14N Ratios Research Articles

Effects of long-term nitrogen addition on the shift of nitrogen cycle from open to closed along an age gradient of larch plantations in North China

The 15N:14N ratio (δ15N) is often used as an integrated indicator of nitrogen (N) status in natural terrestrial ecosystems. However, the mechanisms by which long-term N addition affects N cycling and status in temperate plantations with different ages remain poorly understood. Here, we used an approach of leaf–soil continuum of δ15N with the combination of incubation experiments to evaluate the effects of three rates of decadal N addition (urea) on N status in young, intermediate, and mature larch (Larix principis-rupprechtii) plantations in northern China. We found that leaf δ15N decreased significantly from 1.6‰ in young trees to −0.5‰ and −1.0‰ in intermediate and mature trees, respectively, due to increases in the use of NO– 3-N relative to NH+ 4-N with stand age, and probably a shift in N acquisition from mineral soil in the young plantation to organic and/or surface mineral soil layers in the intermediate and mature plantations. Decadal N addition decreased leaf δ15N, which was likely to be due to the direct imprints of 15N-depleted urea input, the inhibition of soil net mineralization, and nitrification, and greater dependence on N absorption by ectomycorrhizal fungi after N addition. Soil δ15N decreased with stand age, which was likely to be due to reduced soil N transformation (e.g., mineralization) and/or relative abundance of ectomycorrhizal fungi along the chronosequence; however, soil δ15N was not affected by long-term N inputs. Combined with the decreased enrichment factor (ε = δ15Nleaf – δ15Nsoil), these results suggest a shift from more open N cycling (potentially greater ecosystem N losses) in young plantation to more closed N cycling (facilitation of ecosystem N retention) in mature plantation, which showed negative response to decadal N addition. These findings provide new insights into N acquisition strategies and cycling in the typically N-limited temperate plantations under heightened atmospheric N deposition.

Exogenous Threonine-Induced Conversion of Threonine-Xylose Amadori Compound to Heyns Compound for Efficiently Promoting the Formation of Pyrazines.

The involvement of exogenous threonine during the degradation of l-threonine-d-xylose Amadori rearrangement product (Thr-ARP) was found to promote the formation of pyrazines. A model including Thr-ARP and 15N-labeled l-threonine was applied to reveal the role of free threonine in Thr-ARP conversion to pyrazines. Quantitative analyses of pyrazines in the model of Thr-ARP/15N-labeled threonine showed a precedence of the endogenous threonine (formed by the degradation of Thr-ARP) over the exogenous threonine in pyrazines formation, and the ratio of 15N to 14N content in pyrazines increased significantly over time. According to the observed occurrence of the Heyns rearrangement products (HRP) derived from 15N-threonine, as well as the sharp decrease of 15N-threonine content and a rapid increase of 14N endogenous threonine at the initial stage of heat treatment, it was proposed that aldimine condensation between exogenous threonine and Thr-ARP followed by the hydrolysis led to the endogenous threonine and the generation of HRP. Then, the HRP underwent dehydration followed by hydrolysis to form exogenous threonine and deoxyxyosones, and the dehydration and hydrolysis of deoxyxyosones to form organic acids was inhibited, but the retro-aldolization of deoxyxyosones was promoted, facilitating the generation of reactive α-dicarbonyl compounds. In this way, exogenous threonine accelerated the release of endogenous threonine and α-dicarbonyl compounds and the pH decline was slowed down, which was favorable for the formation of pyrazines.

The combined effects of faba bean and endogeic earthworms on soil microbial activity in intercrops

