Using stable isotopes in hummingbird breath to estimate reliance on supplemental feeders

Understanding the ecological consequences of supplemental feeding to both hummingbirds and the plants they pollinate is complicated by logistical challenges associated with assessing relative dietary resource use with commonly applied observational methods. Here, we describe the results of research conducted to assess the relative use of feeder and flower nectar by Broad-tailed (Selasphorus platycercus) and Rufous hummingbirds (Selasphorus rufus) using two distinct methodological variations to measure the δ13C values of exhaled CO2. Because of the relatively quick time in which both species switch from exogenous to endogenous resources to fuel metabolism, our experiment allowed us to assess resource use at two timescales. Our results suggest variability in the relative contributions of the two dietary sources within and among species and timescales, with most birds employing a mixture of feeder and flower sugars as fuel sources. This diversity in relative resource use may mitigate potential negative effects of supplemental feeding on hummingbirds and their plant symbionts.

Greenhouse gases emissions and dissolved carbon export affected by submarine groundwater discharge in a maricultural bay, Hainan Island, China

Greenhouse gases (GHG) emissions in coastal areas are influenced by both mariculture and submarine groundwater discharge (SGD). In this study, we first conducted a comprehensive investigation on carbon dioxide (CO₂) and methane (CH₄) emissions affected by SGD in a typical maricultural bay in north-eastern Hainan Island, China. A radon (²²²Rn) mass balance model revealed considerable high SGD rates (179 ± 92 cm d^-1) in the bay, and the fluxes of SGD-derived dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) were 150.36 and 3.65 g C m^-2 d^-1, respectively. Time-series measurement results, including those for ²²²Rn, CH₄, CO₂, and physicochemical parameters, indicated that GHG dynamics in the maricultural bay mainly varied with tidal fluctuations, and isotopic evidence further revealed that acetate fermentation was the main mechanism of methanogenesis in the maricultural waters. The water-air fluxes in the maricultural area were 1.05 ± 0.32 and 9.49 ± 3.96 mmol m^-2 day^-1 for CH₄ and CO₂, respectively, implying that Qinglan Bay was a potential source of GHG released into the atmosphere. At the bay-scale, the CO₂ emissions followed a spatial pattern, and the CH₄ emissions were mainly affected by mariculture. The high CH₄ emissions in the maricultural waters caused by maricultural activities, SGD, high temperature, and special hydrology resulted in the formation of the CH₄-dominated total CO₂-equivalent emissions model. Our study highlights the importance of considering the link between SGD and GHG emissions in maricultural bays when constraining global GHG fluxes.

The Variations of Leaf δ13C and Its Response to Environmental Changes of Arbuscular and Ectomycorrhizal Plants Depend on Life Forms

Arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM) are the two most common mycorrhizal types and are paid the most attention to, playing a vital common but differentiated function in terrestrial ecosystems. The leaf carbon isotope ratio (δ¹³C) is an important factor in understanding the relationship between plants and the environment. In this study, a new database was established on leaf δ¹³C between AM and ECM plants based on the published data set of leaf δ¹³C in China's C₃ terrestrial plants, which involved 1163 observations. The results showed that the differences in leaf δ¹³C between AM and ECM plants related closely to life forms. Leaf δ¹³C of ECM plants was higher than that of AM plants in trees, which was mainly led by the group of evergreen trees. The responses of leaf δ¹³C to environmental changes were varied between AM and ECM plants. Among the four life forms, leaf δ¹³C of ECM plants decreased more rapidly than that of AM plants, with an increase of longitude, except for deciduous trees. In terms of the sensitivity of leaf δ¹³C to temperature changes, AM plants were higher than ECM plants in the other three life forms, although there was no significant difference in evergreen trees. For the response to water conditions, the leaf δ¹³C of ECM plants was more sensitive than that of AM plants in all life forms, except evergreen and deciduous trees. This study laid a foundation for further understanding the role of mycorrhiza in the relationship between plants and the environment.

Earliest evidence of primate captivity and translocation supports gift diplomacy between Teotihuacan and the Maya

A multimethod archaeometry study (zooarchaeological, isotopic, ancient DNA, paleobotanical, and radiocarbon dating) of a spider monkey sacrificed in the ceremonial center of Teotihuacan, Mexico (1 to 550 CE) is interpreted as a diplomatic gift exchange with neighboring Maya. Not only does this spider monkey provide the earliest known instance of primate translocation and captivity in Mesoamerica, it helps date incipient modes of interregional diplomacy between two major powers during Early Classic Mesoamerica: Teotihuacan and the Maya. Details of human-primate interaction include age at capture and transport (before ∼3 y of age), captive duration (over 2 y), anthropogenic diet (staple was maize, though secondary resources unique to anthropogenic diet including arrowroot and chili pepper were also found), context of sacrifice (tethered and associated with complete golden eagle and an array of other statecrafts), and general site context (including presence of Maya vessels and Maya-style murals). The timing of the spider monkey's sacrifice (250 to 300 CE) and its life history suggest a reconsideration of epigraphically attested militaristic involvement of Teotihuacan at certain Maya sites. We propose that a period of more multilateral and fluid ritual exchange with Maya dignitaries preceded the Teotihuacan state's eventual ascent to prominence.

Beyond width and density: stable carbon and oxygen isotopes in cork-rings provide insights of physiological responses to water stress in Quercus suber L

As climate change increasingly affects forest ecosystems, detailed understanding of major effects is important to anticipate their consequences under future climate scenarios. The Mediterranean region is a prominent climate change hotspot, and evergreen cork oak (Quercus suber L.) woodlands are particularly climatically sensitive due to cork (bark) harvesting. Cork oak's drought avoidance strategy is well-known and includes structural and physiological adaptations that maximise soil water uptake and transport and limit water use, potentially leading to reduced stem and cork growth. Trees' responses to cope with water-limited conditions have been extensively described based on cork-rings width and, more recently, on cork-rings density, in dendroecological studies. However, so far, tree functional attributes and physiological strategies, namely photosynthetic metabolism adjustments affecting cork formation, have never been addressed and/or integrated on these previous cork-rings-based studies. In this study, we address the relation between carbon and oxygen stable isotopes of cork rings and precipitation and temperature, in two distinct locations of southwestern Portugal-the (wetter) Tagus basin peneplain and the (drier) Grândola mountains. We aimed at assessing whether the two climatic factors affect cork-ring isotopic composition under contrasting conditions of water availability, and, therefore, if carbon and oxygen signatures in cork can reflect tree functional (physiological and structural) responses to stressful conditions, which might be aggravated by climate change. Our results indicate differences between the study areas. At the drier site, the stronger statistically significant negative cork δ ¹³C correlations were found with mean temperature, whereas strong positive cork δ ¹⁸O correlations were fewer and found only with precipitation. Moreover, at the wetter site, cork rings are enriched in ¹⁸O and depleted in ¹³C, indicating, respectively, shallow groundwater as the water source for physiological processes related with biosynthesis of non-photosynthetic secondary tissues, such as suberin, and a weak stomatal regulation under high water availability, consistent with non-existent water availability constrains. In contrast, at the drier site, trees use water from deeper ground layers, depleted in ¹⁸O, and strongly regulate stomatal conductance under water stress, thus reducing photosynthetic carbon uptake and probably relying on stored carbon reserves for cork ring formation. These results suggest that although stable isotopes signatures in cork rings are not proxies for net growth, they may be (fairly) robust indicators of trees' physiological and structural adjustments to climate and environmental changes in Mediterranean environments.

