Differences In δ13C Values Research Articles

Fractionation of δ15N and δ13C for Atlantic salmon and its intestinal cestode Eubothrium crassum

Stable isotopes of nitrogen (δ15N) and carbon (δ13C) were measured for Atlantic salmon Salmo salar and their intestinal cestode, Eubothrium crassum, sharing the same diet. Atlantic salmon muscle tissues were enriched in 15N and depleted in 13C compared to their prey (sprat Sprattus sprattus sprattus) and their intestinal cestode. There was no significant difference in δ15N or δ13C between E. crassum and the sprat. Differences in nutrient uptake and intestine physiology between Atlantic salmon and E. crassum are discussed, as well as how these may give rise to different fractionations of stable isotopes between a host and its parasites. Furthermore, Atlantic salmon contained a significantly higher lipid content than their prey, which may partly explain differences in δ13C values between the host and its cestode. In addition, cestodes inhabiting lipid‐rich hosts were also lipid rich. Larger Atlantic salmon were enriched in 15N compared to smaller fish. Cestodes inhabiting large hosts were also enriched in 15N compared to parasites living in smaller hosts. The last two results were explained by larger fish possibly feeding from a higher trophic level, or from larger and older prey, that resulted in both a higher lipid content and an enrichment in 15N.

Isotopic (δ15N and δ13C) evidence for intersexual foraging differences and temporal variation in habitat use in waved albatrosses

Waved albatrosses ( Phoebastria irrorata Salvin, 1883) forage close to their breeding grounds on Isla Española, Galápagos, during the short chick-brooding stage and make long trips to the Peruvian upwelling during incubation and chick rearing. Previous studies have suggested foraging segregation by sex: females spend more time searching than males do while foraging in the Galápagos Marine Reserve (GMR), and band recoveries suggest higher bycatch vulnerability of males in the Peruvian upwelling. We used stable isotope analysis (δ15N and δ13C) of whole blood of adult male and female albatrosses to test for intraspecific foraging segregation in this sexually dimorphic species. Analysis of serial blood samples revealed higher δ15N values in males, suggesting consumption of prey items of higher trophic level. We also detected seasonal variation in foraging ecology, with higher δ15N values at the beginning of the breeding season. Sex and regional differences in δ13C values were not significant, reflecting primarily pelagic foraging sites of both sexes, both in the GMR and the Peruvian upwelling. Our results provide evidence of trophic segregation, suggestive of competitive exclusion, and novel information on marine isoscape values in the Eastern Equatorial Pacific.

The variations of stable-carbon isotope ratios in Qilian juniper in northwestern China

This is the first study of δ13C values that considers elevational influences of the Qilian mountains of China. The δ13C values of different parts of the Qilian juniper (Sabina przewalskii Kom.) at different elevations of the Qilian mountains, China, were measured. Relatively constant differences in δ13C values existed between the tree leaves and the trunk wood. No strong dependency of δ13C values on elevation was found. The temporal changes of wood δ13C values with directions, elevations and height in the tree showed general similarity. These results suggest that the isotopic effects of environmental factors expressed initially at the site of photosynthesis, i.e., the leaves could be contained in the trunks of a tree. Regardless of elevation, direction or height in the tree, wood δ13C values have been decreasing during the past 60 years. A composite 600-year δ13C chronology developed from four trees showed that δ13C values remain relatively constant before 1800. After 1800 AD, however, δ13C values became significantly more negative. The trend in wood δ13C values was consistent with that obtained for δ13C values in atmospheric CO2. The results showed that for Qilian juniper, tree-ring δ13C chronology could be established to ascertain fluctuations of the atmospheric δ13C.

The stable carbon and nitrogen isotopic composition of vegetation in tropical forests of the Amazon Basin, Brazil

