Seasonal changes in the diets of migrant and non-migrant nectarivorous bats as revealed by carbon stable isotope analysis

Three species of nectar-feeding bats migrate from tropical and subtropical Mexico into the Sonoran and Chihuahuan deserts during the spring and summer months. We examined geographic and seasonal changes in the diet of one migrant species, Leptonycteris curasoae, using carbon stable isotope techniques to determine the relative importance of C3 and CAM (Cactaceae, Agavaceae) plants in its diet. We also examined the diet of a non-migratory nectar-feeding bat, Glossophaga soricina, from southern Mexico using the same techniques. We found that L. curasoae feeds extensively or exclusively on CAM plants during migration and in the northern part of its range and feeds mostly on C3 plants in southern Mexico. This bat is a year-round resident on Baja California where it is a CAM specialist. The non-migrant G. soricina feeds mostly on C3 plants year-round. Phenological data suggest that certain species of columnar cacti and at least one group of paniculate Agaves on the Mexican mainland provide a spatio-temporally predictable nectar corridor along which nectarivorous bats may migrate in the spring and fall, respectively. Different flowering schedules of Agaves in Baja California appear to promote year-round dietary specialization and perhaps non-migratory behavior in nectar-feeding bats living there.     

Sources of organic carbon in the littoral of Lake Gooimeer as indicated by stable carbon isotope and carbohydrate compositions

The relative importance of potential carbon sources in the littoral of Lake Gooimeer, a lake in the centre of the Netherlands, was studied using a combination of ¹³C/¹²C-ratio analysis and carbohydrate composition analysis. The littoral is covered on the land side by a 80 m wide Phragmites australis bed. Potential carbon sources were macrophyte litter, seston and benthic algae. Samples of potential carbon sources, sediments and benthic macrofauna from inside and outside the bed were analyzed for their¹³C/¹²C-ratio and some for their carbohydrate composition. Results indicate that inside the bed, macrophyte litter was the main source of carbon for both the sediment organic matter and the benthic macrofauna, and that algal material was of minor importance. Outside the bed, production by benthic algae was the main carbon source, with seston as a second source. No macrophyte derived material could be detected outside the reed bed.Abbreviations DOC (Dissolved Organic Carbon) - SOM (Sediment Organic Matter)     

Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions

Four whole-lake inorganic ¹³C addition experiments were conducted in lakes of differing trophic status. Inorganic ¹³C addition enriched algal carbon in ¹³C and changed the C-DOC by +1.5‰ to +9.5‰, depending on the specific lake. This change in C-DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in C-DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about 20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and 5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient enriched lake. Natural abundance measurements of the C of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results, we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters.     

An insight into the feeding ecology of deep-sea canyon nematodes — Results from field observations and the first in-situC feeding experiment in the Nazaré Canyon

Submarine canyon systems provide a heterogeneous habitat for deep-sea benthos in terms of topography, hydrography, and the quality and quantity of organic matter present. Enhanced meiofauna densities as found in organically enriched canyon sediments suggest that nematodes, as the dominant metazoan meiobenthic taxon, may play an important role in the benthic food web of these sediments. Very little is known about the natural diets and trophic biology of deep-sea nematodes, but enrichment experiments can shed light on nematode feeding selectivity and trophic position. An in-situ pulse-chase experiment (Feedex) was performed in the Nazaré Canyon on the Portuguese margin in summer 2007 to study nematode feeding behaviour. ¹³C-labelled diatoms and bacteria were added to sediment cores which were then sampled over a 14-day period. There was differential uptake by the nematode community of the food sources provided, indicating selective feeding processes. ¹³C isotope results revealed that selective feeding was less pronounced at the surface, compared to the sediment subsurface. This was supported by a higher trophic diversity in surface sediments (Θ⁻¹ = 3.50 ± 0.2) compared to the subsurface (2.78 ± 0.6), implying that more food items may be used by the nematode community at the sediment surface. Predatory and scavenging nematodes contributed relatively more to biomass than other feeding types and can be seen as key contributors to the nematode food web at the canyon site. Non-selective deposit feeding nematodes were the dominant trophic group in terms of abundance and contributed substantially to total nematode biomass. The high levels of ‘fresh’ (bioavailable) organic matter input and moderate hydrodynamic disturbance of the canyon environment lead to a more complex trophic structure in canyon nematode communities than that found on the open continental slope, and favours predator/scavengers and non-selective deposit feeders.     