Hydroclimatic changes since the Last Glacial Maximum recorded in mountain peat deposit on the southwestern margin of the Sichuan Basin, China

Knowledge of the hydroclimatic changes in Southwest China since the Last Glacial Maximum (LGM) is crucial for disentangling the long-term evolution of the Asia Monsoon and predicting the future fate of the mountain peat deposit in the Asia Monsoon region. In this study, we obtained a 530-cm-long peat core from the Ganchi wetland in Southwest China and analyzed its geochemical indices, including total nitrogen (TN), total organic carbon (TOC), stable carbon isotope composition of organics (δ13Corg), and the concentration of several major elements, to investigate the sedimentary and hydroclimate evolution since the LGM. We found that the peat strata in the Ganchi wetland have developed gradually from 13.7 cal kyr BP, which is likely ascribed to the warm climate during the Bølling-Allerød (B/A) period. TOC, δ13Corg, K/Ti, and Fe/Mn records showed notable paleoclimate shifts since the last deglaciation. The first warming period after the LGM was observed starting at 18.2 cal kyr BP, which is consistent with other records from Southwest China. The reconstruction results show that the western margin of the Sichuan Basin during the last deglaciation was most affected by the East Asia summer monsoon (EASM), and less affected by the Indian summer monsoon (ISM). The climate of the early Holocene (11.2–7.5 cal kyr BP) was affected by both the ISM and EASM, resulting in more complex local climatic features. The Holocene Megathermal period observed from 7.5 to 3.5 cal kyr BP, is consistent with the timing detected in other records of Southwest China.

Different survival strategies involve carbon translocation rather than de novo C assimilation under complete submergence in rice plant

This study investigated the effect of transient submergence on the recovery of photosynthetic activity and translocation of photosynthate in IR67520 (Sub1A genotype) and IR72442 (non-Sub1A genotype) using ¹³C-labeled tracer, coupled with some photosynthetic physiological assessments. Plant growth, photosynthetic capacity, and photosynthetic recovery were studied by treating the two rice genotypes without or completely submerged for 7 days in transparent acrylic tanks filled with water to a depth of 80 cm, followed by 7 days of reaeration. Results revealed that the IR67520 was able to obtain new carbon source for assimilation during at 7 days of recovery periods. The IR72442 genotype partitioned ¹³C to the newly developed upper leaves more than the IR67520 genotype did. This was due to its inability to obtain CO₂ from other source during post submergence. Recovery of chlorophyll content, ability to retain higher biomass, and ability to grow faster at 7 days of recovery periods also indicated the ability of Sub1A genotype to reactivate its photosynthetic capacity.

The potential of stable carbon and nitrogen isotope analysis of foxtail and broomcorn millets for investigating ancient farming systems

Foxtail and broomcorn millets are the most important crops in northern China since the early Neolithic. However, little evidence is available on how people managed these two crops in the past, especially in prehistory. Previous research on major C₃ crops in western Eurasia demonstrated the potential of stable carbon and nitrogen isotope analysis of charred archaeobotanical remains to reveal the management of water and manure, respectively. Here, we evaluate the feasibility of a similar approach to C₄ millets. Foxtail and broomcorn millet plants grown in pots in a greenhouse under different manuring and watering regimes were analysed to test the effects of management on stable carbon and nitrogen isotope values of grains. Stable nitrogen isotope values of both millets increased as manuring level increased, ranging from 1.7 ‰ to 5.8 ‰ in different conditions; hence, it appears a feasible tool to identify manuring practices, in agreement with results from recent field studies. However, the two millets exhibit opposing trends in stable carbon isotope values as watering level increased. The shift in stable carbon isotope values of millets is also smaller than that observed in wheat grown in the same experimental environment, making it difficult to identify millet water status archaeologically. In addition, we charred millet grains at different temperatures and for varying durations to replicate macro-botanical remains recovered archaeologically, and to evaluate the offsets in carbon and nitrogen isotope values induced by charring. We found that the stable nitrogen isotope values of foxtail millet and broomcorn millet can shift up to 1-2 ‰ when charred, while the stable carbon isotope values change less than 0.3 ‰. Overall, we demonstrate that stable nitrogen isotope values of charred foxtail and broomcorn millet seeds could provide insight into past field management practices, and both carbon and nitrogen isotope values can together inform palaeodietary reconstruction.

Carbon-isotope composition of artiodactyl tooth enamel and its implications for paleodiets

The stable carbon-isotope composition of mammalian tooth enamel is a powerful tool for reconstructing paleodiet and paleoenvironment. Its application in the fossil record relies on a thorough understanding of the isotopic composition of mammalian diets in modern ecosystems. We compiled and evaluated a global dataset of the carbon-isotope values of artiodactyl tooth enamel, supplemented by new samples, for 79 extant species. After correcting for differences in atmospheric carbon-isotope composition, body mass, and digestive physiology, we compared the inferred carbon-isotope values of ingested forage (δ13Cdiet) among seven feeding categories. The artiodactyl herbivore dietary spectrum is expressed through a wide range of δ13Cdiet values, with the most depleted mean value in frugivores and the most enriched in obligate grazers. In general, grazing species have a broader range of isotope values than browsing species, suggesting a wider dietary niche breadth. Notably, variable grazers exhibit a bimodal distribution of δ13Cdiet values, with North American and Asian taxa consuming C3 diets and African taxa consuming C4 diets, reflecting the amount of C4 vegetation in the environment. Variation in δ13Cdiet values also occurs among terrestrial ecoregions and artiodactyl clades. Grassland ecoregions differ significantly from forest ecoregions. We detected a low but significant phylogenetic signal in the mean δ13Cdiet values of extant species, with some of the oldest ruminant lineages having maintained C3 feeding and pure C4 diets being restricted to two bovid clades. Determining variation in δ13Cdiet values in different feeding categories and lineages will help refine paleoecological and paleoenvironmental reconstructions from the rich fossil record of artiodactyls.

