Natural abundances of 15N and 13C in leaves of some N2-fixing and non-N2-fixing trees and shrubs in Syria

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.     

Estimates of dietary overlap for six species of Amazonian manakin birds using stable isotopes

We used stable isotope ratios to determine the metabolic routing fraction of carbon and nitrogen in feathers in addition to faecal analysis to estimate diet overlap of six sympatric species of manakins in the eastern lowland forest of Ecuador. Collectively, all species varied from?23.7 to?32.7 ‰ for δ¹³C, and from 6.0 to 9.9‰ for δ¹⁵N, with Machaeropterus regulus showing isotopic differences from the other species. We developed a mixing model that explicitly addresses the routing of carbon and nitrogen to feathers. Interestingly, these results suggest a higher proportion of nitrogen and carbon derived from insects than anticipated based on feeding observations and faecal analysis. A concentration-dependent mixing isotopic model was also used to look at dietary proportions. While larvae and arachnids had higher δ¹⁵N values, these two groups may also be preferred prey of manakins and may be more assimilated into tissues, leading to a potential overestimation of the contribution to diet. This study supports the finding that manakin species, previously thought be primarily frugivorous, contain a significant amount of arthropods in their diet.     

Stable isotopes determination in some Romanian wines

This paper presents a study concerning the isotopic fingerprint (¹⁸O and ¹³C) of some wines prepared from relevant Romanian grape varieties (e.g. Feteasca Alba (FA), Feteasca Regala (FR) and Cabernet Sauvignon (CS)) obtained in different vintage years (2002, 2003, 2004, 2007 and 2008). These wines were obtained from different vineyards having a significant role in the wine market: Cotesti, Tohani, Stefanesti, Aiud, Cotnari, Bucium, Murfatlar, Bujoru, Dragasani and Valea Calugareasca. Several observations related to the dependence of isotope ratios on geographical origin and climatic conditions were drawn. The authentic wines obtained from the FA grape variety from six different vineyards showed δ¹⁸O values in the range of+3.28 (Cotesti region – 45 °38′N/27 °04′E) to?2.60 ‰ (Aiud region – 46 °19′N/23 °45′E). The δ¹³C values were very similar for all the samples with an average of about?26 ‰. The difference between the δ¹⁸O values was due to the different climatic zones, which have an influence on the δ¹⁸O values of wine water. For the wine variety CS obtained from the Dealu Mare–Tohani vineyard, production years 2003 and 2004, a greater difference in the δ¹⁸O values of wine water ranging from 1.89 (in 2004) to 5.35 ‰ (in 2003) was noted. This difference is explained by the different mean annual temperatures in 2003 and 2004.     

Characteristics of suspended matter in the River Sava watershed,Slovenia

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.     

Unusual patterns in 15N blood values after a diet switch in red knot shorebirds

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.     

13C and 15N Abundances in the Sediment Core (VER 92/1-St-10-GC2) from Northern Lake Baikal

Abstract

Carbon and nitrogen stable isotope compositions of organic matter, TOC/TN ratio, and manganese concentration in a sediment core that was collected in northern part of Lake Baikal (VER92ST10-GC2, water depth at 922 m, about 3 m long) were investigated to elucidate the origin of the sedimentary organic matter and its associated environmental factors.

The sediment core was composed of mainly two parts: turbidite sections and other sections. Constant δ¹³C and δ¹⁵N values of the turbidite sections were observed (- 26.8 ±0.2 ‰ for δ¹³C and 3.2 ± 0.1 ‰ for δ¹⁵N) throughout the core. The higher δ¹³C in turbidite sections (about - 27 ‰) than that of the other sections (- 31 to - 29 ‰) was clearly observed, and δ¹⁵N was different between turbidite sections (about 3‰) and other sections (3 to 5 ‰). δ¹³C of other sections was close to that of pelagic phytoplankton, indicating that sediment other than turbidite sections is composed of autochthonous components. The variation of stable isotopes in other sections may be possibly caused by the changes in either phytoplankton growth rate or contribution ratios of terrestrial to aquatic plants for δ¹³C. Either denitrification or fluctuation of δ¹⁵N in pelagic phytoplankton can be the cause of variable δ¹⁵N in other sections.     

