Stable carbon and nitrogen isotope discrimination and turnover in a small-bodied insectivorous lizard

Laboratory experiments are useful for estimating the carbon and nitrogen isotope discrimination factors and turnover rates that are critical for drawing field-based inferences on consumer diets using stable isotopes. Although the utility of these discrimination factors is widely recognized, work in terrestrial systems has largely been limited to studies involving mammals and birds. In contrast, scant attention has been paid to the application of isotopic techniques to reptiles, despite their broad diversity in terms of numbers of species as well as their trophic roles. Here we estimate carbon and nitrogen isotope discrimination factors and turnover for the tree lizard (Urosaurus ornatus) using a diet-switch experiment. Lizards were collected from a C₄-dominated grassland and then switched to C₃-based diet (crickets) in the laboratory. We estimated discrimination by lizard claw tissue as Δ¹³C?=?1.2?±?0.1?‰ for carbon and Δ¹⁵N?=?0.7?±?0.1?‰ (mean?±?1 SE) for nitrogen, with 95?% turnover occurring after ～15.5 days. These estimates should be appropriate for use in trophic studies of U. ornatus, and possibly other related small-bodied insectivorous lizards.     

Effect of waterlogging on carbon isotope discrimination during photosynthesis in Larix gmelinii

Soil moisture is a major factor controlling carbon isotope discrimination (Δ¹³C), which has been demonstrated to decrease under dry conditions in many studies; however, few studies on Δ¹³C under waterlogging condition have been conducted. In this study, a pot experiment was conducted with Larix gmelinii, a major larch species in the east Siberian Taiga, to investigate the effect of waterlogging on Δ¹³C during photosynthesis. Assimilation rate and Δ¹³C_RD (instantaneous Δ¹³C calculated with Rayleigh distillation equation) decreased drastically soon after waterlogging, followed by recovery in their values, which was caused by a change in stomatal conductance. Thereafter, assimilation rate decreased gradually, whereas Δ¹³C_RD decreased more gently. These results were thought to be caused by the decrease in both stomatal conductance and carboxylation. Our results indicate that extreme wet events may cause a decrease in Δ¹³C, which is important information for detecting flooding events in the past using tree-ring isotope analyses and for studying impacts of flooding on plants in areas where waterlogging might occur.     

Non-linear dynamics of stable carbon and hydrogen isotope signatures based on a biological kinetic model of aerobic enzymatic methane oxidation

The non-linear dynamics of stable carbon and hydrogen isotope signatures during methane oxidation by the methanotrophic bacteria Methylosinus sporium strain 5 (NCIMB 11126) and Methylocaldum gracile strain 14 L (NCIMB 11912) under copper-rich (8.9 µM Cu²⁺), copper-limited (0.3 µM Cu²⁺) or copper-regular (1.1 µM Cu²⁺) conditions has been described mathematically. The model was calibrated by experimental data of methane quantities and carbon and hydrogen isotope signatures of methane measured previously in laboratory microcosms reported by Feisthauer et al. [1 Feisthauer S, Vogt C, Modrzynski J, Szlenkier M, Krüger M, Siegert M, Richnow HH. Different types of methane monooxygenases produce similar carbon and hydrogen isotope fractionation patterns during methane oxidation. Geochim Cosmochim Acta. 2011;75:1173–1184. doi: 10.1016/j.gca.2010.12.006[Crossref], [Web of Science ®] , [Google Scholar]] M. gracile initially oxidizes methane by a particulate methane monooxygenase and assimilates formaldehyde via the ribulose monophosphate pathway, whereas M. sporium expresses a soluble methane monooxygenase under copper-limited conditions and uses the serine pathway for carbon assimilation. The model shows that during methane solubilization dominant carbon and hydrogen isotope fractionation occurs. An increase of biomass due to growth of methanotrophs causes an increase of particulate or soluble monooxygenase that, in turn, decreases soluble methane concentration intensifying methane solubilization. The specific maximum rate of methane oxidation υ_m was proved to be equal to 4.0 and 1.3 mM mM^?1 h^?1 for M. sporium under copper-rich and copper-limited conditions, respectively, and 0.5 mM mM^?1 h^?1 for M. gracile. The model shows that methane oxidation cannot be described by traditional first-order kinetics. The kinetic isotope fractionation ceases when methane concentrations decrease close to the threshold value. Applicability of the non-linear model was confirmed by dynamics of carbon isotope signature for carbon dioxide that was depleted and later enriched in ¹³C. Contrasting to the common Rayleigh linear graph, the dynamic curves allow identifying inappropriate isotope data due to inaccurate substrate concentration analyses. The non-linear model pretty adequately described experimental data presented in the two-dimensional plot of hydrogen versus carbon stable isotope signatures.     

