scholarly journals C / N ratio, stable isotope (δ<sup>13</sup>C, δ<sup>15</sup>N), and <i>n</i>-alkane patterns of bryophytes along hydrological gradients of low-centred polygon of the Siberian Arctic

2016 ◽  
Author(s):  
Romy Zibulski ◽  
Felix Wesener ◽  
Heinz Wilkes ◽  
Birgit Plessen ◽  
Luidmila A. Pestryakova ◽  
...  
Keyword(s):  
Water Level ◽  
Isotopic Signature ◽  
The Arctic ◽  
Specific Level ◽  
Δ13c And Δ15n ◽  
Lena River ◽  
Isotopic Signatures ◽  
Microbial Symbiosis ◽  
The Stability ◽  
The Individual

Abstract. Mosses are a major component of the arctic vegetation, particularly of wetlands. We present C / N ratio, δ13C and δ15N data of 400 moss samples belonging to 10 species that were collected along hydrological gradients within polygonal mires located on the southern Taymyr Peninsula and the Lena River delta in northern Siberia. Additionally, n alkane patterns of six of these taxa were investigated. The aim of the study is to see whether the inter- and intra-specific differences in biochemical and isotopic signatures are indicative of habitat with particular respect to water-level. Overall, we find high variability in all investigated parameters. The C / N ratios range between 15.4 and 70.4 (median: 42.9) and show large variations at intra-specific level. However, species preferring a dry habitat (xero-mesophilic mosses) show higher C / N ratios than those preferring a wet habitat (meso-hygrophilic mosses). We assume that this mainly originates from the association of mosses from wet habitats with microorganisms which supply them with nitrogen. Furthermore, because of the stability provided by water, they do not need to invest in a sturdy stem-structure and accordingly have lower C contents in their biomass. The δ13C values range between −37.0 and 22.5 ‰ (median = −27.8 ‰). The δ15N values range between −6.59 and +1.69 ‰ (median = 2.17 ‰).We find differences in δ13C and δ15N signatures between both habitat types and, for some species of the meso-hygrophilic group, a significant relation between the individual habitat water-level and isotopic signature was inferred as a function of microbial symbiosis. The n alkane distribution also shows differences primarily between xero-mesophilic and meso-hygrophilic mosses, i.e. having a dominance of n-alkanes with long (n-C29, n-C31) and intermediate chain lengths (n-C25), respectively. Overall, our results reveal that biochemical and isotopic signals of certain moss taxa from polygonal wetlands are characteristic of their habitat and can thus be used in (palaeo-)environmental studies.

scholarly journals C  ∕ N ratio, stable isotope (<i>δ</i><sup>13</sup>C, <i>δ</i><sup>15</sup>N), and <i>n</i>-alkane patterns of brown mosses along hydrological gradients of low-centred polygons of the Siberian Arctic

2017 ◽  
Vol 14 (6) ◽  
pp. 1617-1630 ◽  
Author(s):  
Romy Zibulski ◽  
Felix Wesener ◽  
Heinz Wilkes ◽  
Birgit Plessen ◽  
Luidmila A. Pestryakova ◽  
...  
Keyword(s):  
Water Level ◽  
Atomic Ratio ◽  
The Arctic ◽  
Δ13c And Δ15n ◽  
Moss Species ◽  
Lena River ◽  
Siberian Arctic ◽  
Microbial Symbiosis ◽  
The Individual ◽  
Chain Lengths

