Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

Analysis of primary food sources and trophic relationships of aquatic animals in a mangrove-fringed estuary,Khung Krabaen Bay (Thailand) using dual stable isotope techniques

Stable carbon (¹³C) and nitrogen (¹⁵N) isotopes were used to elucidate primary food sources and trophic relationships of organisms in Khung Krabaen Bay and adjacent offshore waters. The three separate sampling sites were mangroves, inner bay and offshore. The ¹³C values of mangrove leaves were –28.2 to –29.4, seagrass –10.5, macroalgae –14.9 to –18.2, plankton –20.0 to –21.8, benthic detritus –15.1 to –26.3, invertebrates –16.5 to –26.0, and fishes –13.4 to –26.3. The ¹⁵N values of mangrove leaves were 4.3 to 5.7, seagrass 4.3, macroalgae 2.2 to 4.4, plankton 5.7 to 6.4 , benthic detritus 5.1 to 5.3, invertebrates 7.2 to 12.2 , and fishes 6.3 to 15.9. The primary producers had distinct ¹³C values. The ¹³C values of animals collected from mangroves were more negative than those of animals collected far from shore. The primary carbon sources that support food webs clearly depended on location. The contribution of mangroves to food webs was confined only to mangroves, but a mixture of macroalgae and plankton was a major carbon source for organisms in the inner bay area. Offshore organisms clearly derived their carbon through the planktonic food web. The ¹⁵N values of consumers were enriched by 3–4 relative to their diets. The ¹⁵N data suggests that some of aquatic animals had capacity to change their feeding habits according to places and availability of foods and as a result, individuals of the same species could be assigned to different trophic levels at different places.     

Food web structure in the high Arctic Canada Basin: evidence from δ13C and δ15N analysis

The food-web structure of the Arctic deep Canada Basin was investigated in summer 2002 using carbon and nitrogen stable isotope tracers. Overall food-web length of the range of organisms sampled occupied four trophic levels, based on 3.8 trophic level enrichment (¹⁵N range: 5.3–17.7). It was, thus, 0.5–1 trophic levels longer than food webs in both Arctic shelf and temperate deep-sea systems. The food sources, pelagic particulate organic matter (POM) (¹³C=–25.8, ¹⁵N=5.3) and ice POM (¹³C=–26.9, ¹⁵N=4.1), were not significantly different. Organisms of all habitats, ice-associated, pelagic and benthic, covered a large range of ¹⁵N values. In general, ice-associated crustaceans (¹⁵N range 4.6–12.4, mean 6.9) and pelagic species (¹⁵N range 5.9–16.5, mean 11.5) were depleted relative to benthic invertebrates (¹⁵N range 4.6–17.7, mean 13.2). The predominantly herbivorous and predatory sympagic and pelagic species constitute a shorter food chain that is based on fresh material produced in the water column. Many benthic invertebrates were deposit feeders, relying on largely refractory material. However, sufficient fresh phytodetritus appeared to arrive at the seafloor to support some benthic suspension and surface deposit feeders on a low trophic level (e.g., crinoids, cumaceans). The enriched signatures of benthic deposit feeders and predators may be a consequence of low primary production in the high Arctic and the subsequent high degree of reworking of organic material.     

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (¹³C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in¹³C (mean ¹³C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in¹³C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in¹³C is due mainly to changes in methane production pathways.Values of ¹³C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from¹³C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. ¹⁴C content in methane produced fromThai rice paddies (127±1 pMC) show higher ¹⁴Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis

Summary The mean stable-carbon isotope ratios (¹³C) for polar bear (Ursus maritimus) tissues (bone collagen –15.7, muscle –17.7, fat –24.7) were close to those of the same tissues from ringed seals (Phoca hispida) (–16.2, –18.1, and –26.1, respectively), which feed exclusively from the marine food chain. The ¹³C values for 4 species of fruits to which polar bears have access when on land in summer ranged from –27.8 to –26.2, typical of terrestrial plants in the Arctic. An animal's ¹³C signature reflects closely the ¹³C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.     