Partitioning of atmospheric carbon dioxide over Central Europe: insights from combined measurements of CO 2 mixing ratios and their carbon isotope composition

Regular measurements of atmospheric CO ₂ mixing ratios and their carbon isotope composition (¹³C/¹²C and ¹⁴C/¹²C ratios) performed between 2005 and 2009 at two sites of contrasting characteristics (Krakow and the remote mountain site Kasprowy Wierch) located in southern Poland were used to derive fossil fuel-related and biogenic contributions to the total CO ₂ load measured at both sites. Carbon dioxide present in the atmosphere, not coming from fossil fuel and biogenic sources, was considered ‘background’ CO ₂. In Krakow, the average contribution of fossil fuel CO ₂ was approximately 3.4%. The biogenic component was of the same magnitude. Both components revealed a distinct seasonality, with the fossil fuel component reaching maximum values during winter months and the biogenic component shifted in phase by approximately 6 months. The partitioning of the local CO ₂ budget for the Kasprowy Wierch site revealed large differences in the derived components: the fossil fuel component was approximately five times lower than that derived for Krakow, whereas the biogenic component was negative in summer, pointing to the importance of photosynthetic sink associated with extensive forests in the neighbourhood of the station. While the presented study has demonstrated the strength of combined measurements of CO ₂ mixing ratios and their carbon isotope signature as efficient tools for elucidating the partitioning of local atmospheric CO ₂ loads, it also showed the important role of the land cover and the presence of the soil in the footprint of the measurement location, which control the net biogenic surface CO ₂ fluxes.     

Using the 13C/12C carbon isotope ratio to characterise the emission sources of airborne particulate matter: a review of literature

ABSTRACT

Particulate matter (PM) from atmospheric aerosols contains carbons that are harmful for living organisms and the environment. PM can originate from vehicle emissions, wearing of vehicle components, and dust. Size and composition determine PM transport and penetration depth into the respiratory system. Understanding PM emission characteristics is essential for developing strategies to improve air quality. The number of studies on carbon isotope composition (¹³C/¹²C) of PM samples to characterise emission factors has increased. The goal of this review is to integrate and interpret the findings from ¹³C/¹²C carbon isotope ratio (δ¹³C, ‰) analyses for the most common types of emission sources. The review integrates data from 25 studies in 13 countries. The range of δ¹³C of PM from vehicle emissions was from ?28.3 to ?24.5?‰ and for non-vehicle anthropogenic emissions from ?27.4 to ?23.3?‰. In contrast, PM ranges for δ¹³C from biomass burning sources differed markedly. For C₃ plants, δ¹³C ranged from ?34.7 to ?25.4?‰ and for C₄ plants from ?22.2 to ?13.0?‰. The ¹³C/¹²C isotope analysis of PM is valuable for understanding the sources of pollutants and distinguishing vehicle emissions from biomass burning. However, additional markers are needed to further distinguish other anthropogenic sources.     

Development of non-lethal sampling of carbon and nitrogen stable isotope ratios in salmonids: effects of lipid and inorganic components of fins

The preferred tissue for analyses of fish stable isotope ratios for most researchers is muscle, the sampling of which typically requires the specimen to be sacrificed. The use of non-destructive methods in fish isotopic research has been increasing recently, but as yet is not a standard procedure. Previous studies have reported varying levels of success regarding the utility of non-lethally obtained stable isotope materials, e.g. fins, but none have accounted for the potential compounding effects of inorganic components of fin rays or lipids. Comparisons of carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of muscle with adipose and caudal fin of two salmonids, Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.), revealed that caudal fin can be used as a non-destructive surrogate for muscle in stable isotope analysis, but that adipose fin, where available, is a better proxy. The use of a published model to inexpensively counteract the confounding effect of lipids, which are depleted in ¹³C, greatly improved the relationship between fish muscle and fins. However, efforts to account for the inorganic components of fin rays were counterproductive and required twice the biomass of fins clipped from each fish. As this experiment was conducted on wild fish, controlled laboratory studies are required to confirm these field observations.     

