Factors controlling the stable isotope composition and C:N ratio of seston and periphyton in shallow lake mesocosms with contrasting nutrient loadings and temperatures

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Dietary and physiological controls on the hydrogen and oxygen isotope ratios of hair from mid‐20th century indigenous populations

A semimechanistic model has recently been proposed to explain observed correlations between the H and O isotopic composition of hair from modern residents of the USA and the isotopic composition of drinking water, but the applicability of this model to hair from non‐USA and preglobalization populations is unknown. Here we test the model against data from hair samples collected during the 1930s–1950s from populations of five continents. Although C and N isotopes confirm that the samples represent a much larger range of dietary “space” than the modern USA residents, the model is able to reproduce the observed δ²H and δ¹⁸O values given reasonable adjustments to 2 model parameters: the fraction of dietary intake derived from locally produced foods and the fraction of keratin H fixed during the in vivo synthesis of amino acids. The model is most sensitive to the local dietary intake, which appears to constitute between 60% and 80% of diet among the groups sampled. The isotopic data are consistent with a trophic‐level effect on protein H isotopes, which we suggest primarily reflects mixing of ²H‐enriched water and ²H‐depleted food H in the body rather than fractionation during biosynthesis. Samples from Inuit groups suggest that humans with marine‐dominated diets can be identified on the basis of coupled δ²H and δ¹⁸O values of hair. These results indicate a dual role for H and O isotopic measurements of keratin, including both biological (diet, physiology) and environmental (geographic movement, paleoclimate) reconstruction. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Predicting leaf wax n‐alkane 2H/1H ratios: controlled water source and humidity experiments with hydroponically grown trees confirm predictions of Craig–Gordon model

The extent to which both water source and atmospheric humidity affect δ²H values of terrestrial plant leaf waxes will affect the interpretations of δ²H variation of leaf waxes as a proxy for hydrological conditions. To elucidate the effects of these parameters, we conducted a long‐term experiment in which we grew two tree species, Populus fremontii and Betula occidentalis, hydroponically under combinations of six isotopically distinct waters and two different atmospheric humidities. We observed that leaf n‐alkane δ²H values of both species were linearly related to source water δ²H values, but with slope differences associated with differing humidities. When a modified version of the Craig–Gordon model incorporating plant factors was used to predict the δ²H values of leaf water, all modelled leaf water values fit the same linear relationship with n‐alkane δ²H values. These observations suggested a relatively constant biosynthetic fractionation factor between leaf water and n‐alkanes. However, our calculations indicated a small difference in the biosynthetic fractionation factor between the two species, consistent with small differences calculated for species in other studies. At present, it remains unclear if these apparent interspecies differences in biosynthetic fractionation reflect species‐specific biochemistry or a common biosynthetic fractionation factor with insufficient model parameterization.     

Stable isotopes complement focal individual observations and confirm dietary variability in reddish–gray mouse lemurs (Microcebus griseorufus) from southwestern Madagascar

We examine the ecology of reddish‐gray mouse lemurs from three habitats at Beza Mahafaly Special Reserve using focal follows and stable carbon and nitrogen isotope data. Focal observations indicate dietary differences among habitats as well as sexes and seasons. Both sexes consume more arthropods during the rainy season but overall, females consume more sugar‐rich exudates and fruit than males, and individuals from riparian forest consume fewer arthropods and more fruit than those in xeric or dry forest. We ask whether these observations are isotopically detectable. Isotope data support differences between seasons and sexes. Nitrogen isotope values are higher during the rainy season when lemurs consume more arthropods, and higher in males than females, particularly during the dry season. However, differences among populations inferred from focal observations are not fully supported. Lemurs from riparian forest have lower isotope values than those in xeric scrub, but isotope data suggest that lemurs from the dry forest eat the least animal matter and that focal observations overestimated dry forest arthropod consumption. Overall, our results suggest that observational and isotopic data are complementary. Isotope data can be obtained from a larger number of individuals and can quantify ingestion of animal matter, but they apparently cannot quantify the relative consumption of different sugar‐rich foods. Combined focal and isotope data provide valuable insight into the dietary constraints of reddish‐grey mouse lemurs, with implications for their vulnerability to future habitat change. Am J Phys Anthropol 155:77–90, 2014. © 2014 Wiley Periodicals, Inc.     