Evolution of an intermediate C4 photosynthesis in the non-foliar tissues of the Poaceae

Carbon concentrating mechanisms (CCMs) in plants are abaptive features that have evolved to sustain plant growth in unfavorable environments, especially at low atmospheric carbon levels and high temperatures. Uptake of CO₂ and its storage in the aerenchyma tissues of Lycopsids and diurnal acidity fluctuation in aquatic plants during the Palaeozoic era (ca. 300 Ma.) would represent the earliest evolution of a CCM. The CCM parts of the dark reactions of photosynthesis have evolved many times, while the light reactions are conserved across plant lineages. A C₄ type CCM, leaf C₄ photosynthesis is evolved in the PACMAD clade of the Poaceae family. The evolution of C₄ photosynthesis from C₃ photosynthesis was an abaptation. Photosynthesis in reproductive tissues of sorghum and maize (PACMAD clade) has been shown to be of a weaker C₄ type (high CO₂ compensation point, low carbon isotope discrimination, and lack of Rubisco compartmentalization, when compared to the normal C₄ types) than that in the leaves (normal C₄ type). However, this does not fit well with the character polarity concept from an evolutionary perspective. In a recent model proposed for CCM evolution, the development of a rudimentary CCM prior to the evolution of a more efficient CCM (features contrasting to a weaker C₄ type, leading to greater biomass production rate) has been suggested. An intermediate crassulacean acid metabolism (CAM) type of CCM (rudimentary) was reported in the genera, Brassia, Coryanthes, Eriopsis, Peristeria, of the orchids (well-known group of plants that display the CAM pathway). Similarly, we propose here the evolution of a rudimentary CCM (C₄-like type pathway) in the non-foliar tissues of the Poaceae, prior to the evolution of the C₄ pathway as identified in the leaves of the C₄ species of the PACMAD clade.

Paleodietary reconstruction of endemic rodents from the precolumbian Dominican Republic: Discriminating wild feeding behavior from diets linked to human niche construction activities

In the Greater Antilles, certain animal taxa that have long been theorized to have been managed by indigenous peoples prior to AD1492, the main candidates being a group of endemic caviomorph rodents known as hutias (Capromyinae). This isotopic study investigates the paleodiets of several species of endemic rodents from three late precolonial sites in the northern Dominican Republic: El Flaco (cal. ad 990-1452), El Carril (cal. ad 1030-1262), and La Entrada (cal. ad 840-900) to assess whether human influence over animal diets can be determined. We examined bone collagen carbon (δ13Cco) and nitrogen (δ15N) and tooth enamel carbon (δ13Cen) isotope values of three species of hutias, Isolobodon portoricensis, Isolobodon montanus, and Plagiodontia aedium, alongside edible rat (Brotomys sp.), and domestic guinea pig (Cavia porcellus). To estimate dietary source contributions, we employed a Bayesian dietary mixing model (FRUITS v.3.0) and ran three different permutations to assess the relative contributions of C3 or C4/CAM plants. The addition of an extra 79 wild C3 and 40 wild C4/CAM plant species' isotope values from published sources to an established isotopic foodweb for the Caribbean region enabled us to discriminate between wild and domestic C3 and C4/CAM plant food sources in two of these models. Our results provide evidence of the significant consumption of domestic C4/CAM plants by some animals. This likely represents maize (Zea mays) consumption, which is known to have been ubiquitously cultivated by indigenous peoples in the region. This is particularly the case for I. portoricensis, as FRUITS modeling suggests that a few individuals consumed C4/CAM plants well beyond their expected natural diets as determined from feeding studies of extant hutia species. This may indicate human influence over endemic rodent diets due to niche construction activities such as horticultural practices and may reflect either opportunistic feeding on human produce or the purposeful supplementation of hutia diets by humans.

Mercury speciation in Scottish raptors reveals high proportions of inorganic mercury in Scottish golden eagles (Aquila chrysaetos): Potential occurrence of mercury selenide nanoparticles

Knowledge of the uptake and fate of mercury (Hg) compounds in biota is important in understanding the global cycling of Hg and its transfer pathways through food chains. In this study, we analysed total mercury (T-Hg) and methylmercury (MeHg) concentrations in 117 livers of Scottish birds of prey that were found across Scotland and submitted for post-mortem examination through the Raptor Health Scotland project between 2009 and 2019. Statistical comparisons focussed on six species (barn owl, Tyto alba; Eurasian common buzzard, Buteo buteo; golden eagle, Aquila chrysaetos; hen harrier, Circus cyaneus; Eurasian sparrowhawk, Accipiter nisus; and tawny owl, Strix aluco) and showed that golden eagles had a statistically lower fraction of MeHg compared to other raptor species. Further investigation using stable carbon and stable nitrogen isotope ratio measurements carried out for the golden eagles (n = 15) indicated that the increased presence of inorganic mercury (iHg) correlated with a marine influence on the primarily terrestrial diet. Additional bioimaging (n = 1) with laser ablation - inductively coupled plasma - mass spectrometry indicated the co-location of Hg and selenium (Se) within the liver tissue and transmission electron microscopy showed evidence of nanoparticles within the range of 10-20 nm. Further analysis using single particle - inductively coupled plasma - mass spectrometry (n = 4) confirmed the presence of Hg nanoparticles. Together, the evidence suggests the presence of mercury selenide (HgSe) nanoparticles in the liver of some golden eagles that, to our knowledge, has never been directly observed in terrestrial birds of prey. This study points to two alternative hypotheses: these golden eagles may be efficient at breaking down MeHg and form HgSe nanoparticles as a detoxification mechanism (as previously observed in cetaceans), or some golden eagles with elevated iHg may have accumulated these nanoparticles by foraging on stranded cetaceans or seabirds.

Responses to simultaneous anthropogenic and biological stressors were mixed in an experimental saltmarsh ecosystem

Coastal ecosystems are essential for absorbing and bouncing back from the impacts of climate change, yet accelerating climate change is causing anthropogenically-derived stressors in these ecosystems to grow. The effects of stressors are more difficult to foresee when they act simultaneously, however, predicting these effects is critical for understanding ecological change. Spartina alterniflora (Spartina), a foundational saltmarsh plant key to coastal resilience, is subject to biological stress such as herbivory, as well as anthropogenic stress such as chemical pollution. Using saltmarsh mesocosms as a model system in a fully factorial experiment, we tested whether the effects of herbivory and two chemicals (oil and dispersant) were mediated or magnified in combination. Spartina responded to stressors asynchronously; ecophysiology responded negatively to oil and herbivores in the first 2-3 weeks of the experiment, whereas biomass responded negatively to oil and herbivores cumulatively throughout the experiment. We generally found mixed multi-stressor effects, with slightly more antagonistic effects compared to either synergistic or additive effects, despite significant reductions in Spartina biomass and growth from both chemical and herbivore treatments. We also observed an indirect positive effect of oil on Spartina, via a direct negative effect on insect herbivores. Our findings suggest that multi-stressor effects in our model system, 1) are mixed but can be antagonistic more often than expected, a finding contrary to previous assumptions of primarily synergistic effects, 2) can vary in duration, 3) can be difficult to discern a priori, and 4) can lead to ecological surprises through indirect effects with implications for coastal resilience. This leads us to conclude that understanding the simultaneous effects of multiple stressors is critical for predicting foundation-species persistence, discerning ecosystem resilience, and managing and mitigating impacts on ecosystem services.