The rhizosphere is a hotspot of interactions between plants and soil organisms that affect the soil functioning and nutrient cycling. The drilosphere is a hotspot of interactions between earthworms and soil microbial communities affecting plant growth, soil aggregation, and porosity. Central to these interactions are microorganisms, which are affected by both plant species diversity and earthworm activity. Little is known about the effects of earthworms on the microbial community activity under the influence of root-trait diversity in cases of multi-species plant covers. We investigated the impact of plant composition and the presence of endogeic earthworms on the metabolic response of microorganisms to the addition of 10 carbon substrates relevant as rhizodeposition components. A greenhouse experiment was conducted with mesocosms filled with 10 kg of soil, sown with two plants of either the same or different species, chosen based on their contrasting root traits. Five modalities were investigated: 1 faba bean (Vicia faba L. ssp. Minor) intercropped with either 1 rapeseed (Brassica napus L.) or 1 wheat (Triticum aestivum L.) plant, as well as crops of the same species: either 2 rapeseeds, 2 wheats, or 2 faba beans. For each modality, 10 mesocosms were set up, and half of them were inoculated with 5 endogeic earthworms (Aporrectodea caliginosa Savigny). After 91 days, the plants’ dry weight, N content, and 15N:14N ratio were measured. The rhizosphere microbial respiration was assessed using the MicroResp™ method. The results showed that the level of metabolic activity depends on the plant species composition. Faba bean had the highest positive effect on microbial growth and metabolic activity. Microbial activity was also significantly increased by earthworms, but with no specific effect between plant treatments. Our findings suggest that plant traits are the main driver of the metabolic activity of soil microorganisms that is stimulated by earthworms.

Mechanistic insights into an NH4OAc-promoted imine dance in Rh-catalysed multicomponent double C-H annulations through an N-retention/exchange dual channel.

Developing new and understanding multicomponent reactions (MCRs) is an appealing but challenging task. Herein, Rh(iii)-catalyzed multicomponent double C-H annulations of cyclic diimines (or diketones and acetone), alkynes, and ammonium acetate to assemble functionalized 1,1'-biisoquinolines and C-bridged 1,1'-bisisoquinolines with controllable 14N/15N editing in one shot has been developed. Through a combination of isotopic-labeling (2H, 18O, and 15N) experiments, crystallography, and time-dependent ESI-MS, the reaction process was studied in detail. Ammonium acetate accounts for two rounds of Hofmann elimination and iminization, thus leading to an unprecedented imine dance, cyclic imine → N-alkenyl imine → NH imine. The N-alkenyl imine can immediately guide a C-H annulation (N-retention channel), and some of it is converted into NH-imine to trigger another annulation (N-exchange channel). The channels and 15N ratios can be regulated by the reaction mode and acidity. Moreover, the resulting 1,1'-biisoquinolines are a privileged ligand scaffold which is exemplified herein by a hydrazine-iodine exchange reaction to form drug-like benzo[c]cinnolines.

Nitrate removal rates, isotopic fractionation, and denitrifying bacteria in a woodchip-based permeable reactive barrier system: a long-term column experiment.

This study evaluated the effectiveness of using organic carbon materials (i.e., woodchips) to remove nitrate from groundwater. The results of our flow-through column experiment, which was conducted over 1.6years, suggested that denitrifying bacteria reduce nitrate by using it as an electron acceptor and woodchips as an electron donor. The nitrate removal rates were sufficiently high (0.39-1.04mmol L-1day-1) during the operation of the column. Denitrification process was supported by fractionation of nitrogen and oxygen isotopes (δ15N and δ18O), with the δ15N and δ18O values enriched from 7.4‰ and 22.3‰ to 21.2‰ and 30.4‰, respectively. Enrichment factors ([Formula: see text]) for 15N and 18O were calculated using the Rayleigh fractionation model, with values of - 13.2‰ for ε15N and - 7.1‰ for ε18O. The fractionation ratio of 15N to 18O was 1.9:1, confirming denitrification. The most abundant bacterial genera in the soil used for inoculation were Enterobacter (86.7%), Nitrospira (1.8%), and Arthrobacter (1.5%), while those in the column effluent were Macrococcus (37.1%), Escherichia (14.7%), and Shigella (14.6%), indicating that bacterial communities changed in response to geochemical conditions in the column. This study suggests that nitrate in groundwater can be effectively removed using woodchip-based passive treatment systems and that information on isotopic fractionation and denitrifying bacteria can be key tools to understand denitrification.