Abstract. Mosses are a major component of the arctic vegetation, particularly in wetlands. We present C ∕ N atomic ratio, δ13C and δ15N data of 400 brown-moss samples belonging to 10 species that were collected along hydrological gradients within polygonal mires located on the southern Taymyr Peninsula and the Lena River delta in northern Siberia. Additionally, n-alkane patterns of six of these species (16 samples) were investigated. The aim of the study is to see whether the inter- and intraspecific differences in C ∕ N, isotopic compositions and n-alkanes are indicative of habitat, particularly with respect to water level. Overall, we find high variability in all investigated parameters for two different moisture-related groups of moss species. The C ∕ N ratios range between 11 and 53 (median: 32) and show large variations at the intraspecific level. However, species preferring a dry habitat (xero-mesophilic mosses) show higher C ∕ N ratios than those preferring a wet habitat (meso-hygrophilic mosses). The δ13C values range between −37.0 and −22.5 ‰ (median  =  −27.8 ‰). The δ15N values range between −6.6 and +1.7 ‰ (median  =  −2.2 ‰). We find differences in δ13C and δ15N compositions between both habitat types. For some species of the meso-hygrophilic group, we suggest that a relationship between the individual habitat water level and isotopic composition can be inferred as a function of microbial symbiosis. The n-alkane distribution also shows differences primarily between xero-mesophilic and meso-hygrophilic mosses, i.e. having a dominance of n-alkanes with long (n-C29, n-C31) and intermediate (n-C25) chain lengths, respectively. Overall, our results reveal that C ∕ N ratios, isotopic signals and n-alkanes of studied brown-moss taxa from polygonal wetlands are characteristic of their habitat.

Inherent variation in carbon and nitrogen isotopic assimilation in the freshwater macro-invertebrate Cherax destructor

2016 ◽  
Vol 67 (12) ◽  
pp. 1928 ◽  
Author(s):  
Debashish Mazumder ◽  
Li Wen ◽  
Mathew P. Johansen ◽  
Tsuyoshi Kobayashi ◽  
Neil Saintilan
Keyword(s):  
Trophic Ecology ◽  
Individual Variability ◽  
Δ13c And Δ15n ◽  
Isotopic Signatures ◽  
Carbon And Nitrogen ◽  
Source Selection ◽  
Cherax Destructor ◽  
Specific Variation ◽  
The Individual ◽  
Diet Source

Individual variability in diet source selection has often been cited as the main factor for intra-specific variation of isotopic signatures among food-web consumers. We conducted a laboratory study to test how well the individual variability of the δ13C and δ15N ratios in the muscle of an omnivore consumer (yabby: Cherax destructor) corresponded to the variability of various diet types and diet combinations. We found that C. destructor muscle isotope signatures varied in concert with the composition of single-source diets, and that this variability was low. However, when fed the same proportional mixture of multiple diet sources, comparatively high isotopic variability was observed among specimens. Results suggest that a substantial component of isotopic variability in wild populations may be owing to inherent differences in uptake, absorption, and sequestration among individuals, which is distinct from behaviourally driven individualised diet selection. Considering the potential of such individual variability in assimilation to be present in many different consumer populations, we suggest further testing for a range of species and inclusion of this source of variation, for interpretation of isotopic data for trophic ecology.

scholarly journals Whisker isotopic signature depicts migration patterns and multi-year intra- and inter-individual foraging strategies in fur seals

2009 ◽  
Vol 5 (6) ◽  
pp. 830-832 ◽  
Author(s):  
Y. Cherel ◽  
L. Kernaléguen ◽  
P. Richard ◽  
C. Guinet
Keyword(s):  
Population Level ◽  
Isotopic Signature ◽  
Trophic Niche ◽  
Foraging Strategies ◽  
Individual Level ◽  
Dietary History ◽  
Isotopic Signatures ◽  
Fur Seals ◽  
The Individual ◽  
Antarctic Fur Seals

