Jahrestagung der Arbeitsgemeinschaft
Stabile Isotope e.V.
26.–29. September 2021 | TU Darmstadt
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Poster Kurzvorträge - zu Themenblock 4; 1; 5
|Zusammenfassung der Sitzung|
Block 4: Ökosysteme
10:30 - 10:33
Using in-situ and destructive measurements of stable water isotopes to quantify ecohydrological feedback processes of different forest stands
Albert-Ludwigs-Universität Freiburg, Professur für Hydrologie, Deutschland
Stable water isotopes are a promising tracer for studying water movement through ecosystems. Traditionally, destructive sampling techniques are applied to measure the isotopic signature in soils and plant xylem but these methods are limited in their temporal resolution and have proven to be fraught with uncertainty. Recent development of in-situ membrane-based probes for direct measurements of soil and tree xylem water isotopes (SWIP) allow continuous observations along soil profiles or within trees at different heights. Such new in-situ measurements provide an unprecedented combination of high temporal and spatial resolution data. Also, by using the same probes for the soil as well as the plant compartment, all measurements can be compared directly.
Here, we present preliminary results of our in-situ isotope measuring platform from different forest stands in the Black Forest (Germany). The measurement setup encompasses three experimental treatments: i) pure beech, ii) pure spruce and iii) mixed beech and spruce stands. By measuring soil water in different depths as well as xylem water at different heights, we will not only identify species-specific differences in their water uptake patterns but also the impact of interspecific competition for water. Additional destructive measurements of stable water isotopes from throughfall, stemflow, soil and tree xylem water will be used to gain further information but also to compare in-situ with destructive isotope measurement techniques.
10:33 - 10:36
Antibiotics increase methane production rates in freshwater sediments: Evidence from an anaerobic incubation
1iES Landau, Institute for Environmental Sciences, University of Koblenz-Landau; 2Eusserthal Ecosystem Research Station, University of Koblenz-Landau; 3Department of Molecular Ecology, University of Technology Kaiserslautern; 4Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
Methane (CH4) is after carbon dioxide (CO2) the second most important greenhouse gas and is inter alia produced in natural freshwater ecosystems. In the face of increasing CH4 emissions from natural sources, researchers have investigated environmental factors and climate change feedbacks to explain this increment. Despite being omnipresent in freshwaters, knowledge on the influence of chemical stressors of anthropogenic origin (e.g. antibiotics) on methanogenesis is not present to date. To address this knowledge gap, we incubated freshwater sediment for 42 days under anaerobic conditions in presence of a five-component antibiotic mixture at four levels (from 0 to 5000 µg/L). Weekly measurements of CH4 and CO2 in the headspace showed that the CH4 production rate can be increased by up to 94% at 5000 µg/L and up to 29% at field-relevant concentrations (i.e., 50 µg/L). The compound-specific δ13C values of CH4 and CO2 indicate that the processing dynamics are changed while the successional stages are not. Despite the complications of transferring experimental CH4 production rates to realistic field relevant CH4 emissions, the study suggests that chemical stressors contribute to the emissions of greenhouse gases by affecting the methanogenesis in freshwaters.
10:36 - 10:39
Exploring fundamentals of quantitative 13CO2/12CO2 tracer studies of CO2 exchange and biomass in plants: assessment of system performance and determination of isotopic end-members for mixing model
Technical University of Munich, Deutschland
Labelling with carbon isotopes is the technique of choice to study carbon dynamics in plants, including CO2 exchange, biomass and carbohydrates. Labelling experiments consist of two phases: An establishment phase, where plants are grown in the presence of CO2 with constant isotopic composition, and a labeling phase, where the establishment CO2 is replaced by a CO2 with differing isotopic composition. However, labelling systems can be prone to technical artifacts like contamination with extraneous CO2, fluctuations of the isotopic composition of the establishment and labelling CO2 etc. Also, the accurate determination of carbon tracer kinetics requires an accurate determination of the two end-members for isotopic mixing models. So far, systematic testing of labelling systems has been rare and incomplete. Here, we present details of a chamber labelling system for plant mesocosms and the analysis of its performance with respect to possible technical artifacts. This also includes the analysis of different approaches for the end-member determination. We performed labelling experiments with perennial ryegrass (Lolium perenne L.) combined with 13CO2/12CO2 gas exchange and carbohydrate measurements, in growth chambers under three CO2 concentrations: 200, 400, and 800 mmol mol-1. Each treatment was run in two growth chambers, with identical growth conditions but with two different CO2 sources (13C-depleted: δ13C -43.5 ‰ or 13C-rich: δ13C -5.6 ‰). After the establishment phase, the CO2 supplied to each chamber was switched from depleted to enriched or vice versa for a 7 days-long labelling phase. When gas exchange rates were approximately steady on a day-by-day basis, CO2 concentrations and δ13C in the chambers were also virtually constant over time. The spread in δ13C of the CO2 sources during the establishment phase matched the spread in δ13C of the two CO2-sources at the chamber outlets at all CO2 concentrations, showing that chamber CO2 was not contaminated with extraneous CO2. This was also confirmed by the close correspondence of C-isotope discrimination (Δ) during gas exchange in the light at every CO2 concentration. However, due to inevitable opening of the chambers during maintenance and plant sampling operations, Δ determined on respiratory CO2, shoot and root biomass as well as shoot carbohydrates was slightly (1.1 ‰), but consistently (P < 0.01) smaller in the 13C-depleted relative to the 13C-rich CO2 chambers during the establishment phase. Thus, for precise analyses of tracer kinetics in respiratory CO2, biomass or carbohydrates, the determination of the end-members of the mixing model had to be based on sample type-specific Δ measurements.
