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1.
Stable (i.e. non-radioactive) carbon-isotope composition (δ13C) in fuels has been extensively used as an indicator of the processes leading to the generation of their parent crude-oil. With the example of those used in Paris (France), this preliminary study isotopically characterizes fuels and combustibles, as well as the isotopic relations existing with their combustion by-products, i.e. gases (CO2) and particles (bulk carbon). Results show that δ13C in fuels is clearly related to their physical state, with natural gas being strongly depleted in 13C while coal yields the highest δ13C, and liquid fuels display intermediate values. This relation is also valid for combustion gases, although δ13C values of combustion particles form a homogeneous range within which no clear distinction is observed. Combustion processes are accompanied by carbon-isotope fractionation (noted Δ13C) resulting from the combustion being incomplete. Carbon-isotope fractionation is strictly negative (Δ13C = ?1.3‰) during the formation of combustion gases, but generally positive in particle formation even if values close to zero are observed. Using simple mixing equations for describing the closed system formed by fuel, CO2 and carbonaceous particles, we discuss the carbon budget for spark-ignition (unleaded gasoline) and diesel engines. Stable carbon isotopes corroborate the already-proved superior efficiency of diesel combustion mode compared with spark ignition, as carbon is preferentially transformed into CO2.  相似文献   

2.
A survey study was conducted on man-made plantations located at two different areas in the arid region of Syria to determine the variations in natural abundances of the 15N and 13C isotopes in leaves of several woody legume and non-legume species, and to better understand the consequence of such variations on nitrogen fixation and carbon assimilation. In the first study area (non-saline soil), the δ15N values in four legume species (Acacia cyanophylla,?1.73 ‰ Acacia farnesiana,?0.55 ‰ Prosopis juliflora,?1.64 ‰; and Medicago arborea,+1.6 \textperthousand) and one actinorhizal plant (Elaeagnus angustifolia,?0.46 to?2.1 ‰) were found to be close to that of the atmospheric value pointing to a major contribution of N2 fixing in these species; whereas, δ15N values of the non-fixing plant species were highly positive. δ13C ‰; in leaves of the C3 plants were found to be affected by plant species, ranging from a minimum of?28.67 ‰; to a maximum of?23 ‰. However, they were relatively similar within each plant species although they were grown at different sites. In the second study area (salt affected soil), a higher carbon discrimination value (Δ13C ‰) was exhibited by P. juliflora, indicating that the latter is a salt tolerant species; however, its δ15N was highly positive (+7.03 ‰) suggesting a negligible contribution of the fixed N2. Hence, it was concluded that the enhancement of N2 fixation might be achieved by selection of salt-tolerant Rhizobium strains.  相似文献   

3.
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.  相似文献   

4.
High and fluctuating salinity is characteristic for coastal salt marshes, which strongly affect the physiology of halophytes consequently resulting in changes in stable isotope distribution. The natural abundance of stable isotopes (δ13C and δ15N) of the halophyte plant Salicornia brachiata and physico-chemical characteristics of soils were analysed in order to investigate the relationship of stable isotope distribution in different populations in a growing period in the coastal area of Gujarat, India. Aboveground and belowground biomass of S. brachiata was collected from six different populations at five times (September 2014, November 2014, January 2015, March 2015 and May 2015). The δ13C values in aboveground (?30.8 to ?23.6?‰, average: ?26.6?±?0.4?‰) and belowground biomass (?30.0 to ?23.1?‰, average: ?26.3?±?0.4?‰) were similar. The δ13C values were positively correlated with soil salinity and Na concentration, and negatively correlated with soil mineral nitrogen. The δ15N values of aboveground (6.7–16.1?‰, average: 9.6?±?0.4?‰) were comparatively higher than belowground biomass (5.4–13.2?‰, average: 7.8?±?0.3?‰). The δ15N values were negatively correlated with soil available P. We conclude that the variation in δ13C values of S. brachiata was possibly caused by soil salinity (associated Na content) and N limitation which demonstrates the potential of δ13C as an indicator of stress in plants.  相似文献   

