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    ABSTRACT: Carbohydrates represent up to 25% of soil organic matter and derive from fresh plant input or organic matter transformation within the soil. Compound-specific isotope analysis (CSIA) of monosaccharides (sugars) extracted from soil provides a powerful tool to disentangle the dynamics of different carbohydrate pools of soils. The use of high-performance liquid chromatography/oxidation/isotope ratio mass spectrometry (HPLC/o/IRMS) allows isotope measurements without the need for derivatisation and thus increasing accuracy and precision of the isotopic measurement, compared with gas chromatography/combustion/isotope ratio mass spectrometry (GC/c/IRMS). The CSIA of soil carbohydrates was performed using a HPLC/o/IRMS system. The chromatographic and mass spectrometric subunits were coupled with a LC-Isolink interface. Soil sugars were extracted after mild hydrolysis using 4 M trifluoroacetic acid (TFA). Chromatographic separation of the sugars was achieved using a low strength 0.25 mM NaOH solution as mobile phase at a flow rate of 250 μL min(-1) at 10 °C. The chromatographic conditions allowed the baseline separation of the seven most abundant sugars in soil. Complete removal of TFA from the soil hydrolysate ensured chromatographic stability. The accuracy was better than 0.66 ‰ for amounts of >2.5 nM sugar on column. The sugars extracted from an agricultural soil appeared to be more enriched in (13) C than the soil organic carbon, and to have a similar isotopic signature to the soil microbial biomass. The proposed method proved to be suitable for the analysis of the common sugars in soil extracts and represents a precise tool for the study of carbohydrate dynamics. Copyright © 2013 John Wiley & Sons, Ltd.
    No preview · Article · Nov 2013 · Rapid Communications in Mass Spectrometry
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    ABSTRACT: Cadmium (Cd) is a phytotoxic heavy metal that causes rapid growth reduction. To investigate if Cd interferes with the metabolism of auxin, a major growth hormone in plants, poplars (Populus×canescens) expressing a heterologous GH3::GUS reporter gene were exposed to 50 μM Cd in hydroponic solutions. Growth, photosynthetic performance, lignification, peroxidase activity, auxin concentration, and GUS staining were determined in order to record the activities of GH3 enzymes in the stem apex, the elongation zone, wood in the zone of radial growth, and in roots. Cd-induced growth reductions were tissue-specific decreasing in the order: roots>wood>shoot elongation and leaf initiation, whereas Cd concentrations increased in the order: leaves<wood<roots. Cd almost abolished the GH3 signal in the stem apex but caused strong increases in the vascular system of roots as well as in parenchymatic cells in the xylem. These changes were accompanied by increases in lignin and peroxidase activities and decreases in auxin concentrations. Since GH3 enzymes remove auxin from the active pool by conjugation and act as mediators between growth and defence, our data suggest that Cd stress triggered increases in GH3 activities which, in turn, depleted auxin in wood and thereby shunted the metabolism to enhanced formation of lignin.
    Full-text · Article · Dec 2011 · Journal of Experimental Botany
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    ABSTRACT: Aquifers within agricultural catchments are characterised by high spatial heterogeneity of their denitrification potential. Therefore, simple but sophisticated methods for measuring denitrification rates within the groundwater are crucial for predicting and managing N-fluxes within these anthropogenic ecosystems. Here, a newly developed automated online 15N-tracer system is presented for measuring (N2+N2O) production due to denitrification in aquifer samples. The system consists of a self-developed sampler which automatically supplies sample aliquots to a membrane-inlet mass spectrometer. The developed system has been evaluated by a 15N- nitrate tracer incubation experiment using samples (sulphidic and non-sulphidic) from the aquifer of the Fuhrberger Feld in northern Germany. It is shown that the membrane-inlet mass spectrometry (MIMS) system successfully enabled nearly unattended measurement of (N2+N2O) production within a range of 10 to 3300 μg N L-1 over 7 days of incubation. The automated online approach provided results in good agreement with simultaneous measurements obtained with the well-established offline approach using isotope ratio mass spectrometry (IRMS). In addition, three different 15N-aided mathematical approaches have been evaluated for their suitability to analyse the MIMS raw data under the given experimental conditions. Two approaches, which rely on the measurement of 28N 2, 29N2 and 30N2, exhibit the best reliability in the case of a clear 15N enrichment of evolved denitrification gases. The third approach, which uses only the ratio of 29N2/28N2, overestimates the concentration of labelled denitrification products under these conditions. By contrast, at low 15N enrichments and low fractions of denitrified gas, the latter approach is on a par with the other two approaches. Finally, it can be concluded that the newly developed system represents a comprehensive and simply applicable tool for the determination of denitrification in aquifers.
    No preview · Article · Jul 2011 · Rapid Communications in Mass Spectrometry
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