10:39 - 10:42
Unravelling the diet of extinct cave bears in Romania using δ15N isotopic analysis of amino acids
1Senckenberg Gesellschaft für Naturforschung, Deutschland; 2Universität Tübingen, Deutschland; 3Nagoya University Museum, Japan
Compound specific isotopic analysis of individual amino acids (CSIA-AA) was performed to unravel dietary information on Late Pleistocene cave bears (Ursus spelaeus). In contrast to other regions of Europe, U. spelaeus from Romaniashowed variable and exceptionally high δ15N values (5.2 to 9.8‰) that leads to speculation of meat consumption. The CSIA-AA approach used is unique in that it offsets the natural baseline δ15N variation (e.g. environmental, behavioural or physiological traits). It can thereby provide a more accurate estimate of trophic position (TP).
Amino acids from ancient bone collagen of U. spelaeus were derivatized, separated via gas chromatography, combusted/reduced, then measured for δ15N using stable isotope mass spectrometry (GC-C-IRMS). This method is based on the differential fractionation of two amino acid groups: trophic AAs (i.e., glutamic acid) that fractionate 15N greatly (~8.0‰) compared to source AAs (i.e., phenylalanine) that fractionate 15N very little (~0.4‰) per trophic step. The latter (δ15Nphe) thus reflects the nitrogen source baseline (i.e. the primary producers) of the ecosystem.
Results rule out (i) significant dietary aquatic resources; (ii) carnivory as the main feeding behaviour. Rather, TPs of 1.8–2.2 (N = 6) are indicative of a plant-dependent diet, including for those cave bears with high bulk δ15N values. Using CSIA-AA, TPs of 1.9-2.1 were determined for U. spelaeus confirming a pure herbivorous diet (see Figure 1). Bulk collagen δ15N values of can be explained by (i) a δ15N shift of the baseline in the local ecosystem, and/or (ii) the consumption of some specific plants with high δ15N values. Our findings have interesting implications regarding the evolution of herbivory among carnivorans. Furthermore, understanding feeding behaviour of U. spelaeus may provide key insights into their extinction.
We used an Agilent 7890B GC coupled to an Elementar GC5 Interface module in line with a reduction furnace, cryogenic trap (LN2) and an IsoPrime 100 IRMS.
Naito, Y.I., Meleg, I.N., Robu, M. et al. Heavy reliance on plants for Romanian cave bears evidenced by amino acid nitrogen isotope analysis. Sci Rep 10, 6612 (2020). https://doi.org/10.1038/s41598-020-62990-0
10:42 - 10:45
Development of an open-split-based dual-inlet system for mass spectrometers
1Universität Bern, Schweiz; 2Oeschger Centre for Climate Change Research
The inlet system integrated into the Elementar isoprime precisION is a changeover-valve-based dual-inlet system which is not ideally suitable for high-precision measurements of elemental and stable isotope ratios. In order to attain higher precisions an open-split-based dual-inlet system was designed and built by the Climate and Environmental Physics Division of the University of Bern featuring almost no metallic surfaces and altering the pressure of the measured gases in the ionization chamber as little as possible. By means of these two measures the occurrence of fractionation processes during the transfer of gases from the gas containers to the mass spectrometer as well as in the ionization chamber is noticeably reduced by the in-house built dual-inlet system when compared to the dual-inlet system built by Elementar.
