SPIN-MIMS simplifying the SPIN-MAS instrumentation for online measurement of 15N-abundances of ammonium, nitrite and nitrate in aqueous solutions

Common methods for measuring selectively the 15N abundances in individual N-species such as NH4+, NO2- and NO3- in samples with multiple N-species are laborious and time consuming. The SPIN-MAS technique (Stange et al. 2007) offers an automated, rapid and selective determination of 15N abundances in NH4+, NO2- and NO3- in aqueous samples. During a SPIN-MAS measurement one of three different reaction solutions is mixed with the aqueous sample in a Sample Preparation unit for Inorganic N-species (SPIN). The reaction solution is chosen in dependence on the N-species of interest. The gaseous reaction products (N2 or NO) are then conducted to a quadrupole mass spectrometer (MAS) in a helium stream. This measurement technique is not commonly used due to its complex instrumentation. The instrumentation can be significantly simplified by the use of a membrane inlet mass spectrometer (MIMS). The presented SPIN-MIMS approach relies on the use of a reaction capillary in which the sample containing the N-species of interest is mixed with the corresponding reaction solution. The mixture of reaction solution and sample is pumped from the reaction capillary directly to the membrane inlet of the mass spectrometer. The reaction products (N2 or NO) formed during the reaction of NH4+, NO2- and NO3- with the reaction solutions are passed through the gas-permeable membrane of the inlet directly into the ion source of the mass spectrometer. 15N standards with different at% 15N (NH4+, NO2- and NO3- respectively in dist. Water) were used to assess the performance of the system. Overall, SPIN-MIMS measurements showed a good agreement between measured and expected 15N abundances (range 0.36 – 10 at% 15N deviations: <0.5 at% 15N for NH4+-, <0.23 for NO2-- and <0.15 at% 15N for NO3-- standards)

Turnover of soil monosaccharides: Recycling versus Stabilization

Soil organic matter (SOM) represents a mixture of differently degradable compounds. Each of these compounds are characterised by different dynamics due to different chemical recalcitrance, transformation or stabilisation processes in soil. Carbohydrates represent one of these compounds and contribute up to 25 % to the soil organic matter. Vascular plants are the main source of pentose sugars (Arabinose and Xylose), whereas hexoses (Galactose and Mannose) are primarily produced by microorganisms. Several studies suggest that the mean turnover times of the carbon in soil sugars are similar to the turnover dynamics of the bulk carbon in soil. The aim of the study is to characterise the influence of stabilisation and turnover of soil carbohydrates. Soil samples are collected from (i)a continuous maize cropping experiment (“Höhere Landbauschule” Rotthalmünster, Bavaria) established 1979 on a Stagnic Luvisol and (ii) from a continuous wheat cropping, established 1969, as reference site. The effect of stabilisation is estimated by the comparison of turnover times of microbial and plant derived soil carbohydrates. As the dynamics of plant derived carbohydrate are solely influenced by stabilisation processes, whereas the dynamics of microbial derived carbohydrates are affected by recycling of organic carbon compounds derived from C3 plant substrate as well as stabilisation processes. The compound specific isotopic analysis (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)

Stable isotope analysis (δ¹³C and δ¹⁵N) of soil nematodes from four feeding groups