Here we present the within-site, seasonal, and interannual variations of the carbon (δ13C) and nitrogen (δ15N) isotope ratios of leaves, wood, bark and litter from four sites in the Amazon region, Brazil. Samples were collected in Manaus (3° 06′07′′ S; 60°01′30′′ W), Ji-Parana (10°53′07′′ S; 61°57′06′′ W), and Santarem (2°26′35′′ S; 54°42′30′′ W) with mean annual precipitation of 2207, 2040 and 1909 mm respectively. The overall average for all leaf samples was \(-32.3\pm2.5\permille\) for δ13C and \(+5.8\pm1.6\permille\) for δ15N (n=756). The leaf δ values at these sites were often but not always statistically distinct from each other. The δ13C values varied from \(-37.8\permille\) to \(-25.9\permille\). Pronounced differences in δ13C values occurred with height associated with differences in forest structure. The δ13C of leaf dry matter showed seasonal variations associated with the length of the dry season, despite the fact that total annual precipitation was similar among the studied sites. Leaf δ15N values ranged from \(+0.9\permille\) to a maximum value of \(+10.9\permille\), and the Santarem sites showed more enriched values than Manaus and Ji-Parana sites. No seasonal variation was detected in the δ15N of leaves, but significant differences were observed among sites and with changes in canopy height. The isotope ratio data are consistent with our current understanding of the roles of light, water availability, and recycling of soil-respired CO2 influences on δ13C and consistent with our understanding that an open nitrogen cycle can lead to high δ15N values despite a significant number of legumes in the vegetation.

Stable carbon and nitrogen isotope analysis of Nephrops norvegicus / Merluccius merluccius fishing grounds in the Bay of Biscay (Northeast Atlantic)

The trophic structure of the benthic ecosystem of the Grande Vasière (Great Mud Bank), a heavily trawled area in the Bay of Biscay, is largely unknown. To better understand the biotic interactions between exploited species (mainly Norway lobster, Nephrops norvegicus, and European hake, Merluccius merluccius) and their competitors and prey, we applied a dual stable carbon (13C/12C) and nitrogen (15N/14N) isotope analysis to determine trophic levels and differences in the potential food sources of species in the benthic and demersal communities. Five main groups of species constitute the basis of the trophic structure. They are distributed in three main trophic levels: primary consumers; secondary consumers including N. norvegicus and juvenile M. merluccius; and top predators including adult M. merluccius (δ15N = 14.5‰). The large differences in δ13C values within the primary consumers attest to two different food components: a pelagic component composed of fresh sedimenting particulate organic matter, which mainly supplies supra- and epi-benthic suspension feeders, and zooplankton, and a benthic component, which mainly supplies deposit feeders. For the predators, the target species, and their competitors, diet changes during the life-span are reflected by differences in isotope values for the size classes.

Land‐use related organic matter dynamics in North Cameroon soils assessed by 13C analysis of soil organic matter fractions

SummaryTopsoil samples from cultivated and adjacent non‐cultivated fields on three major agricultural soils in North Cameroon were fractionated into particle‐size fractions that were analysed subsequently for their C and 13C contents. The aim was to obtain further insight into the dynamics of soil organic matter (SOM) in relation to land use in Cameroon. Since organic carbon contents of the fractions were often very small, samples and analyses were extensively replicated to obtain robust statistical estimates of observed differences. For each soil type, differences in δ13C values between fields could be related to changes in the input and decomposition of organic matter arising from soil type, land management and, for example, the nature and abundance of weeds. Turnover of organic matter appeared to be fastest in the sand fraction, which is in line with results from earlier studies. In the finer fractions, clear differences in reaction to changes in input and decomposition were observed, that seem to be linked to differences in clay mineralogy. The results illustrate that SOM in the various fractions is much less stable and more strongly affected by changes in land use than might be assumed on the basis of changes in total SOM contents alone. At the same time, they demonstrate the relevance of 13C isotope analyses of SOM for studies on the impact of land use on these savannah soils with little SOM that are highly susceptible to degradation.

The dynamics of organic matter in soil size and density fractions traced by stable carbon isotopes

On the basis of different photosynthetic pathways, there is an obvious difference in δ13C values between C3 plants and C4 plants. In terms of this characteristic, we analyzed the δ13C values in different size and density fractions from two profile-soil samples either in farmland and forestlands near the Maolan Karst virgin forest, Southwest China, where there were developed C3 plants previously and now are C4 plants. Results showed that the δ13C values of different size fractions in forestland soil are δl3Ccoarse sand δ13 Cfine sand > δ13 Ccoarse silt > δ13 Cclay > δ13 Cfine silt, indicating that soil organic matter is fresh in coarse sand and oldest in fine silt. The δ13 C values of different density fractions in forestland soil are δ13 Clight δ13Cheavy, indicating that the soil organic matter is fresh in light fractions and old in heavy fractions.