The movement and dietary history of individuals can be studied using stable isotope records in archival keratinous tissues. Here, we present a chronology of temporally fine-scale data on the trophic niche of otariid seals by measuring the isotopic signature of serially sampled whiskers. Whiskers of male Antarctic fur seals breeding at the Crozet Islands showed synchronous and regular oscillations in both their δ 13 C and δ 15 N values that are likely to represent their annual migrations over the long term (mean 4.8 years). At the population level, male Antarctic fur seals showed substantial variation in both δ 13 C and δ 15 N values, occupying nearly all the ‘isotopic space’ created by the diversity of potential oceanic habitats (from high Antarctica to the subtropics) and prey (from Antarctic krill to subantarctic and subtropical mesopelagic fishes). At the individual level, whisker isotopic signatures depict a large diversity of foraging strategies. Some seals remained in either subantarctic or Antarctic waters, while the migratory cycle of most animals encompassed a wide latitudinal gradient where they fed on different prey. The isotopic signature of whiskers, therefore, revealed new multi-year foraging strategies of male Antarctic fur seals and is a powerful tool for investigating the ecological niche during cryptic stages of mammals' life.

Testing different methods for the extraction and purification of leaf and phloem sugars for oxygen isotope analysis

2020 ◽  
Author(s):  
Melanie Egli ◽  
Marco M. Lehmann ◽  
Nadine Brinkmann ◽  
Roland A. Werner ◽  
Matthias Saurer ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Isotope Analysis ◽  
Isotopic Signature ◽  
Phloem Tissue ◽  
Oxygen Isotope Fractionation ◽  
Isotopic Signatures ◽  
Extraction And Purification ◽  
Oxygen Isotopic ◽  
The Individual ◽  
The Impact

&lt;p&gt;Oxygen isotope analysis of plant material, such as sugars in different tissues, provides an important tool to understand how plants function, interact with their environment and also cope with climate change. Knowing how to extract and purify carbohydrates without artificially altering their oxygen isotope ratio (&lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O) is therefore essential.&lt;/p&gt;&lt;p&gt;We aimed to resolve the impact of different steps on sugars' &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O values during their extraction and purification from leaf and phloem tissue. More precisely, we investigated (1) different drying processes (oven- vs freeze-drying), and (2) how extraction and purification affect leaf sugars. To clearly see fractionation and exchange processes, these experiments were performed using &lt;sup&gt;18&lt;/sup&gt;O-labelled water. We further examined (3) the influence of different EDTA media and immersion times to facilitate sugar exudation and subsequent yield from twig phloem tissue. Finally, we analysed (4) the sugar phloem composition, as well as the individual compounds&amp;#8217; carbon isotopic signatures (&lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C).&lt;/p&gt;&lt;p&gt;Comparison of freeze- and oven-dried sugars showed lower &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O memory effects and more consistent oxygen isotopic signatures across different sugars, indicating lyophilisation as the more reliable method. The extraction and purification can be conducted without significant oxygen isotope fractionation. However, &lt;sup&gt;18&lt;/sup&gt;O-depletion was observed when sugars were dissolved and dried multiple times. This suggests that additional dissolution and drying steps should best be avoided whenever possible. Different immersion times and exudation media during twig phloem extraction revealed to have a substantial influence on the phloem sugars' overall oxygen isotopic signature, their composition, and the individual compounds' &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C values.&lt;/p&gt;&lt;p&gt;Our research illustrates which precautions during sample preparation &amp;#8211; from drying to extracting and purifying &amp;#8211; need to be taken when plant sugars and their oxygen isotopic signature are of interest. Regarding the preservation of the phloem sugars' original &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O values and stabilising their composition (prevention of sucrose degradation) as much as possible, we recommend a short immersion time of approx. 1 hour. After a thorough initial rinse of the tissue, the sap should be eluted in pure water without any additives (no EDTA). This further reduces the possibility of hexoses to exchange oxygen with that of the surrounding water.&lt;/p&gt;

Implications of Person Fluctuation for the Stability and Validity of Test Scores

Methodology ◽  
2006 ◽  
Vol 2 (4) ◽  
pp. 142-148 ◽  
Author(s):  
Pere J. Ferrando
Keyword(s):  
Item Response ◽  
Test Scores ◽  
Temporal Stability ◽  
Person Fit ◽  
Item Parameters ◽  
Individual Trait ◽  
The Stability ◽  
The Individual ◽  
Different Levels ◽  
Fluctuation Model

