Tracing nitrogen transformations during spring development of winter wheat induced by N labeled cattle slurry applied with different techniques.

Slurry application is often associated with considerable nitrogen (N) losses: ammonia (NH), nitrous oxide (NO) and a mostly unknown contribution of dinitrogen (N) emission, as well as N leaching. Thus, an outdoor lysimeter experiment with growing winter wheat in undisturbed soil cores was set up to follow the transformation of cattle slurry NH and soil NO using a double labeling approach. Slurry treatments included the following application techniques: a trailing hose with/without acidification, and open slot injection with/without nitrification inhibitor.

Sources of nitrous oxide emissions from hydroponic tomato cultivation: Evidence from stable isotope analyses.

Introduction: Hydroponic vegetable cultivation is characterized by high intensity and frequent nitrogen fertilizer application, which is related to greenhouse gas emissions, especially in the form of nitrous oxide (NO). So far, there is little knowledge about the sources of NO emissions from hydroponic systems, with the few studies indicating that denitrification could play a major role.

Methods: Here, we use evidence from an experiment with tomato plants () grown in a hydroponic greenhouse setup to further shed light into the process of NO production based on the NO isotopocule method and the N tracing approach.

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.

Development and verification of a novel isotopic N O measurement technique for discrete static chamber samples using cavity ring-down spectroscopy.

Rationale: N O isotopomers are a useful tool to study soil N cycling processes. The reliability of such measurements requires a consistent set of international N O isotope reference materials to improve inter-laboratory and inter-instrument comparability and avoid reporting inaccurate results. All these are the more important given the role of N O in anthropogenic climate change and the pressing need to develop our understanding of soil N cycling and N O emission to mitigate such emissions.

Biologically mediated release of endogenous NO and NO gases in a hydrothermal, hypoxic subterranean environment.

The migration of geogenic gases in continental areas with geothermal activity and active faults is an important process releasing greenhouse gases (GHG) to the lower troposphere. In this respect, caves in hypogenic environments are natural laboratories to study the compositional evolution of deep-endogenous fluids through the Critical Zone. Vapour Cave (Alhama, Murcia, Spain) is a hypogenic cave formed by the upwelling of hydrothermal CO-rich fluids.

Quantifying NO reduction to N during denitrification in soils via isotopic mapping approach: Model evaluation and uncertainty analysis.

The last step of denitrification, i.e. the reduction of NO to N, has been intensively studied in the laboratory to understand the denitrification process, predict nitrogen fertiliser losses, and to establish mitigation strategies for NO.

Indications for enzymatic denitrification to NO at low pH in an ammonia-oxidizing archaeon.

Nitrous oxide (NO) is a key climate change gas and nitrifying microbes living in terrestrial ecosystems contribute significantly to its formation. Many soils are acidic and global change will cause acidification of aquatic and terrestrial ecosystems, but the effect of decreasing pH on NO formation by nitrifiers is poorly understood. Here, we used isotope-ratio mass spectrometry to investigate the effect of acidification on production of NO by pure cultures of two ammonia-oxidizing archaea (AOA; Nitrosocosmicus oleophilus and Nitrosotenuis chungbukensis) and an ammonia-oxidizing bacterium (AOB; Nitrosomonas europaea).

Improved isotopic model based on N tracing and Rayleigh-type isotope fractionation for simulating differential sources of N O emissions in a clay grassland soil.

Rationale: Isotopic signatures of N O can help distinguish between two sources (fertiliser N or endogenous soil N) of N O emissions. The contribution of each source to N O emissions after N-application is difficult to determine. Here, isotopologue signatures of emitted N O are used in an improved isotopic model based on Rayleigh-type equations.

Improvement of the N gas flux method for in situ measurement of soil denitrification and its product stoichiometry.

Rationale: Field measurement of denitrification in agricultural ecosystems using the N gas flux method has been limited by poor sensitivity because current isotope ratio mass spectrometry is not precise enough to detect low N fluxes in the presence of a high atmospheric N background. For laboratory studies, detection limits are improved by incubating soils in closed systems and under N -depleted atmospheres.

Methods: We developed a new procedure to conduct the N gas flux method suitable for field application using an artificially N -depleted atmosphere to improve the detection limit at the given precision of mass spectrometry.

Nitrous oxide effluxes from plants as a potentially important source to the atmosphere.

The global budget for nitrous oxide (N O), an important greenhouse gas and probably dominant ozone-depleting substance emitted in the 21 century, is far from being fully understood. Cycling of N O in terrestrial ecosystems has traditionally exclusively focused on gas exchange between the soil surface (nitrification-denitrification processes) and the atmosphere. Terrestrial vegetation has not been considered in the global budget so far, even though plants are known to release N O.

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.

Estimating N O processes during grassland renewal and grassland conversion to maize cropping using N O isotopocules.

Rationale: Enhanced nitrous oxide (N O) emissions can occur following grassland break-up for renewal or conversion to maize cropping, but knowledge about N O production pathways and N O reduction to N is very limited. A promising tool to address this is the combination of mass spectrometric analysis of N O isotopocules and an enhanced approach for data interpretation.

Methods: The isotopocule mapping approach was applied to field data using a δ N and δ O map to simultaneously determine N O production pathways contribution and N O reduction for the first time.

Stability of buried carbon in deep-ploughed forest and cropland soils - implications for carbon stocks.

Accumulation of soil organic carbon (SOC) may play a key role in climate change mitigation and adaptation. In particular, subsoil provides a great potential for additional SOC storage due to the assumed higher stability of subsoil SOC. The fastest way in which SOC reaches the subsoil is via burial, e.

Use of oxygen isotopes to differentiate between nitrous oxide produced by fungi or bacteria during denitrification.

Rationale: Fungal denitrifiers can contribute substantially to N O emissions from arable soil and show a distinct site preference for N O (SP(N O)). This study sought to identify another process-specific isotopic tool to improve precise identification of N O of fungal origin by mass spectrometric analysis of the N O produced.

Methods: Three pure bacterial and three fungal species were incubated under denitrifying conditions in treatments with natural abundance and stable isotope labelling to analyse the N O produced.

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.

Gas entrapment and microbial NO reduction reduce NO emissions from a biochar-amended sandy clay loam soil.

Nitrous oxide (NO) is a potent greenhouse gas that is produced during microbial nitrogen transformation processes such as nitrification and denitrification. Soils represent the largest sources of NO emissions with nitrogen fertilizer application being the main driver of rising atmospheric NO concentrations. Soil biochar amendment has been proposed as a promising tool to mitigate NO emissions from soils.

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.

Influence of Lumbricus terrestris and Folsomia candida on N O formation pathways in two different soils - with particular focus on N emissions.

Rationale: The gaseous N losses mediated by soil denitrifiers are generally inferred by measuring N O fluxes, but should include associated N emissions, which may be affected by abiotic soil characteristics and biotic interactions. Soil fauna, particularly anecic earthworms and euedaphic collembola, alter the activity of denitrifiers, creating hotspots for denitrification. These soil fauna are abundant in perennial agroecosystems intended to contribute to more sustainable production of bioenergy.

Deep ploughing increases agricultural soil organic matter stocks.

Subsoils play an important role within the global C cycle, since they have high soil organic carbon (SOC) storage capacity due to generally low SOC concentrations. However, measures for enhancing SOC storage commonly focus on topsoils. This study assessed the long-term storage and stability of SOC in topsoils buried in arable subsoils by deep ploughing, a globally applied method for breaking up hard pans and improving soil structure to optimize crop growing conditions.

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.