The diverse dietary profiles of MIS 3 cave bears from the Romanian Carpathians: insights from stable isotope (δ13C and δ15N) analysis

Late Pleistocene European cave bears (Ursus spelaeus ) have been considered to be largely vegetarian, although stable isotope data (δ¹³C and δ¹⁵N values) from the Romanian Carpathians has suggested considerable dietary variation. Here we evaluate previous and additional adult cave bear isotopic data from four Marine Isotope Stage 3 (MIS 3) sites in the Carpathians. Pe?tera Ur?ilor (N  =  35), Pe?tera Cioclovina (N  =  32), Pe?tera Muierilor (N  =  8), and Pe?tera cu Oase (N  =  72) provide both a dichotomy between samples suggesting vegetarian diets (from Cioclovina and Muierilor) and more omnivorous diets (from Ur?ilor and Oase), and considerable isotopic variation within samples from each site. While an inference of a strictly vegetarian diet may apply to groups that lived in ecosystems which restricted the available animal protein for these large ursids, the within and between sample isotopic variation among the Carpathian cave bears indicates considerable flexibility in their sources of protein and hence in their dietary regimes. In addition, developmental assessment of Cioclovina isotopic profiles (neonates, juveniles, sub‐adults and adults) provides patterns of transfer of stable isotope signatures throughout immature life for both δ¹³C and δ¹⁵N (increase and decrease, respectively), whereas those from Ur?ilor show little developmental shift.     

The influence of lipid‐extraction and long‐term DMSO preservation on carbon (δ13C) and nitrogen (δ15N) isotope values in cetacean skin

Stable isotope analysis (SIA) has rapidly become a useful tool to study the ecology of wild animal populations, especially for elusive, wide‐ranging predators like marine mammals. The development of projectile biopsy techniques resulted in the collection of thousands of cetacean tissue samples that were archived in a dimethyl sulfoxide (DMSO) solution for long‐term, multidecadal preservation. Here we examine the influence of DMSO preservation on carbon (δ¹³C) and nitrogen (δ¹⁵N) values by comparing a set of paired delphinid skin samples stored frozen without preservative and in DMSO for up to 22 yr. Treatment of paired frozen and DMSO‐preserved skin in a 2:1 chloroform:methanol solution yielded similar δ¹³C and δ¹⁵N values, revealing that DMSO and lipid contamination have similar isotopic effects on skin, and that these effects can be removed using routine lipid‐extraction methods. Further, amino acid concentrations in DMSO‐preserved and frozen skin tissue were similar, providing independent evidence of minimal protein alteration due to preservation. Access to a rich archive of skin samples preserved in DMSO will expand our ability to examine temporal and spatial variability in the isotope values of cetaceans, which will aid our understanding of how their ecology has been influenced by historical changes in environmental conditions.     

The isotopic biosignatures of photo‐ vs. thiotrophic bivalves: are they preserved in fossil shells?

Symbiont‐bearing and non‐symbiotic marine bivalves were used as model organisms to establish biosignatures for the detection of distinctive symbioses in ancient bivalves. For this purpose, the isotopic composition of lipids (δ¹³C) and bulk organic shell matrix (δ¹³C, δ³⁴S, δ¹⁵N) from shells of several thiotrophic, phototrophic, or non‐symbiotic bivalves were compared (phototrophic: Fragum fragum, Fragum unedo, Tridacna maxima; thiotrophic: Codakia tigerina, Fimbria fimbriata, Anodontia sp.; non‐symbiotic: Tapes dorsatus, Vasticardium vertebratum, Scutarcopagia sp.). ?¹³C values of bulk organic shell matrices, most likely representing mainly original shell protein/chitin biomass, were depleted in thio‐ and phototrophic bivalves compared to non‐symbiotic bivalves. As the bulk organic shell matrix also showed a major depletion of δ¹⁵N (down to –2.2 ‰) for thiotrophic bivalves, combined δ¹³C and δ¹⁵N values are useful to differentiate between thio‐, phototrophic, and non‐symbiotic lifestyles. However, the use of these isotopic signatures for the study of ancient bivalves is limited by the preservation of the bulk organic shell matrix in fossils. Substantial alteration was clearly shown by detailed microscopic analyses of fossil (late Pleistocene) T. maxima and Trachycardium lacunosum shell, demonstrating a severe loss of quantity and quality of bulk organic shell matrix with time. Likewise, the composition and δ¹³C‐values of lipids from empty shells indicated that a large part of these compounds derived from prokaryotic decomposers. The use of lipids from ancient shells for the reconstruction of the bivalve's life style therefore appears to be restricted.     

