Variability of stable isotope signatures (δC and δN) in two spider crab populations (Maja brachydactyla) in Western Europe

The ontogenic variations of nitrogen and carbon stable isotopic signatures (δ¹⁵N and δ¹³C) were investigated in two spider crab (Maja brachydactyla) populations inhabiting in different biotopes of Western Europe. The Iroise Sea population is localized in Western Brittany and characterized by a seasonal migration occurring on a large bathymetric and habitat gradient while the Seine Bay population, in the Eastern English Channel, remains in a more homogeneous environment during its migration. In the Iroise Sea population, δ¹³C values increased significantly both with body size and age, revealing a shift towards “benthic-component” prey with spider crab growth. On the contrary, neither body size nor ageing gave rise to a significant trophic level change (derived from the δ¹⁵N). In this M. brachydactyla population, the seasonal migrations from coastal waters in summer to offshore habitats in winter involved significant but slight differences in both δ¹³C and δ¹⁵N. In the Seine Bay population, low variations for both carbon and nitrogen were recorded related to either sex or size or seasonal migration. Thus, the δ¹³C and δ¹⁵N variability in the spider crab depends on the availability and diversity of prey in its different living habitats, as well as on the morphological aptitudes of individuals to feed on prey (individual's size).     

Determining the appropriate pretreatment procedures and the utility of liver tissue for bulk stable isotope (δ13C and δ15N) studies in sharks

Stable-isotope analysis (SIA) provides a valuable tool to address complex questions pertaining to elasmobranch ecology. Liver, a metabolically active, high turnover tissue (~166 days for 95% turnover), has the potential to reveal novel insights into recent feeding/movement behaviours of this diverse group. To date, limited work has used this tissue, but ecological application of SIA in liver requires consideration of tissue preparation techniques given the potential for high concentrations of urea and lipid that could bias δ¹³C and δ¹⁵N values (i.e., result in artificially lower δ¹³C and δ¹⁵N values). Here we investigated the effectiveness of (a) deionized water washing (WW) for urea removal from liver tissue and (b) chloroform-methanol for extraction of lipids from this lipid rich tissue. We then (a) established C:N thresholds for deriving ecologically relevant liver isotopic values given complications of removing all lipid and (b) undertook a preliminary comparison of δ¹³C values between tissue pairs (muscle and liver) to test if observed isotopic differences correlated with known movement behaviour. Tests were conducted on four large shark species: the dusky (DUS, Carcharhinus obscurus), sand tiger (RAG, Carcharias taurus), scalloped hammerhead (SCA, Sphyrna lewini) and white shark (GRE, Carcharodon carcharias). There was no significant difference in δ¹⁵N values between lipid-extracted (LE) liver and lipid-extracted/water washed (WW) treatments, however, WW resulted in significant increases in %N, δ¹³C and %C. Following lipid extraction (repeated three times), some samples were still biased by lipids. Our species-specific “C:N thresholds” provide a method to derive ecologically viable isotope data given the complexities of this lipid rich tissue (C:N thresholds of 4.0, 3.6, 4.7 and 3.9 for DUS, RAG, SCA and GRE liver_LEWW tissue, respectively). The preliminary comparison of C:N threshold corrected liver and muscle δ¹³C values corresponded with movement/habitat behaviours for each shark; minor differences in δ¹³C values were observed for known regional movements of DUS and RAG (δ¹³C_Diffs = 0.24 ± 0.99‰ and 0.57 ± 0.38‰, respectively), while SCA and GRE showed greater differences (1.24 ± 0.63‰ and 1.08 ± 0.71‰, respectively) correlated to large-scale movements between temperate/tropical and pelagic/coastal environments. These data provide an approach for the successful application of liver δ¹³C and δ¹⁵N values to examine elasmobranch ecology.     

Differences in the C age, δC and δO of Holocene tufa and speleothem in the Dinaric Karst

We studied Holocene speleothems and tufa samples collected in numerous caves and rivers in the Dinaric Karst of Croatia, Slovenia, Bosnia and Herzegovina, as well as Serbia and Montenegro. Differences in the formation process of tufa and speleothems are discussed in the context of their isotopic composition (¹⁴C, ¹³C and ¹⁸O), as well as the chemistry of surface water (rivers, lakes) and drip water (in caves). The physical and chemical parameters monitored in the surface water (tufa precipitation) and drip water (speleothem precipitation) show that more stable conditions accompany speleothem rather than tufa formation. This is particularly obvious in the water temperature variations (2-22°C in surface water and 7-12°C in drip water) and in saturation index variation (3-11 in surface water and 1-6 in drip water). The range of ¹⁴C ages recorded by Holocene speleothems (∼12?000 yr) is wider by several thousands years than that of Holocene tufa samples (∼6000 yr). δ¹³C values for tufa samples range from −12‰ to −6‰ and for speleothem samples from −12‰ to +3‰ reflecting higher soil carbon and/or vegetation impact on the process of tufa than on speleothem formation. The differences in δ¹⁸O values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water. The study shows that speleothems from the Dinaric Karst can be used as global palaeoclimatic records, whereas tufa records changes in the local palaeoenvironment.     