Assessment of nutritional status in rhesus monkeys: comparison of dual-energy X-ray absorptiometry and stable isotope dilution

Body composition estimates from dual-energy X-ray absorptiometry and stable isotope dilution ((2)H and (18)O) were compared in 61 rhesus monkeys (Macaca mulatta) from the ongoing long-term energy restriction study at the University of Wisconsin. Their average age was 18.9 +/- 2.5 y/o. Of the animals, 51% were in the energy restricted group and 38% were females. Although the correlation between methods was highly significant for fat mass (R(2) = 0.97, SEE = 0.25 kg or 7.5%, P < 0.0001) and fat-free mass (R(2) = 0.98, SEE = 0.29 kg or 3.6%, P < 0.0001), we observed that dual-energy X-ray absorptiometry underestimated fat mass by 0.67 +/- 0.26 kg (7.5%, P < 0.0001) and overestimated fat-free mass by 0.57 +/- 0.29 kg (20%, P < 0.0001) when compared with isotope dilution. Taken together with data from the literature, the present results emphasize the usefulness of dual-energy X-ray absorptiometry to derive body composition and thus nutritional status in monkeys, but demonstrate the importance of validation experiments for a given DXA model and software.     

The paleoecology of early Pleistocene Gigantopithecus blacki inferred from isotopic analyses

This study presents isotopic analyses of Gigantopithecus blacki and contemporaneous fauna from Early Pleistocene southern China cave localities with a view to reconstructing the paleoecology of this large extinct ape. Carbon and oxygen stable isotope compositions were determined using tooth enamel carbonate of Gigantopithecus and eight other taxa from Longgudong Cave and additional Gigantopithecus specimens from Juyuandong Cave. Carbon isotopic values of Gigantopithecus fauna reflect a densely forested habitat rarely preserved in the fossil record. These values overlap with those of other ape habitats including Miocene Sivapithecus faunas in the Siwaliks of Pakistan and modern chimpanzee faunas at Kibale National Park, Uganda, and the Ituri Forest, Democratic Republic of the Congo. Despite the overlap, Gigantopithecus fauna carbon values are significantly lower than those of the Siwaliks and Kibale, likely reflecting a more continuous canopy or more humid forest. Carbon isotope values suggest the habitat consisted of vegetation similar to current subtropical monsoon forests of southern China. Ranges of carbon and oxygen isotopic values for Gigantopithecus suggest a broad diet comprising both terrestrial and canopy plants. Am J Phys Anthropol 155:571–578, 2014. © 2014 Wiley Periodicals, Inc.     

Plasma plant sterols serve as poor markers of cholesterol absorption in man

The validation of the use of plasma plant sterols as a marker of cholesterol absorption is frail. Nevertheless, plant sterol concentrations are routinely used to describe treatment-induced changes in cholesterol absorption. Their use has also been advocated as a clinical tool to tailor cholesterol-lowering therapy. Prior to wider implementation, however, the validity of plant sterols as absorption markers needs solid evaluation. Therefore, we compared plasma plant sterol concentrations to gold-standard stable isotope-determined cholesterol absorption. Plasma campesterol/TC concentrations (camp/TC) were measured in a population of 175 mildly hypercholesterolemic individuals (age: 59.7 ± 5.6 years; BMI: 25.5 ± 2.9kg/m²; LDL-C: 4.01 ± 0.56 mmol/l). We compared cholesterol absorption according to the plasma dual-isotope method in subjects with the highest camp/TC concentrations (N = 41, camp/TC: 2.14 ± 0.68 μg/mg) and the lowest camp/TC concentrations (N = 39, camp/TC: 0.97 ± 0.22 μg/mg). Fractional cholesterol absorption did not differ between the groups (24 ± 12% versus 25 ± 16%, P = 0.60), nor was it associated with plasma camp/TC concentrations in the total population of 80 individuals (β = 0.13; P = 0.30, adjusted for BMI and plasma triglycerides). Our findings do not support a relation between plasma plant sterol concentrations and true cholesterol absorption and, therefore, do not favor the use of these sterols as markers of cholesterol absorption. This bears direct consequences for the interpretation of earlier studies, as well as for future studies targeting intestinal regulation of cholesterol metabolism.     