Resource allocation to reproduction and soma in Drosophila: a stable isotope analysis of carbon from dietary sugar

Metabolic resources in adults of holometabolous insects may derive either from larval or adult feeding. In Drosophila melanogaster, reproduction and lifespan are differently affected by larval vs. adult resource availability, and it is unknown how larval vs. adult acquired nutrients are differentially allocated to somatic and reproductive function. Here we describe the allocation of carbon derived from dietary sugar in aging female D. melanogaster. Larval and adult flies were fed diets contrasting in sucrose (13)C/(12)C, from which we determined the extent to which carbon acquired at each stage contributed to adult somatic tissue and to egg manufacture. Dietary sugar is very important in egg provisioning; at every age, roughly one half of the carbon in eggs was derived from sugar, which turned over from predominantly larval to entirely adult dietary sources. Sucrose provided approximately 40% of total somatic carbon, of which adult dietary sucrose came to supply approximately 75%. Unlike in eggs, however, adult acquired sucrose did not entirely replace the somatic carbon from larvally acquired sucrose. Because carbon from larval sucrose appears to be fairly "replaceable", larval sucrose cannot be a limiting substrate in resource allocation between reproduction and lifespan.     

Carbon fluxes to the soil in a mature temperate forest assessed by <Superscript>13</Superscript>C isotope tracing

Photosynthetic carbon uptake and respiratory C release from soil are major components of the global carbon balance. The use of ¹³C depleted CO₂ (¹³C = –30) in a free air CO₂ enrichment experiment in a mature deciduous forest permitted us to trace the carbon transfer from tree crowns to the rhizosphere of 100–120 years old trees. During the first season of CO₂ enrichment the CO₂ released from soil originated substantially from concurrent assimilation. The small contribution of recent carbon in fine roots suggests a much slower fine root turnover than is often assumed.¹³C abundance in soil air correlated best with temperature data taken from 4 to 10 days before air sampling time and is thus rapidly available for root and rhizosphere respiration. The spatial variability of ¹³C in soil air showed relationships to above ground tree types such as conifers versus broad-leaved trees. Considering the complexity and strong overlap of roots from different individuals in a forest, this finding opens an exciting new possibility of associating respiration with different species. What might be seen as signal noise does in fact contain valuable information on the spatial heterogeneity of tree-soil interaction.     

Inter-annual and seasonal variability of radial growth, wood density and carbon isotope ratios in tree rings of beech (Fagus sylvatica) growing in Germany and Italy

We investigated the variability of tree-ring width, wood density and ¹³C/¹²C in beech tree rings (Fagus sylvatica L.), and analyzed the influence of climatic variables and carbohydrate storage on these parameters. Wood cores were taken from dominant beech trees in three stands in Germany and Italy. We used densitometry to obtain density profiles of tree rings and laser-ablation-combustion-GC-IRMS to estimate carbon isotope composition (δ ¹³C) of wood. The sensitivity of ring width, wood density and δ ¹³C to climatic variables differed; with tree-ring width responding to environmental conditions (temperature or precipitation) during the first half of a growing season and maximum density correlated with temperatures in the second part of a growing season (July–September). δ ¹³C variations indicate re-allocation and storage processes and effects of drought during the main growing season. About 20% of inter-annual variation of tree-ring width was explained by the tree-ring width of the previous year. This was confirmed by δ ¹³C of wood which showed a contribution of stored carbohydrates to growth in spring and a storage effect that competes with growth in autumn. Only mid-season δ ¹³C of wood was related to concurrent assimilation and climate. The comparison of seasonal changes in tree-ring maximum wood density and isotope composition revealed that an increasing seasonal water deficit changes the relationship between density and ¹³C composition from a negative relation in years with optimal moisture to a positive relationship in years with strong water deficit. The climate signal, however, is over-ridden by effects of stand density and crown structure (e.g., by forest management). There was an unexpected high variability in mid season δ ¹³C values of wood between individual trees (−31 to −24‰) which was attributed to competition between dominant trees as indicated by crown area, and microclimatological variations within the canopy. Maximum wood density showed less variation (930–990 g cm⁻³). The relationship between seasonal changes in tree-ring structure and ¹³C composition can be used to study carbon storage and re-allocation, which is important for improving models of tree-ring growth and carbon isotope fractionation. About 20–30% of the tree-ring is affected by storage processes. The effects of storage on tree-ring width and the effects of forest structure put an additional uncertainty on using tree rings of broad leaved trees for climate reconstruction.     