The variation of soil organic matter in a forest-cultivation sequence traced by stable carbon isotopes

On the basis of different photosynthetic pathways, there is an obvious difference in δ13C values between C3 and C4 plants. In terms of this characteristic, we analyzed the organic carbon content (forestlands: 1.81% –16.00%; farmland: 0.43% –2.22%) and δ13C values (forestlands: -23. 86‰ -−27. 12‰; farmland: −19. 66‰ -−23.26‰) of three profile-soil samples either in farmland or in forestland near the Maolan Karst virgin forest, where there were developed plant C3 plants previously and now are C4 plants. Results showed that the deforestation has accelerated the decomposition rate of soil organic matter and reduced the proportion of active components in soil organic matter and thus soil fertility.

The changes in soil organic matter in a forest-cultivation sequence traced by stable carbon isotopes

There is an obvious difference in δ13C values between plants that assimilate carbon via the C3 photosynthetic pathway and those that do so by the C4 photosynthetic pathway. In terms of this characteristic, we analysed the organic carbon content and δ13C values of total soil and δ13C values in different size and density fractions of profile-soil samples either in farmland or in forestland near the Maolan Karst virgin forest, south-west China. This is an area where C3 plants grew previously, now replaced by C4 plants. Deforestation has accelerated the decomposition rate of soil organic matter and reduced the proportion of active components in soil organic matter and thus soil fertility. The δ13C values of different size fractions in forest soil are δ13Ccoarse sand < δ13Cfine sand < δ13Ccoarse silt < δ13Cclay < δ13Cfine silt, and the δ13C values of different size fractions in farmland soil are δ13Ccoarse sand > δ13Cfine sand > δ13Ccoarse silt > δ13Cclay > δ13Cfine silt, indicating that soil organic matter is fresh in coarse sand and oldest in fine silt. The δ13C values of different density fractions in forest soil are δ13Clight < δ13Cheavy, and the δ13C values of different density fractions in farmland soil are δ13Clight > δ13Cheavy, indicating that the soil organic matter is fresh in light fractions and old in heavy fractions.

Radiocarbon and stable carbon isotope compositions of organic compound classes in sediments from the NE Pacific and Southern Oceans

Radiocarbon (Δ14C) abundance and stable carbon isotope (δ13C) compositions were measured for total lipid, total hydrolyzable amino acids (THAA), total carbohydrates (TCHO), and acid-insoluble organic fractions separated from phytoplankton, zooplankton, and sediment cores collected from two abyssal sites, one in the northeast (NE) Pacific Ocean and one in the Southern Ocean. These results are compared with those obtained for a separate core from the NE Pacific and reported by Wang et al. [Geochim. Cosmochim. Acta 62 (1998) 1365.]. An uncharacterized acid-insoluble fraction dominated (43-57%) the sediment TOC pool at both sites. Sediment collected from the NE Pacific exhibited higher TOC, TN. and higher Δ14C values and contained both labile (THAA and TCHO) and refractory (lipid and acid-insoluble) fractions. In contrast, sediment from the Southern Ocean had much lower TOC and Δ14C values, which indicated that organic matter was extremely refractory. Sedimentation rates calculated from 14C ages of TOC for both sites indicate that the differences in the organic composition and Δ14C signatures of organic matter in the sediments likely resulted from the differences in production and deposition of organic matter to the sediment, and the diagenetic stages of sedimentary organic matter in the two oceans. Unlike Δ14C, stable carbon isotopic (δ13C) compositions of TOC in the sediments of the two oceans had similar values, which reflect not only the organic matter input from marine-derived sources but also the nature of degraded, predominately uncharacterized organic fraction in these sediments. The differences in δ13C values among the compound classes in sediments at both sites can be attributed to the carbon isotopic signatures in original sources during photosynthesis and associated environmental factors. Preferential degradation of organic matter and heterotrophic effects may also play important roles for the observed δ13C variations and these effects need to be further investigated. © 2001 Elsevier Science B.V.

Carbon isotope ratios of amylose, amylopectin and mutant starches

Abstract Carbon isotope ratios (expressed as δ13C values) were determined for various sources of starch and the starch fractions amylose and amylopectin. The δ13C values of amylose were consistently less negative, 0.4–2.3 ‰, than those of amylopectin in kernal starch from maize (Zea mays) and barley (Hordeum vulgare) and in tuber starch from potato (Solanum tuberosum). Kernel starch isolated from the maize mutants wx1 and ae1, with known genetic lesions in the starch biosynthetic pathway, also showed significant differences in δ13C values. Collectively, these results suggest that variation in carbon isotope ratios in the amylose and amylopectin components of starch may be attributed to isotopic discrimination by the enzymes involved in starch biosynthesis.

