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The carbon isotopic composition (δ13C) of foliage is often used as proxy for plant performance. However, the effect of N O 3 – vs. N H 4 + supply on δ13C of leaf metabolites and respired CO2 is largely unknown. We supplied tobacco plants with a gradient of N O 3 – to N H 4 + concentration ratios and determined gas exchange variables, concentrations and δ13C of tricarboxylic acid (TCA) cycle intermediates, δ13C of dark-respired CO2, and activities of key enzymes nitrate reductase, malic enzyme and phosphoenolpyruvate carboxylase. Net assimilation rate, dry biomass and concentrations of organic acids and starch decreased along the gradient. In contrast, respiration rates, concentrations of intercellular CO2, soluble sugars and amino acids increased. As N O 3 – decreased, activities of all measured enzymes decreased. δ13C of CO2 and organic acids closely co-varied and were more positive under N O 3 – supply, suggesting organic acids as potential substrates for respiration. Together with estimates of intra-molecular 13C enrichment in malate, we conclude that a change in the anaplerotic reaction of the TCA cycle possibly contributes to 13C enrichment in organic acids and respired CO2 under N O 3 – supply. Thus, the effect of N O 3 – vs. N H 4 + on δ13C is highly relevant, particularly if δ13C of leaf metabolites or respiration is used as proxy for plant performance. [ABSTRACT FROM AUTHOR]

Balsamic vinegars are important and well-acknowledged products and have become more important all over Europe during the recent past. For their analytical control, stable isotope methods play an important role to check the authenticity of the raw materials applied. For vinegar, but not yet for balsamic vinegar analysis, stable isotope methods using hydrogen, carbon, and oxygen isotope analyses by isotope ratio mass spectrometry and2H-NMR have already been introduced as official methods. Nevertheless, the official procedure can be also applied for balsamic vinegars. The evaluation of the stable isotope parameters obtained for the ingredients of balsamic vinegars requires a knowledge and understanding of the natural and industrial processes on which the production of balsamic vinegars is based. Ranges and ‘cut-off’ values for the multi element stable isotope parameters of balsamic vinegars are described, and a suitable analytical strategy is suggested. [ABSTRACT FROM AUTHOR]

The article presents career profile of chemistry professor, Hanns-Ludwig Schmidt.

Many physical and chemical processes in living systems are accompanied by isotope fractionation on H, C, N, O and S. Although kinetic or thermodynamic isotope effects are always the basis, theirin vivomanifestation is often modulated by secondary influences. These include metabolic branching events or metabolite channeling, metabolite pool sizes, reaction mechanisms, anatomical properties and compartmentation of plants and animals, and climatological or environmental conditions. In the present contribution, the fundamentals of isotope effects and their manifestation underin vivoconditions are outlined. The knowledge about and the understanding of these interferences provide a potent tool for the reconstruction of physiological events in plants and animals, their geographical origin, the history of bulk biomass and the biosynthesis of defined representatives. It allows the use of isotope characteristics of biomass for the elucidation of biochemical pathways and reaction mechanisms and for the reconstruction of climatic, physiological, ecological and environmental conditions during biosynthesis. Thus, it can be used for the origin and authenticity control of food, the study of ecosystems and animal physiology, the reconstruction of present and prehistoric nutrition chains and paleaoclimatological conditions. This is demonstrated by the outline of fundamental and application-orientated examples for all bio-elements. The aim of the review is to inform (advanced) students from various disciplines about the whole potential and the scope of stable isotope characteristics and fractionations and to provide them with a comprehensive introduction to the literature on fundamental aspects and applications. [ABSTRACT FROM AUTHOR]