Annual variability in dentin δ15N and δ13C reveal sex differences in weaning age and feeding habits in Risso's dolphins (Grampus griseus)

Teeth of odontocetes accumulate annual dentinal growth layer groups (GLGs) that record isotope ratios, which reflect the time of their synthesis. Collectively, they provide lifetime records of individual feeding patterns from which life history traits can be inferred. We subsampled the prenatal dentin and postnatal GLGs in Risso's dolphins (Grampus griseus) (n = 65) that stranded or were collected as bycatch in Taiwan (1994–2014) and analyzed them for δ¹⁵N and δ¹³C. Age‐specific δ¹⁵N and δ¹³C values were corrected for effects of calendar year, stranding site, C/N, and sex. δ¹⁵N values were higher in prenatal layers (14.94‰ ± 0.74‰) than in adult female GLGs (12.58‰ ± 0.20‰), suggesting fetal enrichment during gestation. Decreasing δ¹⁵N values in early GLGs suggested changes in dietary protein sources during transition to complete weaning. Weaning age was earlier in males (1.09 yr) than in females (1.81 yr). Significant differences in δ¹⁵N values between weaned males and females suggest potential sexual segregation in feeding habits. δ¹³C values increased from the prenatal to the 4th GLG by ~1.0‰, indicative of a diet shift from ¹³C‐depleted milk to prey items. Our results provide novel insights into the sex‐specific ontogenetic changes in feeding patterns and some life history traits of Risso's dolphins.     

Early life histories of the London poor using δ13C and δ15N stable isotope incremental dentine sampling

High resolution incremental isotopic analysis of the dentine from early forming teeth, especially first molars (M1s), provides a means to assess the effects of poor childhood nutrition and healthcare on individuals in an assemblage where there are no infants to study. This approach is applied to an 18th and 19th century cemetery population associated with St Saviour's Almshouse burial ground in Southwark, London, to assess whether, or how, early dietary history, including weaning age, influenced health and nutritional status. The results show a general pattern in which non‐breast milk foods were introduced before or by 6 months of age, as indicated by elevated δ¹⁵N during this period. Almost all individuals for which we also have second molar (M2) records, showed lower δ¹⁵N values from a very young age (>1 year) until approximately 8–10 years, compared to adult values. The overall results show a significant difference in δ¹³C (p = 0 to 4sf, F = 17.327) and a weaker statistical difference in δ¹⁵N between males and females (p = 0.019, F = 5.581). One possible cause of this is a difference in the diet of males and females early in life, or alternatively, a greater susceptibility of males to nutritional deprivation compared to females. The latter argument is strengthened by a significant difference in the incidence of enamel hypoplasia between the males and females, with 7.7% of male teeth showing defects, compared to 3.9% of females. Am J Phys Anthropol 154:585–593, 2014. © 2014 Wiley Periodicals, Inc.     