Conference Report

Soil from Free-Air Carbon dioxide Enrichment (FACE) plots (FAL, Braunschweig) under ambient air (375 ppm; δ¹³C–CO₂?9.8‰) and elevated CO₂ (550 ppm; for six years; δ¹³C–CO₂?23‰), either under 100% nitrogen (N) (180 kg ha^?1) or 50% N (90 kg ha^?1) fertilisation treatments, was analysed by thermogravimetry. Soil samples were heated up to the respective temperatures and the remaining soil was analysed for δ¹³C and δ¹⁵N by Isotope Ratio Mass Spectrometry (IRMS). Based on differential weight losses, four temperature intervals were distinguished. Weight losses in the temperature range 20–200 °C were connected mostly with water volatilisation. The maximum weight losses and carbon (C) content were measured in the soil organic matter (SOM) pool decomposed at 200–360 °C. The largest amount of N was detected in SOM pools decomposed at 200–360 °C and 360–500 °C. In all temperature ranges, the δ¹³C values of SOM pools were significantly more negative under elevated CO₂ versus ambient CO₂. The incorporation of new C into SOM pools was not inversely proportional to its thermal stability. 50% N fertilisation treatment gained higher C exchange under elevated CO₂ in the thermally labile SOM pool (200–360 °C), whereas 100% N treatment induced higher C turnover in the thermally stable SOM pools (360–500 °C, 500–1000 °C). Mean Residence Time of SOM under 100% N and 50% N fertilisation showed no dependence between SOM pools isolated by increasing temperature of heating and the renovation of organic C in those SOM pools. Thus, the separation of SOM based on its thermal stability was not sufficient to reveal pools with contrasting turnover rates of C.     

Seasonal variation in natural abundance of δ13C and 15N in Salicornia brachiata Roxb. populations from a coastal area of India

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.     

The Effect of Diet Quality on δ13C and δ15N in the Tissues of Locusts,Locusta migratoria L

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.     

Temporal diet changes recorded by stable isotopes in Asiatic black bear (Ursus thibetanus) hair

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.     

Carbon-13 Kinetic Isotope Effects in the Decarbonylation of Liquid Formic Acid Assisted with Acetic Anhydride

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.     

Spatial and temporal variability of stable isotopes and biological parameters for the Danube River in Serbia

This paper presents the results of hydrological, physicochemical, biological, and isotopic investigations of the Danube River along the stretch through Serbian territory conducted during four campaigns in September and November 2007, September 2008 and April 2009. The stable isotope values exhibited significant changes both in the Danube (?10.7 to?9.5‰ for δ¹⁸O and?73.7 to?67.1 ‰ for δ²H) and in its tributaries (?9.1 to?8.5‰ for δ¹⁸O and?69.4 to?59.4‰ for δ²H) depending on the time of survey, which could be partly attributed to the influences of seasonal effects. Results emphasise the dominant role of tributaries inflows from aquifers along the Danube. The very narrow range of δ¹³C_POC (from?28.9 to?27.4 ‰) was associated with relatively high C/N ratios (C/N>9), and together with δ¹⁵N_TPN values, the date suggested that, in early spring, a major fraction of particulate organic matter was derived from allochthonous matter. An orthogonal varimax rotation of the principal components analysis identified four latent factors (‘mineral related’, ‘biological’, ‘hardness’, and ‘soil inlets’) which are responsible for the data structure covering 79% of the observed variations among the variables studied. A reliable grouping of samples with respect to the season was found.     

Estimation of microbial methane generation and oxidation rates in the municipal solid waste landfill of Kaluga city,Russia