A Liquid Chromatography–Mass Spectrometry Method to Measure Stable Isotopic Tracer Enrichments of Glycerol and Glucose in Human Serum

Stable isotopes are commonly used as tracers for the measurement of glycerol and glucose kinetics in metabolic studies. Traditionally, the analysis of these isotopes has been performed using gas chromatography-mass spectrometry, which requires that the analytes first be derivatized. The derivatization process adds considerable complexity to the method. Liquid chromatography-mass spectrometry (LCMS) can measure many metabolites directly with limited sample preparation. We present a novel analytical method for the measurement of [1,1,2,3,3-(2)H(5)]glycerol (d(5)-glycerol) and [6,6-(2)H(2)]glucose (d(2)-glucose) isotopic tracer enrichments in human serum in a single run by LCMS. After a simple extraction step, the sample is separated isocratically by HPLC, and the isotopes are measured using positive electrospray ionization with selected ion monitoring of the sodium-adduct ions. The method is linear over a wide range of d(2)-glucose and d(5)-glycerol enrichments. The within-day standard deviation of measurement of serum samples was 0.05 mole% excess (MPE) for d(2)-glucose and 0.25 MPE for d(5)-glycerol. The variation of tracer enrichment among days was about double that measured within 1 day.     

Natural 15N abundance of vegetation and soil in the Kapalga savanna,Australia

Abstract The natural abundance of the stable isotope ¹⁵N was measured in different vegetation components and in the soil of a northern Australian savanna. Most of the vegetation was found to be ¹⁵N-depleted compared to atmospheric N₂. Herbaceous legumes, perennial grasses, tree legumes, non-legume trees and annual grasses exhibited mean δ¹⁵N of ? 1.7, ? 0.8, ? 0.7, 0.0 and + 0.3‰, respectively. These results are in good agreement with previous studies. Legumes exhibit slightly negative values, indicating that they are likely to be nitrogen-fixing plants. Non-legume plants have a δ¹⁵N close to zero, which could equally result from non-symbiotic fixation, soil organic matter mineralization, or fresh root litter mineralization. In contrast, soil organic matter was ¹⁵N-enriched. Values of δ¹⁵N increased with depth and were + 2.5, + 5.2 and +6.1‰ in the 0–10, 10–20 and 20–40cm layers, respectively. Soil organic matter δ¹⁵N shows a typical profile of mature soils.     

The 'lost years' of green turtles: using stable isotopes to study cryptic lifestages

Ignorance of the location or inaccessible locations of lifestages can impede the study and management of species. We used stable isotopes of carbon and nitrogen to identify the habitats and diets and to estimate the duration of a 'missing' lifestage: the early juvenile stage of the green turtle, Chelonia mydas. Stable isotopes in scute from young herbivorous green turtles in shallow-water habitats revealed that they spend 3-5 years as carnivores in oceanic habitats before making a rapid ontogenetic shift in diet and habitat. Stable isotopes in persistent and continuously growing tissues, such as some fish scales, bird bills and claws and mammal hair and claws, can be used to evaluate the ecology of inaccessible lifestages.     

Nitrogen uptake and turnover in riparian woody vegetation

The nutrient balance of streams and adjacent riparian ecosystems may be modified by the elimination of anadromous fish runs and perhaps by forest fertilization. To better understand nitrogen (N) dynamics within stream and riparian ecosystems we fertilized two streams and their adjacent riparian corridors in central Idaho. On each stream two nitrogen doses were applied to a swathe approximately 35 m wide centered on the stream. The fertilizer N was enriched in ¹⁵N to 18. This enrichment is light relative to many previous labeling studies, yet sufficient to yield a traceable signal in riparian and stream biota. This paper reports pre-treatment differences in ¹⁵N and the first-year N response to fertilizer within the riparian woody plant community. Future papers will describe the transfer of allochthonous litter N to the stream and its subsequent processing by stream biota. Pre-treatment ¹⁵N differed between the two creeks (P=0.0002), possibly due to residual salmon nitrogen in one of the creeks. Pre-treatment ¹⁵N of current-year needles was enriched compared to leaf litter, which was in turn enriched compared to needles aged 4 years and older. We conclude that fractionation due to retranslocation occurs in at least two phases. The first phase, which optimizes allocation of N in younger needle age classes, is distinctly different from the second, which conserves N prior to abscission. The ¹⁵N difference between creeks was eliminated by the fertilization (P=0.42). In the two dominant conifer species, Abies lasiocarpa and Picea engelmannii, most fertilizer N was found in the current-year foliage; little was found in older needles and none was detected in litter (P=0.53). The only N-fixing shrub species, Alnus incana, took up only a small amount of fertilizer N [mean percent N derived from fertilizer (%Ndff) 5.0±1.6% (SE)]. Far more fertilizer N was taken up by other deciduous shrubs (mean %Ndff=33.9±4.5%). Fertilizer N made up 25% (±4.2%) of the N in deciduous shrub litter. These results demonstrate the feasibility of light labeling with ¹⁵N and the potential influence of riparian plant species composition on stream nutrient dynamics via allochthonous leaf litter inputs.     