5.
Abstract

Natural nitrogen isotope ratios were measured in different compartments (needles or leaves and twigs of different age classes and crown positions, roots and soil of different horizons) of spruce (Picea abies), larch (Larix decidua) and beech (Fagus sylvatica) trees in an 11-year-old mixed stand in the Fichtelgebirge, NE Bavaria, Germany. In addition, samples of understorey vegetation (mainly ericaceous shrubs and grass) and of ectomycorrhizal and saprophytic fungi were analyzed. The δ15N values found for all samples ranged between ?7.5 and + 4.5‰. No significant differences were found for the nitrogen isotope ratios of the three tree species despite of their evergreen versus deciduous foliage and despite of their different rooting depth. Ericaceous shrubs had the most negative and fungi and soil from the mineral horizon the most positive δ15N values. Positive δ15N values of the fungi indicate their ability to utilize organic soil nitrogen, but the data do not unequivocally show that plants forming mycorrhizas profit from this organic nitrogen source.  相似文献   

6.
Abstract

Leaf carbon isotope ratios (δ13C), an indicator of long-term intercellular carbon dioxide concentration, and also stem and root carbon isotope ratios were measured on the obligate CAM species Crassula argentea cultivated in pure and mixed cultures with the succulent C3 Peperomia obtusifolia in open-air conditions under two different levels of nitrogen and water supply.

As expected, a diminished water supply and a relatively dry and hot summer climate cause a shift of δ13C values to a less strong 13C discrimination (less negative δ13C values). A diminished nitrogen supply causes a shift of the δ13C values in direction of a higher 13C discrimination (more negative δ13C values), particularly in the leaves. Competition causes also an increased 13C discrimination, especially valid for shoot axes.

The shift of 13C/12C isotope ratios in case of nitrogen deficiency is discussed to be a result of a decreased PEPCase activity in the night.  相似文献   

7.
Abstract

Apple snails Pomacea lineata (SPIX 1827) are widespread in the tropical regions of Brazil as well as in the Pantanal wetland of Mato Grosso in the western part of the country. They have a key position in the Pantanal food web and serve as food for many animals e.g. fishes, birds, and caimans. However, little is known about their feeding preferences and growth rates. Stable isotopes have been used successfully on numerous studies as food source indicator. Therefore, the δ15N and δ13C values of snails from 0.45 to 3.03cm in length, which were collected in the rainy season from March through May, were analyzed. Snails signatures revealed ambiguous evidence for food preferences. δ15N and δ13C values ranged between ?2.8 and 12.4‰ and between ?24.2 and ?16.4‰, respectively. This range of values mirrors the highly variable isotope values of possible food sources comprising C3 and C4 macrophytes. To test whether all common food sources were similarly assimilated, feeding experiments with different diets were conducted. Snail eggs were reared in tanks and offered different but single plants. Snails fed different diets and δ13C values of the food were reflected in the animal tissue. Growth varied considerably in experiments with different diets indicating the preference for certain food sources. Also, the fractionation of nitrogen isotopes between food and animal varied from 0.1 to 17.0‰. The results are explained by different feeding habits, and it is supposed that animals fed either on the plant itself or on bacteria mats growing in the tanks. In an additional experiment juvenile snails were offered one single food with a distinctive C4 grass signature. These snails did not grow detectably, but nevertheless isotope signatures approached to values of the diet.  相似文献   

8.
Abstract

The metabolism of tumor-cells differs in many ways from normal (healthy) cells. One of the major differences is the high glycolytic activity in tumor-cells with the subsequent formation of lactate from glucose, even in the presence of oxygen. The question whether this high rate of glycolysis has any effect on the 13C/12C-relation of the cells is examined in experiments with a tumor-cell line (HT29) and in specimens of human breast cancer.

The HT29 cells show a clear decrease in 13C content compared to their culture medium (Δδ = 3.28‰).