Carbon isotope composition in respired CO2and organic matter of individual organs were measured on peanut seedlings during early ontogeny in order to compare fractionation during heterotrophic growth and transition to autotrophy in a species with lipid seed reserves with earlier results obtained on beans. Despite a high lipid content in peanut seeds (48 %) compared with bean seeds (1.5 %), the isotope composition of leaf- and root-respired CO2as well as its changes during ontogeny were similar to already published data on bean seedlings: leaf-respired CO2became13C-enriched reaching −21.5 ‰, while root-respired CO2became13C-depleted reaching around −31 ‰ at the four-leaf stage. The opposite respiratory fractionation in leaves vs. roots already reported for C3herbs was thus confirmed for peanuts. However, contrarily to beans, the peanut cotyledon-respired CO2was markedly13C-enriched, and its13C-depletion was noted from the two-leaf stage onwards only. Carbohydrate amounts being very low in peanut seeds, this cannot be attributed solely to their use as respiratory substrate. The potential role of isotope fractionation during glyoxylate cycle and/or gluconeogenesis on the13C-enriched cotyledon-respired CO2is discussed. [ABSTRACT FROM AUTHOR]

Although the instrumental coupling of gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-Py-IRMS) for compound-specific δ18O analysis has been commercially available for more than a decade, this method has been hardly applied so far. Here we present the first GC-Py-IRMS δ18O results for trimethylsilyl-derivatives of plant sap-relevant sugars and a polyalcohol (glucose, fructose, sucrose, raffinose and pinitol). Particularly, we focus on sucrose, which is assimilated in leaves and which is the most important transport sugar in plants and hence of utmost relevance in plant physiology and paleoclimate studies. Replication measurements of sucrose standards and concentration series indicate that the GC-Py-IRMS δ18O measurements are not stable over time and that they are amount (area) dependent. We, therefore, suggest running sample batch replication measurements in alternation with standard concentration series of reference material. This allows for carrying out (i) a drift correction, (ii) a calibration against reference material and (iii) an amount (area) correction. Tests with18O-enriched water do not provide any evidence for oxygen isotope exchange reactions affecting sucrose and raffinose. We present the first application of GC-Py-IRMS δ18O analysis for sucrose from needle extract (soluble carbohydrate) samples. The obtained δ18Osucrose/ Vienna Standard Mean Ocean Water (VSMOW)values are more positive and vary in a wider range (32.1–40.1 ‰) than the δ18Obulk/ VSMOWvalues (24.6–27.2 ‰). Furthermore, they are shown to depend on the climate parameters maximum day temperature, relative air humidity and cloud cover. These findings suggest that δ18Osucroseof the investigated needles very sensitively reflects the climatically controlled evaporative18O enrichment of leaf water and thus highlights the great potential of GC-Py-IRMS δ18Osucroseanalysis for plant physiology and paleoclimate studies. [ABSTRACT FROM AUTHOR]

Continuous analysis of the 13C/12C ratio of atmospheric CO2 (δ13C-CO2) is a powerful tool to quantify CO2 flux strengths of the two major ecosystem processes assimilation and respiration. Traditional laboratory techniques such as isotope ratio mass spectrometry (IRMS) in combination with flask sampling are subject to technical limitations that do not allow to fully characterising variations of atmospheric δ13C-CO2 at all relevant timescales. In our study, we demonstrate the strength of Fourier transform infrared (FTIR) spectroscopy in combination with a PLS-based calibration strategy for online analysis of δ13C-CO2 in ambient air. The ability of the instrument to measure δ13C-CO2 was tested on a grassland field-site and compared with standard laboratory-based IRMS measurements made on field-collected flask samples. Both methods were in excellent agreement, with an average difference of 0.4‰ (n=81). Simultaneously, other important trace gases such as CO, N2O and CH4 were analysed by FTIR spectroscopy. [ABSTRACT FROM AUTHOR]