Tracing sources of carbon and hydrogen to stored lipids in the migratory moth,Mythimna unipuncta using stable isotopes (δ2H, δ13C)

Stable isotope measurements of insect tissues can be used to determine origin and migratory patterns. The isotopic links between diet and stored lipids in laboratory reared true armyworm moths (Mythimna unipuncta, Haw.) were investigated using δ¹³C and δ²H measurements. Newly emerged moths were fed synthetic nectars, consisting of different carbohydrate and water sources that were isotopically distinct from those in the larval diet. After 4 days of feeding, insects were sacrificed, and fat‐body lipids were extracted for isotopic analysis. When held on a constant nectar source, adult diet contributed ～87% of the C and 44% H of lipids. For H, 27% and ～ 17% of lipid was derived from carbohydrates and water, respectively, with the remainder presumably from the larval stage. When the isotopic composition of the nectar source was switched there was rapid and exponential temporal change in lipid isotopic profiles. The relevance of our findings to tracing origins of stored lipids in migrant Lepidoptera is discussed.     

Growth decline and divergent tree ring isotopic composition (δ13C and δ18O) contradict predictions of CO2 stimulation in high altitudinal forests

Human‐induced changes in atmospheric composition are expected to affect primary productivity across terrestrial biomes. Recent changes in productivity have been observed in many forest ecosystems, but low‐latitude upper tree line forests remain to be investigated. Here, we use dendrochronological methods and isotopic analysis to examine changes in productivity, and their physiological basis, in Abies religiosa (Ar) and Pinus hartwegii (Ph) trees growing in high‐elevation forests of central Mexico. Six sites were selected across a longitudinal transect (Transverse Volcanic Axis), from the Pacific Ocean toward the Gulf of Mexico, where mature dominant trees were sampled at altitudes ranging from 3200 to 4000 m asl. A total of 60 Ar and 84 Ph trees were analyzed to describe changes in growth (annual‐resolution) and isotopic composition (decadal‐resolution) since the early 1900s. Our results show an initial widespread increase in basal area increment (BAI) during the first half of the past century. However, BAI has decreased significantly since the 1950s with accentuated decline after the 1980s in both species and across sites. We found a consistent reduction in atmosphere to wood ¹³C discrimination, resulting from increasing water use efficiency (20–60%), coinciding with rising atmospheric CO₂. Changes in ¹³C discrimination were not followed, however, by shifts in tree ring δ¹⁸O, indicating site‐ and species‐specific differences in water source or uptake strategy. Our results indicate that CO₂ stimulation has not been enough to counteract warming‐induced drought stress, but other stressors, such as progressive nutrient limitation, could also have contributed to growth decline. Future studies should explore the distinct role of resource limitation (water vs. nutrients) in modulating the response of high‐elevation ecosystems to atmospheric change.     

Spatio‐temporal isotopic signatures (δ13C and δ15N) reveal that two sympatric West African mullet species do not feed on the same basal production sources

Potential trophic competition between two sympatric mullet species, Mugil cephalus and Mugil curema, was explored in the hypersaline estuary of the Saloum Delta (Senegal) using δ¹³C and δ¹⁵N composition of muscle tissues. Between species, δ¹⁵N compositions were similar, suggesting a similar trophic level, while the difference in δ¹³C compositions indicated that these species did not feed from exactly the same basal production sources or at least not in the same proportions. This result provides the first evidence of isotopic niche segregation between two limno‐benthophageous species belonging to the geographically widespread, and often locally abundant, Mugilidae family.     