Using a theoretical model and mass isotopic balance, biogas (methane and CO₂) released from buried products at their microbial degradation was analysed in the landfill of municipal and non-toxic industrial solid organic waste near Kaluga city, Russia. The landfill contains about 1.34×10⁶ tons of waste buried using a ‘sandwich technique’ (successive application of sand–clay and waste layers). The δ¹³C values of biogenic methane with respect to CO₂ were?56.8 (±2.5) ‰, whereas the δ¹³C of CO₂ peaked at+9.12‰ (+1.4±2.3‰ on average), reflecting a virtual fractionation of carbon isotopes in the course of bacterial CO₂ reduction at the landfill body. After passing through the aerated soil layers, methane was partially oxidised and characterised by δ¹³C in the range of?50.6 to?38.2‰, evidencing enrichment in ¹³C, while the released carbon dioxide had δ¹³C of?23.3 to?4.04‰, respectively. On the mass isotopic balance for the δ¹³C values, the methane production in the landfill anaerobic zone and the methane emitted through the aerated landfill surface to the atmosphere, the portion of methane oxidised by methanotrophic bacteria was calculated to be from 10 to 40% (averaged about 25%). According to the theoretical estimation and field measurements, the annual rate of methane production in the landfill reached about 2.9(±1.4)×10⁹ g C CH₄ yr^?1 or 5.3(±2.6)×10⁶ m³ CH₄ yr^?1. The average rates of methane production in the landfill and methane emission from landfill to the atmosphere are estimated as about 53 (±26) g C CH₄ m^?2 d^?1 (or 4 (±2) mol CH₄ m^?2 d^?1) and 33 (±12) g C CH₄ m^?2 d^?1 (or 2.7 (±1) mol CH₄ m^?2 d^?1), respectively. The calculated part of methane consumed by methanotrophic bacteria in the aerated part of the landfill was 13(±7) g C CH₄ m^?2 d^?1 (or 1.1(±0.6) mol CH₄ m^?2 d^?1) on average.     

Diet–consumer nitrogen isotope fractionation for prolonged fasting arthropods

Nitrogen acquisition for cellular metabolism during diapause is a primary concern for herbivorous arthropods. Analyses of naturally occurring stable isotopes of nitrogen help elucidate the mechanism. Relevant articles have cited (58 times up to mid-June 2011) anomalously elevated δ¹⁵N (per mil deviation of ¹⁵N/¹⁴N, relative to atmospheric nitrogen=0 ‰) values (diet–consumer nitrogen isotope fractionation; up to 12 ‰) for a prolonged fasting raspberry beetle (Byturus tomentosus Degeer (Coleoptera: Byturidae)), which feeds on red raspberries (Rubus idaeus: δ¹⁵N=～+2 ‰). Biologists have hypothesised that extensive recycling of amino acid nitrogen is responsible for the prolonged fasting. Since this hypothesis was proposed in 1995, scientists have integrated biochemical and molecular knowledge to support the mechanism of prolonged diapausing of animals. To test the validity of the recycling hypothesis, we analysed tissue nitrogen isotope ratios for four Japanese arthropods: the shield bug Parastrachia japonensis Scott (Hemiptera: Cydnidae), the burrower bug Canthophorus niveimarginatus Scott (Hemiptera: Cydnidae), leaf beetle Gastrophysa atrocyanea Motschulsky (Coleoptera: Chrysomelidae) and the Japanese oak silkworm Antheraea yamamai (Lepidoptera: Saturniidae), all of which fast for more than 6 months as part of their life-history strategy. Resulting diet–consumer nitrogen isotope discrimination during fasting ranged from 0 to 7‰, as in many commonly known terrestrial arthropods. We conclude that prolonged fasting of arthropods does not always result in anomalous diet–consumer nitrogen isotope fractionation, since the recycling process is closed or nearly closed with respect to nitrogen isotopes.     

15N natural abundance of non-fixing woody species in the Brazilian dry forest (caatinga)

Foliar δ¹⁵N values are useful to calculate N₂ fixation and N losses from ecosystems. However, a definite pattern among vegetation types is not recognised and few data are available for semi-arid areas. We sampled four sites in the Brazilian caatinga, along a water availability gradient. Sites with lower annual rainfall (700 mm) but more uniform distribution (six months) had δ¹⁵N values of 9.4 and 10.1 ‰, among the highest already reported, and significantly greater than those (6.5 and 6.3 ‰) of sites with higher rainfall (800 mm) but less uniform distribution (three months). There were no significant differences at each site among species or between non-fixing legume and non-legume species, in spite of the higher N content of the first group. Therefore, they constitute ideal reference plants in estimations of legume N₂ fixation. The higher values could result from higher losses of ¹⁵N depleted gases or lower losses of enriched ¹⁵N material.     