Multidisciplinary lines of evidence reveal East/Northeast Asian origins of agriculturalist/pastoralist residents at a Han dynasty military outpost in ancient Xinjiang

Han/non-Han interactions were engrained among the border regions of ancient Imperial China. Yet, little is known about either the genetic origins or the lifeways of these border peoples. Our study applies tools from ancient deoxyribonucleic acid (DNA) and stable isotope analysis to the study of a Han dynasty population at the Shichengzi site in modern-day Xinjiang. Isotopic analysis (δ13C and δ15N) of human (n = 8), animal (n = 26), and crop remains (n = 23) from Shichengzi indicated that dietary patterns among site inhabitants could be split among agro-pastoral and agricultural groups based on differences in the collagen 15N ratios. DNA analysis divided the four Shichengzi samples into two groups, with one group primarily harboring the ancient Northeast Asian (ANA) related ancestry, while the other showed a dominant Late Neolithic Yellow River (YR_LN) related ancestry. Both ancient DNA and stable isotope evidence point to the Northeast Asian origins of pastoralists and East Asian origins of Han agriculturalists, who, nonetheless, shared a single burial space at Shichengzi. This study thus provides clear evidence for the multiple origins and identities of populations across the porous border represented by the Han Empire and surrounding regions and proposes a new model for the interpretation of border culture in early Imperial China.

Alternate wetting–drying enhances soil nitrogen availability by altering organic nitrogen partitioning in rice-microbe system

Alternate wetting and drying (AWD) irrigation influences soil nutrient cycling and the functioning of soil microorganisms. However, the effects of AWD on organic nitrogen (ON) partitioning in rice-microbe ecosystems and soil microbial communities are poorly understood. A root-box microcosm experiment with two rice varieties (Nipponbare, Nip; Yangdao 6, YD6), two irrigation regimes (conventional flood irrigation (CF); AWD) and three N application levels (zero N, N0; medium N, N1; high N, N2) was performed based on the 13C,15N-labelled glycine and 13C-phospholipid fatty acids (PLFA) techniques. Compared to CF, AWD increased soil dissolved oxygen, microbial growth and the enzymes related to N transformation, thus enhancing rice growth and the N utilization index (NUI). Approximately 4.9–10.3% and 7.7–13.6% of the exogenous glycine was directly utilized by Nip and YD6 seedlings, respectively, and its ratio increased with increasing N levels, whereas 4.4–11.2% and 4.6–10.3% were incorporated into soil microbes. It seems that rice has an appreciable capacity to utilize organic N despite fierce competition with soil microbes. The 13C:15N ratio showed that 12.5–37.5% and 11.0–41.0% of the added glycine was taken up intact by soil microorganisms in the rhizospheres of Nip and YD6. At the N1 and N2 levels, AWD increased rice 15N-glycine uptake but decreased microbial 15N-glycine uptake. Rice intact glycine uptake and soil inorganic N contents were positively correlated with rice biomass and NUI, indicating that the enhanced inorganic N under AWD is beneficial for soil ON availability and rice growth. Gram-negative and general bacteria were the dominant competitors with rice for soil ON. AWD increased the contents of gram-negative bacteria and fungi and the ratio of fungi:bacteria in rhizosphere soils. Collectively, AWD creates a good rhizosphere oxygen environment for rice and microbial growth. ON partitioning in the rice-microbe system and the adaptive adjustment of the microbial community play important roles in modulating soil nutrients for optimal rice growth.

Can plant or lichen natural abundance 15N ratios indicate the influence of oil sands N emissions on bogs?

Study regionThe 140,329 km2 Athabasca Oil Sands Administrative Area (OSAA), which contains 8982 km2 of bogs. Since the late 1970s, N emissions from oil sands development in the OSAA have steadily increased, reaching over 80,000 metric tonnes yr−1 in 2017. Study focusIf oil sands N emissions have distinct stable isotopic signatures, it may be possible to quantify the extent to which these emissions have affected N cycling in surrounding aquatic, wetland, and terrestrial ecosystems. To assess the potential for 15N as a tracer of oil sands N emissions, we measured natural abundance 15N ratios and tissue N concentrations in 10 plant or lichen species at 6 peatland sites at different distances from the oil sands region, collected on 17 sampling dates over three years (2009–2011). New hydrological insightsTo understand how the pressures of changing N and S deposition regimes and hydrologic disturbance interactively affect the region’s wetlands, it is critical to understand how these pressures act individually. The epiphytic lichen, Evernia mesomorpha, was the only species that exhibited patterns that could be interpreted as being influenced by oil sands N emissions. The paucity of data on δ15N signatures of oil sands related N sources precludes definitive interpretations of δ15N in plant or lichen tissues with respect to oil sands N emissions.