Water sources of riparian plants during a rainy season in Taihu Lake Basin,China: a stable isotope study

In this study, we investigated water sources of three typical plant species, i.e., Ginkgo biloba (Ginkgo biloba L.), Green soybean (Glycine max (L) Merr.), and Mulberry tree (Morus alba L.) in a rainy season by using a dual stable isotope approach (δ¹⁸O and δ²H). Potential water sources were divided into direct or internal (i.e. soil water at different depths) and indirect or external water sources (i.e. precipitation, river water and groundwater). The results indicated that the surface soil water δ¹⁸O and δ²H is enriched probably due to evaporation. Ginkgo biloba and Green soybean prefer using soil water from the upper soil layer (0–60 cm) and precipitation, and the Mulberry tree mainly used deep soil water (120-150 cm) and groundwater. The different water use strategies of the three plant species are likely to be determined by their different root distribution at the above correspondent soil depths.     

Stable nitrogen and carbon isotope ratios in bone collagen as indices of prehistoric dietary dependence on marine and terrestrial resources in southern California

The ratios of 15N to 14N and 13C to 12C tend to be higher in marine than in terrestrial organisms. The concentrations of these isotopes in human bone collagen consequently can be used to make inferences about the contribution of marine and terrestrial resources to prehistoric diets. The utility of studying 15N/14N and 13C/12C ratios in conjunction with each other is illustrated by our analysis of 40 human burials from archaeological sites in the Santa Barbara Channel area of southern California. The mean delta 13C and delta 15N values (in per mil) of collagen from these skeletons decrease progressively from the Channel Islands (delta 13C = -14.0, delta 15N = +16.3) to the mainland coast (delta 13C = -14.5, delta 15N = +14.9) to the interior (delta 13C = -17.2, delta 15N = +10.9). These data suggest that Indians living on the Channel Islands during the late prehistoric period were heavily dependent on marine resources. The inhabitants of the mainland interior, in contrast, had a diet composed largely of terrestrial foods. From their isotope ratios, it appears that the Indians who lived on the mainland coast consumed a mixed diet containing substantial quantities of both marine and terrestrial resources. Differences in 15N/14N and 13C/12C ratios of individuals from mainland sites dating from the early and late prehistoric periods show that the marine component of the diet increased substantially through time. These isotopic data are consistent with pathological, faunal, and artifactual evidence of increased marine resource exploitation during the late prehistoric period.     

Nitrogen isotope ratios and fatty acid composition as indicators of animal diets in belowground systems

This study analyses trophic interactions between soil fungi, micro- and mesofauna in microcosm experiments. The trophic shift of ¹⁵N and fatty acids (FAs) was investigated in different food chains, which comprised either two (fungi and grazers) or three (fungi, nematodes and Collembola) levels. Contrary to the widely accepted assumption of ¹⁵N enrichment in trophic cascades the experiments revealed enrichment, depletion or no change in ¹⁵N of consumers compared to their diet. Factors responsible for this pattern were suggested to be: (1) the main metabolic pathway used for N excretion in ammonotelic nematodes to be similar or depleted in the heavier isotope, and uricotelic Collembola mostly enriched in the heavier isotope; (2) a higher shift in ¹⁵N with a high-protein diet (e.g. for predators); (3) compensation due to low-quality food altering the fractionation of ¹⁵N. Analysis of the lipid composition showed phospholipids to be generally unaffected and neutral lipids closely related to the FA pattern of the food source. Dietary routing of FAs into neutral lipids occurred, as evidenced by corresponding frequencies of FAs in host and consumer profiles. Additionally, several FAs were only detected in the grazer when present in the food source. Oleic acid showed a shift over three trophic levels, from fungi to nematodes to Collembola. The assimilation of dietary FAs resulted in a more diverse neutral lipid profile, i.e. animals higher in the food chain contained more individual FAs compared to animals lower in the food chain. The results indicate that monoenoic C18 and monoenoic C20 FAs have the potential to act as tools for the bioindication of feeding strategies in belowground systems. We suggest that primary consumers will have no or only trace amounts of monoenoic C20 acids in their neutral lipid profile, whereas consumers feeding on a eukaryote diet will show a considerably higher frequency.     