Measuring δ13C values of atmospheric acetaldehyde via sodium bisulfite adsorption and cysteamine derivatisation

δ¹³C values of gaseous acetaldehyde were measured by gas chromatograph–combustion–isotope ratio mass spectrometer (GC–C–IRMS) via sodium bisulfite (NaHSO₃) adsorption and cysteamine derivatisation. Gaseous acetaldehyde was collected via NaHSO₃-coated Sep-Pak^® silica gel cartridge, then derivatised with cysteamine, and then the δ¹³C value of the acetaldehyde–cysteamine derivative was measured by GC–C–IRMS. Using two acetaldehydes with different δ¹³C values, derivatisation experiments were carried out to cover concentrations between 0.009×10^?3 and 1.96×10^?3 mg·l^?1) of atmospheric acetaldehyde, and then δ¹³C fractionation was evaluated in the derivatisation of acetaldehyde based on stoichiometric mass balance after measuring the δ¹³C values of acetaldehyde, cysteamine and the acetaldehyde–cysteamine derivative. δ¹³C measurements in the derivertisation process showed good reproducibility (<0.5 ‰) for gaseous acetaldehyde. The differences between predicted and measured δ¹³C values were 0.04–0.31 ‰ for acetaldehyde–cysteamine derivative, indicating that the derivatisation introduces no isotope fractionation for gaseous acetaldehyde, and obtained δ¹³C values of acetaldehyde in ambient air at the two sites were distinct (?34.00 ‰ at an urban site versus?31.00 ‰ at a forest site), implying potential application of the method to study atmospheric acetaldehyde.     

Groundwater of the Crimean peninsula: a first systematic study using stable isotopes

ABSTRACT

Karst springs in the Main Range of the Crimean Mountains and the Crimean Piedmont show a restricted range of values (δ¹⁸O?=?–10.5 to –8.0 ‰, δ²H?=?–72 to –58 ‰), somewhat more negative than the weighted mean of meteoric precipitation. This suggests preferential recharge at higher elevations during winter months. Groundwater tapped by boreholes splits in three groups. A first group has isotopic properties similar to those of the springs. The second group shows significantly lower values (δ¹⁸O?=?–13.3 to –12.0 ‰, δ²H?=?–95 to –82 ‰), suggesting recharge during colder Pleistocene times. The third group has high isotope values (δ¹⁸O?=?–2.5 to +1.0 ‰, δ²H?=?–24 to –22 ‰); the data points are shifted to the right of the Local Meteoric Water Line, suggesting water–rock exchange processes in the aquifer. These boreholes are located in the Crimean Plains and discharge mineralized (ca. 25 g L^?1) thermal (65°C) water from a depth of 1600–1800 m. Groundwater associated with mud volcanoes on the Kerch peninsula have distinct isotope characteristics (δ¹⁸O?=?–1.6 to +9.4 ‰, δ²H?=?–30 to –18 ‰). Restricted δ²H variability along with variable and high δ¹⁸O values suggest water–rock interactions at temperatures exceeding 95 °C.     

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.     

Differential response of two Pinus spp. to avian nitrogen input as revealed by nitrogen isotope analysis for tree rings

Temporal variations in N concentration and δ¹⁵N value of annual tree rings (1 year of time resolution) of two Japanese Black Pine (Pinus thunbergii) and three Japanese Red Pine (Pinus densiflora) trees under current breeding activity of the Great Cormorant (Pharacrocorax carbo) and the Black-tailed Gull (Larus crassirostris), respectively, in central and northeastern Japan were studied. Both species from control sites where no avian input occurs show negative values (δ¹⁵N = around?4 ‰ to?2 ‰) which are common among higher plants growing under high rainfall regimes. The δ¹⁵N values of P. densiflora show uniformly positive values several years before and after the breeding event, indicating N translocation that moved the absorbed N of a given growth year to tree rings of the previous year while a clear historical value of soil N dynamics was kept intact in the annual rings of P. thunbergii. Long-term N trends inferred from tree rings must take into account tree species with limited translocation rates that can retain actual N annual acquisition.     

Characterising ontogenetic niche shifts in Nile crocodile using stable isotope (δ13C, δ15N) analyses of scute keratin

Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35–463 cm total length), we found prominent size-related changes in the scute keratin δ¹³ C and δ¹⁵ N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods.