structure in experimental grassland ecosystems. Total microbial biomass and community structure were determined by phospholipid fatty acid (PLFA) analysis. The diversity gradient covered 1, 2, 4, 8, 16 and 60 plant species and 1, 2, 3 and 4 plant functional groups (grasses, legumes, small herbs and tall herbs). In May 2007, soil samples were taken from experimental plots and from nearby fields and meadows. Beside soil texture, plant species richness was the main driver of soil microbial biomass. Structural equation modeling revealed that the positive plant diversity effect was mainly mediated by higher leaf area index resulting in higher soil moisture in the top soil layer. The fungal-to-bacterial biomass ratio was positively affected by plant functional group richness and negatively by the presence of legumes. Bacteria were more closely related to abiotic differences caused by plant diversity, while fungi were more affected by plant-derived organic matter inputs. We found diverse plant communities promoted faster transition of soil microbial communities typical for arable land towards grassland communities. Although some mechanisms underlying the plant diversity effect on soil microorganisms could be identified, future studies have to determine plant traits shaping soil microbial community structure. We suspect differences in root traits among different plant communities, such as root turnover rates and chemical composition of root exudates, to structure soil microbial communities.
    PLoS ONE 01/2014; 9(5):e96182. · 3.53 Impact Factor
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    ABSTRACT: Effects of elevated CO2 and warming on the soil carbon cycle. Figure optionsDownload full-size imageDownload as PowerPoint slide
    Soil Biology and Biochemistry 01/2014; 76:57–69. · 4.41 Impact Factor
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    ABSTRACT: The observation that the hydrogen isotope composition (δD) of leaf wax lipids is determined mainly by precipitation δD values, has resulted in the application of these biomarkers to reconstruct paleo-climate from geological records. However, because the δD values of leaf wax lipids are additionally affected by vegetation type and ecosystem evapotranspiration, paleo-climatic reconstruction remains at best semi-quantitative. Here, we have used published results for the carbon isotope composition (δ13C) of n-alkanes in common plants along a latitudinal gradient in C3/C4 vegetation and relative humidity in Cameroon and demonstrate that pentacyclic triterpene methyl ethers (PTMEs) and n-C29 and n-C31 in the same soil, derived mainly from C4 graminoids (e.g. grasses) and C3 plants (e.g. trees and shrubs), respectively. We found that the δD values of soil n-C27, n-C29 and n-C31, and PTMEs correlated significantly with surface water δD values, supporting previous observations that leaf wax lipid δD values are an effective proxy for reconstructing precipitation δD values even if plant type changes significantly. The apparent fractionation (εapp) between leaf wax lipid and precipitation δD values remained relatively constant for C3-derived long chain n-alkanes, whereas εapp of C4-derived PTMEs decreased by 20‰ along the latitudinal gradient encompassing a relative humidity range from 80% to 45%. Our results indicate that PTME δD values derived from C4 graminoids may be a more reliable paleo-ecohydrological proxy for ecosystem evapotranspiration within tropical and sub-tropical Africa than n-alkane δD values, the latter being a better proxy for surface water δD values. We suggest that vegetation change associated with different plant water sources and/or difference in timing of leaf wax synthesis between C3 trees of the transitional class and C3 shrubs of the savanna resulted in a D depletion in soil long chain n-alkanes, thereby counteracting the effect of evapotranspiration Denrichment along the gradient. In contrast, evaporative D enrichment of leaf and soil water was significant enough to be recorded in the δD values of PTMEs derived from C4 graminoids, likely because PTMEs record the hydrogen isotopic composition of the same vegetation type.
    Organic Geochemistry 01/2014; · 2.52 Impact Factor
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    ABSTRACT: Background and aims Soil aggregate stability depends on plant community properties, such as functional group composition, diversity and biomass production. However, little is known about the relative importance of these drivers and the role of soil organisms in mediating plant community effects. Methods We studied soil aggregate stability in an experimental grassland plant diversity gradient and considered several explanatory variables to mechanistically explain effects of plant diversity and plant functional group composition. Three soil aggregate stability measures (slaking, mechanical breakdown and microcracking) were considered in path analyses. Results Soil aggregate stability increased significantly from monocultures to plant species mixtures and in the presence of grasses, while it decreased in the presence of legumes, though effects differed somewhat between soil aggregate stability measures. Using path analysis plant community effects could be explained by variations in root biomass, soil microbial biomass, soil organic carbon concentrations (all positive relationships), and earthworm biomass (negative relationship with mechanical breakdown). Conclusions The present study identified important drivers of plant community effects on soil aggregate stability. The effects of root biomass, soil microbial biomass, and soil organic carbon concentrations were largely consistent across plant diversity levels suggesting that the mechanisms identified are of general relevance.