Tissue from human breast cancer has more 13C than normal breast tissue taken from the same patient ((Δδ = 2.74‰). But the content of fat is much higher in the normal tissue and its δ-value is negatively correlated with its fat content. It is concluded that the difference between normal and tumor tissue is due to the heterogeneous composition of the normal tissue samples.  相似文献   

9.
Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002–2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ13C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ13CDIC values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO3 (I sat values 4–10) and with δ13CDIC values between?11.5 and?8.5 ‰. In spring waters, the δ13CDIC values were more negative, from?14 to?12 ‰, and I sat values of 1–2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ13CDIC correlated with the increase in the δ13C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.  相似文献   

10.
Abstract

Locust nymphs were raised from hatching to adult locusts on either seedling wheat (C3) or maize (C4), to determine whether relative enrichments/depletions of 15N and 13C within body tissues are influenced by diet. The maize contained less hexose sugars and protein per gram than wheat.

The isotopic spacing between the food and the whole insect was found to differ between the two diets. The lower quality maize diet showed an overall +5.1‰ enrichment in δ15N compared to + 2.8‰ for wheat, possibly due to increased fractionation due to protein recycling.

The maize diet resulted in increased depletion in lipid and trehalose and depletion in chitin relative to diet. The results for both δ15N and δ13C suggest that substrate recycling was occurring on the low quality maize diet. Therefore diet quality determines the enrichment/depletion in δ15N and δ13C within organisms.  相似文献   

11.
Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of 15N. A short review displays that δ15N of plant–soil systems may often serve as an integrated indicator of N-cycles with more positive δ15N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs show that intensively grazed pastures are significantly enriched in 15N compared to the less-exploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive δ15N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in 15N, indicating that here the N-cycle is relatively closed. However, significantly higher δ15N values characterise the upper montane forest zone at the transition to the subalpine zone. We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the 15N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening.  相似文献   

12.
When a diet switch results in a change in dietary isotopic values, isotope ratios of the consumer's tissues will change until a new equilibrium is reached. This change is generally best described by an exponential decay curve. Indeed, after a diet switch in captive red knot shorebirds (Calidris canutus islandica), the depletion of 13C in both blood cells and plasma followed an exponential decay curve. Surprisingly, the diet switch with a dietary 15N/14N ratio (δ15N) change from 11.4 to 8.8 ‰ had little effect on δ15N in the same tissues. The diet-plasma and diet-cellular discrimination factors of 15N with the initial diet were very low (0.5 and 0.2 ‰, respectively). δ15N in blood cells and plasma decreased linearly with increasing body mass, explaining about 40 % of the variation in δ15N. δ15N in plasma also decreased with increasing body-mass change (r 2=.07). This suggests that the unusual variation in δ15N with time after the diet switch was due to interferences with simultaneous changes in body-protein turnover.  相似文献   

13.
Abstract

Customary 13CO2 breath tests—and also 15N urine tests—always start with an oral administration of a test substrate. The test person swallows a stable isotope labelled diagnostic agent. This technique has been used to study several pathophysiological changes in gastrointestinal organs. However, to study pathophysiological changes of the bronchial and lung epithelium, the inhalative administration of a stable isotope labelled agent appeared more suitable to us. [1-13C]Hexadecanol and [1-13C]glucose were chosen. Inhaled [1-13C]hexadecanol did not yield 13CO2 in the exhaled air, but [1-13C]glucose did. To study the practicability of the [1-13C]glucose method and the reproducibility of the results, 18 inhalation tests were performed with healthy subjects. In 6 self-tests, the optimum inhalative dose of [13C]glucose was determined to be 205 mg. Using the APS aerosol provocation system with the nebulizer ‘Medic Aid’ (Erich Jaeger Würzburg), a 25% aqueous solution was inhaled. Then, breath samples were collected at 15 min. intervals and analysed for 13CO2. 75–120min after the end of inhalation a well-reproducible maximum δ13C value of 6‰ over baseline (DOB) was detected for 12 healthy probands.

Speculating that the pulmonary resorption of the [13C]glucose is the rate-limiting step of elimination, decompensations in the epithelium ought to be reflected in changed [1-13C]glucose resorption rates and changed 13CO2 output.