Soil nematode feeding groups are a long-established trophic categorisation largely based on morphology and are used in ecological indices to monitor and analyse the biological state of soils. Stable isotope ratio analysis (13C/12C and 15N/14N, expressed as δ13C and δ15N) has provided verification of, and novel insights into, the feeding ecology of soil animals such as earthworms and mites. However, isotopic studies of soil nematodes have been limited to date as conventional stable isotope ratio analysis needs impractically large numbers of nematodes (up to 1,000) to achieve required minimum sample weights (typically >100 µg C and N). Here, micro-sample near-conventional elemental analysis–isotopic ratio mass spectrometry (μEA–IRMS) of C and N using microgram samples (typically 20 µg dry weight), was employed to compare the trophic position of selected soil nematode taxa from four feeding groups: predators (Anatonchus and Mononchus), bacterial feeders (Plectus and Rhabditis), omnivores (Aporcelaimidae and Qudsianematidae) and plant feeder (Rotylenchus). Free-living nematodes were collected from conventionally and organically managed arable soils. As few as 15 nematodes, for omnivores and predators, were sufficient to reach the 20 µg dry weight target. There was no significant difference in δ15N (p = 0.290) or δ13C (p = 0.706) between conventional and organic agronomic treatments but, within treatments, there was a significant difference in N and C stable isotope ratios between the plant feeder, Rotylenchus (δ15N = 1.08 to 3.22 mUr‰, δ13C = –29.58 to –27.87 mUr) and all other groups. There was an average difference of 9.62 mUr in δ15N between the plant feeder and the predator group (δ15N = 9.89 to 12.79 mUr, δ13C = –27.04 to –25.51 mUr). Isotopic niche widths were calculated as Bayesian derived standard ellipse areas and were smallest for the plant feeder (1.37 mUr2) and the predators (1.73 mUr2), but largest for omnivores (3.83 mUr2). These data may reflect more preferential feeding by the plant feeder and predators, as assumed by classical morphology-based feeding groups, and indicate that omnivory may be more widespread across detritivore groups i.e. bacterial feeders (3.81 mUr2). Trophic information for soil nematodes derived from stable isotope analysis, scaled as finely as species level in some cases, will complement existing indices for soil biological assessment and monitoring, and can potentially be used to identify new trophic interactions in soils. The isotopic technique used here, to compare nematode feeding group members largely confirm their trophic relations based on morphological studies

Die unterschätzte Rolle des Recyclings intakter Metabolite für die Umsatzraten der organischen Bodensubstanz

Obwohl Sorption an Mineraloberflächen als dominierender Prozess zur Erklärung des langsamen Umsatzes mineralassoziierter organischer Bodensubstanz (OBS) dient, widerspricht diese Idee einer zunehmenden Zahl an Inkubationsstudien, die zeigen, dass für niedermolekulare Substanzen nicht nur die mikrobielle Aufnahme kompetitivier als die Sorption ist, sondern auch sorbierte Substanzen in hohem Maße desorbiert und mikrobiell verwertet werden können. Dabei wurde gezeigt, dass sich die Verstoffwechselung desorbierter Substanzen zugunsten eines erhöhten Recyclings verschiebt. Dies wirft die Frage auf, ob Recycling von intakten Metaboliten, d.h. unter Erhalt des Kohlenstoffgerüstes, generell ein bisher stark unterschätzter Prozess ist, der die relativ hohen 14C Alter der OBS teilweise erklären kann. Nach Applikation hoher Toxindosen konnte nachgewiesen werden, dass die nachfolgende Reetablierung der mikrobiellen Gemeinschaft zu großem Anteil auf Recycling der Nekromasskomponenten der Vorgeneration basiert. Intaktes Metabolitrecycling ist jedoch unter steady-state Bedingungen nur äußerst schwierig von der direkten Stabiliserung zu unterscheiden. Um diesen Prozess im Fließgleichgewicht nachzuweisen muss 1) ein Biomolekül untersucht werden, dessen Biosyntheseweg so aufwändig ist, dass Recycling einen deutlichen Vorteil für die Zelle im Vergleich zur Neusynthese darstellt, 2) dieses Biomolkül in lebenden Zellen in einer anderen Form gebunden sein, als die zu recycelnde Einheit in der Bodenlösung, so dass beide Zustandsformen unterschieden werden können und 3) dieses Biomolekül positionsspezifisch isotopenmarkiert zugegeben werden, so dass über einen identischen Einbau der Positionen die Intaktheit des Kohlenstoffgerüstes nachgewiesen werden kann. Am Beispiel der Alkylketten von Fettsäuren, die in mikrobiellen Zellen primär als Phospholipide in den Membranen gebunden sind, soll dieses Prinzip veranschaulicht werden. Eine erste Abschätzung des intakten Recyclings von Alkylketten durch Mikroorganismen in Böden zeigt, dass von den 0.03% der basierend auf Alkyl-Kohlenstoff neugebildeten PLFA mehr als 75% aus intaktem Recycling dieser Ketten hervor gingen. Obwohl der Beitrag des Recyclings intakter Metabolite zur Umsatzzeit der gesamten OBS aufgrund der geringen Anzahl bisher untersuchter Metabolite noch nicht final quantifiziert werden kann, untermauern die hier vorgestellten Ergebnisse jedoch die hohe Relevanz dieses Prozesses für die Dynamik der OBS

Is tagging with visual implant elastomer a reliable technique for marking earthworms?