    Plant and Soil 12/2013; · 3.24 Impact Factor
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    ABSTRACT: We used electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) to identify the molecular composition of dissolved organic matter (DOM) collected from different ecosystems along a transect crossing Siberia's northern and middle Taiga. This information is urgently needed to help elucidate global carbon cycling and export through Russian rivers. In total, we analyzed DOM samples from eleven Yenisei tributaries and seven bogs. Freeze-dried and re-dissolved DOM was desalted via solid phase extraction (SPE) and eluted in methanol for ESI-FT-ICR-MS measurements. We recorded 15209 different masses and identified 7382 molecular formulae in the mass range between m/z = 150 and 800. We utilized the relative FT-ICR-MS signal intensities of 3384 molecular formulae above a conservatively set limit of detection and summarized the molecular characteristics for each measurement using ten magnitude-weighted parameters ((O/C)w, (H/C)w, (N/C)w, (DBE)w, (DBE/C)w, (DBE/O)w, (DBE-O)w, (C#)w, (MW)w and (AI)w) for redundancy analysis. Consequently, we revealed that the molecular composition of DOM depends mainly on pH and geographical latitude. After applying variation partitioning to the peak data, we isolated molecular formulae that were strongly positive or negatively correlated with latitude and pH. We used the chemical information from 13 parameters (C#, H#, N#, O#, O/C, H/C, DBE, DBE/C, DBE/O, AI, N/C, DBE-O and MW) to characterize the extracted molecular formulae. Using latitude along the gradient representing climatic variation, we found a higher abundance of smaller molecules, nitrogen-containing compounds and unsaturated CC functionalities at higher latitudes. As possible reasons for the different molecular characteristics occurring along this gradient, we suggested that the decomposition was temperature dependent resulting to a higher abundance of non-degraded lignin-derived phenolic substances. We demonstrated that bog samples, which were differentiated from river samples by their lower pH values, distinguish themselves by their higher unsaturation and molecular size. These molecular characteristics might suggest less phenol oxidase degradation occurs alongside a higher abundance of phenolic substances in bogs due to low pH and anoxic conditions. We concluded that heating at the higher latitudes will increase decomposition and feedback on the nitrogen cycle due to the increased mineralization of organic nitrogen compounds, although the peat system will be less affected due to pH inhibition.
    Geochimica et Cosmochimica Acta 12/2013; · 3.88 Impact Factor
  • AGU Fall Meeting, San Francisco; 12/2013
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    Carolin Thoms, Gerd Gleixner
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    ABSTRACT: The linkage between tree diversity and the soil food web in temperate deciduous forest ecosystems remains uncertain. Using microbial phospholipid fatty acids (PLFAs), we analyzed the effect of tree species composition on microbial communities from topsoil collected in Hainich National Park, Germany. Previous results had shown minimal direct effects of tree species on the microbial community in autumn, most likely due to low plant activity and high nutrient and energy input from litterfall. However, microbial composition was affected indirectly through an influence of tree species on soil pH. In this study, we analyzed PLFA profiles in early summer and compared them with the results from autumn sampling. We hypothesized that plant-based traits would have stronger direct effects on the abundance and structure of the microbial community during the photosynthetically active period. The results showed that the soil microbial community differed more markedly between the tree diversity levels in early summer than in autumn. The acidifying character of the decaying beech litter strongly influenced the soil pH values and structured the soil microbial community indirectly in early summer as it had in autumn. However, the measured differences in the microbial composition in early summer could be attributed primarily to litter quality. This direct influence of plant traits appeared to be eclipsed in autumn because of the high nutrient supply from fresh litter input. Following litter decomposition in the topsoil, however, litter-based plant traits emerged as a factor structuring the soil microbial community in early summer. Our results suggest that the PLFAs i14:0 and i15:0, indicative of Gram-positive bacteria, are strongly involved in decomposition processes and may be promoted by readily available nutrients. Furthermore, our results indicate that a dense root network in association with arbuscular mycorrhizal fungi strongly supported microbial growth in the more diverse forest stands. High proportions of arbuscular mycorrhizal fungi (PLFA 16:1ω5), root-associated microorganisms (PLFAs 16:1ω9, 16:1ω7, 17:1ω8 and 18:1ω7) and bacterial grazers (PLFA 20:5) characterized the microbial community in early summer on these study plots. We conclude that microbial communities are strongly influenced by abiotic controls. However, seasonal differences in litter decomposition rates and root activity should be considered in the analysis of the effects of tree diversity or species on soil microbial communities.