Were there royal herds? Understanding herd management and mobility using isotopic characterizations of cattle tooth enamel from Early Dynastic Ur

During the third millennium BC, Mesopotamia (the land between the Tigris and Euphrates Rivers, in modern Iraq-Syria), was dominated by the world’s earliest cities and states, which were ruled by powerful elites. Ur, in present-day southern Iraq, was one of the largest and most important of these cities, and irrigation-based agriculture and large herds of domesticated animals were the twin mainstays of the economy and diet. Texts suggest that the societies of the Mesopotamian city-states were extremely hierarchical and underpinned by institutionalised and heavily-managed farming systems. Prevailing narratives suggest that the animal management strategies within these farming systems in the third millennium BC were homogenous. There have been few systematic science-based studies of human and animal diets, mobility, or other forms of human-animal interaction in Mesopotamia, but such approaches can inform understanding of past economies, including animal management, social hierarchies, diet and migration. Oxygen, carbon and strontium isotopic analysis of animal tooth enamel from both royal and private/non-royal burial contexts at Early Dynastic Ur (2900–2350 BC) indicate that a variety of herd management strategies and habitats were exploited. These data also suggest that there is no correlation between animal-management practices and the cattle found in royal or private/non-royal burial contexts. The results demonstrate considerable divergence between agro-pastoral models promoted by the state and the realities of day-to-day management practices. The data from Ur suggest that the animals exploited different plant and water sources, and that animals reared in similar ways ended up in different depositional contexts.

Time Since Dose and Dietary Vitamin A Intake Affect Tracer Mixing in the 13C-Retinol Isotope Dilution Test in Male Rats

BACKGROUND

Retinol isotope dilution (RID) estimates total liver vitamin A reserves (TLRs), the gold-standard vitamin A (VA) biomarker. RID equation assumptions are based on limited data.

OBJECTIVES

We measured the impact of tracer choice, mixing period, and VA intake on tracer mixing [ratio of tracer enrichment in serum to that in liver stores (S)] in VA-deficient, -adequate, and hypervitaminotic rats.

METHODS

Study 1 was a 3 × 2 × 3 design (18 groups, n = 5/group). Male Sprague-Dawley rats (21 d old) received 50, 100, or 3500 nmol VA/d for 21 d, were administered 52 nmol 13C2- or 13C10-retinyl acetate orally, and killed 5, 10, or 15 d later. Unlabeled VA (50 nmol/d) was given on days 11-14. Study 2 used 100 nmol VA/d for 21 d with 3 groups (n = 6-7): 52 nmol 13C2- or 13C10-retinyl acetate and 100 nmol VA/d throughout 14-d mixing, or 13C2-retinyl acetate without VA. Repeated-measures, 1-factor, and 3-factor ANOVAs were used for analysis.

RESULTS

Mean ± SD TLRs (μmol/g liver) reflected intake: 0.11 ± 0.04 (50 nmol VA/d), 0.16 ± 0.04 (100 nmol VA/d), and 5.07 ± 1.58 (3500 nmol VA/d) in Study 1 and 0.24 ± 0.08 (100 nmol VA/d) in Study 2. In Study 1, mean ± SD S was 1.65 ± 0.26 (5 d), 1.16 ± 0.09 (10 d), and 0.92 ± 0.08 (15 d). The interactions tracer*VA intake and time*VA intake were significant between days 10 and 15 (P < 0.05). In Study 2, mean ± SD S was 1.07 ± 0.02 without VA during mixing, and 0.81 ± 0.04 (13C2) and 0.79 ± 0.03 (13C10) with VA intake throughout. Estimated:measured TLRs varied by VA intake and time in Study 1 but not between groups in Study 2.

CONCLUSIONS

The 13C-content effect on RID through S is inconsistent. S is highly variable at 5 d, contraindicating early-time point RID. VA intake effects on S vary with timing and quantity. Assuming S = 0.8 at 14 d with consistent VA intake in human studies is likely appropriate.

Stable carbon and nitrogen isotope values in hair reveal management differences and hidden practices in wild boar populations

The analysis of stable isotopes in different tissues has been widely used to obtain information on the ecology and nutritional patterns of wildlife. The isotope ratios of the stable isotopes of carbon and nitrogen (δ¹³C and δ¹⁵N) analysed in different tissues are directly related to the animal's diet and, to some extent, to the environment where the individual has growth. Specifically, this type of analysis in hair samples has become relevant as it provides information on the quality and long-term composition of the diet that produced the isotope accumulation during the tissue growth. We took samples of wild boar (Sus scrofa) hair from 7 different populations in the south-west of Spain (Mediterranean habitats), in the 2018/2019 hunting season. The main objectives of this study were (i) to investigate the use of hair stable isotopes to reveal differences in composition and quality of the diet of wild boar within the same population or between populations, and (ii) to use hair isotopes as a tool to uncover hidden management practices that may occur in hunting areas associated with the use of supplementary feeding or even captive breeding and release. Each animal had a hair (long 10 cm) analysed in duplicate, previously cut into parts of equal size (from the oldest part of the hair to the most recent part), that were analysed separately. We found differences in δ¹³C and δ ¹⁵N between hair parts and populations, which can be related to management actions at different times during the hair growth. Moreover, the use of corn, a type of plant not occurring naturally in the study area, can be documented with the isotope analysis to prove unauthorized supplementary feeding or captive origin of wild boar in hunting areas.

Subterranean carbon flows from source to stygofauna: a case study on the atyid shrimp Stygiocaris stylifera (Holthuis, 1960) from Barrow Island (WA)

Groundwater biota are crucial for the ecological functioning of subterranean ecosystems. However, while knowledge of the taxonomic diversity of groundwater invertebrates (stygofauna) is increasing, functional ecological information is still limited. Here, we investigate seldom empirically tested assumptions around stygofaunal trophic plasticity in coping with oligotrophic habitats. We focus on Barrow Island (Western Australia), an ideal natural laboratory due to the occurrence of natural oil seeps in association with aquifers. The trophic position and food source use of the endemic atyid shrimp Stygiocaris stylifera (Holthuis, 1960) were assessed via δ¹³C and δ¹⁵N stable isotope analysis (SIA). Background information on the environmental conditions was gathered through hydrochemical data and δ¹³C SIA combined with ¹⁴C data from dissolved inorganic/organic carbon and particulate organic carbon from groundwater samples. Our results indicate carbon enrichment in proximity to the natural oil seepage coupled with changes in trophic positions of S. stylifera from higher consumers/predators to biofilm grazers/decomposers. These results are consistent with an increased involvement of hydrocarbon seeps and associated microbial communities in the carbon flows and confirm potential for the trophic flexibility in stygofauna. Further investigations involving other trophic groups will help elucidate the functioning of the ecosystems at a community level.

Niche overlap in rodents increases with competition but not ecological opportunity: A role of inter-individual difference?