Genotypic variability for carbon isotope discrimination in the mutant and improved lines of barley

Drought tolerance is an important breeding objective in dry and semi-dry conditions. Carbon isotope discrimination (Δ) is a tool that may be used to improve water-use efficiency (WUE) as an indirect selection criterion. The study investigated the variability for Δ in improved F₇ lines and their parents (three cultivars and two mutant lines), which were sampled randomly from an F₆ nursery performing well under semi-dry conditions. In total, 40 entries were grown in sand culture, arranged in three-replicated randomized complete block designs in two sets of experiments in Antalya, Turkey. There were statistically significant differences (p<0.01) among genotypes in both sets of experiments for Δ, and Δ values range from 20.14 to 21.86. Low coefficient of variation (C.V.) values, i.e. 2 and 1.65 %, for both data sets revealed efficient control of experimental error for Δ and indicated little effect of environment. Consequently, broad-sense heritability estimates for Δ were 0.63 and 0.74. As Δ showed a considerably high heritability and consistency over the two sets of experiments and low C.V. values, it was concluded that this trait could be used in breeding programmes aimed at developing drought tolerance lines. The early heading mutant, M-K-88, and the cultivar selected from land race, Tokak 157-37, showed lowest Δ values, indicating that they had the best water-use efficiency. Low Δ values of these two genotypes were inheritable.     

Tracing changes in the diet and habitat use of black-tailed godwits in Western France,using a stable isotope approach

Western France is at the crossroads of the migratory routes of two subspecies of black-tailed godwit, Limosa limosa. After leaving Iceland, the godwit L.l. islandica Icelandic black-tailed godwit (IBTG) winters on the coast of western Europe, while the continental black-tailed godwit (CBTG) L.l. limosa can stop in France when migrating between Iberia or Africa and their main breeding grounds in the Netherlands. In this study, we analysed δ¹⁵N and δ¹³C from flight feathers and whole blood throughout the non-breeding period to trace variations in habitat use for both subspecies on the western French coast. Adults and juveniles of IBTG adopt the same feeding habitats as soon as they arrive in the study area, progressively losing the Icelandic freshwater habitat signal, and becoming clearly restricted to marine habitats in winter. Some individuals begin to move locally to freshwater habitats, joining CBTG in a stopover at the end of the wintering period in preparation for northward migration.     

Modelling the specific pathway of CH4 and CO2 formation using carbon isotope fractionation: an example for a boreal mesotrophic fen

We described mathematically the process of peat methanization in a boreal mesotrophic fen. Gaseous and dissolved CH₄ and CO₂ as well as their δ¹³C signatures were considered in the dynamic equations for incubation bottles. In accordance with the model, acetate, H₂, and CO₂ were produced during cellulose hydrolysis and acidogenesis. ¹³C/¹²C in CO₂ was a key variable reflecting dynamic changes in the rates of cellulose hydrolysis and acidogenesis, acetoclastic and hydrogenotrophic methanogenesis. As CO₂ is the substrate in hydrogenotrophic methanogenesis, δ¹³C–CO₂ increased from the start till the dissolved hydrogen concentration became very low. Thereafter, the rate of acetoclastic methanogenesis with the significant current acetate concentration dominated over the rate of hydrogenotrophic methanogenesis leading to the decreasing δ¹³C–CO₂ and the increasing δ¹³C–CH₄. The model was validated by describing the system’s dynamics under strong and weak inhibition of acetoclastic and hydrogenotrophic methanogenesis by methyl fluoride, respectively. During peat methanization at the lowered temperature of 10?°C, the processes of hydrogenotrophic methanogenesis and homoacetogenesis competing for H₂ may occur. However, based on dynamics of the carbon isotope signatures, especially on dynamics of δ¹³C–CO₂, the model showed no significant contribution of homoacetogens in peat methanization.     

Seasonal variability of soil CO2 flux and its carbon isotope composition in Krakow urban area,Southern Poland

As urban atmosphere is depleted of ¹³CO₂, its imprint should be detectable in the local vegetation and therefore in its CO₂ respiratory emissions. This work was aimed at characterising strength and isotope signature of CO₂ fluxes from soil in urban areas with varying distances from anthropogenic CO₂ emissions. The soil CO₂ flux and its δ¹³C isotope signature were measured using a chamber method on a monthly basis from July 2009 to May 2012 within the metropolitan area of Krakow, Southern Poland, at two locations representing different levels of anthropogenic influence: a lawn adjacent to a busy street (A) and an urban meadow (B). The small-scale spatial variability of the soil CO₂ flux was also investigated at site B. Site B revealed significantly higher summer CO₂ fluxes (by approximately 46 %) than site A, but no significant differences were found between their δ¹³CO₂ signatures.     