Non‐lethal predator effects on the performance of a native and an exotic crayfish species

1. I tested the hypothesis that the potential for non‐lethal effects of predators are more important for overall performance of the fast‐growing exotic signal crayfish (Pacifastacus leniusculus Dana) than for the slower growing native noble crayfish (Astacus astacus L.). I further tested if omnivorous crayfish switched to feed on less risky food sources in the presence of predators, a behaviour that could reduce the feeding costs associated with predator avoidance. 2. In a 2 month long outdoor pool experiment, I measured behaviour, survival, cheliped loss, growth, and food consumption in juvenile noble or signal crayfish in pools with either a caged predatory dragonfly larvae (Aeshna sp.), a planktivorous fish that do not feed on crayfish (sunbleak, Leucaspius delineatus Heckel), or predator‐free controls. Crayfish had access to multiple food sources: live zooplankton, detritus and periphyton. Frozen chironomid larvae were also supplied ad libitum outside crayfish refuges, simulating food in a risky habitat. 3. Crayfish were mainly active during hours of darkness, with signal crayfish spending significantly more time outside refuges than noble crayfish. The proportion of crayfish outside refuges varied between crayfish species, time and predator treatment, with signal crayfish spending more time in refuges at night in the presence of fish. 4. Survival in noble crayfish was higher than in signal crayfish, and signal crayfish had a higher frequency of lost chelipeds, indicating a high level of intraspecific interactions. Crayfish survival was not affected by the presence of predators. 5. Gut‐contents analysis and stable isotope values of carbon (δ¹³C) and nitrogen (δ¹⁵N) indicated that the two crayfish species had similar food preferences, and that crayfish received most of their energy from feeding on invertebrates (e.g. chironomid larvae), although detritus was the most frequent food item in their guts. Signal crayfish guts were more full than those of noble crayfish, but signal crayfish in pools with fish contained significantly less food and fewer had consumed chironomids compared with predator‐free controls. Length increase of signal crayfish (35%) was significantly higher than of noble crayfish (20%), but signal crayfish in pools with fish grew less than in control pools. 6. This short‐term study indicates that fish species that do not pose a lethal threat to an organism may indirectly cause reductions in growth by affecting behaviour and feeding. This may occur even though prey are omnivorous and have access to and consume multiple food sources. These non‐lethal effects of predators are expected to be particularly important in exotic crayfish species that show a general response to fish, have high individual growth rates, and when their feeding on the most profitable food source is reduced.     

Leaf wax n-alkane δD values are determined early in the ontogeny of Populus trichocarpa leaves when grown under controlled environmental conditions

The stable hydrogen isotope ratios (δD) of leaf wax n-alkanes record valuable information on plant and ecosystem water relations. It remains, however, unknown if leaf wax n-alkane δD values record only environmental variation during the brief period of time of leaf growth or if leaf wax n-alkane δD values are affected by environmental variability throughout the entire lifespan of a leaf. To resolve these uncertainties, we irrigated Populus trichocarpa trees with a pulse of deuterium-enriched water and used compound-specific stable hydrogen isotope analyses to test if the applied tracer could be recovered from leaf wax n-alkanes of leaves that were at different stages of their development during the tracer application. Our experiment revealed that only leaf wax n-alkanes from leaves that had developed during the time of the tracer application were affected, while leaves that were already fully matured at the time of the tracer application were not. We conclude from our study that under controlled environmental conditions, leaf wax n-alkanes are synthesized only early in the ontogeny of a leaf. Our experiment has implications for the interpretation of leaf wax n-alkane δD values in an environmental context, as it suggests that these compounds record only a brief period of the environmental variability that a leaf experiences throughout its life.     