Niche variation at population level mediates niche packing (i.e., patterns of species' spread within the niche space) and species coexistence at community level. Competition and ecological opportunity (resource diversity) are two of the main mechanisms underlying niche variation. Dense niche packing could occur through increased niche partitioning or increased niche overlap. In this study we used stable carbon and nitrogen isotope data of 635 individual rodents from 4 species across 9 sites in the montane region of a subtropical island to test the effects of competition and ecological opportunity on population isotope niche size, inter-individual niche difference within population, and inter-specific niche overlap within community. We used the Bayesian Standard Ellipse Area (SEAB, the ellipse area enclosed by carbon and nitrogen isotope values of organisms on a bi-plot) to estimate population niche size and inter-specific niche overlap. Inter-individual niche difference within population was quantified as isotopic divergence and isotopic uniqueness. We used rodent abundance (the number of unique individuals captured) to measure competition and plant isotope niche size (plant SEAB) to measure ecological opportunity. The rodents experienced competition as evidenced by a negative relationship between population change rate and conspecific abundance. Rodent population niche size increased with ecological opportunity but not competition. The inter-individual niche difference (isotopic uniqueness) increased with competition (inter-specific competition only) but not ecological opportunity. At community level, inter-specific niche overlap (herbivore-omnivore pair only) increased with competition (the combined abundance of the pair) but not ecological opportunity. This study demonstrated that isotope niche variation of the rodents could be hierarchically influenced by ecological opportunity and competition, with the former setting the limit of population niche size across communities and the latter shaping inter-individual niche difference and inter-specific niche overlap within communities. Under strong intra-specific competition and limited ecological opportunity for niche expansion, individuals may choose to increase their isotopic uniqueness from conspecifics at the cost of overlapping with heterospecifics of different trophic roles within the community niche space as overall competition increases. Denser niche packing of these rodent communities might be achieved through increased niche overlap.

Using breeding and quantitative genetics to understand the C4 pathway

Reducing photorespiration in C3 crops could significantly increase rates of photosynthesis and yield. One method to achieve this would be to integrate C4 photosynthesis into C3 species. This objective is challenging as it involves engineering incompletely understood traits into C3 leaves, including complex changes to their biochemistry, cell biology, and anatomy. Quantitative genetics and selective breeding offer underexplored routes to identify regulators of these processes. We first review examples of natural intraspecific variation in C4 photosynthesis as well as the potential for hybridization between C3 and C4 species. We then discuss how quantitative genetic approaches including artificial selection and genome-wide association could be used to better understand the C4 syndrome and in so doing guide the engineering of the C4 pathway into C3 crops.

Dynamic of riverine pCO2, biogeochemical characteristics, and carbon sources inferred from δ13C in a subtropical river system

Rivers significantly contribute to the global carbon budget, but data limitations and uncertainty are hampered by CO₂ quantification in the global rivers. Thus, this study estimated riverine pCO₂ by employing the pH-alkalinity-temperature method, and dissolved inorganic (DIC), dissolved organic (DOC), particulate organic (POC) carbon, and their isotopes (δ¹³C) with Chlorophyll-a (Chl a) were measured in river water samples from 26 sampling sites for characterization and source identification in the Yangtze River system. The estimated pCO₂ varies from (120 ppm) to (3400 ppm) with an average (1085 ppm) across the Yangtze River and pCO₂ is almost three times oversaturated than the ambient air (380 ppm). The downstream sites pronounced elevated pCO₂ than the upstream sites. The relationship of δ¹³C_DIC and pCO₂ indicated that pCO₂ control is seasonally independent. The significant correlations between DOC, POC, and pCO₂ revealed that organic carbon influenced pCO₂ in the river. The seasonal fluctuations of pCO₂ were observed with an average of (762.23 ppm) and (1407.35 ppm) in winter and summer, respectively. δ¹³C_DIC showed that the metabolic process has a negligible influence on DIC, δ¹³C_DIC, and pCO₂. δ¹³C_DIC values increased from -8.95‰ to -4.91‰ during summer, whereas winter increased from -19.76‰ to -1.97‰ suggesting that DIC derived from carbonate weathering, dissolution of atmospheric and soil CO₂. The δ¹³C_DOC (-30.43‰ to -24.05‰) and δ¹³C_POC (-29.87‰ to -23.37‰) values confirmed that organic carbon mainly derived from the degradation of organic materials in soil. δ¹³C_DIC revealed that anthropogenic sewage discharge slightly modified DIC composition. Overall, this study provides new insight into recent seasonal fluctuations of the pCO₂, DOC, POC, DIC, δ¹³C, and their inputs. Thus, these variations and inputs of carbon transported by the Yangtze River could have a significant influence not only on the biogeochemical cycle and ecosystem process but also on the global carbon budget.

Upregulation of C4 characteristics does not consistently improve photosynthetic performance in intraspecific hybrids of a grass

C₄ photosynthesis is thought to have evolved via intermediate stages, with changes towards the C₄ phenotype gradually enhancing photosynthetic performance. This hypothesis is widely supported by modelling studies, but experimental tests are missing. Mixing of C₄ components to generate artificial intermediates can be achieved via crossing, and the grass Alloteropsis semialata represents an outstanding study system since it includes C₄ and non-C₄ populations. Here, we analyse F1 hybrids between C₃ and C₄ , and C₃ +C₄ and C₄ genotypes to determine whether the acquisition of C₄ characteristics increases photosynthetic performance. The hybrids have leaf anatomical characters and C₄ gene expression profiles that are largely intermediate between those of their parents. Carbon isotope ratios are similarly intermediate, which suggests that a partial C₄ cycle coexists with C₃ carbon fixation in the hybrids. This partial C₄ phenotype is associated with C₄ -like photosynthetic efficiency in C₃ +C₄  × C₄ , but not in C₃  × C₄ hybrids, which are overall less efficient than both parents. Our results support the hypothesis that the photosynthetic gains from the upregulation of C₄ characteristics depend on coordinated changes in anatomy and biochemistry. The order of acquisition of C₄ components is thus constrained, with C₃ +C₄ species providing an essential step for C₄ evolution.

Upregulation of C4 characteristics does not consistently improve photosynthetic performance in intraspecific hybrids of a grass

C₄ photosynthesis is thought to have evolved via intermediate stages, with changes towards the C₄ phenotype gradually enhancing photosynthetic performance. This hypothesis is widely supported by modelling studies, but experimental tests are missing. Mixing of C₄ components to generate artificial intermediates can be achieved via crossing, and the grass Alloteropsis semialata represents an outstanding study system since it includes C₄ and non-C₄ populations. Here, we analyse F1 hybrids between C₃ and C₄ , and C₃ +C₄ and C₄ genotypes to determine whether the acquisition of C₄ characteristics increases photosynthetic performance. The hybrids have leaf anatomical characters and C₄ gene expression profiles that are largely intermediate between those of their parents. Carbon isotope ratios are similarly intermediate, which suggests that a partial C₄ cycle coexists with C₃ carbon fixation in the hybrids. This partial C₄ phenotype is associated with C₄ -like photosynthetic efficiency in C₃ +C₄  × C₄ , but not in C₃  × C₄ hybrids, which are overall less efficient than both parents. Our results support the hypothesis that the photosynthetic gains from the upregulation of C₄ characteristics depend on coordinated changes in anatomy and biochemistry. The order of acquisition of C₄ components is thus constrained, with C₃ +C₄ species providing an essential step for C₄ evolution.

