Galactosamine and mannosamine are integral parts of bacterial and fungal extracellular polymeric substances.

Extracellular polymeric substances (EPS) are produced by microorganisms and interact to form a complex matrix called biofilm. In soils, EPS are important contributors to the microbial necromass and, thus, to soil organic carbon (SOC). Amino sugars (AS) are used as indicators for microbial necromass in soil, although the origin of galactosamine and mannosamine is largely unknown.

Intracellular carbon storage by microorganisms is an overlooked pathway of biomass growth.

The concept of biomass growth is central to microbial carbon (C) cycling and ecosystem nutrient turnover. Microbial biomass is usually assumed to grow by cellular replication, despite microorganisms' capacity to increase biomass by synthesizing storage compounds. Resource investment in storage allows microbes to decouple their metabolic activity from immediate resource supply, supporting more diverse microbial responses to environmental changes.

Evidence of considerable C and N transfer from peas to cereals via direct root contact but not via mycorrhiza.

Intercropping of legumes and cereals is an important management method for improving yield stability, especially in organic farming systems. However, knowledge is restricted on the relevance of different nutrient transfer pathways. The objective of the study was to quantify nitrogen (N) and carbon (C) transfer from peas to triticale by (1) direct root contact (= R), (2) arbuscular mycorrhizal fungi (AMF; = A), and (3) diffusion (= D).

Nitrogen isotope analysis of aqueous ammonium and nitrate by membrane inlet isotope ratio mass spectrometry (MIRMS) at natural abundance levels.

Rationale: Existing methods for the measurement of the N/ N isotopic composition of ammonium and nitrate are either only suitable for labelled samples or require considerable sample preparation efforts (or both). Our goal was to modify an existing analytical approach to allow for natural abundance precision levels.

Methods: Published reaction protocols were used to convert ammonium into N by NaOBr and nitrate into N O by TiCl .

Nitrite isotope characteristics and associated soil N transformations.

Nitrite (NO) is a crucial compound in the N soil cycle. As an intermediate of nearly all N transformations, its isotopic signature may provide precious information on the active pathways and processes. NO analyses have already been applied in N tracing studies, increasing their interpretation perspectives.

Contribution of the Fenton reaction and ligninolytic enzymes to soil organic matter mineralisation under anoxic conditions.

Mechanisms of carbon dioxide (CO) release from soil in the absence of oxygen were studied considering the Fenton process, which encompasses the reaction of HO with Fe(II) yielding a hydroxyl radical (OH), in combination with manganese peroxidase (MnP) and lignin peroxidase (LiP). This study aimed to explain the high rate of soil organic matter (SOM) mineralisation and CO release from humid temperate rainforest soils under oxygen-limited conditions. The investigated mechanisms challenge the traditional view that SOM mineralisation in rainforest is slow due to anaerobic (micro)environments under high precipitation and explain intensive CO release even under oxygen limitation.

NO Reduction to NO Improves Nitrate N Abundance Analysis by Membrane Inlet Quadrupole Mass Spectrometry.

Earlier an automated sample preparation unit for inorganic nitrogen (SPIN) coupled to a membrane inlet quadrupole mass spectrometer (MIMS) was developed for automated and sensitive determination of the N abundances and concentrations of nitrate, nitrite and ammonium of aqueous solutions without any sample preparation. Here we describe an alternative analytical protocol to convert NO to NO instead of NO before measurement. This is advantageous because NO strongly interacts with surfaces, requires long purge times, and still shows considerable carryover between samples, all of which is avoided when NO is used as analyte.

Preliminary assessment of stable nitrogen and oxygen isotopic composition of USGS51 and USGS52 nitrous oxide reference gases and perspectives on calibration needs.

Rationale: Despite a long history and growing interest in isotopic analyses of N O, there is a lack of isotopically characterized N O isotopic reference materials (standards) to enable normalization and reporting of isotope-delta values. Here we report the isotopic characterization of two pure N O gas reference materials, USGS51 and USGS52, which are now available for laboratory calibration (https://isotopes.usgs.

A closer look into the nitrogen blank in elemental analyser/isotope ratio mass spectrometry measurements.

Rationale: One important limitation for the precise measurement of minute amounts of nitrogen (N) in solid samples by elemental analyser/isotope ratio mass spectrometry (EA/IRMS) is the accurate determination of the analyser blank value. This study was performed to identify different sources, amounts and isotopic composition of N blanks in EA/IRMS in order to identify measures for minimising the effect of the N blank on N isotopic data quality.

Methods: Different types of autosamplers, with and without zero-blank functionality, were tested by analysing different amounts of substances of varying isotopic composition by EA/IRMS.

Measuring N Abundance and Concentration of Aqueous Nitrate, Nitrite, and Ammonium by Membrane Inlet Quadrupole Mass Spectrometry.

An automated sample preparation unit for inorganic nitrogen (SPIN) coupled to a membrane inlet quadrupole mass spectrometer (MIMS) was developed for automated and sensitive determination of the N abundances and concentrations of nitrate, nitrite, and ammonium in aqueous solutions without any sample preparation. The minimum N concentration for an accurate determination of the N abundance is 7 μmol/L for nitrite and nitrate, with a relative standard deviation (RSD) of repeated measurements of <1%, and 70 μmol/L with an RSD < 0.4% in the case of ammonium.

Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N O decomposition by microwave discharge.

Rationale: Triple oxygen and nitrogen isotope ratios in nitrate are powerful tools for assessing atmospheric nitrate formation pathways and their contribution to ecosystems. N O decomposition using microwave-induced plasma (MIP) has been used only for measurements of oxygen isotopes to date, but it is also possible to measure nitrogen isotopes during the same analytical run.

Methods: The main improvements to a previous system are (i) an automated distribution system of nitrate to the bacterial medium, (ii) N O separation by gas chromatography before N O decomposition using the MIP, (iii) use of a corundum tube for microwave discharge, and (iv) development of an automated system for isotopic measurements.

Stable isotope analysis (δ (13)C and δ (15)N) 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 ((13)C/(12)C and (15)N/(14)N, expressed as δ (13)C and δ (15)N) 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).

Photoautotrophic microorganisms as a carbon source for temperate soil invertebrates.

We tested experimentally if photoautotrophic microorganisms are a carbon source for invertebrates in temperate soils. We exposed forest or arable soils to a (13)CO2-enriched atmosphere and quantified (13)C assimilation by three common animal groups: earthworms (Oligochaeta), springtails (Hexapoda) and slugs (Gastropoda). Endogeic earthworms (Allolobophora chlorotica) and hemiedaphic springtails (Ceratophysella denticulata) were highly (13)C enriched when incubated under light, deriving up to 3.

Comparison of methods to determine triple oxygen isotope composition of N2O.

Rationale: The oxygen isotope anomaly, Δ(17) O, of N2 O and nitrate is useful to elucidate nitrogen oxide dynamics. A comparison of different methods for Δ(17) O measurement was performed.

Methods: For Δ(17) O measurements, N2 O was converted into O2 and N2 using microwave-induced plasma in a quartz or corundum tube reactor, respectively, or conversion was carried out in a gold wire oven.

Interlaboratory assessment of nitrous oxide isotopomer analysis by isotope ratio mass spectrometry and laser spectroscopy: current status and perspectives.

Rationale: In recent years, research and applications of the N2O site-specific nitrogen isotope composition have advanced, reflecting awareness of the contribution of N2O to the anthropogenic greenhouse effect, and leading to significant progress in instrument development. Further dissemination of N2O isotopomer analysis, however, is hampered by a lack of internationally agreed gaseous N2O reference materials and an uncertain compatibility of different laboratories and analytical techniques.

Methods: In a first comparison approach, eleven laboratories were each provided with N2O at tropospheric mole fractions (target gas T) and two reference gases (REF1 and REF2).

Combined ¹³C and ¹⁵N isotope analysis on small samples using a near-conventional elemental analyzer/isotope ratio mass spectrometer setup.

Rationale: A high sensitivity elemental analyzer/isotope ratio mass spectrometer setup was developed to allow analysis of (13)C and (15)N isotopic composition on microgram amounts of C and N, respectively.

Methods: Increased sensitivity of a conventional elemental analyzer equipped with a low blank autosampler was obtained by decreased carrier gas flow of 35 mL/min. The diameters of the oxidation and reduction reactors and water trap were reduced to 7.

Compound-specific δ C analysis of monosaccharides from soil extracts by high-performance liquid chromatography/isotope ratio mass spectrometry.

Rationale: 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).

Assessment of tree response to drought: validation of a methodology to identify and test proxies for monitoring past environmental changes in trees.

A thinning experiment stand at Avoca, Ballinvalley, on the east coast of the Republic of Ireland was used to test a developed methodology aimed at monitoring drought stress, based on the analysis of growth rings obtained by coring. The stand incorporated six plots representing three thinning regimes (light, moderate and heavy) and was planted in the spring of 1943 on a brown earth soil. Radial growth (early- and latewood) was measured for the purpose of this study.

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.

Dual 13C, 15N labelling of terrestrial slugs (Deroceras reticulatum).

A simple, rapid and cost-effective laboratory method is described for labelling terrestrial slugs simultaneously with 13C and 15N. Slugs (Deroceras reticulatum) were provided with a mixture of [U-13C6]glucose, 15N-enriched lettuce powder, and wheat bran. Assimilation efficiencies for 13C (24.

Effects of elevated carbon dioxide concentration on growth and N2 fixation of young Robinia pseudoacacia.

Effects of elevated CO2 concentration ([CO2]) on carbon (C) and nitrogen (N) uptake and N source partitioning (N2 fixation versus mineral soil N uptake) of 1-year-old Robinia pseudoacacia were determined in a dual 13C and 15N continuous labeling experiment. Seedlings were grown for 16 weeks in ambient (350 ppm) or elevated [CO2] (700 ppm) with 15NH4 15NO3 as the only mineral nitrogen source. Elevated [CO2] increased the fraction of new C in total C, but it did not alter C partitioning among plant compartments.

Influence of tree internal nitrogen reserves on the response of beech (Fagus sylvatica) trees to elevated atmospheric carbon dioxide concentration.

We examined the influence of plant internal nitrogen (N) reserves on the response of 3-year-old beech (Fagus sylvatica L.) trees to elevated atmospheric CO2 concentration ([CO2]) in a dual 15N and 13C long-term labeling experiment. Trees were grown on sand and received either no N nutrition (-N treatment) or 4 mM N (+N treatment) for 1 year.