δ13C signature of organic carbon in estuarine bottom sediment as an indicator of carbon export from adjacent marshes

The ¹³C signature of organic carbon in estuarine bottom sediment in Louisiana Barataria Basin was used for estimating carbon flux from adjacent marsh. The stable carbon isotope composition of plants, soils and sediments from the basin were determined. The ¹³C content of marsh vegetation ranged from -26.3 to -27.8% for C₃ freshwater vegetation in the upper basin to -13.0 to -13.3% for C₄ vegetation in the lower basin. The ¹³C content of the highly organic marsh soils were similar to ¹³C content of vegetation present. The ¹³C content of organic carbon from bottom sediment of open water bodies ranged from 27.3 in the upper basin (freshwater) to 16.4 in bottom sediment of salt marsh ponds. The¹³C signature of organic carbon in bottom sediment from saline regions corresponded to the size of the body of water. The smaller salt marsh ponds contain sediment with ¹³C values close to that of the C₄ plantSpartina alterniflora. Results suggest that phytoplankton rather thanSpartina alterniffora is the likely organic source in bottom sediment of the larger bay near the coast (e.g. Caminada Bay).     

Trophic ecology of the Lake Superior wave zone: a stable isotope approach

Stable carbon and nitrogen isotope ratio analyses were used to characterize the primary energy sources and trophic positions of 16 common Lake Superior wave zone invertebrate species. Isotope data from six tributary species that were taxonomically and ecologically matched with common wave zone species revealed broad energetic separation between these similarly structured benthic food webs. Previously published stable isotope data for Lake Superior wetland and pelagic food webs were used to assess the relative importance of inter-habitat energy flow within the Lake Superior ecosystem. The results of these comparisons indicate that the Lake Superior wave zone is energetically distinct from its tributaries, wetlands, and to a lesser extent from its vast pelagic realm. This information and approach should prove useful in future studies on the bioenergetics of inter-zonal migrants and other species that forage in multiple habitats within the lake and also in revealing energetic connections among terrestrial, riverine, littoral, and pelagic food webs in the coastal ecosystems of Lake Superior.     

Determination of the relative uptake of ground vs. surface water by Populus deltoides during phytoremediation

The use of plants to remediate polluted groundwater is becoming an attractive alternative to more expensive traditional techniques. In order to adequately assess the effectiveness of the phytoremediation treatment, a clear understanding of water-use habits by the selected plant species is essential. We examined the relative uptake of surface water (i.e., precipitation) vs. groundwater by mature Populus deltoides by applying irrigation water at a rate equivalent to a 5-cm rain event. We used stable isotopes of hydrogen (D) and oxygen (18O) to identify groundwater and surface water (irrigation water) in the xylem sap water. Pretreatment isotopic ratios of both deuterium and 18O, ranked from heaviest to lightest, were irrigation water > groundwater > xylem sap. The discrepancy in preirrigation isotopic signatures between groundwater and xylem sap suggests that in the absence of a surface source of water (i.e., between rain events) there is an unknown amount of water being extracted from sources other than groundwater (i.e., soil surface water). We examined changes in volumetric soil water content (%), total hourly sapflux rates, and trichloroethene (TCE) concentrations. Following the irrigation treatment, volumetric soil water increased by 86% and sapflux increased by as much as 61%. Isotopic signatures of the xylem sap became substantially heavier following irrigation, suggesting that the applied irrigation water was quickly taken up by the plants. TCE concentrations in the xylem sap were diluted by an average of 21% following irrigation; however, dilution was low relative to the increase in sapflux. Our results show that water use by Populus deltoides is variable. Hence, studies addressing phytoremediation effectiveness must account for the relative proportion of surface vs. groundwater uptake.     

Oligoelements and isotopic geochemistry: a multidisciplinary approach to the reconstruction of the paleodiet

Man's biological evolution, state of health and lifestyle are closely associated with dietary changes. The methods for acquiring useful information on the diet of our ancestors are an important aspect of anthropological research; hence it was retained interesting to apply the oligoelement and isotopic techniques in parallel on the same sample, in order to compare the two methodologies, construct a complete nutritional picture, and compare the analytical results with the ancient literary sources and with the findings from archaeological excavations.