Considerations on the use of carbon and nitrogen isotopic ratios for sediment fingerprinting

Carbon and nitrogen stable isotopic ratios are increasingly used in sediment fingerprinting studies. However, questions remain regarding tracer conservativeness during sediment transport and other error considerations. We investigate conservativeness processes, including carbon oxidation and nitrogen mineralization, using experiments. We also test how other considerations impact the isotopic ratios including algae accrual into temporary sediment deposits in the river, the physical loss of organic matter via disaggregation, concentration dependent mixing, and time-varying isotopic ratios of sediment sources. Results show all processes and considerations can change isotope abundance, however, significance varied. Carbon oxidation, nitrogen mineralization and upland seasonality of sediment sources did not significantly change isotopic ratios. Algae accrual, concentration dependency mixing, physical loss of organic matter during transport, and seasonality of the in-stream sediment source significantly changed the isotopic ratios for the conditions tested. Fertilization significantly impacted the stable carbon isotopic ratio in one case considered. Results from sediment fingerprinting simulations and testing how well the virtual mixture fits the mass balance equation agreed with significance results for tracer changes, and some uncertainty considerations changed fractional contribution of sources by as much as 50%. A noteworthy recommendation is the mean isotopic ratios of sediment sources should be separated by at least 1‰ to lessen tracer conservativeness concerns in fingerprinting simulation. We recommend concentration dependent mixing becomes the accepted practice when using isotopic ratios, however, we warn against using particle size corrections. We recommend the loss of organic matter during disaggregation be accounted for in fingerprinting estimates. We recommend algae accrual in in-stream sediment deposits should either be accounted for or in-stream sediment should be treated as a time-varying source in sediment fingerprinting simulations. Finally, we recommend both the carbon and nitrogen isotopic ratio should be tested as potential tracers because the two tracers performed similarly when testing how well the virtual mixture fits the mass balance equations.

Dietary isotopes of Madagascar's extinct megafauna reveal holocene browsing and grazing guilds

Megafauna play a disproportionate role in developing and maintaining their biomes, by regulating plant dispersal, community structure and nutrient cycling. Understanding the ecological roles of extinct megafaunal communities, for example through dietary reconstruction using isotope analysis, is necessary to determine pre-human states and set evidence-based restoration goals. We use δ¹³C and δ¹⁵N isotopic analyses to reconstruct Holocene feeding guilds in Madagascar's extinct megaherbivores, which included elephant birds, hippopotami and giant tortoises that occurred across multiple habitats and elevations. We compare isotopic data from seven taxa and two elephant bird eggshell morphotypes against contemporary regional floral baselines to infer dietary subsistence strategies. Most taxa show high consumption of C₃ and/or CAM plants, providing evidence of widespread browsing ecology. However, Aepyornis hildebrandti, an elephant bird restricted to the central highlands region, has isotope values with much higher δ¹³C values than other taxa. This species is interpreted as having obtained up to 48% of its diet from C₄ grasses. These findings provide new evidence for distinct browsing and grazing guilds in Madagascar's Holocene megaherbivore fauna, with implications for past regional distribution of ecosystems dominated by endemic C₄ grasses.

Water levels primarily drive variation in photosynthesis and nutrient use of scrub Red Mangroves in the southeastern Florida Everglades

We investigated how mangrove-island micro-elevation (i.e., habitat: center vs edge) affects tree physiology in a scrub mangrove forest of the southeastern Everglades. We measured leaf gas exchange rates of scrub Rhizophora mangle L. trees monthly during 2019, hypothesizing that CO2 assimilation (Anet) and stomatal conductance (gsw) would decline with increasing water levels and salinity, expecting more considerable differences at mangrove-island edges than centers, where physiological stress is greatest. Water levels varied between 0 and 60 cm from the soil surface, rising during the wet season (May-October) relative to the dry season (November-April). Porewater salinity ranged from 15 to 30 p.p.t., being higher at mangrove-island edges than centers. Anet maximized at 15.1 μmol m-2 s-1, and gsw was typically <0.2 mol m-2 s-1, both of which were greater in the dry than the wet season and greater at island centers than edges, with seasonal variability being roughly equal to variation between habitats. After accounting for season and habitat, water level positively affected Anet in both seasons but did not affect gsw. Our findings suggest that inundation stress (i.e., water level) is the primary driver of variation in leaf gas exchange rates of scrub mangroves in the Florida Everglades, while also constraining Anet more than gsw. The interaction between inundation stress due to permanent flooding and habitat varies with season as physiological stress is alleviated at higher-elevation mangrove-island center habitats during the dry season. Freshwater inflows during the wet season increase water levels and inundation stress at higher-elevation mangrove-island centers, but also potentially alleviate salt and sulfide stress in soils. Thus, habitat heterogeneity leads to differences in nutrient and water acquisition and use between trees growing in island centers versus edges, creating distinct physiological controls on photosynthesis, which likely affect carbon flux dynamics of scrub mangroves in the Everglades.

A comparative authentication study of fresh fruit and vegetable juices using whole juice and sugar-specific stable isotopes

Not-from-concentrate (NFC) juice has better nutrition, flavor and higher price than reconstituted juice. Accordingly, NFC juice is prone to adulteration and is an ongoing industry problem that has not yet been resolved. Undeclared addition of water and sugar are the main forms of NFC juice adulteration. This paper investigates the carbon and oxygen stable isotope ratios (δ¹³C and δ¹⁸O values) of the bulk juice and different juice components from 21 fruit and vegetable juices, and qualitatively and quantitatively analyzes the addition of water and sugar in NFC juices. The results show that the use of fruit pulp can help to qualitatively and quantitatively indicate the presence of C4 plant sugars in NFC juice, and can reliably detect added C4 plant sugars above 7 %. Sugar-specific isotope analysis (SSIA) technology was used to determine the δ¹³C values of different sugars (sucrose, glucose and fructose) and carbon content to qualitatively infer C3 plant sugar addition. Pulp extracted from juice had a good linear relationship with the juice water δ¹⁸O values (R² >0.90). The addition of water to NFC juice can also be determined by comparing δ¹⁸O values of extraneous water, pulp and filtered juice. Stable isotope technology confirmed NFC juice adulteration of in-market samples using the pulp as an internal reference and was found to be a useful tool to detect adulteration of in-market NFC juice.