Identification of local populations of Lake Biwa catfish Silurus biwaensis in Japan on the basis of δ13C and δ15N analyses

Carbon and nitrogen stable isotope ratios were used to examine the mixing of adult Lake Biwa catfish, Silurus biwaensis, in different areas of the lake and to identify the local populations. The isotopic signatures of its prey, the bluegill, Lepomis macrochirus, were also examined as indicators of each local food web. We analyzed 141 Lake Biwa catfish and 60 bluegills captured in the lake. The differences in δ13C values indicated that the two groups of catfish captured in the northern- and the southern-most spawning areas did not mix with each other frequently and were thus identified as local populations. The catfish captured in the mid-eastern area, where no spawning ground was found, were considered to be a group of migrators from the southernmost area, not a local population. These results are consistent with those obtained using ultrasonic tracking. It was therefore clearly demonstrated that stable isotope analysis is useful for identifying local populations of aquatic animals.

Isotopic tracking of foraging and long-distance migration in northeastern Pacific pinnipeds.

We investigated the impact of foraging location (nearshore vs offshore) and foraging latitude (high vs middle) on the carbon (δ13C) and nitrogen (δ15N) isotope compositions of bone collagen of northern fur seals (Callorhinus ursinus), harbor seals (Phoca vitulina), California sea lions (Zalophus californianus), and northern elephant seals (Mirounga angustirostris). Nearshore-foraging harbor seals from California had δ13C values 2.0‰ higher than female northern elephant seals foraging offshore at similar latitudes. Likewise, nearshore-foraging harbor seals from Alaska had values 1.7‰ higher than male northern fur seals, which forage offshore at high latitudes. Middle-latitude pinnipeds foraging in either the nearshore or offshore were 13C enriched by ∼1.0‰ over similar populations from high latitudes. Male northern elephant seals migrate between middle and high latitudes, but they had δ13C values similar to high-latitude, nearshore foragers. Female northern fur seal δ13C values were intermediate between those of high- and middle-latitude offshore foragers, reflecting their migration between high- and middle-latitude waters. The δ13C values of California sea lions were intermediate between nearshore- and offshore-foraging pinnipeds at middle latitudes, yet there was no observational support for the suggestion that they use offshore food webs. We suggest that their "intermediate" values reflect migration between highly productive and less-productive, nearshore ecosystems on the Pacific coasts of California and Mexico. The relative uniformity among all of these pinnipeds in δ15N values, which are strongly sensitive to trophic level, reveals that the carbon isotope patterns result from differences in the δ13C of organic carbon at the base of the food web, rather than differences in trophic structure, among these regions. Finally, the magnitude and direction of the observed nearshore-offshore and high-to middle-latitude differences in δ13C values suggest that these gradients may chiefly reflect differences in rates and magnitudes of phytoplankton production as well as the δ13C value of inorganic carbon available for photosynthesis, rather than the input of 13C-enriched macroalgal carbon to nearshore food webs.

Factors affecting variation in CH4 emission from paddy soils grown with different rice cultivars: A pot experiment

The growth of rice plants greatly influences CH4 emission from paddy fields through the supply of organic materials such as root exudates and sloughed tissues, the release of oxygen to the root environment, and the transfer of CH4 from the rhizosphere into the atmosphere through the aerenchyma. In the present pot experiments, the effects of the release of water‐soluble organic substances from roots, the air space in roots, and the CH4‐oxidizing capacity of roots on intervarietal differences in CH4 emission were examined using three Japonica type cultivars (Norin 25, Nipponbare, and Aoinokaze), which differ in morphological properties. The CH4 emission rates varied among the cultivars from mid‐July (tillering stage) to the beginning of September (heading stage).Total CH4 emission throughout the rice growth period was largest for Norin 25, followed by Nipponbare, and Aoinokaze. In August, the rate of release of water‐soluble organic substances from roots was largest for Norin 25. The air space in roots was also largest in Norin 25 and least in Aoinokaze. The stable carbon isotopic ratios (δ13C) of CH4 in roots were 3–10‰ higher than those in soil in August. The difference in δ13C values of CH4 between roots and soil was largest for Aoinokaze and smallest for Norin 25. In September, the difference in δ13C values of CH4 between roots and soil became small (2–3‰). These findings suggest that the proportion of CH4 oxidation in the rhizosphere was largest in the cultivar which emitted the smallest amount of CH4 and that the proportion became smaller with continued plant growth.