Technical note: A linear model for predicting δ13Cprotein

Objective : Development of a model for the prediction of δ¹³C_protein from δ¹³C_collagen and Δ¹³C_ap‐co. Model‐generated values could, in turn, serve as “consumer” inputs for multisource mixture modeling of paleodiet. Methods : Linear regression analysis of previously published controlled diet data facilitated the development of a mathematical model for predicting δ¹³C_protein (and an experimentally generated error term) from isotopic data routinely generated during the analysis of osseous remains (δ¹³C_co and Δ¹³C_ap‐co). Results : Regression analysis resulted in a two‐term linear model (δ¹³C_protein (%) = (0.78 × δ¹³C_co) ? (0.58× Δ¹³C_ap‐co) ? 4.7), possessing a high R‐value of 0.93 (r² = 0.86, P < 0.01), and experimentally generated error terms of ±1.9% for any predicted individual value of δ¹³C_protein. This model was tested using isotopic data from Formative Period individuals from northern Chile's Atacama Desert. Conclusions : The model presented here appears to hold significant potential for the prediction of the carbon isotope signature of dietary protein using only such data as is routinely generated in the course of stable isotope analysis of human osseous remains. These predicted values are ideal for use in multisource mixture modeling of dietary protein source contribution. Am J Phys Anthropol 157:694–703, 2015. © 2015 Wiley Periodicals, Inc.     

Nitrogen and carbon contents and δ15N and δ13C signatures in six bryophyte species: assessment of long‐term deposition changes (1980–2010) in Spanish beech forests

In this study we used recent (2010) and herbarium material (1980) of six bryophyte species to assess long‐term atmospheric deposition in natural forested areas in northern Spain. For this purpose, tissue nitrogen and carbon content, as well as δ¹³C and δ¹⁵N signatures of samples of Hypnum cupressiforme, Polytrichastrum formosum, Leucobryum juniperoideum, Rhytidiadelphus loreus, Homalothecium lutescens and Diplophyllum albicans were analysed and comparisons made between years and species. In addition, the usefulness of each of the six species was evaluated. The range of values observed was similar to that in other studies carried out in rural areas. Significantly lower values were found in 2010 for N (H. cupressiforme), δ¹⁵N (R. loreus and D. albicans), C (R. loreus) and δ¹³C (all except L. juniperoideum). Our natural areas are thus now less influenced by atmospheric pollutants than they were, most probably due to changes in some traditional local activities. Differences were observed between species for all the four parameters studied, so different species must not be analysed together. Finally, R. loreus and H. lutescens seem to be good bioindicators, sensitive even with a few samples, although further studies are needed to corroborate their usefulness.     

A new mode of ammonite preservation – implications for dating of condensed phosphorite deposits

Unusual phosphatic casts of the ammonites Mortoniceras (Subschloenbachia) sp. and Stoliczkaia sp. from the upper Albian condensed phosphorite bed at Annopol, Poland, are discussed in terms of their taphonomic history. These specimens are interpreted as ‘secondary’ external casts of ammonite replicas preserved originally as attachment scars on oyster shells. The following genetic history is suggested for this previously undocumented mode of ammonite preservation: (1) settling of shells of dead ammonites on the seafloor; (2) colonization of these shells by oysters and formation of ammonite replicas on left valves of oysters; (3) dissolution of ammonite shells; (4) reworking and fragmentation of oyster shells; (5) casting of ammonite replicas by phosphatic material; and (6) separation of ammonite casts from oyster shells, either through mechanical disintegration or dissolution of the latter. The specimens studied were formed after dissolution of the ammonite conchs, not prior to this event as in the case of typical ammonite steinkerns (internal moulds). Therefore, they are here referred to as ‘pseudo‐steinkerns’. The time interval between loss of the original ammonite shells and the formation of oyster‐mediated pseudo‐steinkerns may be very extensive. Therefore, the pseudo‐steinkerns may potentially mislead in biostratigraphic dating of condensed phosphorite deposits.     