The long-term 'biodegradation' on soil amino acids was examined in the control plots of '42 parcelles' experiment, established in 1928 at INRA, Versailles (France). None of the plots is cultivated, but is kept free of weeds, and mixed to a depth of 25 cm twice yearly. Topsoil (0-10 cm depth) samples collected in 1929, 1963 and 1997 were subjected to acid hydrolysis (6 N HCl) for comparison. The distribution and δ 15 N natural abundance of 20 individual amino acids in the soils were determined, using ion chromatography (IC) and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The total N and amino acid-N (AA-N), respectively, decreased by 54 % and 73 % in the period from 1929 to 1997. The average N loss was comparable for 1929-1963 (period 1) and 1963-1997 (period 2), but AA-N loss was three times faster in the former period. This significant reduction in total AA-N content was mirrored in the individual amino acids, which decreased by 74 % ± 1 % (ranging 58-89 %) between 1929 and 1997. The bulk δ 15 N values generally increased from 1929 to 1997, mainly associated with comparable or even higher increase of δ 15 N of the non-AA-N in the soil. The residence time ( t 1/2 , time in which half of N was lost from a specific soil pool) was ca. 65 ± 5 years for the bulk soil, and comparable for periods 1 and 2. However, between periods 1 and 2 it decreased from 128 to 41 years in the non-AA pool, but increased from 59 to 92 years in the AA-N pool. Proline and amino acids that appear early in soil microbial metabolic pathways ( e.g. glutamic acid, alanine, aspartic acid and valine) had relatively high δ 15 N values. Phenylalanine, threonine, glycine and leucine had relatively depleted δ 15 N values. The average δ 15 N value of the individual amino acids (IAAs) increased by 1δ unit from 1929 to 1997, associated with a similar rise from 1929 to 1963, and no change thereafter till 1997. However, the δ 15 N values of phenylalanine decreased by more than 7δ 15 N units between 1929 and 1997. The δ 15 N shift of IAAs from 1929 to 1963 and from 1929 to 1997 was not influenced by the relative amount of N remaining compared with the 1929 soil concentrations. The only exception was phenylalanine which showed decreasing δ 15 N associated with its decreasing concentration in the soil. We conclude therefore that in the absence of plant and fertiliser inputs, no change in the δ 15 N value of individual soil amino acids occurs, hence the original δ 15 N values are preserved and diagnostic information on past soil N (cycling) is retained. The exception was phenylalanine, its δ 15 N decreased with decreasing concentration from 1929 to 1997, hence it acted as a 'potential' marker for the land use changes ( i.e. arable cropping to a fallow). The long term biological processing and reworking of residual amino acids resulted in a (partial) stabilisation in the soil, evidenced by reduced N loss and increased residence time of amino acid N during the period 1963-1997. * Revised version of the Isotopenpreis winner's contribution to the 26 th Annual Meeting of the German Association for Stable Isotope Research (GASIR) October, 6-8, 2003, Cologne, Germany. ‡ Current address: Institut für Pflanzenwissenschaften, ETH Zürich, 8092 Zürich, Switzerland. [ABSTRACT FROM AUTHOR]

Oxygen is a globally important element, in inorganic compounds it is involved in key structural compounds of the earth, and it is providing functional groups for most organic compounds. Oxygen isotope ratio analyses on these compounds provide information on the oxygen sources and (formation) reactions in which the compound was involved. Therefore generally applicable analytical methods for the δ 18 O determination are highly desirable. After a description of online high temperature "carbon reduction" methods for the conversion of oxygen in the compounds mentioned into CO and discussion of problems involved, especially in analysis of inorganic substances like carbonates and silicates, selected examples for the application of these carbon reduction methods will be presented. The well-known correlation of δ 18 O values of cellulose (in tree rings) to that of (leaf) water is used since the 1970's as climate indicator. The observed enrichment in 18 O in cellulose by about 27‰ in comparison to leaf water is attributed to an oxygen equilibrium isotope effect between carbonyl groups and water. But not all carbohydrates show this "general" 18 O enrichment relative to water. By means of a recently published model a non-statistical oxygen isotope distribution in carbohydrates is postulated. Oxygen isotope discrimination has been recognized long ago as an important principle of authenticity evaluation in food and beverages. Though many basic mechanisms of isotope discrimination in nature are known, the corresponding application of data is often based only on empirical observations in this field. The fact that oxygen in natural organic plant material is derived from three sources (CO 2 , H 2 O, O 2 ) with distinct differences in δ 18 O and that their incorporation by different reactions implies oxygen isotope effects of different sizes, is therefore of special importance, and it is attempted by means of individual isotopic increments of functional groups to predict global δ 18 O values of natural and nature-identical compounds. Vice versa δ 18 O values can also give hints on the elucidation of biosynthetic pathways. [ABSTRACT FROM AUTHOR]