Visual implant elastomer (VIE) has recently been employed to investigate different aspects of earthworm ecology. However, a number of fundamental questions relating to the detection and positioning of the tag, its persistence and potential effects on earthworms remain unknown. Seven earthworm species belonging to three ecological groupings, with different pigmentation and burrowing behaviour, were tagged using different coloured VIE. External inspection after two days, one week and 1, 10 and 27 months were followed by preservation, dissection and internal inspection. Tags could be seen in living specimens to 27 months, and dissection revealed that in most cases they were lodged in the coelomic cavity, held in place by septa. However, over longer time periods (more than two years), the chlorogogenous tissue tended to bind to the tags and made external observation increasingly difficult. Migration of the VIE material towards the posterior of the earthworm and potential loss of the tag were only observed on rare occasions, and a recovery rate in excess of 98% was recorded. By introducing a reasonable amount of VIE into segments, just after the clitellum, this technique can become a valuable tool in earthworm ecology and life history studies, particularly in short-medium term laboratory and field experiments

Carbon sequestration and turnover in soil under the energy crop Miscanthus: Repeated ¹³C natural abundance approach and literature synthesis

© 2017 John Wiley & Sons Ltd. The stability and turnover of soil organic matter (SOM) are a very important but poorly understood part of carbon (C) cycling. Conversion of C 3 grassland to the C 4 energy crop Miscanthus provides an ideal opportunity to quantify medium-term SOM dynamics without disturbance (e.g., plowing), due to the natural shift in the δ 13 C signature of soil C. For the first time, we used a repeated 13 C natural abundance approach to measure C turnover in a loamy Gleyic Cambisol after 9 and 21 years of Miscanthus cultivation. This is the longest C 3 -C 4 vegetation change study on C turnover in soil under energy crops. SOM stocks under Miscanthus and reference grassland were similar down to 1 m depth. However, both increased between 9 and 21 years from 105 to 140 mg C ha -1 (P 9 years) increased with depth from 19 years (0-10 cm) to 30-152 years (10-50 cm), and remained stable below 50 cm. From 41 literature observations, the average SOM increase after conversion from cropland or grassland to Miscanthus was 6.4 and 0.4 mg C ha -1 , respectively. The MRT of total C in topsoil under Miscanthus remained stable at ~60 years, independent of plantation age, corroborating the idea that C dynamics are dominated by recycling processes rather than by C stabilization. In conclusion, growing Miscanthus on C-poor arable soils caused immediate C sequestration because of higher C input and decreased SOM decomposition. However, after replacing grasslands with Miscanthus, SOM stocks remained stable and the MRT of old C 3 -C increased strongly with depth

Determination of fungal activity in modified wood by means of micro-calorimetry and determination of total esterase activity

Beech and pine wood blocks were treated with 1,3-dimethylol-4,5-dihydroxyethylen urea (DMDHEU) to increasing weight percent gains (WPG). The resistance of the treated specimens against Trametes versicolor and Coniophora puteana, determined as mass loss, increased with increasing WPG of DMDHEU. Metabolic activity of the fungi in the wood blocks was assessed as total esterase activity (TEA) based on the hydrolysis of fluorescein diacetate and as heat or energy production determined by isothermal micro-calorimetry. Both methods revealed that the fungal activity was related with the WPG and the mass loss caused by the fungi. Still, fungal activity was detected even in wood blocks of the highest WPG and showed that the treatment was not toxic to the fungi. Energy production showed a higher consistency with the mass loss after decay than TEA; higher mass loss was more stringently reflected by higher heat production rate. Heat production did not proceed linearly, possibly due to the inhibition of fungal activity by an excess of carbon dioxide

Inter-laboratory comparison of cryogenic water extraction systems for stable isotope analysis of soil water

For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20 % gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for δ18O and δ2H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to −108.4 ‰ for δ2H and +11.8 to −14.9 ‰ for δ18O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.</p