Competition of Plants and Microorganisms for Added Nitrogen in Different Fertilizer Forms in a Semi-Arid Climate

In nitrogen (N) -limited agricultural systems, a high microbial immobilization of applied fertilizer-N can limit its availability to plants. However, there is scarce information on the effect of the form of fertilizer used on the plant–microorganism competition in clay-rich soils under a severe semi-arid climate. In a field study, we investigated the wheat–microorganism competition after the direct application of NH415NO3 closely to seeds in arable fields in North Kazakhstan, documenting the effect of the use of liquid versus granular fertilizer and mini-tillage versus no-tillage. Our results barely showed any fertilizer-N translocation in the soil. Plants outcompete microorganisms for fertilizer-N during the vegetation period. Microbial-to-plant 15N ratios revealed a predominant fertilizer-15N uptake by plants. The strong competition for N was mainly related to the placement of the fertilizer close to the seeds. Moreover, the long time interval between fertilization and sampling enhanced the competition for N, meaning that previously microbially immobilized N became available to plants through the death of microorganisms and their subsequent mineralization. The fertilizer distribution between microorganisms and plants did depend on the form of fertilizer used, owing to the good solubility of granular fertilizer. The smaller fertilizer-N uptake under the no-tilling condition was probably due to the more intense soil compaction, which caused a reduction in plant growth. The application of fertilizer close to the seeds and the small fertilizer translocation during the vegetation period ultimately resulted in a high level of plant N being derived from the fertilizer.

Seasonality of nitrogen sources, cycling, and loading in a New England river discerned from nitrate isotope ratios

Abstract. Coastal waters globally are increasingly impacted due to the anthropogenic loading of nitrogen (N) from the watershed. To assess dominant sources contributing to the eutrophication of the Little Narragansett Bay estuary in New England, we carried out an annual study of N loading from the Pawcatuck River. We conducted weekly monitoring of nutrients and nitrate (NO3-) isotope ratios (15N / 14N, 18O / 16O, and 17O / 16O) at the mouth of the river and from the larger of two wastewater treatment facilities (WWTFs) along the estuary, as well as seasonal along-river surveys. Our observations reveal a direct relationship between N loading and the magnitude of river discharge and a consequent seasonality to N loading into the estuary – rendering loading from the WWTFs and from an industrial site more important at lower river flows during warmer months, comprising ∼ 23 % and ∼ 18 % of N loading, respectively. Riverine nutrients derived predominantly from deeper groundwater and the industrial point source upriver in summer and from shallower groundwater and surface flow during colder months – wherein NO3- associated with deeper groundwater had higher 15N / 14N ratios than shallower groundwater. Corresponding NO3- 18O / 16O ratios were lower during the warm season, due to increased biological cycling in-river. Uncycled atmospheric NO3-, detected from its unique mass-independent NO3- 17O / 16O vs. 18O / 16O fractionation, accounted for < 3 % of riverine NO3-, even at elevated discharge. Along-river, NO3- 15N / 14N ratios showed a correspondence to regional land use, increasing from agricultural and forested catchments to the more urbanized watershed downriver. The evolution of 18O / 16O isotope ratios along-river conformed to the notion of nutrient spiraling, reflecting the input of NO3- from the catchment and from in-river nitrification and its coincident removal by biological consumption. These findings stress the importance of considering seasonality of riverine N sources and loading to mitigate eutrophication in receiving estuaries. Our study further advances a conceptual framework that reconciles with the current theory of riverine nutrient cycling, from which to robustly interpret NO3- isotope ratios to constrain cycling and source partitioning in river systems.