Trophodynamic linkage between river runoff and coastal fishery yield elucidated by stable isotope data in the Gulf of Lions (NW Mediterranean)

The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lions (NW Mediterranean) was analysed using carbon- and nitrogen stable isotopes along the flatfish food webs. Off the Rhone River, the main terrestrial (river POM) and marine (seawater POM) sources of carbon differed in ¹³C (–26.11 and –22.36, respectively). Surface sediment and suspended POM in plume water exhibited low ¹³C (–24.38 and –24.70, respectively) that differed more from the seawater POM than from river POM, demonstrating the dominance of terrestrial material in those carbon pools. Benthic invertebrates showed a wide range in ¹⁵N (mean 4.30 to 9.77) and ¹³C (mean –23.81 to –18.47), suggesting different trophic levels, diets and organic sources. Among the macroinvertebrates, the surface (mean ¹³C –23.71) and subsurface (mean ¹³C –23.81) deposit-feeding polychaetes were particularly ¹³C depleted, indicating that their carbon was mainly derived from terrestrial material. In flatfish, ¹⁵N (mean 9.42 to 10.93) and ¹³C (mean –19.95 to –17.69) varied among species, indicating differences in food source and terrestrial POM use. A significant negative correlation was observed between the percentage by weight of polychaetes in the diet and the ¹³C of flatfish white muscle. Solea solea (the main polychaete feeder) had the lowest mean ¹³C, Arnoglossus laterna and Buglossidium luteum (crustacean, mollusc and polychaete feeders) had intermediate values, and Solea impar (mollusc feeder) and Citharus linguatula (crustacean and fish feeder) exhibited the highest ¹³C. Two different benthic food webs were thus identified off the Rhone River, one based on marine planktonic carbon and the other on the terrestrial POM carried by the river. Deposit-feeding polychaetes were responsible for the main transfer of terrestrial POM to upper trophic levels, linking sole population dynamics to river runoff fluctuations.     

Insect food preferences analysed using 13C/12C ratios

Summary Stable carbon isotope ratio analysis is a powerful technique in tracing ecosystem carbon flows, especially those between primary and secondary producers. The distinctive ¹³C/¹²C ratios of plant species tend to pass along the food chain with little further fractionation, hence the stable carbon isotope composition of an animal is an important clue to what it has eaten. We compared the stable carbon isotope composition of plants and insects in an old field in Georgia. Of the dominant plants in the old field, 6 were C₄ species and had ¹³C¹ values of-10.9 to 12.9, and 7 were C₃ species with values of-27.3 to-29.1. Insects known to be feeding on only one plant species had ¹³C values within 1 of the isotopic composition of the plant. Wasp larvae parasitizing two insect species had ¹³C values 1.3 and 1.7 higher than that of the food plant. A variety of insects of unknown food habits collected on monospecific and mixed species plant stands in the old field had ¹³C values ranging from-10.1 to-30.0. Two species of leafhopper and a grasshopper had isotopic compositions within the range of C₄ plant values; a tortoise beetle and a lace bug had isotopic compositions within C₃ plant values. Other insects had intermediate ¹³C values, suggesting a mixed diet composed of both C₃ and C₄ plants. The carbon isotopic ratios of field collected insects appears to be a useful qualitative indicator of their feeding preference.     

Photosynthetic pathways and the ecological distribution of the chenopodiaceae in Isreal

Summary Fifty-four species of the Chenopodiaceae in Israel were examined for their anatomical features, ¹³C values, habitat and phytogeographical distribution. 17 species have ¹³C values between -20 and -30and non-Kranz anatomy (NK) and are therefore considered as C₃ plants. 37 species have ¹³C values between -10 and -18 and Kranz or C₄-Suaeda type anatomy and are therefore considered as C₄ plants. Some C₄ plants have leaf structure which seems to be intermediate between the Kranz and the C₄-Suaeda type of leaf anatomy.The segregation of the species into photosynthetic groups shows tribal and phytogeographical grouping. Most of the C₃ Chenopods are either mesoruderal plants or coastal halophytes, with a distribution area which covers the Euro-Siberian as well as the Mediterranean phytogeographical regions. The C₄ Chenopods are mainly desert or steppe xerohalophytes with a distribution area which includes the Saharo-Arabian and/or Irano-Turanian phytogeographical regions.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

Carbon isotope composition of biochemical fractions isolated from leaves of Bryophyllum daigremontianum berger,a plant with crassulacean acid metabolism: Some physiological aspects related to CO2 dark fixation