δ18O‐derived incubation temperatures of oviraptorosaur eggs

In order to determine the incubation temperature of eggs laid by non‐avian dinosaurs, we analysed the oxygen isotope compositions of both eggshell carbonate (δ¹⁸O_c) and embryo bone phosphate (δ¹⁸O_p) from seven oviraptorosaur eggs with preserved in ovo embryo bones. These eggs come from the Upper Cretaceous Nanxiong Formation of Jiangxi Province, China. Oviraptorosaur theropods were selected because of their known brooding behaviour as evidenced by preserved adult specimens fossilized in brooding posture on their clutch. Incubation temperature of these embryos was estimated based on the following considerations: eggshell δ¹⁸O_c value reflects the oxygen isotope composition of egg water fluid; embryo bones precipitate from the same egg fluid; and oxygen isotope fractionation between phosphate and water is controlled by the egg temperature. A time‐dependent model predicting the δ¹⁸O_p evolution of the embryo skeleton during incubation as a function of egg temperature was built, and measured δ¹⁸O_c and δ¹⁸O_p values used as boundary conditions. According to the model outputs, oviraptorosaurs incubated their eggs within a 35–40°C range, similar to extant birds and compatible with the known active brooding behaviour of these theropod dinosaurs. Provided that both eggshell and embryo bones preserved their original oxygen isotope compositions, this method could be extended to investigate some reproductive traits of other extinct groups of oviparous amniotes.     

Records of upwelling, seasonality and growth in stable-isotope profiles of Pliocene mollusk shells from Florida

Oxygen and carbon isotopic profiles across the shells of well-preserved bivalves and gastropods from the Pliocene Pinecrest Beds near Sarasota, Florida, provide detailed records of the paleoen-vironmental and paleoclimatic conditions under which these high-density shell beds accumulated, as well as offer insight into shell-growth rates and longevity. Eight turritellid gastropods were analyzed from within and surrounding two Turritella-rich beds, an upper bed within unit 2(2.5-2.0 Ma) and a lower bed situated near the top of the main shell bed, unit 6/7(3.5-2.5 Ma). Three bivalves plus another turritellid specimen from a lower horizon (middle of unit 6/7), considered to represent offshore, normal-marine conditions, were also analyzed. The isotopic profiles of all shells reflect year-round shell growth in a seasonal, subtropical to warm-temperate paleoenvironment. Cyclical patterns in δ¹⁸O reflect annual variations in water temperature which on average ranged from 15 to 24d?C; minimum paleoseasonality contrasts varied from 7 to 9d?C. Summer paleo-temperatures compare favorably with those detemined from ostracodes, whereas winter temperatures appear slightly cooler. Except for one pectinid specimen, temperature differences between horizons and specimens are small. Annual δ¹⁸O cycles indicate: Turritella apicalis lived longer and grew slightly faster than Turritella gladeensis; and, shell growth rates and increment formation in Mercenaria campechiensis are comparable to modern Florida populations. Coincident episodes of heavy δ¹⁸O and light δ¹⁸C in both turritellids and bivalves suggest a pattern of seasonal upwelling. This cool, nutrient-rich, upwelled water may be partially responsible for the great abundance of Pinecrest fossils. □Stable isotopes, Pliocene, Pinecrest Beds, Florida, upwelling, paleotemperature, mollusk, Turritella.      

Changes in wood and foliar δ13C in sugar maple at Gatineau Park,Quebec, Canada

Leaf samples and tree rings formed between the mid‐1960s and mid‐1990s from sugar maple (Acer saccharum Marsh.) at Gatineau Park (45°30′ N, 75°54′ W), Quebec were analysed for δ¹³C. Leaf samples were collected at ground level (1–2 m above ground) at monthly intervals during the summer, whereas tree cores were extracted from the largest trees (d.b.h. > 30 cm) in the young deciduous forest in August 1998. Significant linear decreases in δ¹³C over time were found in foliage and tree rings, but the decrease in δ¹³C was significantly greater in foliage than in the wood. The apparent isotopic discrimination (Δ) of tree rings varied insignificantly around a mean of 18‰, whereas foliar Δ increased significantly from 19‰ in the 1960s to around 23‰ by the mid 1990s, likely as a result of an increasing canopy effect as the forest matured. Using models of carbon discrimination and Δ‐values of the tree rings, we calculate that the intrinsic water use efficiency of mature sugar maple has increased by approximately 4% over the study period.     