Linking Isotopes and Panmixia: High Within-Colony Variation in Feather δ2H, δ13C,and δ15N across the Range of the American White Pelican

Complete panmixia across the entire range of a species is a relatively rare phenomenon; however, this pattern may be found in species that have limited philopatry and frequent dispersal. American white pelicans (Pelecanus erythrorhyncos) provide a unique opportunity to examine the role of long-distance dispersal in facilitating gene flow in a species recently reported as panmictic across its broad breeding range. This species is also undergoing a range expansion, with new colonies arising hundreds of kilometers outside previous range boundaries. In this study, we use a multiple stable isotope (δ²H, δ¹³C, δ¹⁵N) approach to examine feather isotopic structuring at 19 pelican colonies across North America, with the goal of establishing an isotopic basemap that could be used for assigning individuals at newly established breeding sites to source colonies. Within-colony isotopic variation was extremely high, exceeding 100‰ in δ²H within some colonies (with relatively high variation also observed for δ¹³C and δ¹⁵N). The high degree of within-site variation greatly limited the utility of assignment-based approaches (42% cross-validation success rate; range: 0–90% success). Furthermore, clustering algorithms identified four likely isotopic clusters; however, those clusters were generally unrelated to geographic location. Taken together, the high degree of within-site isotopic variation and lack of geographically-defined isotopic clusters preclude the establishment of an isotopic basemap for American white pelicans, but may indicate that a high incidence of long-distance dispersal is facilitating gene flow, leading to genetic panmixia.     

Effect of increased sediment sulfide concentrations on the composition of stable sulfur isotopes (δS) and sulfur accumulation in the seagrasses Zostera marina and Posidonia oceanica

The effect of increased sediment sulfide concentrations on the sulfur isotopic composition (δ³⁴S), total sulfur (TS) and elemental sulfur (S⁰) concentrations in plant tissues was studied for the two seagrasses Zostera marina (3 weeks in laboratory) and Posidonia oceanica (4 months in situ). Porewater sulfide concentrations were experimentally regulated and plants exposed to high sediment sulfide concentrations had δ³⁴S signals closer to the δ³⁴S of sulfide, whereas plants exposed to no / low sulfide concentrations had δ³⁴S signals closer to the δ³⁴S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to high sulfide concentrations. The δ³⁴S varied between the plant tissues in both species with the leaves having more positive δ³⁴S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS and S⁰ concentrations were higher in plants exposed to sulfide in both experiments suggesting that sulfur derived from sediment sulfide accumulated in the plants. The δ³⁴S signal in S⁰ was similar to sediment sulfide verifying that S⁰ found in the seagrasses originated from sediment sulfide. Direct comparisons of δ³⁴S in the two different seagrasses and across the treatments were not possible due to large differences in δ³⁴S of the sulfur sources. F_sulfide adjusted for these differences and may be a useful alternative, when δ³⁴S of the sulfur sources varies between study sites. There were no significant effects of sulfide exposure on plant growth and mortality in Z. marina and P. oceanica after 3 weeks and 8 weeks exposure, respectively, but P. oceanica showed indications of reduced growth and higher mortality after 16 weeks of sulfide exposure probably due to sulfide invasion/toxicity.     

Ecosystem structure and soil-surface conditions drive the variability in the foliar δ13C and δ15N of Stipa tenacissima in semiarid Mediterranean steppes

We evaluated the effects of ecosystem composition and structure (species richness and diversity, cover and spatial attributes of vegetation), abiotic factors (climate and topographical features) and the condition of the bare-ground areas (evaluated using soil-surface indicators) on the performance of Stipa tenacissima [evaluated using foliar ¹³C, ¹⁵N, nitrogen concentration and the carbon-to-nitrogen (C:N) ratio] in 15 steppes of SE Spain. Foliar ¹³C values of S. tenacissima showed a low degree of variation in the studied steppes, with average values ranging from –24.1 to –22.9. Higher variation was found in the ¹⁵N values, which ranged from –5.5 to –2.4. The nitrogen concentration and the C:N ratio varied between 5.0 and 8.0 mg g^–1, and between 55.4 and 85.3, respectively. The ¹³C values became less negative with increasing spatial aggregation of perennial vegetation, while the C:N values increased with increasing perennial vegetation cover. The ¹⁵N values became more negative with increasing infiltration in the bare-ground areas, but the nitrogen concentration was not related to any of the environmental variables measured. Our results suggest that the relative importance of ecosystem structure and soil-surface conditions in the bare ground areas was higher than that of abiotic factors as determinants of the performance of S. tenacissima. The results also show that even subtle changes in these ecosystem features may lead to modifications in plant performance in semiarid S. tenacissima steppes, and thus to modifications in the associated ecosystem functions in the mid- to long-term.     

δ13C and δ15N indicators of fish and shrimp community diet and trophic structure in a mangrove ecosystem in Thailand

Stable carbon and nitrogen isotope ratios were used to elucidate primary carbon sources and trophic relationships of the fish and shrimp community in the Klong Ngao mangrove ecosystem, southern Thailand. There were no significant differences in isotopic compositions of biota between mangrove and offshore sites (Welch–Aspin test). The δ¹⁵N values of eight fish species and two shrimp species at both sites were also not significantly different by the test, meaning that at both sites they feed on the same diets due to the discharge of large quantities of mangrove sediments. The δ¹⁵N isotopic enrichment of consumers suggested that there are four trophic levels in the Klong Ngao food web, with at least two fish species capable of switching feeding strategies and thus altering their apparent trophic positions. Phytoplankton culture experiments indicated that mangrove-derived sediments could play an important role in stimulating phytoplankton growth for low turbidity offshore areas, thus providing an alternate food source. The isotopic associations among sources and consumers indicated that mangroves were the major carbon source supporting aquatic food webs in the Klong Ngao ecosystem.     

Effect of nutritional condition on variation in δ13C and δ15N stable isotope values in Pumpkinseed sunfish (Lepomis gibbosus) fed different diets

Stable isotope analysis is frequently used to infer resource use in natural populations of fishes. Studies have examined factors, other than diet, that influence δ¹⁵N and δ¹³C including tissue-specific rates of equilibration and starvation. Most such studies completed under laboratory conditions tightly control food quantity and its isotopic composition, but it is also necessary to evaluate the influence of these factors under more natural conditions. Using pumpkinseed sunfish (Lepomis gibbosus) we evaluated whether restricted rations below minimum daily requirements affects tissue equilibration to a change in diet by holding fish on two treatments that often reflect divergent resource use in natural populations (pelagic zooplankton or littoral macroinvertebrates). Over 42 days, δ¹⁵N values increased while δ¹³C values did not change, additionally neither were related to diet treatment. Increased δ¹⁵N values were negatively related to body condition while δ¹³C values were not, indicating that stable isotope values were more affected by decreasing body condition than by diet. Additionally, δ¹⁵N values changed more in the blood and liver tissues than in white muscle tissue, indicating that restricting food availability had greater effects on tissues with greater metabolic activity. We hypothesize that stable isotope values of consumers are subject to a tissue-specific trade-off between sensitivity to changes in resource use and resistance to the effects of low resource availability. This trade-off may require consideration in stable isotope studies of wild populations facing periodic limitations of food availability.     

Growth and migration patterns of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary,Japan—combination of stable isotope ratio and otolith microstructure analyses

It is important to know the characteristics of migration pattern and vital rates of juveniles to understand the early life history and its effect on the population dynamics of fishes. The relationship between growth and migration pattern of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary was examined by combination of stable carbon isotope ratio (δ¹³C) and otolith microstructure. Gut fullness indices were also examined to know the feeding condition of juveniles. δ¹³C values of seabass juveniles in the lower estuary and surf zone (LES) were enriched, while those in freshwater zone (FW) were depleted, consistent with δ¹³C differences in prey items. The back-calculated growth rates of juveniles in FW were significantly lower than those of juveniles that resided in the LES from 50 days to 90 days old, implying that juveniles with poor growth ascended the river while those with better growth remained in the LES. However, the growth rates of the juveniles, which resided in FW for more than 1 month, caught up with and even overtook those of juveniles in LES within 1 month after ascended the river. The higher water temperature and better feeding conditions would contribute to better growth rates of juveniles in FW than those in LES.     

Identifying carbon sources and trophic position of coral reef fishes using diet and stable isotope (δ15N and δ13C) analyses in two contrasted bays in Moorea, French Polynesia

Stable isotope ratios (δ¹⁵N and δ¹³C) and diet of three fish species, Stegastes nigricans, Chaetodon citrinellus and Epinephelus merra, were analyzed on the fringing coral reefs of two bays that are differentially exposed to river runoff on Moorea Island, French Polynesia. S. nigricans and C. citrinellus relied mostly on turf algae and presented similar trophic levels and δ¹⁵N values, whereas E. merra fed on large invertebrates (crabs and shrimps) and had higher trophic levels and δ¹⁵N values. Discrepancies existed between stomach content and stable isotope analyses for the relative importance of food items. Bayesian mixing models indicated that sedimented organic matter was also an important additional food for S. nigricans and C. citrinellus, and fishes for E. merra. The main sources of organic matter involved in the food webs ending with these species were algal turfs and surface sediments, while water particulate organic matter was barely used. Significant spatial differences in C and N isotopic ratios for sources and fishes were found within and between bays. Lower ¹³C and higher ¹⁵N values were observed for various compartments of the studied trophic network at the end of each bay than at the entrance. Differences were observed between bays, with organic sources and consumers being, on average, slightly more ¹³C-depleted and ¹⁵N-enriched in Cook’s Bay than in Opunohu Bay, linked with a higher mean annual flow of the river at Cook’s Bay. Our results suggest that rivers bring continental material into these two bays, which is partly incorporated into the food webs of fringing coral reefs at least close to river mouths. Thus, continental inputs can influence the transfer of organic matter within coral reef food webs depending on the diet of organisms.     

Spatial Variation in δ15N and δ13C Isotopes in the San Juan River, New Mexico and Utah: Implications for the Conservation of Native Fishes

Synopsis Spatial patterns of resource use by small-bodied fishes in the San Juan River were examined using stable isotopes. Using δ¹⁵N of fishes as an index of trophic position, our data suggest both native and non-native fishes primarily consumed macro-invertebrates. The δ¹³C of these fishes further suggested a detritus-based food web, from which most species fed on chironomids in low-velocity habitats. A two-way ANOVA revealed a significant interaction between trophic level of fish species and longitudinal position in the river. This interaction was primarily attributed to a decline in trophic level of non-native red shiner Cyprinella lutrensis, relative to other species, in upstream reaches of the river. In addition, ANCOVA results suggest trophic position of fishes was dependent on channel type (primary vs. secondary), as there was less variability in resource use in secondary channels. These data provided a spatial framework of trophic interactions that can be used to predict the outcome of management actions. Overall, we confirmed high overlap in resource used between native and non-native fishes. However, spatial variation in trophic interactions both longitudinally and laterally in the river present a challenge to resource managers attempting to managing entire river systems.     

Seasonal variation in stable C and N isotope ratios of the Rhone River inputs to the Mediterranean Sea (2004–2005)

The temporal variation in the stable carbon and nitrogen isotope ratios of particulate organic matter (POM) in the Rhone River was investigated on a monthly basis during a 2-year period (2004–2005). In spite of high month-to-month variation, interannually consistent seasonal trends appeared, with significantly lower δ¹³C (<?28.2‰) in spring than in the other seasons. In contrast, δ¹⁵N did not exhibit significant temporal variation. In spring and summer, high chlorophyll a and b concentrations were associated with low C/N values (<8) and a high percentage of organic carbon (%C) and organic nitrogen (%N), testifying to high development of autochthonous riverine phytoplankton (mainly diatoms and chlorophytes). In fall and winter, higher δ¹³C (>?27.2‰) and C/N (>8) values, and lower %C, %N, and chlorophylls concentrations indicated the predominance of allochthonous terrestrial detritus material in the river POM. The lower δ¹³C values recorded in spring–summer, when the phytoplankton biomass was high, were related to the lower carbon isotopic signatures of freshwater diatoms and chlorophytes compared to those of terrestrial plants. Overall, Rhone River POM was mainly composed of terrestrially derived material (90%), with autochthonous phytoplankton representing only 10% as a mean, in spite of a higher mean contribution of phytoplankton (27%) to river POM in summer.     

N,O versus O,O coordination in β-imino diketonato complexes: Role of the metal center and of the imino substituent

β-Imino carbonyl enolato metal(II) complexes of general formula [M((RCO)(R′CO)CC(R″)NH)₂] (M = Mn, Fe, Co, Ni, Cu, Zn, Pd, R = R′ = Me, R″ = CCl₃; M = Cu, Pd, R = R′ = Me, R″ = PhCO; R = Me, R′ = Ph, R″ = PhCO; R = R′ = Ph, R″ = PhCO) are easily synthesized by the reaction of metal(II) acetates with the proper β-enaminodiones in 1/2 molar ratio in ethanol at room temperature. In all the cases the trifunctional NOO β-imino carbonyl enolate ligand acts as bidentate to give ML₂ complexes, whose structure depends on the metal center and on the nature of the substituent R″ at the imino carbon. With R″ = CCl₃ an O,O coordination is observed for all the metal centers but one, in fact palladium(II) exhibits an N,O coordination through the imino nitrogen and one keto oxygen. By contrast with R″ = PhCO the ligand is always coordinated through the imino nitrogen and one keto oxygen atom.     

Variations in the foliar δ13C and C3/C4 species richness in the Japanese flora of Poaceae among climates and habitat types under human activity

For 383 Poaceae species harvested over the Japanese islands and stored as herbarium specimens along several decades, we determined C₃ and C₄ types of photosynthesis from leaf stable carbon isotope ratio (δ¹³C). Then, we sought the relationships between C₄ species richness and climatic factors or habitat types. Except for the two Panicum species (P. lanuginosum and P. scoparium) having the possibility of C₃–C₄ intermediate, 227 and 154 species were classified into C₃ and C₄. The C₄ species richness increased from northern to southern islands in Japan, positively correlated with mean annual air temperature. Greater C₄ species richness in the seashore habitats, and smaller C₄ species richness in the shaded, wet and highland habitats would be related to the photosynthetic responses to local environmental factors such as irradiance level and temperature regime. No difference of leaf δ-value of C₃ Poaceae was obtained between the habitats with different soil water availability, suggesting the less importance of soil water availability on leaf water-use efficiency in C₃ Poaceae species in Japan having humid climate. Additionally, possible effects of human activity around the harvested time or site on leaf δ-value were estimated, because the habitat includes the sites with high human activity. Leaf δ-value was decreased with sampling year, and it was higher in the densely inhabited district for both C₃ and C₄. They are probably due to a historical decrease in the atmospheric δ-value via increasing human activity, and high gas emission at the districts of high human density.     

Diversity,metabolic types and δ13C carbon isotope ratios in the grass flora of Namibia in relation to growth form,precipitation and habitat conditions

The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in ¹³C values along a rainfall gradient (50–600 mm) and in different habitat conditions. However, there are significant differences in the ¹³C values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest ¹³C values (–11.7 ) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower ¹³C values (–13.4 ) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (–12.5 ) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative ¹³C values than PCK species and ¹³C values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, ¹³C values decreased from –11 in the inland region (600 mm precipitation) to –15 near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.     

Natal origins and timing of migration of two passerine species through the southern Alps: inferences from multiple stable isotopes (δ2H, δ13C, δ15N, δ34S) and ringing data

Understanding spatial linkages between areas used by migratory animals during the annual cycle is fundamental to their conservation. Stable isotope measurements of animal tissues can be a valuable tool in understanding spatial connectivity and migration phenology of migratory wildlife. We inferred natal origins of two migratory passerines, European Pied Flycatcher Ficedula hypoleuca and European Robin Erithacus rubecula, captured during autumn migration in the Italian Alps, by combining feather δ²H (δ²H_f) and ring recovery data. We used a spatially explicit likelihood-based method to assign individuals to a precipitation δ²H surface calibrated to represent feather δ²H, together with the directional probability of origin from ring recoveries. The highest probabilities of origin for most individuals of both species were in central and north-eastern Europe. Seasonal trends in δ²H_f, which described the species’ migratory phenology through the Italian Alps, were correlated with feather δ¹³C, δ¹⁵N and δ³⁴S values, indicating strong spatial discrimination related to continental patterns for these isotopes. We demonstrate how this combined information can define catchment areas and migratory connectivity of birds intercepted in the Alps. We highlight the importance of ringing data in defining directional priors to define Bayesian-based probability surfaces using continental δ²H_f isoscapes, and how such information can be used to inform estimates of migratory connectivity.     

Stable isotopic (δ13C and δ18O) signatures of biogenic calcretes marking discontinuity surfaces: a case study from Upper Cretaceous carbonates of central Dalmatia and eastern Istria,Croatia

Biogenic calcretes associated with a regional Cretaceous to Paleogene subaerial unconformity and an intraformational composite (polygenic) surface in Upper Cretaceous intra-platform peritidal successions in central Dalmatia and eastern Istria, Croatia (Adriatic-Dinaridic Carbonate Platform), were analyzed for their δ¹³C and δ¹⁸O signatures in order to provide insight into the conditions of subaerial exposure and calcrete development. The distinctly negative δ¹³C signatures of biogenic calcretes marking the regional subaerial unconformity differ considerably from the δ¹³C values of the host marine limestones. This indicates carbon isotope exchange of primary marine CaCO₃ with CO₂ released by root and rhizomicrobial respiration and subsequent precipitation of pedogenic calcrete. The range of δ¹³C (from ?13.1 to ?8.2 ‰ Vienna PeeDee Belemnite standard, VPDB) and δ¹⁸O (from ?10.1 to ?6.1 ‰ VPDB) values of calcretes are similar to those reported from calcretes elsewhere, and the δ¹³C values of biogenic calcretes with typical Microcodium aggregates (?13.1 to ?12.3 ‰ VPDB) at the ?ibenik locality are very close to, or at the lower limit of, values for soil carbonates formed in isotopic equilibrium with soil CO₂. These values are expected for authigenic pedogenic carbonates formed under the influence of C₃ plant communities, without influence from heavier carbon from pre-existing carbonate and lack of input of atmospheric CO₂. Such low δ¹³C values support the interpretation of Microcodium aggregates as being precipitated under a direct biological control within the soil, although the relationship between formation mechanisms and stable isotope signatures of Microcodium needs further investigation. The δ¹³C values (?4.4 to ?3.6 ‰ VPDB) of rhizogenic calcretes formed inside firmground Thalassinoides burrows of the composite surface at the ?ibenik locality are more negative than the δ¹³C values of the host marine limestones, which confirms that the composite surface went through a phase of meteoric pedo(dia)genesis. However, the overall δ¹³C values of calcretes are less negative than expected, which might reflect contamination from associated primary marine carbonate. This study represents the first detailed stable isotope investigation of calcretes from carbonate successions of the External Dinarides, and the results may be applied to discontinuities present in other shallow-water carbonate rock successions.     

Seasonal dynamics in the stable carbon isotope composition δ¹³C from non-leafy branch, trunk and coarse root CO₂ efflux of adult deciduous (Fagus sylvatica) and evergreen (Picea abies) trees

Respiration is a substantial driver of carbon (C) flux in forest ecosystems and stable C isotopes provide an excellent tool for its investigation. We studied seasonal dynamics in δ¹³C of CO₂ efflux (δ¹³C_E) from non‐leafy branches, upper and lower trunks and coarse roots of adult trees, comparing deciduous Fagus sylvatica (European beech) with evergreen Picea abies (Norway spruce). In both species, we observed strong and similar seasonal dynamics in the δ¹³C_E of above‐ground plant components, whereas δ¹³C_E of coarse roots was rather stable. During summer, δ¹³C_E of trunks was about ?28.2‰ (Beech) and ?26.8‰ (Spruce). During winter dormancy, δ¹³C_E increased by 5.6–9.1‰. The observed dynamics are likely related to a switch from growth to starch accumulation during fall and remobilization of starch, low TCA cycle activity and accumulation of malate by PEPc during winter. The seasonal δ¹³C_E pattern of branches of Beech and upper trunks of Spruce was less variable, probably because these organs were additionally supplied by winter photosynthesis. In view of our results and pervious studies, we conclude that the pronounced increases in δ¹³C_E of trunks during the winter results from interrupted access to recent photosynthates.     

On the structure of the lipopolysaccharide core in the cell wall of Escherichia coli K12 W2252-11U− and its ter-mutant cells

From Escherichia coli K12 W2252-11U^? (wild type I and II) and its Ter-mutants, lipopolysaccharides were isolated and the primary structure of its core region was elucidated, the configuration of the glucose III (1→2)-linked to the glucose II residue in the core of parents (wild type I and II) changes into the configuration of the glucose (1→3)-linkage by the Ter-mutation. Also, the structure of the core in the Ter-15 mutant differs from that in the parent (wild type I) and is similar to that in Escherichia coli C used as an indicator for φ×174 phage. D-ribose residue in the core of the Ter-21 mutant links to the glucose I residue instead of the galactose residue in the core of the parent (wild type II).