Use of the <sup>13</sup>C/<sup>12</sup>C, <sup>15</sup>N/<sup>14</sup>N and <sup>18</sup>O/<sup>16</sup>O Isotopic Ratios of Theobromine and Caffeine in the Characterization of Geographic Origin

The aim of this work is to characterize the geographical origin of cocoa beans and coffee beans. This study aims to contribute to the traceability of raw materials in order to fight against falsification. For this purpose, we based our work on the measurement of isotope ratios in 13C, 15N and 18O. The multi-element isotope ratios have been evaluated as a means to distinguish fermented cocoa beans of different geographic and varietal origins. The isotopic ratios of 13C, 15N and 18O were measured in theobromine obtained from samples of fermented cocoa beans. Twenty-two (22) samples of different geographical origins covering the four mainland cocoa producing areas were analyzed on the one hand and on the other hand, 16 caffeine samples from various origins were also analyzed. The treatment of the values resulting from these isotopic analyzes by statistical methods, namely the principal component analysis (PCA) makes it possible to visualize the discriminations between the different origins. The most discriminating variables identified as responsible for the geographic and varietal differences were the δ15N, δ13C and δ18O values of cocoa beans and certain extracts and tissues. We have shown that the isotope ratios are correlated with the altitude and precipitation conditions encountered in the different cocoa growing regions.

Depletion and fractionation of nitrogen in collapsing cores

Measurements of the nitrogen isotopic ratio in Solar System comets show a constant value, ≈140, which is three times lower than the protosolar ratio, a highly significant difference that remains unexplained. Observations of static starless cores at early stages of collapse confirm the theoretical expectation that nitrogen fractionation in interstellar conditions is marginal for most species. Yet, observed isotopic ratios in N2H+ are at variance with model predictions. These gaps in our understanding of how the isotopic reservoirs of nitrogen evolve, from interstellar clouds to comets, and, more generally, to protosolar nebulae, may have their origin in missing processes or misconceptions in the chemistry of interstellar nitrogen. So far, theoretical studies of nitrogen fractionation in starless cores have addressed the quasi-static phase of their evolution such that the effect of dynamical collapse on the isotopic ratio is not known. In this paper, we investigate the fractionation of 14N and 15N during the gravitational collapse of a pre-stellar core through gas-phase and grain adsorption and desorption reactions. The initial chemical conditions, which are obtained in steady state after typically a few Myr, show low degrees of fractionation in the gas phase, in agreement with earlier studies. However, during collapse, the differential rate of adsorption of 14N- and 15N-containing species onto grains results in enhanced 15N:14N ratios, in better agreement with the observations. Furthermore, we find differences in the behavior, with increasing density, of the isotopic ratio in different species. We find that the collapse must take place on approximately one free-fall timescale, based on the CO abundance profile in L183. Various chemical effects that bring models into better agreement with observations are considered. Thus, the observed values of 14N2H+:N15NH+ and 14N2H+:15NNH+ could be explained by different temperature dependences of the rates of dissociative recombination of these species. We also study the impact of the isotopic sensitivity of the charge-exchange reaction of N2 with He+ on the fractionation of ammonia and its singly deuterated analog and find significant depletion in the 15N variants. However, these chemical processes require further experimental and theoretical investigations, especially at low temperature. These new findings, such as the depletion-driven fractionation, may also be relevant to the dense, UV-shielded regions of protoplanetary disks.

Formation and mobility of soil organic carbon in a buried humic horizon of a volcanic ash soil

A buried humic horizon (14C age between 5.4 and 6.8 kyr BP) of a volcanic ash soil in Aomori, Japan, which was collected from the depth between 147 and 187 cm at 5 cm-interval (total eight sub-horizon samples), was investigated to clarify the degree of biological transformation and mobility of soil organic carbon (SOC) fractions. The SOC fractions were prepared from each sub-horizon sample by extraction and precipitation procedures with controlling pH of the extracted solution, resulting in humin, humic acid (HA), and four fulvic acid (FA) fractions (two hydrophilic FA fractions: FA1 and FA2, and two hydrophobic FA fractions: FA3 and FAIHSS). The prepared SOC fractions were characterized by 14C age and stable isotopic ratios of 13C (δ13C) and 15N (δ15N). The hydrophilic FA fractions showed the highest δ13C and δ15N values, indicating that these SOC fractions had been most enriched with 13C and 15N by biological metabolic processes. On the other hand, the HA fraction showed the lowest δ13C and δ15N values, therefore this fraction would have been less-metabolized, although HA fraction has been regarded as well-processed in general. The 14C age of the HA fraction was almost same as the deposition age of the corresponding sub-horizon, indicating that the C in the HA fraction would have been fixed in situ right after photosynthesis by plants at the early stage of soil formation and chemically stabilized at soil surface, by fire event, etc. The average rates of vertical translocation of the SOC fractions were low (humin and HA fractions: <1 mm per century, FA fractions: 1–4 mm per century), implying that the vertical translocation of SOC would not be the main mechanisms for forming thick humic horizons. The present study showed strong evidence of the in situ formation of SOC on soil surface, and successive up-building accumulation of soil particles containing SOC would contribute to the formation of the thick humic horizons.