Records of palaeo‐seawater condition from oxygen‐isotope profiles of early Pleistocene fossil molluscs from the Seoguipo Formation (Korea)

Kim, J.K., Khim, B.‐K., Woo, K.S., & Yoon, S.H. 2009: Records of palaeo‐seawater condition from oxygen‐isotope profiles of early Pleistocene fossil molluscs from the Seoguipo Formation (Korea). Lethaia, Vol. 43, pp. 170–181. High‐resolution δ¹⁸O profiles of early Pleistocene fossil molluscs (Mizuhopecten tokyoensis hokurikuensis) from the shallow‐marine sedimentary Seoguipo Formation (Korea) were found to exhibit distinct annual cycles identified by their unique seasonality (δ¹⁸O amplitude). A direct comparison of fossil δ¹⁸O profiles with that of living shells (Amusium japonicum japonicumi) indicated that the palaeoseawater conditions differed from present‐day seawater. Specifically, the positive δ¹⁸O shift in the isotope profile of the fossil specimens relative to that of the living mollusc shell reflected that palaeotemperature was lower than that today. However, a comparison of the coldest palaeotemperatures (determined from the heaviest δ¹⁸O values of fossil shells), with the present‐day winter temperatures indicates that temperature variation alone cannot account for the entire positive δ¹⁸O offset. These findings indicate that variation in the seawater δ¹⁸O_w values plays a dominant role in the biogenic carbonate precipitation of fossils. Thus, the fossil shells obtained from stratigraphic units suggest different palaeoenvironmental conditions, including lower temperatures and ¹⁸O‐enriched glacial seawater, when compared with the present‐day conditions. The Seoguipo Formation records at least five cycles of relative sea‐level fluctuations, with changes in fossil δ¹⁸O amplitudes separated by sequence boundaries likely to reflect variations of unique palaeoseawater condition, although the oxygen‐isotope profile of fossil molluscs appears to provide a snap‐shot of the palaeoclimatic signature. □Early Pleistocene, mollusc fossils, oxygen isotope, palaeoenvironment, seawater temperature.     

Relationship between δ13C of chironomid remains and methane flux in Swedish lakes

1. Methanogenic carbon can be incorporated by methane‐oxidising bacteria, leading to a ¹³C‐depleted stable carbon isotopic composition (δ¹³C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the δ¹³C of other abundant chironomid groups and the relationship between chironomid δ¹³C and methane production in lakes. 2. Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with δ¹³C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini). 3. Remains of Orthocladiinae in the seven study lakes had the highest δ¹³C values (?31.3 to ?27.0‰), most likely reflecting δ¹³C of algae and other plant‐derived organic matter. Remains of Chironomini and Tanypodinae had lower δ¹³C values (?33.2 to ?27.6‰ and ?33.6 to ?28.0‰, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and δ¹³C of Chironomini (r = ?0.90, P = 0.006). Methane release from the sediments was also negatively correlated with δ¹³C of Chironomini (r = ?0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05). 4. Selective incorporation of methane‐derived carbon can explain the observed correlations between methane fluxes and δ¹³C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal δ¹³C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini δ¹³C. More detailed studies with a higher number of analysed samples and detailed measurement of δ¹³C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to δ¹³C of chironomid remains.     

Sclerochronological study of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from Hokkaido,northern Japan