Isotope analysis of the biochemical fractions isolated quantitatively from young and mature leaves of Bryophyllum daigremontianum Berger have been carried out before and after a dark period of accumulation of organic acids. The mature leaf is enriched in ¹³C compared to the young leaf. The ¹³C values of the different leaf constituents vary between the ¹³C values of C₄ plants (-11) and those of C₃ plants (-27). During the dark period, the two types of leaves store organic acids with ¹³C values of -15 and lose insoluble sugars, including starch with a ¹³C value of -12. Furthermore, young leaves store phosphorylated compounds with ¹³C values of -11 and lose weakly polymerised sugars with ¹³C values of -18. These results led to the formulation of a hypothesis of the origin of the two substrates of -carboxylation: phosphoenolpyruvate arises from the glycolytic breakdown of the insoluble sugars rich in ¹³C, and the major portion of the CO₂ is the result of the complete breakdown (respiration) of the soluble sugars rich in ¹²C. The existence of two independent sugar pools leads to the assumption that there are two separate glycolytic pathways. The ¹³C enrichment of the stored products of the young leaves in the day seems to be the result of a weak discrimination for ¹³C by ribulose diphosphate carboxylase, which reassimilates to a great extent the CO₂ released from malate accumulated in the night.Abbreviations CAM crassulacean acid metabolism - C₃ metabolism metabolism with primary carbon fixed by the Calvin and Benson pathway - C₄ metabolism metabolism with primary carbon fixed by the Hatch and Slack pathway - ¹³C() (R_sample-R_PDB) 10³/R_PDB where PDB=Pee Dee belemnite (belemite from the Pee Dee formation South Carolina) and R=¹³C/¹²C - NAD-MDH(EC1.1.1.37) NAD-malate dehydrogenase - NADP-ME (EC1.1.1.40) NADP-malic enzyme - PEP phosphoenolpyruvate - PEPC (EC4.1.1.31) PEP carboxylase - PGA phosphoglyceric acid - Py.di-PK(EC2.7.9.1) pyruvate, Pi-dikinase - RuDP ribulose diphosphate - RuDPC (EC4.1.1.39) RuDP carboxylase     

Tracing mangrove carbon in suspended matter and aquatic fauna of the Gautami–Godavari Delta,Bay of Bengal (India)

Stable carbon isotopic composition and C/N ratio were used to trace the input of carbon associated with mangrove litter into the estuary of the Godavari–Gautami delta system and Kakinada bay (Andhra Pradesh, India). Suspended organic matter in the mangrove channels was more depleted in ¹³C (average ¹³C = –24.5) than in Kakinada bay which showed ¹³C values for suspended matter (average ¹³C = –22.7) closer to those expected for marine phytoplankton. Suspended organic matter from mangrove channels was enriched in nitrogen (average C/N atom ratio 12.7) and ¹³C (average ¹³C = –24.5) relative to mangrove leaf litter, which had a C/N ratio of 75 and a ¹³C value of –28. Lowest C/N ratios for suspended matter were observed during southwest monsoon when rainfall was highest. Although in general, mangrove litter fall was also lower during this period, no clear correlation was observed between litter fall and C/N ratio of suspended matter. In general, the composition of suspended matter pointed towards phytoplankton as a major component. Isotopic composition of zooplankton suggested selective feeding on ¹³C-enriched, marine phytoplankton in open Kakinada bay and on ¹³C-depleted organic matter, such as estuarine phytoplankton and mangrove litter, in the mangrove channels. From the ¹³C signature, it appeared that mangrove carbon was present to some extent in zooplankton and macrofauna from the mangrove mudflats and channels, but the signal rapidly decreased in Kakinada bay. Nitrogen isotopic composition of zooplankton and macrofauna indicated a progressive enrichment of ¹⁵N away from the mangrove forest towards the northern part of Kakinada bay, in approach of Kakinada city. This is thought to reflect input of anthropogenic nitrogen enriched in ¹⁵N and subsequent uptake of this enriched nitrogen into the aquatic food chain.     

Microfungal variations relative to post-fire changes in soil environment

Summary Living and dead Zostera marina blades, plankton samples, sediments, and several animal components of an eelgrass bed near Beaufort, N.C. were collected and analyzed for ¹³C/¹²C ratios ( ¹³C). The ¹³C values of producer and consumer organisms were compared in order to examine the possible origins of organic matter present in the consumers. Living and dead eelgrass blades displayed similar ¹³C values,-12.2 and-10.6 per mil respectively, while the epiphytic community growing on the grass blades had a mean isotope ratio of-16.0. Animal components analyzed represented five major feeding-mode categories: invertebrates living on grass blades an presumably feeding on the epibiota (-15.1), deposit feeding invertebrates (-15.0), predatory and omnivorous invertebrates (-16.7), suspension and surface feeding invertebrates (-18.3) and omnivorous fish (-16.8).Organisms commonly found on the grass blades appeared to feed primarily on the epibiota growing on the blades. It is hypothesized that the epibiota derive some of their carbon from DOC released by the Zostera blade. The urchin, Lytechinus variegatus, and the brittle star, Ophioderma brevispinum, both deposit feeders, appeared to derive a major proportion of their carbon from eelgrass. With the exception of the shrimp, Alpheus heterochaelis, and the pipefish, Syngnathus floridae, the majority of other organisms analyzed appeared to be linked more directly to a plankton-carbon food chanin than to a seagrass-carbon system in this relatively young eelgrass bed.This research was supported in part through a cooperative agreement between the National Marine Fisheries Service and the U.S. Department of Energy [E(49-7)-5] and in part through a National Science Foundation International Decade of Ocean Exploration grant to the University of Texas at Austin (#OCE76-01306) Contribution Number 78-12B of the Southeast Fisheries Center, Beaufort Laboratory     