Therefore, we speculate that the inhalation of suitable 13C-labelled substrates will pave the way for a new group of 13CO2 breath tests aiding investigations of specific pathophysiological changes in the pulmonary tract, such as inflammations of certain sections and decompensations of cell functions.  相似文献   

14.
A combination of C/N ratios, δ13C and δ15N values in suspended matter was used to examine the seasonal (late summer 2004 and spring 2005) relationship with hydrological characteristics of the River Sava watershed in Slovenia. The values of C/N ratios range from 1.2 to 19.1, δ13C values range from?29.2 to?23.0 ‰ and δ15N values from 0.5 to 16.7 ‰ and indicate that the samples are a mixture of two end members: modern soils and plant litter. A simple mixing model was used to indicate that soil organic carbon prevails over plant litter and contributes more than 50% of suspended material. The calculated annual particulate organic carbon flux is estimated as 5.2×1010 g C/year, the annual particulate nitrogen flux 8.5×109 g N/year and the total suspended solid flux is estimated to be 1.3×1012 g/year. Anthropogenic impact was detected only in a tributary stream of the River Sava, which is located in an agriculture–industrial area and is reflected in higher δ15N values in suspended matter and high nitrate concentrations in the late summer season.  相似文献   

15.
Abstract

The modification of nitrogen isotopic signals during particle sedimentation in the sea is of great interest for the use of sedimentary δ15N-values as a paleoceanographic tool. The effect of organic matter degradation on such modification was studied by analyzing nitrogen, hydrolyzable amino acids (THAA) and δ15N-values in a suit of marine settling particles collected from the Bay of Bengal, Indian Ocean, by using time-series sediment traps, and in underlying sediments. The flux of settling particles showed temporal variations which are related to the monsoons, the major climatic feature of this marine region. During high flux periods settling particles are enriched in nitrogenous material that is less degraded and exhibit higher δ15N-values than particles showing characteristics of degradation. At the sediment surface more than 95% of the settling particulate nitrogen is lost and the δ15N-values of the residual sedimentary nitrogen are higher than those of settling particles. The observed increase is interpreted to be due to fractionation during degradation of organic matter.  相似文献   

16.
[5-13C,15N]Glutamine, with 1J(13C–15N) of 16 Hz, was observed in vivo in the brain of spontaneously breathing rats by 13C MRS at 4.7 T. The brain [5-13C]glutamine peak consisted of the doublet from [5-13C,15N]glutamine and the center [5-13C,14N]glutamine peak, resulting in an apparent triplet with a separation of 8 Hz. The time course of formation of brain [5-13C,15N]glutamine was monitored in vivo with a time resolution of 20–35 min. This [5-13C,15N]glutamine was formed by glial uptake of released neurotransmitter [5-13C]glutamate and its reaction with 15NH3 catalyzed by the glia-specific glutamine synthetase. The neurotransmitter glutamate C5 was selectively13C-enriched by intravenous [2,5-13C]glucose infusion to 13C-label whole-brain glutamate C5, followed by [12C]glucose infusion to chase 13C from the small and rapidly turning-over glial glutamate pool, leaving 13C mainly in the neurotransmitter [5-13C]glutamate pool, which is sequestered in vesicles until release. Hence, the observed [5-13C,15N]glutamine arises from a coupling between 13C of neuronal origin and 15N of glial origin. Measurement of the rate of brain [5-13C,15N]glutamine formation provides a novel noninvasive method of studying the kinetics of neurotransmitter uptake into glia in vivo, a process that is crucial for protecting the brain from glutamate excitotoxicity.  相似文献   

17.
Abstract

We evaluated the use of δ15N- and δ13C-values to monitor the development of food web complexity and biodiversity in a regenerating ecosystem. Therefore a model food chain was established feeding cultivated woodlice (Porcellio dilatatus) on a cellulolytic fungus (Chaetomium globosum) grown on cellulose paper. Two diets of different quality (C:N ratios of 54 vs. 200) with different δ15N- (1.3‰ vs. 3.1‰) but identical δ13C-values caused low and high dietary stress in animals of treatment A and B, respectively. After an incubation time of 7 weeks amount, elemental and isotopic composition of collected faeces and exuviae as well as woodlice and remaining food were determined.