Study of isotopes of carbon,thorium, and uranium in travertine and thermal spring samples: implications for effects of changes in geochemical environment and processes

Data on modern radiocarbon activity in the old travertine formations of the Pymvashor hydrothermal system were used, in combination with ²³⁰Th/U dating of the travertine, to estimate the ¹⁴C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine (¹⁴C_calc). With the known values of ¹⁴C_calc and average age of the thermal water, and under the assumption that the residence time of the water in aquifer was constant over the last 13.9?±?1.5 ka, the initial ¹⁴C contents (¹⁴C₀) in the ancient thermal water were estimated. The findings in this study are that (1) both ¹⁴C₀ and δ¹³С have decreased in young waters compared to the ancient waters; (2) although atmospheric ¹⁴C activity (¹⁴C_atm) has also decreased in the same time, the decrease in ¹⁴C₀ is faster than the decrease in ¹⁴C_atm. Under certain assumptions, one could link changes in ¹⁴C₀ and δ¹³C to climate change. Decrease in δ¹³С of soil CO₂ and decrease in ¹⁴C₀ was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in ¹⁴C_atm. There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO₂, caused by thawing permafrost.     

Food webs in Mongolian grasslands: The analysis of 13C and 15N natural abundances

Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the δ¹³C and δ¹⁵N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central Mongolia to understand the predominant food-web pathways in this grassland ecosystem. The δ¹³C and δ¹⁵N values of mammals showed little variation within species, but varied considerably with slope position for arthropods. The apparent isotopic discrimination between body tissue and hair of mammals was estimated as 2.0 ‰ for δ¹³C and 2.1 ‰ for δ¹⁵N, which was large enough to cause overestimation of the trophic level of mammals if not taken into account when using hair samples to measure isotopic enrichment.     

Determination of carbon isotope ratios of methanol and acetaldehyde in air samples by gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction

Isotopic signatures of atmospheric methanol and acetaldehyde have the potential to improve our ability to quantitatively assess their importance in atmospheric chemistry. However, isotopic measurements of atmospheric methanol and acetaldehyde and their individual source and sink processes have been limited. In this study, we examined gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction to measure the carbon isotope ratios of methanol and acetaldehyde in air samples. The method enabled us to determine carbon isotope ratios with a precision (1 standard deviation) of±0.6 ‰ for 20 ml of air sample containing more than 3 ppm of methanol and±0.7 ‰ for 20 ml of air sample containing more than 2 ppm of acetaldehyde. Moreover, the applicability of this method to determine isotope ratios of methanol and acetaldehyde emitted from detached plant leaves was demonstrated.     

Hydrology of the North Klondike River: carbon export,water balance and inter-annual climate influences within a sub-alpine permafrost catchment

Arctic and sub-arctic watersheds are undergoing significant changes due to recent climate warming and degrading permafrost, engendering enhanced monitoring of arctic rivers. Smaller catchments provide understanding of discharge, solute flux and groundwater recharge at the process level that contributes to an understanding of how larger arctic watersheds are responding to climate change. The North Klondike River, located in west central Yukon, is a sub-alpine permafrost catchment, which maintains an active hydrological monitoring station with a record of >40 years. In addition to being able to monitor intra-annual variability, this data set allows for more complex analysis of streamflow records. Streamflow data, geochemistry and stable isotope data for 2014 show a groundwater-dominated system, predominantly recharged during periods of snowmelt. Radiocarbon is shown to be a valuable tracer of soil zone recharge processes and carbon sources. Winter groundwater baseflow contributes 20?% of total annual discharge, and accounts for up to 50?% of total river discharge during the spring and summer months. Although total stream discharge remains unchanged, mean annual groundwater baseflow has increased over the 40-year monitoring period. Wavelet analysis reveals a catchment that responds to El Niño and longer solar cycles, as well as climatic shifts such as the Pacific Decadal Oscillation.

Dedicated to Professor Peter Fritz on the occasion of his 80th birthday