Influences of different nitrogen sources on nitrogen- and water-use efficiency, and carbon isotope discrimination, in C 3 Triticum aestivum L. and C 4 Zea mays L. plants

The impacts of various nitrogen sources, i.e. NO−3, NH4+ or NH4NO3 in combination with gaseous NH3, on nitrogen-, carbon- and water-use efficiency and 13C discrimination (δ13C) by plants of the C3 species Triticum aestivum L. (wheat) and the C4 species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m−3 of N supplied as NO−3, NH4+ or NH4NO3 for 21 and 18 d, respectively, and thereafter exposed to gaseous NH3 at 320 μg · m−3 or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH4NO3-N > NO−3-N > NH4+-N and NO−3-N > NH4NO3-N > NH4+-N, respectively. Fumigation with NH3 decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use efficiency (WUE) values in the decreasing order of NH4+-N > NO−3-N≈NH4NO3-N in non-fumigated T. aestivum, while fumigation with NH3 increased the WUE of NO−3-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ13C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH4+-grown plants of T. aestivum and Z. mays than in those supplied with NH4NO3 or NO−3. Regardless of the N-form supplied to the roots of the plant species, exposure to NH3 caused more-positive δ13C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant variations in δ13C values in plants of T. aestivum and Z. mays. These differences in δ13C values are in the direction expected from differences in WUE values over long or short growth periods and with differences in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net C acquisition, as a function of N-source.

Measurement of 13C/12 C Ratios of Sugars, Malic Acid, and Citric Acid as Authenticity Probes of Citrus Juices and Concentrates

abstract The carbon-13 content of sugars, malic acid, and citric acid has been determined in authentic orange, lemon, and tangerine juices. After a cleanup step, sugars and organic acids were separated from each other by an anion-exchange process, and pure malic and citric acids were isolated by preparative reversed-phase liquid chromatography. This method has been applied to the stable isotope analysis of citrus juice samples of different botanical and geographical origins and of different years. Correlations between the carbon isotope ratios of all metabolites have been found, and typical ranges for the differences in δ13C values between them have been defined for each fruit. These data provide new tools for detecting adulterations that cannot be detected by the conventional carbon-13 method with the whole juice.

Compound-Specific Carbon Isotopic Analysis of Aroclors, Clophens, Kaneclors, and Phenoclors

Advances in instrumentation have allowed the measure ment of the isotopic composition of 13C/12C (δ13C) in the effluent of a gas chromatograph for each individual peak; this technique is called compound-specific isotope analysis (CSIA). CSIA has been used in a variety of biogeochemical studies to determine the sources of hydrocarbons. We have utilized the technique of CSIA to examine δ13C of the individual congeners in the polychlorinated biphenyl (PCB) mixtures Aroclor 1242 and 1254; Clophen A30, A50, and T241; Kanechlor 200, 300, 400, 500, and 600; and Phenoclor DP-3, DP-4, DP-5, and DP-6. In addition, the bulk δ13C values (i.e., the entire mixture) were determined for comparison to the CSIA values. Bulk δ13C values ranged from −22.34‰ (Phenoclor DP-3) to −26.95‰ (Clophen A30). The analogues Aroclor 1254, Clophen A50, Kanechlor 500, and Phenoclor DP-5 had different bulk δ13C values. The bulk values fall within the CSIA values and are similar to the average of the δ13C values of the individual congeners. In both the bulk δ13C analysis and the CSIA, the PCBs show increased 13C depletion with increasing chlorine content. Values for congeners within a PCB mixture also showed a wide range of δ13C isotope values; for example, δ13C values in the Kanechlor 600 mixture range from −18.65‰ (PCB 52) to −27.98‰ (PCB 180). Large differences in δ13C values for individual congeners between mixtures were found (e.g., PCB congener 52, Clophen A30−28.35‰ vs Kanechlor 600−18.65‰). The δ13C values for individual congeners in the PCB mixtures showed a similar pattern of 13C depletion with increasing chlorine content, this trend is probably a result of kinetic isotope effects caused by the position of the chlorine atom on the biphenyl molecule. The wide range in δ13C ratios between PCB mixtures and individual congeners may prove to be a powerful tool in the determination of sources of PCBs in the environment, and this technique may have wide applications in environmental chemistry.