Uptake of organic nitrogen by coastal wetland plants under elevated CO2

This study was conducted to answer the question of whether elevated CO2 and the presence or absence of inorganic nitrogen (NH4+) affect the uptake of different forms of organic nitrogen in two dominant saltmarsh species Schoenoplectus americanus and Spartina patens. S. americanus and S. patens were grown under elevated and ambient CO2 conditions and a series of hydroponic assays were conducted using dual labelled 13C15N– glycine, glutamic acid and urea supplied in both the absence and presence of NH4+. Results show rates of glycine and urea uptake were lower under elevated CO2 conditions for both species. Ratios of 13C and 15N in S. patens roots showed that at least 68 and 79% of glycine under ambient and elevated CO2, respectively, was taken up intact. Provision of NH4+ with organic N caused organic N uptake rates to decline by up to 75% in S. americanus and up to 50% in S. patens compared with plants that only received organic N. The reduction in organic N uptake in the presence of NH4+ suggests that plants rely primarily on mineral N in the field. In addition, we can deduce that organic N uptake is not likely to supply plants with the additional N required under elevated CO2, and that the repressive effects of elevated CO2 on organic N uptake may have negative consequences for ecosystem productivity and carbon sequestration.

Heteronuclear cross-relaxation effect modulated by the dynamics of N-functional groups in the solid state under 15N DP-MAS DNP

In a typical magic-angle spinning (MAS) dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiment, several mechanisms are simultaneously involved when transferring much larger polarization of electron spins to NMR active nuclei of interest. Recently, specific cross-relaxation enhancement by active motions under DNP (SCREAM-DNP) [Daube et al. JACS 2016] has been reported as one of these mechanisms. Thereby 13C enhancement with inverted sign was observed in a direct polarization (DP) MAS DNP experiment, caused by reorientation dynamics of methyl that was not frozen out at 100 K. Here, we report on the spontaneous polarization transfer from hyperpolarized 1H to both primary amine and ammonium nitrogens, resulting in an additional positive signal enhancement in the 15N NMR spectra during 15N DP-MAS DNP. The cross-relaxation induced signal enhancement (CRE) for 15N is of opposite sign compared to that observed for 13C due to the negative sign of the gyromagnetic ratio of 15N. The influence on CRE efficiency caused by variation of the radical solution composition and by temperature was also investigated.

Ratio of naturally retained 15N to 13C in rat brain regions as a marker of brain function and activity

Our aim in the present study was to clarify the activity-dependent and function-associated retention of stable isotopes (SIs) in rat brain regions. We measured regional distributions of the natural stable isotopes 15N and 13C in brain using a mass spectrometer with a dual inlet system and a double collector for ratiometry, and compared them with distributions obtained from internal organs and skeletal muscle. Although levels of 15N and 13C were very high in brain regions of prenatal rats, and robustly decreased after birth, developmental changes in brain regions became obvious when the ratio of 15N to 13C (abbreviated as 15N/13C) in each brain region was compared. A high correlation was observed between free motor activity and 15N/13C in the hippocampus, cerebrum, and striatum. A significantly higher 15N/13C was also observed in the hippocampus and striatum of rats with higher intelligence, which was evaluated by radial maze learning. Furthermore, 15N/13C in brain regions of trained rats were significantly higher than those of untrained age-matched rats. Our study suggests that the 15N/13C in a specific brain region may reflect the physiological feature of the region. This ratio may hence be applicable as a maker for pathological research on undiagnosed brain diseases.

Long-term fertilizer management in NERICA cultivated upland affects on soil bio-chemical properties

ABSTRACT This study aims to characterize soil chemical properties and microbial biomass, greenhouse gas production, and organic matter dynamics in upland rice field as affected by the long-term fertilizer managements in Uganda. Soil total C (TC) and N (TN) contents were in the relatively smaller range under different fertilizer treatments, even after 20 crop seasons. However, available phosphate contents showed positive correlation with average yield of upland rice. Incubation experiments were conducted under aerobic or under flooding conditions to measure CO2, methane, and nitrous oxide productions. After the incubation, soil samples were extracted to quantify nitrification rate for aerobic condition and ammonification rate for flooding condition. Soil microbial biomass carbon (MBC) and nitrogen were measured. Stable isotope ratio of 13C and 15N were also determined for the soil samples. CO2 production potential under aerobic condition was higher than the flooding condition. The qCO2 (CO2/MBC) in the treatment applied with compost tended to be higher than the other treatments. Positive correlation between nitrous oxide production and nitrification was found. The delta 13C values of the soil samples indicated that the effect of C4 plants before rice cultivation still remained, while the contribution of biological N2 fixation was little according to delta 15N values. These results indicate that soil microbial biomass in upland rice field of the long-term fertilizer experiment in Uganda was characterized with higher qCO2. Greenhouse gas production was affected by fertilizer management, while soil organic C before the long-term experiment still remained in the experiment.

High resolution optical spectroscopy of the N2-rich comet C/2016 R2 (PanSTARRS)

Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma dominated by strong emission bands of CO+ and, more surprisingly, N2+. Aims. The strong detection of N2+ in the coma of C/2016 R2 provided an ideal opportunity to measure the 14N∕15N isotopic ratio directly from N2+ for the first time, and to estimate the N2∕CO ratio, which is an important diagnostic to constrain formation models of planetesimals, in addition to the more general study of coma composition. Methods. We obtained high resolution spectra of the comet in February 2018 when it was at 2.8 au from the Sun. We used the UVES spectrograph of the European Southern Observatory Very Large Telescope, complemented with narrowband images obtained with the TRAPPIST telescopes. Results. We detect strong emissions from the N2+ and CO+ ions, but also CO2+, emission lines from the CH radical, and much fainter emissions of the CN, C2, and C3 radicals that were not detected in previous observations of this comet. We do not detect OH or H2O+, and we derive an upper limit of the H2O+∕CO+ ratio of 0.4, implying that the comet has a low water abundance. We measure a N2+/CO+ ratio of 0.06 ± 0.01. The non-detection of NH2 indicates that most of the nitrogen content of the comet is in N2. Together with the high N2+/CO+ ratio, this could indicate a low formation temperature of the comet or that the comet is a fragment of a large differentiated Kuiper Belt object. The CO2+/CO+ ratio is 1.1 ± 0.3. We do not detect 14N15N+ lines and can only put a lower limit on the 14N∕15N ratio (measured from N2+) of about 100, which is compatible with measurements of the same isotopic ratio for NH2 and CN in other comets. Finally, in addition to the [OI] and [CI] forbidden lines, we detect for the first time the forbidden nitrogen lines [NI] doublet at 519.79 and 520.03 nm in the coma of a comet.

Do artificial structures affect the feed of Patella caerulea limpets?

Do artificial structures affect the feed of Patella caerulea limpets?

Distinguishing vegan-, vegetarian-, and omnivorous diets by hair isotopic analysis

Dietary risks contribute heavily to disability-adjusted life years (DALYs), being more important than hypertension, obesity, or smoking. To measure dietary exposure remains a challenge in nutrition research. The aim of the present study was to test the hypothesis that isotope ratios of 15N and 13C in human hair could distinguish between subjects adhering to different habitual diets. 20 male and 29 female subjects average 31 years old (range 19-53), with stable dietary habits volunteered. Diets were vegan, vegetarian and omnivorous. Hair samples were processed on an elemental analyser coupled to isotope-ratio mass spectrometry. δ15N differed between vegan, vegetarian and omnivorous diets, p<0.05 for all. δ13C differed between vegan and omnivorous diets, p<0.05, but neither of these diets were separated from the vegetarian diet. Elemental Analysis of δ13C and especially δ15N with isotope ratio mass spectrometry seems to be a promising, non-invasive and objective way to distinguish groups of subjects on different habitual diets, at least if n=>10.