10:45 - 10:48
Tracing nitrogen transformations induced by 15N labelled cattle slurry applied with different techniques in winter wheat
Thünen-Institut für Agrarklimaschutz, Deutschland
The effects of slurry application techniques on ammonia (NH3) volatilisation and nitrous oxide (N2O) fluxes are well documented. However, application techniques may also impact dinitrogen (N2) fluxes, as they can influence denitrification activity by changing slurry and soil aeration (e.g. by injection techniques), nitrate formation (e.g. by adding nitrification inhibitors) and the pH value (e.g. by slurry acidification). Up to now, measuring N2 fluxes and following pathways of slurry nitrogen (N) transformation under field conditions is still challenging.
Thus, we applied a combined 15N labelling approach including slurry NH4+-N and soil NO3--N in undisturbed soil cores, set up as lysimeters and with growing winter wheat for a study period of 60 days. Slurry treatments include the following application techniques: trailing hose with and without acidification (H2SO4), slot injection with and without nitrification inhibitor (DMPP). Soil cores without slurry application were used as control. In a first step, soil nitrate was 15N labelled by homogeneous injection of a K15NO3- solution at a low N application rate (4 kg N ha-1), while one week later, 68 kg N ha-115N-labelled cattle slurry was applied. The 15N labelled cattle slurry consisted of fresh dairy cattle faeces (natural abundance), water and 15N labelled synthetic urine. N2O and N2 emission were measured using the modified 15N gas flux method with N2-depleted atmosphere. To close the N balance and follow the different N transformation pathways, 15N losses by leaching, 15N uptake by plant and residual 15N in belowground biomass, microbial biomass and soil were analysed by IRMS.
The major gaseous loss pathway was NH3 with up to 8 kg N ha-1 in the trailing hose treatment, while slot injection significantly reduced NH3-N losses. Regardless the application technique, N2O fluxes were very low (up to 0.1 kg N2O-N ha-1), while N2 reached up to 3 kg N ha-1. The N2O/(N2O+N2) ratio of dentification was always <0.1. The main pathways of the total N budget were gaseous N losses (NH3, N2O, N2) with 11-44%, soil N pool with 32-48% and plant uptake with 18-26% of 15N applied. N leaching and changes in the residual mineral nitrogen pool played only a minor role in the total N balance. Although there were no differences in the application techniques, it should be highlighted that the 15N recovery was almost complete, indicating that the experiment was able to capture the relevant 15N fates with the comprehensive setup that was applied.
10:48 - 10:50
Applying the 15N gas flux method in a lab incubation as an alternative to laborious field studies
1Thünen Institut für Agrarklimaschutz, Deutschland; 2Universität Trier, Raum- und Umweltwissenschaften, Bodenkunde, Deutschland
Applying the 15N gas flux method (15NGF) in the field can be very challenging. The establishment of a reliable setup is time consuming, expensive, and requires a decent infrastructure at the field sites. Additionally, the atmospheric N2 background reduces measurement precision for detecting low tracer-derived N2 emissions. We incubated undisturbed soil cores (14.4 cm diameter and 35 cm height) from two remote field sites: an annual cropping system (Zea mays) and a perennial cropping system (Silphium perfoliatum). The incubation took place in a fully-automated facility, which provided us with an N2-reduced atmosphere, options to control temperature, irrigation and drainage, and allowed better control over the homogeneity of 15N-nitrate pool labelling, as compared to what is possible in the field. Using the 15NGF method with undisturbed soil cores allowed us to quantify differences in source-specific N2 and N2O emissions while including the effect of soil structure under dynamic waterlogged conditions. Additional information about nitrogen transformation processes between the cropping systems were obtained in bulk soil by analysing soil mineral 15N (NO3- and NH4+) via membrane-inlet mass spectrometry. The incubation experiment consisted of three different phases with increasing soil water content: (1) entire core just below field capacity; (2) lower 10 cm waterlogged; and (3) lower 25 cm waterlogged. The soil from the S. perfoliatum field had a significantly lower product ratio of denitrification (N2O/N2+N2O) with increasing waterlogging than the Z. mays soil. However, pool-derived N2O emissions from the S. perfoliatum soil were not significantly lower than from Z. mays soil. Hence, we could show that the soil structure from the perennial cropping field resulted in higher N2 emissions rather than lower N2O emissions. Although perennial systems are generally expected to provide a greenhouse gas mitigation potential, we were able to replicate conditions that could not have been easily addressed in the field, and show that, in comparing soil from these fields, that was not the case.
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