Here, we present the first sclerochronological investigation of shells of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from the middle Campanian cold seep carbonate‐bearing strata of the Yezo Basin in Hokkaido (northern Japan). Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope values were measured in the aragonitic and calcitic shell layers of both species and compared to those of other co‐occurring benthic (mainly bivalves and gastropods) and demersal molluscs (ammonites). Sedimentological and stable isotope data suggest that these bivalves lived near cold seeps and were exposed to high H₂S level in the seawater. The inoceramid shells exhibited higher δ¹³C and lower δ¹⁸O values than the coeval non‐cold seep molluscs. We ascribed the anomalous isotopic pattern to a combination of vital and environmental effects determined by the hosting of chemosymbionts and the exposure to warm interstitial waters. Inoceramid δ¹³C minima coincided with growth lines and likely reflect changes in nutrient supply by the chemosymbionts. Absolute temperatures estimated from δ¹⁸O values of Sphenoceramus schmidti and S. sachalinensis were, on average, ca. 4–5°C warmer than those reconstructed for the non‐seepage environment (19.3 ± 0.7°C). Short‐term δ¹⁸O fluctuations of the inoceramid material indicate local temperature ranges of up to 5.2°C, that is four times larger than those reconstructed from the benthic and demersal fauna (1.3°C). In general, our data suggest that the stable carbon and oxygen isotope values of the studied Sphenoceramus spp. were strongly affected by short‐term fluctuations in seepage activity and do not reflect seasonal fluctuations.     

Reconstructing the δ18O of atmospheric water vapour via the CAM epiphyte Tillandsia usneoides: seasonal controls on δ18O in the field and large‐scale reconstruction of δ18Oa

Using both oxygen isotope ratios of leaf water (δ¹⁸O_L) and cellulose (δ¹⁸O_C) of Tillandsia usneoides in situ, this paper examined how short‐ and long‐term responses to environmental variation and model parameterization affected the reconstruction of the atmospheric water vapour (δ¹⁸O_a). During sample‐intensive field campaigns, predictions of δ¹⁸O_L matched observations well using a non‐steady‐state model, but the model required data‐rich parameterization. Predictions from the more easily parameterized maximum enrichment model (δ¹⁸O_L–M) matched observed δ¹⁸O_L and observed δ¹⁸O_a when leaf water turnover was less than 3.5 d. Using the δ¹⁸O_L–M model and weekly samples of δ¹⁸O_L across two growing seasons in Florida, USA, reconstructed δ¹⁸O_a was ?12.6 ± 0.3‰. This is compared with δ¹⁸O_a of ?12.4 ± 0.2‰ resolved from the growing‐season‐weighted δ¹⁸O_C. Both of these values were similar to δ¹⁸O_a in equilibrium with precipitation, ?12.9‰. δ¹⁸O_a was also reconstructed through a large‐scale transect with δ¹⁸O_L and the growing‐season‐integrated δ¹⁸O_C across the southeastern United States. There was considerable large‐scale variation, but there was regional, weather‐induced coherence in δ¹⁸O_a when using δ¹⁸O_L. The reconstruction of δ¹⁸O_a with δ¹⁸O_C generally supported the assumption of δ¹⁸O_a being in equilibrium with precipitation δ¹⁸O (δ¹⁸O_ppt), but the pool of δ¹⁸O_ppt with which δ¹⁸O_a was in equilibrium – growing season versus annual δ¹⁸O_ppt – changed with latitude.     

Foliar δ13C response patterns along a moisture gradient arising from genetic variation and phenotypic plasticity in grassland species of Inner Mongolia

Plants depend upon both genetic differences and phenotypic plasticity to cope with environmental variation over different timescales. The spatial variation in foliar δ¹³C levels along a moisture gradient represents an overlay of genetic and plastic responses. We hypothesized that such a spatial variation would be more obvious than the variation arising purely from a plastic response to moisture change. Leymus chinensis and Stipa spp. were sampled from Inner Mongolia along a dry‐wet transect, and some of these species were transplanted to an area with a moisture gradient. For Stipa spp., the slope of foliar δ¹³C and mean annual precipitation along the transect was significantly steeper than that of foliar δ¹³C and mean annual precipitation after the watering treatment. For L. chinensis, there was a general decreasing trend in foliar δ¹³C under the different (increasing) watering levels; however, its populations showed an irregular relationship between foliar δ¹³C and moisture origin. Therefore, support for our hypothesis was obtained from Stipa spp., but not from L. chinensis.