In the IRT person-fluctuation model, the individual trait levels fluctuate within a single test administration whereas the items have fixed locations. This article studies the relations between the person and item parameters of this model and two central properties of item and test scores: temporal stability and external validity. For temporal stability, formulas are derived for predicting and interpreting item response changes in a test-retest situation on the basis of the individual fluctuations. As for validity, formulas are derived for obtaining disattenuated estimates and for predicting changes in validity in groups with different levels of fluctuation. These latter formulas are related to previous research in the person-fit domain. The results obtained and the relations discussed are illustrated with an empirical example.

Determination of allostatic load dynamics in the assessment of adaptation in temporary workers in the Arctic

2020 ◽  
pp. 547-548
Author(s):  
O. Yu. Atkov ◽  
S. G. Gorokhova
Keyword(s):  
Body Mass Index ◽  
Glucose Level ◽  
Shift Work ◽  
Allostatic Load ◽  
The Arctic ◽  
Temporary Workers ◽  
Short Term ◽  
Short Term Adaptation ◽  
The Individual

The individual dynamics of the allostatic load index was revealed mainly due to changes in the glucose level, body mass index, which makes it applicable for assessing the short-term adaptation to the stay in the conditions of shift work

Examining sharp restart in a Monte Carlo method for the linearized Poisson–Boltzmann equation

2020 ◽  
Vol 26 (3) ◽  
pp. 223-244
Author(s):  
W. John Thrasher ◽  
Michael Mascagni
Keyword(s):  
Monte Carlo ◽  
Free Energy ◽  
Monte Carlo Algorithm ◽  
Significant Bias ◽  
Poisson Boltzmann ◽  
Electrostatic Free Energy ◽  
Poisson Boltzmann Equation ◽  
The Stability ◽  
Potential Methods ◽  
The Individual

AbstractIt has been shown that when using a Monte Carlo algorithm to estimate the electrostatic free energy of a biomolecule in a solution, individual random walks can become entrapped in the geometry. We examine a proposed solution, using a sharp restart during the Walk-on-Subdomains step, in more detail. We show that the point at which this solution introduces significant bias is related to properties intrinsic to the molecule being examined. We also examine two potential methods of generating a sharp restart point and show that they both cause no significant bias in the examined molecules and increase the stability of the run times of the individual walks.

scholarly journals The δ13C, δ18O and Δ47 records in biogenic, pedogenic and geogenic carbonate types from paleosol-loess sequence and their paleoenvironmental meaning

2021 ◽  
pp. 1-17
Author(s):  
Kazem Zamanian ◽  
Alex R. Lechler ◽  
Andrew J. Schauer ◽  
Yakov Kuzyakov ◽  
Katharine W. Huntington
Keyword(s):  
Land Snail ◽  
Isotopic Signature ◽  
Sediment Layer ◽  
Isotopic Signatures ◽  
Pedogenic Carbonates ◽  
Rhine Valley ◽  
Clumped Isotope ◽  
Time Specific ◽  
Sediment Layers ◽  
Paleoenvironmental Reconstructions