Comparisons of δ13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants

Summary The ¹³C values of submerged aquatic plants from contrasting but relatively defined habitats, and the ¹³C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the ¹³C values of dissolved inorganic carbon in the water were also measured. Plant ¹³C values in the vicinity of-40 to-50 were found in rapidly flowing spring waters with carbonate ¹³C values of-16 to-21, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO₂ via RuP₂ carboxylase. Plant ¹³C values in the vicinity of-10 to-15 in sluggish water with carbonate ¹³C values of about-5 were observed, consistent with the notion that boundary layer diffusion and/or HCO₃ ^- uptake may determine the ¹³C value of submerged aquatic plants in these circumstances. Comparisons of ¹³C values of the same or related species growing in waters of similar carbonate ¹³C value but different flow rates confirmed this view; more negative ¹³C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the ¹³C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The ¹³C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO₂, as opposed to atmospheric carbon. The contributions of these variations in ¹³C of the carbon source, and of isotope fractionation in diffusion, to the ¹³C value of submerged parts of dimorphic plants is discussed.     

Stratification of δ13C values of leaves in Amazonian rain forests

Summary The contribution of soil respiration to the photosynthesis of the shade flora in the Amazon forest was evaluated by measuring the ¹³C values of leaves collected at different levels in two forest communities. Canopy leaves have an average ¹³C of-30.5 in the podsol forest and-28.7 in the laterite forest. Leaves from plants in the lower forest strata have a significantly lower value of-35.2 in the podsol forest and-34.3 in the laterite forest.Mailing address of the first author: Before May 31, 1980: Department of Biological Sciences, Stanford University, Stanford, California 94305 USA. After May 31: Centro de Ecologia, IVIC Aptdo. 1827. Caracas, Venezuela     

Stable carbon isotope composition,depth distribution and fate of macroalgae from the Antarctic Peninsula region

Summary Stable carbon isotope composition of macroalgae collected at King George Island (Antarctica) ranged from about -8 to -34. We hypothesize that the ¹³C values are related to the depth distribution: species inhabiting greater depth had much lower values (around-30) compared to species from shallower waters (around -17). Isotopic studies on sediment trap samples from the King George Basin (2,000 m deep) revealed that benthic macroalgae contributed strongly to the total organic carbon pool of the deeper basin waters during austral spring and summer. Fragments of brown macroalgae (Desmarestiales) were detected in microscopical analyses of semi-thin sections of sediment samples from the Bransfield Strait. Possible mechanisms regarding the erosion of benthic macroalgae and their transport to the deeper waters and to the sediment are summarized.     

Stable isotope ecology in the Ituri Forest

The Ituri Forest, Democratic Republic of Congo (formerly Zaire) is an example of a closed canopy forest showing extreme depletion in ¹³C. ¹³C values for plants from the canopy top, from gaps in the canopy, and from the subcanopy average –29.0±1.7, –30.4±0.9, and –34.0±1.5, respectively. The ¹³C of forest mammals show these differences, with the subcanopy browsers (okapi, dwarf antelope) having ¹³C values for tooth enamel much more negative than subcanopy frugivores who derive their food from the canopy top, and from folivores and omnivores living in gap or clearing areas. Nitrogen isotopes in plants from this ecosystem have an average ¹⁵N value of 5.4±1.8 and do not show significant differences at the 95% confidence interval between plants from the canopy top, from gaps in the canopy, and from the subcanopy. The ¹⁸O_SMOW values of surface waters in the study area are between –2.0 and –2.7. The ¹⁸O_PDB for tooth enamel ranged from –3 to +7.     