    Soil Biology and Biochemistry 11/2013; 66:239-248. · 4.41 Impact Factor
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    Quaternary International 11/2013; · 2.13 Impact Factor
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    Ashish Malik, Gerd Gleixner
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    Dataset: Removed
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    Gerd Gleixner
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    ABSTRACT: Current attempts to explain the persistence of carbon in soils focuses on explanations such as the recalcitrant plant residues and the physical isolation of substrates from decomposers. A pool of organic matter that can persist for centuries to millennia is hypothesized because of the evidence provided by the persistence of pre-disturbance C in fallow or vegetation change experiments, and the radiocarbon age of soil carbon. However, new information, which became available through advances in the ability to measure the isotope signatures of specific compounds, favors a new picture of organic matter dynamics. Instead of persistence of plant-derived residues like lignin in the soil, the majority of mineral soil is in molecules derived from microbial synthesis. Carbon recycled multiple times through the microbial community can be old, decoupling the radiocarbon age of C atoms from the chemical or biological lability of the molecules they comprise. In consequence is soil microbiology, a major control on soil carbon dynamics, which highlights the potential vulnerability of soil organic matter to changing environmental conditions. Moreover, it emphasizes the need to devise new management options to restore, increase, and secure this valuable resource.
    Ecological Research 09/2013; · 1.55 Impact Factor
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    Ashish Malik, Gerd Gleixner
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    ABSTRACT: Soil dissolved organic carbon (DOC) sources and its seasonal dynamics are poorly known. We aimed to determine the contribution of plant and soil organic matter (SOM) to size classes of DOC in a field experiment with C3 to C4 vegetation change on two soil types through different seasons. Stable isotope ratios of DOC size classes were measured using size-exclusion chromatography (SEC) coupled on-line to liquid chromatography-isotope ratio mass spectrometry (LC-IRMS). SEC resolved DOC into three size classes: very high molecular weight/vHMW (>10 kDa), high molecular weight/HMW (0.4-10 kDa) and low molecular weight/LMW (< 0.4 kDa). HMW DOC was most abundant in all seasons, soil types and depths. In contrast, vHMW DOC was only seen post snowmelt in upper 20 cm and was mainly (87±9%) plant-derived. Through all seasons, HMW and LMW DOC had less than 30% recent plant contribution. Similar size range and source of DOC size classes and soil chloroform fumigation extracts suggest microbial origin of DOC. Thus microbial SOM recycling is an important process in DOC production. We suggest that DOC molecules get partitioned manifold between soil solution and the mineral matrix (chromatography) thereby getting constantly decomposed, altered or produced anew by soil microorganisms (reactive transport). This article is protected by copyright. All rights reserved.
    FEMS Microbiology Ecology 07/2013; · 3.56 Impact Factor

Publication Stats

3k Citations
348.60 Total Impact Points

Institutions

  • 1999–2014
    • Max Planck Institute for Biogeochemistry Jena
      • Department of Biogeochemical Processes
      Jena, Thuringia, Germany
    • University of Rostock
      • Faculty of Agricultural and Environmental Sciences
      Rostock, Mecklenburg-Vorpommern, Germany
  • 2000–2013
    • Friedrich-Schiller-University Jena
      • • Institut für Ökologie
      • • Department of Geosciences
      Jena, Thuringia, Germany
  • 2011
    • Helmholtz Zentrum München
      München, Bavaria, Germany
  • 2010
    • Bayerisches Landesamt für Umwelt
      Augsberg, Bavaria, Germany
  • 2009
    • University of Vienna
      • Department of Terrestrial Ecosystem Research
      Vienna, Vienna, Austria
    • University of California, Berkeley
      • Department of Integrative Biology
      Berkeley, CA, United States
  • 2008
    • Northeast Institute of Geography and Agroecology
      • Institute of Tibetan Plateau Research
      Beijing, Beijing Shi, China
    • University of Nottingham
      • School of Geography
      Nottingham, ENG, United Kingdom
  • 2006
    • Hohenheim University
      • Institute of Food Chemistry
      Stuttgart, Baden-Wuerttemberg, Germany
  • 2005
    • University of Southern Denmark
      • Center for Experimental Bioinformatics
      Copenhagen, Capital Region, Denmark
  • 2004
    • Christian-Albrechts-Universität zu Kiel
      • Leibniz-Labor für Altersbestimmung und Isotopenforschung
      Kiel, Schleswig-Holstein, Germany