Absolute Carbon Stable Isotope Ratio in the Vienna Peedee Belemnite Isotope Reference Determined by 1H NMR Spectroscopy

The Vienna Peedee Belemnite (VPDB) isotope reference defines the zero point of the carbon stable isotope scale that is used to describe the relative abundance of ¹³C and ¹²C. An accurate and precise characterization of this isotope reference is valuable for interlaboratory comparisons and conducting robust carbon stable isotope analyses in a vast array of fields, such as chemical forensics, (bio)geochemistry, ecology, or (astro)biology. Here, we report an absolute ¹³C/¹²C ratio for VPDB that has been obtained, for the first time, using proton nuclear magnetic resonance spectroscopy (¹H NMR). Four different NMR instruments were used to determine ¹³C/¹²C ratios in a set of glycine reference materials from the US Geological Survey (USGS64, USGS65, and USGS66) and a set of formate samples that were characterized by isotope ratios mass spectrometry (IRMS). Intercalibration of the NMR-derived ¹³C/¹²C ratios with relative abundance (δ¹³C_VPDB) measurements from IRMS yields a value of 0.011100 for the absolute ¹³C/¹²C ratio in VPDB, with an expanded uncertainty of ±0.000026 (2σ, n = 114). This is significantly different from the value of 0.011180 that is commonly used but falls within the range of values recently revised using IRMS and infrared absorption measurements. ¹H NMR was found to be an effective method for measuring absolute ¹³C/¹²C ratios due to its ability to simultaneously detect signals associated with ¹²C and ¹³C. Results provide a new and independent measure of the carbon isotope composition of VPDB, improving our understanding of this important isotope reference.

The diet at the onset of the Andean Civilization: New stable isotope data from Caral and Áspero, North-Central Coast of Peru

OBJECTIVES

The subsistence system of the first urban centers with monumental architecture from the North-Central Coast of Peru, the core area for the social complexity process of Central Andes, has been debated since the late 1960s. To shed light on this aspect, we report paleodietary data from the two most important sites of the Supe Valley: Caral (3000-200 BC), the major settlement of the middle valley, and Áspero (3000-1800 BC), a notable coastal settlement. Our main objective was to test the Maritime Foundations of Andean Civilization hypothesis.

MATERIALS AND METHODS

Stable isotope values (δ¹³ C_col , δ¹³ C_ap , and δ¹⁵ N) from 52 individuals (70 samples: 44 bones and 26 teeth) were analyzed using conventional methods and Bayesian Mixing Models to address the role of marine products and plants in people's diet at both sites over time.

RESULTS

Our results suggest high C₃ carbohydrate consumption (55%-68% total calories in Áspero and >70% in Caral). The consumption of marine resources was stable for Áspero between 3300 and 1800 BC, but it decreased for Caral between 2550 and 200 BC.

DISCUSSION

Marine protein was more important in Áspero than in Caral over time. C₃ plants, possibly tubers, formed the foundation of the diet in both sites during the Formative period (~3000-200 BC). Maize was a marginal food (<12% of calories) at least until 800 BC (29% of calories). The Maritime Foundations hypothesis does not completely account for these findings. Our results suggest the predominance of crop-focused agriculture during the evaluated period.

13C signatures of aerosol organic and elemental carbon from major combustion sources in China compared to worldwide estimates

Carbon isotope signatures are used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions) using a dual ¹⁴C-¹³C isotope approach. The dual-isotope source apportionment crucially relies on accurate knowledge of ¹³C source signatures, which are seldom measured for EC. In this work, we present ¹³C signatures of organic carbon (OC) and EC for relevant sources in China. EC was isolated for ¹³C analysis based on the OC/EC split point of a thermal-optical method (EUSAAR_2 protocol). A series of sensitivity studies were conducted to investigate the EC separation and the relationship of the thermal-optical method to other EC isolation methods. Our results show that, first, the ¹³C signatures of raw materials and EC related to traffic emissions can be separated into three groups according to geographical location. Second, the ¹³C signature of OC emitted by the flaming combustion of C4 plants is strongly depleted in ¹³C compared to the source materials, and therefore EC is a better tracer for this source than total carbon (TC). A comprehensive literature review of ¹³C source signatures (of raw materials, of TC, and of EC isolated using a variety of thermal methods) was conducted. Accordingly, we recommend composite ¹³C source signatures of EC with uncertainties and detailed application conditions. Using these source signatures of EC in an example dual-isotope source apportionment study shows an improvement in precision. In addition, ¹³C signatures of OC were measured at three different desorption temperatures roughly corresponding to semi-volatile, low-volatile, and non-volatile OC fractions. Each source category shows a characteristic trend of ¹³C signatures with desorption temperature, which is likely related to different OC formation processes during combustion.

You eat what you find - Local patterns in vegetation structure control diets of African fungus-growing termites

Fungus-growing termites and their symbiotic Termitomyces fungi are critically important carbon and nutrient recyclers in arid and semiarid environments of sub-Saharan Africa. A major proportion of plant litter produced in these ecosystems is decomposed within nest chambers of termite mounds, where temperature and humidity are kept optimal for the fungal symbionts. While fungus-growing termites are generally believed to exploit a wide range of different plant substrates, the actual diets of most species remain elusive. We studied dietary niches of two Macrotermes species across the semiarid savanna landscape in the Tsavo Ecosystem, southern Kenya, based on carbon (C) and nitrogen (N) stable isotopes in Termitomyces fungus combs. We applied Bayesian mixing models to determine the proportion of grass and woody plant matter in the combs, these being the two major food sources available for Macrotermes species in the region. Our results showed that both termite species, and colonies cultivating different Termitomyces fungi, occupied broad and largely overlapping isotopic niches, indicating no dietary specialization. Including laser scanning derived vegetation cover estimates to the dietary mixing model revealed that the proportion of woody plant matter in fungus combs increased with increasing woody plant cover in the nest surroundings. Nitrogen content of fungus combs was positively correlated with woody plant cover around the mounds and negatively correlated with the proportion of grass matter in the comb. Considering the high N demand of large Macrotermes colonies, woody plant matter seems to thus represent a more profitable food source than grass. As grass is also utilized by grazing mammals, and the availability of grass matter typically fluctuates over the year, mixed woodland-grasslands and bushlands seem to represent more favorable habitats for large Macrotermes colonies than open grasslands.

Linking Increased Isotope Fractionation at Low Concentrations to Enzyme Activity Regulation: 4-Cl Phenol Degradation by Arthrobacter chlorophenolicus A6

Slow microbial degradation of organic trace chemicals ("micropollutants") has been attributed to either downregulation of enzymatic turnover or rate-limiting substrate supply at low concentrations. In previous biodegradation studies, a drastic decrease in isotope fractionation of atrazine revealed a transition from rate-limiting enzyme turnover to membrane permeation as a bottleneck when concentrations fell below the Monod constant of microbial growth. With degradation of the pollutant 4-chlorophenol (4-CP) by Arthrobacter chlorophenolicus A6, this study targeted a bacterium which adapts its enzyme activity to concentrations. Unlike with atrazine degradation, isotope fractionation of 4-CP increased at lower concentrations, from ε(C) = -1.0 ± 0.5‰ in chemostats (D = 0.090 h^-1, 88 mg L^-1) and ε(C) = -2.1 ± 0.5‰ in batch (c₀ = 220 mg L^-1) to ε(C) = -4.1 ± 0.2‰ in chemostats at 90 μg L^-1. Surprisingly, fatty acid composition indicated increased cell wall permeability at high concentrations, while proteomics revealed that catabolic enzymes (CphCI and CphCII) were differentially expressed at D = 0.090 h^-1. These observations support regulation on the enzyme activity level─through either a metabolic shift between catabolic pathways or decreased enzymatic turnover at low concentrations─and, hence, reveal an alternative end-member scenario for bacterial adaptation at low concentrations. Including more degrader strains into this multidisciplinary analytical approach offers the perspective to build a knowledge base on bottlenecks of bioremediation at low concentrations that considers bacterial adaptation.