Effect of organic and inorganic fertigation on yields, δ15N values, and δ13C values of tomato (Lycopersicon esculentum Mill. cv. Saturn)

We examined the effects of fertilizer application, especially the effects of fertigation and types of fertilizer (inorganic and organic) on yields and ¹⁵N and ¹³C values of tomato (Lycopersicon esculentum Mill. cv. Saturn). Fertigation is a method in which an appropriate diluted liquid fertilizer is applied to the plants each time they are drip-irrigated. We developed a method of organic fertigation using corn steep liquor (CSL) as the liquid fertilizer, because it is an industrial byproduct of cornstarch manufacture and can be used very effectively. We compared fruit yield, mineral content, ¹⁵N value, and ¹³C value of tomatoes grown under three different fertilizer treatments, basal dressing: basal dressing with granular chemical fertilizer; inorganic fertigation: fertigation with liquid chemical fertilizer; and organic fertigation: fertigaion with CSL. Mineral contents of tomatoes grown with basal dressing were generally lower than those grown under either fertigation treatment. These results indicated that yields and mineral contents were influenced more by the method of fertilizer application than by whether the fertilizers were inorganic or organic. There were, however, significant differences in the ¹⁵N values of tomato fruits grown under different types of fertilizer applications, especially between inorganic and organic fertilizers. The ¹⁵N value of the chemical fertilizer used for basal dressing was 0.81 ± 0.45{}, that of the chemical fertilizer for fertigation was 0.00 ± 0.04{}, and that of CSL was 8.50 ± 0.71{}. The ¹⁵N values of the soils reflected the ¹⁵N values of the fertilizers. Moreover, the ¹⁵N values of the fruits corresponded to the ¹⁵N values of the applied fertilizers. The ¹⁵N values were 3.18 ± 1.34{} in the fruits grown with a basal dressing of chemical fertilizer, 0.30 ± 0.61 in those grown under inorganic fertigation, and 7.09 ± 0.68 in those grown under organic fertigation. On the other hand, although the ¹³C values in the soil also reflected the ¹³C values of the applied fertilizers, there was no significant difference in the ¹³C values of fruits among the different treatments. In conclusion, because the ¹⁵N values of fertilizers correlated well with those of the fruits, it may be possible to use ¹⁵N values as an indicator of organic products.     

Fine-scale movement and assimilation of carbon in saltmarsh and mangrove habitat by resident animals

Despite theories of large-scale movement and assimilation of carbon in estuaries, recent evidence suggests that in some estuaries much more limited exchange occurs. We measured the fine-scale movement and assimilation of carbon by resident macroinvertebrates between adjacent saltmarsh and mangrove habitats in an Australian estuary using ¹³C analysis of animals at different distances into adjacent patches of habitat. ¹³C values of crabs (Parasesarma erythrodactyla –15.7 ± 0.1, Australoplax tridentata –14.7 ± 0.1) and slugs (Onchidina australis –16.2 ± 0.3) in saltmarsh closely matched that of the salt couch grass Sporobolus virginicus (–15.5 ± 0.1). In mangroves, ¹³C values of crabs (P. erythrodactyla –22.0 ± 0.2, A. tridentata –19.2 ± 0.3) and slugs (–19.7 ± 0.3) were enriched relative to those of mangroves (–27.9 ± 0.2) but were more similar to those of microphytobenthos (–23.7 ± 0.3). The ¹³C values of animals across the saltmarsh-mangrove interface fitted a sigmoidal curve, with a transition zone of rapidly changing values at the saltmarsh-mangrove boundary. The width of this transition indicated that the movement and assimilation of carbon is limited to between 5 and 7 m. The ¹³C values of crabs and slugs, especially those in saltmarsh habitat, clearly indicate that the movement and assimilation of carbon between adjacent saltmarsh and mangrove habitat is restricted to just a few metres, although some contribution from unmeasured sources elsewhere in the estuary is possible. Such evidence demonstrating the extent of carbon movement and assimilation by animals in estuarine habitats is useful in determining the spatial arrangement of habitats needed in marine protected areas to capture food web processes.     

Foliar 15N natural abundance in Hawaiian rainforest: patterns and possible mechanisms

Summary Foliar samples were obtained from symbiotic nitrogen-fixers and control plants (non-fixers) along elevational and primary successional gradients in volcanic sites in Hawai'i. Most control plants had negative ¹⁵N values (range-10.1 to +0.7), while most nitrogen-fixers were near 0. Foliar ¹⁵N in the native tree Metrosideros polymorpha did not vary with elevation (from sea level to tree-line), but it did increase substantially towards 0 on older soils. The soil in an 197-yr-old site had a ¹⁵N value of approximately-2, while in a 67000-yr-old site it was +3.6. We suggest that inputs of ¹⁵N-depleted nitrogen from precipitation coupled with very low nitrogen outputs cause the strongly negative ¹⁵N values in non-nitrogen-fixing plants on early successional sites.