The increase of δ15N-values of woodlice relative to the diet was 5.7‰ and 2.5‰ in treatments A and B, respectively, whereas δ13C-shifts were 1.0‰ and 1.6‰, showing a reverse relationship. Modelling of elemental and isotopic mass balances indicated that faeces recycling explains the unexpected high 15N-enrichments. Moreover, 13C-enrichments were positively correlated to the degree of starvation. Considering the effects of starvation and recycling of faeces, stable isotopes represent a useful tool to elucidate trophic interactions in regenerating food webs.  相似文献   

18.
Abstract

In estuarine ecosystems, large spatial and seasonal variations in δ13C values of primary producers can occur, and knowledge of these variations may be crucial when interpreting stable isotope data of higher trophic levels. Obtaining clean phytoplankton samples for isotope analysis is usually impossible in such systems, and analysis of total suspended matter is not a simple proxy for phytoplankton δ13C variations. Based on a few simple assumptions regarding the C and N content of the two end-members (terrestrial detritus and phytoplankton) and the δ13C of the terrestrial component, we here present a simple model to estimate the phytoplankton δ13C variations using an existing dataset on the δ13C and elemental (C:N) composition of suspended organic matter from an estuarine mangrove ecosystem in southeast India.

These variations are related to the monthly rainfall pattern during the sampling period. It is stressed that this method estimates approximate phytoplankton δ13C values, which should not be used in e.g., mixing models. However, we propose that in cases where sufficiently large datasets are available, the described procedure could provide a valuable method to semi-quantitatively estimate the seasonal or spatial variations of the phytoplankton δ13C signal.  相似文献   

19.
Data from a 10-month monitoring study during 2007 in the Everglades ecosystem provide insight into the variation of δ18O, δD, and ion chemistry in surface water and shallow groundwater. Surface waters are sensitive to dilution from rainfall and input from external sources. Shallow groundwater, on the other hand, remains geochemically stable during the year. Surface water input from canals derived from draining agricultural areas to the north and east of the Everglades is evident in the ion data. δ18O and δD values in shallow groundwater remain near the mean of?2.4 and?12 ‰, respectively. 18O and D values are enriched in surface water compared with shallow groundwater and fluctuate in sync with those measured in rainfall. The local meteoric water line (LMWL) for precipitation is in close agreement with the global meteoric water line; however, the local evaporation line (LEL) for surface water and shallow groundwater is δ D=5.6 δ18O+1.5, a sign that these waters have experienced evaporation. The intercept of the LMWL and LEL indicates that the primary recharge to the Everglades is tropical cyclones or fronts. δ deuterium to δ18O excess (Dex values) generally reveal two moisture sources for precipitation, a maritime source during the fall and winter (D ex>10 ‰) and a continental-influenced source (D ex<10 ‰) in the spring and summer.  相似文献   

20.
Carbon and nitrogen stable isotope ratios were measured in hair samples of the Asiatic black bear (Ursus thibetanus) inhabiting the Northern Japanese Alps (NJA) (n?=?20) and the periphery of Nagano City (NC) (n?=?6), in Nagano Prefecture, Japan. The hair of NJA bears, which did not have access to anthropogenic foods, showed lower values of δ13C and δ15N than that of NC bears which had access to garbage and corn fields, especially during the summer. These results reflect somewhat differing diets between the NJA and NC bears. We attempted to assess the feeding history during the hair growth cycle using the growth section analysis method. Each hair sample had been cut into 3?mm lengths from root to tip, labeled, and analyzed along the hair growth. We measured the carbon and nitrogen stable isotope ratios of each 3?mm length of hair sample from one NC bear which had been killed while raiding a corn field. The sections showed wide ranges of isotope ratios, from ?23.2‰ to ?14.6‰ for δ13C, and from 0.3‰ to 4.6‰ for δ15N. It was shown that the diet of this bear shifted dramatically from principally C3 plants to more C4 plants and to foods of animal origin. An analysis of the whole hair reflects just the average feeding habit during hair growth, but the present method can trace its diet history. This method can contribute to obtain precise ecological information of wildlife.  相似文献   

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