Differential patterns of benthic foraminiferal extinctions near the Paleocene/Eocene boundary in the North Atlantic and the western Tethys

Bathyal benthic foraminifera and stable isotopes from the Caravaca and Zumaya sections of Spain, indicate that the mass extinction near the Paleocene/Eocene (P/E) boundary (upper planktic foraminiferal Zone P6a) was rapid, coinciding with a negative δ13C-shift of 2–4%., the onset of dark grey shale deposition and increased carbonate dissolution. Prior to the extinction event, diverse benthic foraminiferal assemblages and high δ13C values suggest the presence of a stable intermediate-deep watermass rich in oxygen and saturated in calcium carbonate in both Caravaca and Zumaya sections. After the extinction event, small finely agglutinated (Haplophragmoides, Glomospira) and thin-walled epifaunal taxa (Nuttallides truempyi) dominate in the North Atlantic, Zumaya section. This assemblage indicates sluggish circulation, bottom waters undersaturated in calcium carbonate and dysaerobic conditions. Low oxygen conditions prevailed for the succeeding 400 kyr and are characterized by 1–2%. fluctuations in benthic δ13C. In the western Tethys, Caravaca section, infaunal taxa (“buliminids”) dominate after the extinction event and prevailed through the succeeding 400 to 450 kyr of decreased δ13C values, indicating low oxygen conditions.Despite these common features, benthic foraminiferal assemblages from these two sections exhibit significant differences during the extinction event. At the Zumaya section, the extinction event occurred over less than 50 kyr and resulted in a sudden reduction in species richness after the δ13C-shift. In contrast, at the Caravaca section species diversity declined gradually, beginning prior to and in concert with the gradually declining δ13C values. This gradual change occurred over a period of 250 kyr and culminated in a 4%. δ13C-shift. These differences in δ13C values and benthic assemblages between Caravaca and Zumaya, suggest that the P-E oceanographic changes that triggered the benthic foraminiferal mass extinction, exhibited its first manifestation in the Tethys region.

The carbon isotopic composition of individual fatty acids as indicators of dietary history in arctic foxes on Svalbard

We have measured the carbon isotopic compositions of individual fatty acids isolated from the adipose tissue of arctic foxes ( Alopex lagopus ) from the island of Svalbard on the Spitsbergen archipelago to examine whether dietary sources can be distinguished in the fatty acid isotopic signature. The diets of Svalbard arctic foxes are unusual in that some members of the population are believed to feed largely in the terrestrial food chain while others feed mainly from the marine food chain. Isotopic data were obtained for the five major fatty acids present (16:0, 16:1, 18:0, 18:1, and 20:1). A wide range in δ13C values for specific fatty acids in Arctic foxes is observed and the mixing lines produced by the correlation in δ13C of the 16- and 18-carbon fatty acids indicate that both marine and terrestrial dietary sources determine fatty acid isotope composition. The differences in δ13C values between marine and terrestrial organisms appear to be passed on to individual fatty acids. The abundance and isotopic composition of 16:1 indicates that the foxes derive this acid from marine sources, whereas, 16:0 and 18:0 appear to have predominantly terrestrial sources.

Heterotrophic Carbon Gain of the Parasitic Angiosperm Tapinanthus oleifolius

Tapinanthus oleifolius is a xylem-tapping mistletoe, parasitising a wide range of host trees including acacias, which are potentially nitrogen fixing, and Euphorbia virosa, which acquires CO2 mainly by nocturnal fixation via phosphoenolpyruvate carboxylase. Heterotrophic carbon gain by T. oleifolius was estimated by two different approaches. Firstly, δ13C values of leaves were calculated from cI/ca values and compared with measured δ13C ratios of these leaves and corresponding host xylem saps. Secondly, carbon intake from the host was determined by measuring carbon content of the host xylem sap and transpiration of the mistletoe leaves. This taken together with the photosynthetic CO2 net uptake allowed the calculation of a carbon budget and hence the proportion of heterotrophically-derived carbon. There was good agreement between the methods of determining heterotrophic carbon gain. For young leaves of T. oleifolius, heterotrophic carbon gain was around 55% on E. virosa and Acacia nebrownii. In old leaves parasitising E. virosa, heterotrophic carbon accounted for more than 80% of the total carbon. Although nitrogen content of mistletoe and host leaves was highly correlated, we could not confirm earlier findings that the difference in δ13C values of parasite-host associations depends on the nitrogen content of the host. The photosynthetic characteristics (carboxylation efficiency, photosynthetic capacity) of the parasite were only little affected by the host species being parasitised.