Abstract Paleoenvironmental reconstructions are commonly based on isotopic signatures of a variety of carbonate types, including rhizoliths and land-snail shells, present in paleosol-loess sequences. However, various carbonate types are formed through distinct biotic and abiotic processes over various periods, and therefore may record diverging environmental information in the same sedimentological layer. Here, we investigate the effects of carbonate type on δ13C, δ18O, and clumped isotope-derived paleotemperature [T(Δ47)] from the Quaternary Nussloch paleosol-loess sequence (Rhine Valley, SW Germany). δ13C, δ18O, and T(Δ47) values of co-occurring rhizoliths (-8.2‰ to -5.8‰, -6.1‰ to -5.9‰, 12–32°C, respectively), loess dolls (-7.0‰, -5.6‰, 23°C), land-snail shells (-8.1‰ to -3.2‰, -4.0‰ to -2.2‰, 12–38°C), earthworm biospheroliths (-11‰, -4.7‰, 8°C), and “bulk” carbonates (-1.9‰ to -0.5‰, -5.6‰ to -5.3‰, 78–120°C) from three sediment layers depend systematically on the carbonate type, admixture from geogenic carbonate, and the duration of formation periods. Based on these findings, we provide a comprehensive summary for the application of the three isotopic proxies of δ13C, δ18O, and Δ47 in biogenic and pedogenic carbonates present in the same sediment layer to reconstruct paleoenvironments (e.g., local vegetation, evaporative conditions, and temperature). We conclude that bulk carbonates in Nussloch loess should be excluded from paleoenvironmental reconstructions. Instead, pedogenic and biogenic carbonates should be used to provide context for interpreting the isotopic signature for detailed site- and time-specific paleoenvironmental information.

scholarly journals Diversity and Diet Differences of Small Mammals in Commensal Habitats

Diversity ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 346
Author(s):  
Linas Balčiauskas ◽  
Laima Balčiauskienė ◽  
Andrius Garbaras ◽  
Vitalijus Stirkė
Keyword(s):  
Small Mammals ◽  
Small Mammal ◽  
Trophic Ecology ◽  
Mammal Species ◽  
Additional Food ◽  
Δ13c And Δ15n ◽  
Degree Of Separation ◽  
Kitchen Gardens ◽  
Dietary Plasticity ◽  
The Stability

The stability of diversity of syntopic (inhabiting the same habitat in the same time) small mammals in commensal habitats, such as farmsteads and kitchen gardens, and, as a proxy of their diet, their isotopic niches, was investigated in Lithuania in 2019–2020. We tested whether the separation of species corresponds to the trophic guilds, whether their diets are related to possibilities of getting additional food from humans, and whether their diets are subject to seasonal trends. We analyzed diversity, dominance and distribution of hair δ13C and δ15N values. Diversity and dominance was not stable and differed according to human influence. The highest small mammal species richness occurred in commensal habitats that provided additional food. The degree of separation of species was higher in homestead habitats than in kitchen gardens, where a 1.27 to 35.97% overlap of isotopic niches was observed between pairs of species. Temporal changes in δ13C and δ15N values in the hair of the mammals were not equally expressed in different species. The isotopic overlap may depend on dietary plasticity, minimizing interspecific competition and allowing co-existence of syntopic species. Thus, small mammal trophic ecology is likely related to intensity of agricultural activities in the limited space of commensal habitats.

The great Chinese surprise: the rupture with the United States is real and is happening

2020 ◽  
Vol 96 (2) ◽  
pp. 419-437
Author(s):  
Xiangfeng Yang
Keyword(s):  
United States ◽  
The United States ◽  
Donald Trump ◽  
Ample Evidence ◽  
Pendulum Swing ◽  
The Us ◽  
Methodological Problems ◽  
Trade War ◽  
The Stability ◽  
The Individual

Abstract Ample evidence exists that China was caught off guard by the Trump administration's onslaught of punishing acts—the trade war being a prime, but far from the only, example. This article, in addition to contextualizing their earlier optimism about the relations with the United States under President Trump, examines why Chinese leaders and analysts were surprised by the turn of events. It argues that three main factors contributed to the lapse of judgment. First, Chinese officials and analysts grossly misunderstood Donald Trump the individual. By overemphasizing his pragmatism while downplaying his unpredictability, they ended up underprepared for the policies he unleashed. Second, some ingrained Chinese beliefs, manifested in the analogies of the pendulum swing and the ‘bickering couple’, as well as the narrative of the ‘ballast’, lulled officials and scholars into undue optimism about the stability of the broader relationship. Third, analytical and methodological problems as well as political considerations prevented them from fully grasping the strategic shift against China in the US.

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