Stable isotopes reveal overlooked incorporation of diffuse land-based sources of nutrients and organic matter by intertidal communities at Rapa Nui (Easter Island)

Rapa Nui is an important hotspot of endemic marine biodiversity, where diffuse land-based sources (e.g., nutrients and organic matter) entering into coastal waters could develop eutrophication in coastal environments, with deleterious impacts on the marine ecosystem. Stable isotopes (δ¹³C and δ¹⁵N) of intertidal communities (macroalgae and invertebrates) were studied from sites with contrasting human influence (populated and unpopulated), to evaluate the incorporation and transfer of diffuse land-based sources through food webs. Macroalgae showed differences between some sites, and invertebrates showed a ¹⁵N-enrichment pattern at populated areas relative to unpopulated, being these differences significant in gastropods, barnacles and sea urchins. Moreover, trophic structure metrics suggest a higher trophic diversity in populated areas relative to unpopulated and support the isotopic partitioning between sites, associated with the incorporation of sources with ¹⁵N-enriched values. The above suggests that diffuse land-based sources could be incorporated by macroalgae, transferred into benthic consumers, and altering the trophic structure.

The unravelling of radiocarbon composition of organic carbon in river sediments to document past anthropogenic impacts on river systems

As carriers of dissolved and particulate loads that connect continental surfaces to oceans, river systems play a major role in the global carbon cycle. Indeed, riverine particulate organic carbon (POC) is a melange of various origins characterized by their own ¹⁴C labeling. In addition, civil nuclear activities have brought new ¹⁴C source that remains poorly documented. We propose to unravel the Δ¹⁴C value of POC stored in a sedimentary archive collected downstream the most nuclearized European rivers (the Loire River). We postulate that riverine POC is a mixture of aquatic POC (which could be impacted by the liquid discharge from nuclear industry), terrestrial and petrogenic POC. With a combination of radiocarbon measurements, POC analyses and the palynofacies method, we assessed the respective Δ¹⁴C value of the POC origins. The gaps between the Δ¹⁴C values of the sedimentary POC and those of the atmosphere were the result of the dilution from dead-C, the freshwater reservoir effect imprinting the Δ¹⁴C of aquatic POC and the age and transit time of terrestrial POC within the catchment. Importantly, we consider that the unravelling of radiocarbon composition of riverine POC could be useful to determine either the transit time of material from source to sink, some past industrial or natural events, the resilience of the river system and milestones of the social and economic trajectory of a catchment. For the last three decades, riverine sediments could also act as a source of radiocarbon for the atmosphere.

Diet reveals potential for competition and coexistence among coyotes (Canis latrans), red foxes (Vulpes vulpes), and gray foxes (Urocyon cinereoargenteus)

Species can alleviate competition by reducing diet overlap. Non-native coyotes (Canis latrans Say, 1823) and historically native gray foxes (Urocyon cinereoargenteus (Schreber, 1775)) have expanded their ranges and may compete with native red foxes (Vulpes vulpes (Linnaeus, 1758)). To examine potential competition among canids in Maine, USA, we compared δ13C and δ15N from muscle and hair samples to assess relative resource use, and we compared frequency of occurrence of prey items from stomach contents to assess diets. For these species, red foxes consumed anthropogenically based foods the most in fall and early winter, gray foxes consumed anthropogenically based foods the most in summer, and coyotes consumed anthropogenically based foods the least in all seasons. Coyotes held the highest relative trophic position in fall and early winter, red foxes held the highest relative trophic position in summer, and gray foxes held the lowest relative trophic position. Based on stomach contents, gray foxes had the broadest diet and consumed the most plants, and coyotes had the narrowest diet. Red foxes were the only species to show isotopic niche overlap with both potential competitors across seasons. Thus, they may be most susceptible to competitive exclusion among these canids, with implications for community dynamics as ranges shift due to human activity.

Soil δ13C and δ15N baselines clarify biogeographic heterogeneity in isotopic discrimination of European badgers (Meles meles)

Isotopic techniques have been used to study phenomena in the geological, environmental, and ecological sciences. For example, isotopic values of multiple elements elucidate the pathways energy and nutrients take in the environment. Isoscapes interpolate isotopic values across a geographical surface and are used to study environmental processes in space and time. Thus, isoscapes can reveal ecological shifts at local scales, and show distribution thresholds in the wider environment at the macro-scale. This study demonstrates a further application of isoscapes, using soil isoscapes of ¹³C/¹²C and ¹⁵N/¹⁴N as an environmental baseline, to understand variation in trophic ecology across a population of Eurasian badgers (Meles meles) at a regional scale. The use of soil isoscapes reduced error, and elevated the statistical signal, where aggregated badger hairs were used, and where individuals were identified using genetic microarray analysis. Stable isotope values were affected by land-use type, elevation, and meteorology. Badgers in lowland habitats had diets richer in protein and were adversely affected by poor weather conditions in all land classes. It is concluded that soil isoscapes are an effective way of reducing confounding biases in macroscale, isotopic studies. The method elucidated variation in the trophic and spatial ecology of economically important taxa at a landscape level. These results have implications for the management of badgers and other carnivores with omnivorous tendencies in heterogeneous landscapes.

Functional macrophyte trait variation as a response to the source of inorganic carbon acquisition

BACKGROUND

This study aims to compare variation in a range of aquatic macrophyte species leaf traits into three carbon acquisition groups: HCO3 -, free CO2 and atmospheric CO2.

METHODS

The leaf functional traits were measured for 30 species from 30 softwater lakes. Macrophyte species were classified into (1) free CO2, (2) atmospheric CO2 and (3) bicarbonate HCO3 - groups. In each lake we collected water samples and measured eight environmental variables: depth, Secchi depth, photosynthetically active radiation (PAR), pH of water, conductivity, calcium concentration, total nitrogen and total phosphorus. In this study we applied the RLQ analysis to investigate the relationships between species functional traits (Q) and their relationship with environmental variables (R) constrained by species abundance (L).

RESULTS

The results showed that: (1) Aquatic macrophytes exhibited high leaf trait variations as a response to different inorganic carbon acquisition; (2) Traits of leaves refer to the acquisition of carbon for photosynthesis and serve to maximise this process; (3) In the wide softwater habitat, macrophyte species exhibited an extreme range of leaf economic spectrum (leaf area, leaf dry weight and specific leaf area) and wide range of shape trait expressed as circularity; (4) Macrophyte leaf traits are the result of adaptation to carbon acquisition in ambient environment.