Origin and cycling of riverine inorganic carbon in the Sava River watershed (Slovenia) inferred from major solutes and stable carbon isotopes

The Sava River and its tributaries in Slovenia represent waters strongly influenced by chemical weathering of limestone and dolomite. The carbon isotopic compositions of dissolved inorganic carbon (DIC) and suspended organic carbon (POC) fractions as well as major solute concentrations yielded insights into the origin and fluxes of carbon in the upper Sava River system. The major solute composition was dominated by carbonic acid dissolution of calcite and dolomite. Waters were generally supersaturated with respect to calcite, and dissolved CO₂ was about fivefold supersaturated relative to the atmosphere. The δ¹³C of DIC ranged from −13.5 to −3.3‰. Mass balances for riverine inorganic carbon suggest that carbonate dissolution contributes up to 26%, degradation of organic matter ∼17% and exchange with atmospheric CO₂ up to 5%. The concentration and stable isotope diffusion models indicated that atmospheric exchange of CO₂ predominates in streams draining impermeable shales and clays while in the carbonate-dominated watersheds dissolution of the Mesozoic carbonates predominates.     

大肠杆菌碳分解代谢抑制及混合 C 源共利用的研究进展简

总结了大肠杆菌中C源分解代谢（ carbon catabolite repression,CCR）现象的原理及特点,综述并分析了如何通过对宿主菌进行基因工程改造以解除碳代谢抑制,以实现大肠杆菌利用多种C源。     

Effects of lipid removal and preservatives on carbon and nitrogen stable isotope ratios of squid tissues: Implications for ecological studies

Stable isotope analysis of carbon (C) and nitrogen (N) in animal tissues is an important approach to investigate the tropic status and habitat of marine species. Some biases due to lipid extractions and preservation can hinder the interpretation of results, yet their effects have not been investigated in squid. In this study, we evaluated the effects of lipid extraction and preservatives (dimethylsulfoxide (DMSO), 70% ethanol, and 10% buffered formaldehyde) on the δ¹³C, δ¹⁵N and C:N ratios in squid muscle. Beaks were placed under the same treatments with the exception of DMSO. Muscle and beak samples remained under treatment for 375 days and 416 days, respectively. Our results indicate that lipid extractions increased the mean values of unpreserved samples by 0.8‰ for δ¹³C and by 0.68‰ for δ¹⁵N. Preservatives also affected the isotopic composition in muscle at different magnitudes. DMSO remarkably reduced and increased the variability for δ¹³C and δ¹⁵N values among samples, formalin mainly reduced δ¹³C values by 1.5‰, whereas ethanol increased both δ¹³C and δ¹⁵N by ≤ 0.8‰. Lipid extractions eliminated the effect of DMSO and ethanol for δ¹³C and δ¹⁵N, and formalin only for δ¹⁵N. In beak, negligible shifts in δ¹³C, δ¹⁵N and C:N ratios were recorded after preservation in ethanol and formalin. Although lipid extractions can be recommended to reduce the effect of preservation, further research is needed to develop correction models for isotopic shifts associated with both lipid extractions in unpreserved and preserved muscle tissues. Lipid extractions per se could introduce a bias that may have important implications for ecological studies.     

Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition

We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (¹³C_POC) and suspended matter (¹³C_POC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest ¹³C_DIC values are observed due to enhanced input of CO₂ from decomposition of ¹³C-depleted terrestrial plant detritus (average ¹³C_DIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative ¹³C_DIC values (average ¹³C_DIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl^–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl^–1. Furthermore, in winter the very narrow range of ¹³C_POC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer ¹³C_POC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in ¹³C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of ¹³C/¹²C fractionation by phytoplankton is attempted.     

Lipid content and carbon assimilation in Collembola: implications for the use of compound-specific carbon isotope analysis in animal dietary studies

In an effort to understand the relationships between both the lipid content and ¹³C values of Collembola and their diet, isotopically labelled (C₃ and C₄) bakers yeasts were cultured and fed to two Collembolan species, Folsomia candida and Proisotoma minuta. The fatty acid composition of Collembola generally reflected that of the diet with the addition of the polyunsaturated components 18:2(n-6), 20:4(n-6) and 20:5(n-3), which appeared to be biosynthesised by the Collembola. Whilst ergosterol was the only sterol detected in the yeast diets, only cholesterol was detected in Collembola, and although the ¹³C values of diet and consumer sterols differed by >2, the ¹³C values indicated that cholesterol was derived entirely from dietary sterol. The bulk ¹³C values of Collembola were similar to those of the diets, but fatty acid ¹³C values did not necessarily reflect those of the dietary fatty acids, indicating significant de novo biosynthesis of fatty acids within Collembola. Switching the Collembola from C₃ to C₄ yeast enabled the determination of the rates of incorporation of dietary carbon into Collembolan lipids, and showed that half-lives of the incorporation of dietary carbon varied between 1.5 and 5.8 days at 20°C. Cholesterol exhibited the slowest rate of incorporation in both species, while bulk carbon in F. candida possessed an intermediate rate. These results demonstrate that an understanding of the sources of isotopic fractionation and the role of biochemistry in regulating the ¹³C values of individual compounds is important in the application of compound-specific isotopic analysis to the study of animal trophic activities.     

半干旱沙丘与草甸典型植被类型区大气-叶片-凋落物-土壤连续体碳同位素特征

稳定碳同位素技术能够指示生态系统的物质循环与能量流动,根据生态系统碳转移动态,可以探明生态系统中碳循环过程和固碳能力。以科尔沁沙地半流动沙丘固沙植被差巴嘎蒿(Artemisia halodendron)、半流动半固定沙丘固沙植被小叶锦鸡儿(Caragana microphylla)和黄柳(Salix gordejevii Chang),以及在草甸地广泛分布的芦苇(Phragmites australis)与玉米(Zea mays Linn)5种典型植被为研究对象,分析了各植被群落冠层处大气、叶片、凋落物、土壤连续体的δ¹³C值和碳含量的分布特征及各组分间的关系。结果表明：沙丘植被冠层处大气CO₂浓度显著低于草甸植被,受控于土壤水分特征和植物生长特性。在逆境胁迫下,小叶锦鸡儿叶片水分利用效率最高,固碳耗水成本最低。叶片碳含量和δ¹³C值均受叶片生育期的影响,新叶片潜在碳蓄积能力更强,水分利用效率更高。叶片凋落物δ¹³C值在不同植被间存在显著差异,说明了植物功能性的驱动作用。随着土壤深度的增加,有机质分...     

Trophic structure of common marine species in the Bohai Strait,North China Sea,based on carbon and nitrogen stable isotope ratios

Trophic relationships among common coastal species in the Bohai Strait, North China Sea, were investigated in this study using stable isotope ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) as tracers. During the research cruises of this study, 16 species of invertebrates and 18 species of fishes were collected, as were various food sources (phytoplankton, macroalgae, and sediment). The carbon and nitrogen isotope ratios of all collected samples were measured and used for trophic level analyses. The results showed that the grazers Oregonia gracilis, Notoacmea schrenckii, Chlorostoma rustica, and Chelon affinis, preferentially consumed Zostera marina (p < 0.01), whereas Anthocidaris crassispina preferred Ulva conglobata (p < 0.01). Two trophic models based on nitrogen isotope ratios were built to identify the trophic level of each species. The model that combined food sources was more appropriate than the model that used a single primary producer to identify the relative trophic positions of primary consumers. Scombermorus niphonius, an important fishery resource, was at the top trophic level. The seastar Asterias amurensis was at the highest level among the invertebrates and directly threatened production of shellfish. Based on the trophic level and food source relationships identified in this study, we gave some advice for ecological restoration, such as optimizing the structure of food source distribution, limiting seastar numbers, and improving the applicability of habitat for fishery species.