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1.
Charred modern grass epidermis preserves the carbon isotopic composition of the parent plant photosynthetic pathway. Fifty-nine modern grasses and sedges were collected in lowland western Uganda. All charred epidermal samples from C4 grasses or sedges preserve a carbon isotopic value within the range typical for C4 plants (−17 to −10‰), and charred epidermal fragments from C3 plants have carbon isotopic values between −30 and −26‰. The process of charring results in a slightly enriched carbon isotopic signature (−11.9‰ mean charred value as compared to −12.8‰ mean unaltered grass tissue value). δ13C measurements of replicate samples from the same plant vary within 1–2‰, yet all values for the same plant stay within the expected values for the photosynthetic pathway of the plant. δ13C measurements on >180-μm charred grass epidermal fragments extracted from surface sediment samples from three lakes on the lowland western Ugandan landscape confirm the predominant lowland C4 grass input (δ13C=−16 to −19‰). These results demonstrate the utility of using carbon isotopic analysis of charred grass epidermis to reconstruct C3 vs. C4 grassland assemblages on the landscape. Furthermore, such downcore δ13C profiles can be used to highlight key zones of C3 vs. C4 grass change for which taxonomic analysis of fossil grass epidermis could provide more detailed information regarding grassland community composition.  相似文献   

2.
Carbon: freshwater plants   总被引:15,自引:1,他引:14  
δ13C values for freshwater aquatic plant matter varies from ?11 to ?50‰ and is not a clear indicator of photosynthetic pathway as in terrestrial plants. Several factors affect δ13C of aquatic plant matter. These include: (1) The δ13C signature of the source carbon has been observed to range from +1‰ for HCO3? derived from limestone to ?30‰ for CO2 derived from respiration. (2) Some plants assimilate HCO3?, which is –7 to –11‰ less negative than CO2. (3) C3, C4, and CAM photosynthetic pathways are present in aquatic plants. (4) Diffusional resistances are orders of magnitude greater in the aquatic environment than in the aerial environment. The greater viscosity of water acts to reduce mixing of the carbon pool in the boundary layer with that of the bulk solution. In effect, many aquatic plants draw from a finite carbon pool, and as in terrestrial plants growing in a closed system, biochemical discrimination is reduced. In standing water, this factor results in most aquatic plants having a δ13C value similar to the source carbon. Using Farquhar's equation and other physiological data, it is possible to use δ13C values to evaluate various parameters affecting photosynthesis, such as limitations imposed by CO2 diffusion and carbon source.  相似文献   

3.
Stable-isotope analysis (SIA) provides a valuable tool to address complex questions pertaining to elasmobranch ecology. Liver, a metabolically active, high turnover tissue (~166 days for 95% turnover), has the potential to reveal novel insights into recent feeding/movement behaviours of this diverse group. To date, limited work has used this tissue, but ecological application of SIA in liver requires consideration of tissue preparation techniques given the potential for high concentrations of urea and lipid that could bias δ13C and δ15N values (i.e., result in artificially lower δ13C and δ15N values). Here we investigated the effectiveness of (a) deionized water washing (WW) for urea removal from liver tissue and (b) chloroform-methanol for extraction of lipids from this lipid rich tissue. We then (a) established C:N thresholds for deriving ecologically relevant liver isotopic values given complications of removing all lipid and (b) undertook a preliminary comparison of δ13C values between tissue pairs (muscle and liver) to test if observed isotopic differences correlated with known movement behaviour. Tests were conducted on four large shark species: the dusky (DUS, Carcharhinus obscurus), sand tiger (RAG, Carcharias taurus), scalloped hammerhead (SCA, Sphyrna lewini) and white shark (GRE, Carcharodon carcharias). There was no significant difference in δ15N values between lipid-extracted (LE) liver and lipid-extracted/water washed (WW) treatments, however, WW resulted in significant increases in %N, δ13C and %C. Following lipid extraction (repeated three times), some samples were still biased by lipids. Our species-specific “C:N thresholds” provide a method to derive ecologically viable isotope data given the complexities of this lipid rich tissue (C:N thresholds of 4.0, 3.6, 4.7 and 3.9 for DUS, RAG, SCA and GRE liverLEWW tissue, respectively). The preliminary comparison of C:N threshold corrected liver and muscle δ13C values corresponded with movement/habitat behaviours for each shark; minor differences in δ13C values were observed for known regional movements of DUS and RAG (δ13CDiffs = 0.24 ± 0.99‰ and 0.57 ± 0.38‰, respectively), while SCA and GRE showed greater differences (1.24 ± 0.63‰ and 1.08 ± 0.71‰, respectively) correlated to large-scale movements between temperate/tropical and pelagic/coastal environments. These data provide an approach for the successful application of liver δ13C and δ15N values to examine elasmobranch ecology.  相似文献   

4.
Abstract: While atmospheric species of bromeliads have narrow leaves, densely covered with water‐absorbing trichomes throughout their life cycles, many tank bromeliads with broad leaves, forming phytotelmata, go through an atmospheric juvenile phase. The effect of the different habits and the phase change in tank‐forming bromeliads on water and nutrient relations was investigated by analysing the relationship between plant size, C/N ratios and the natural abundance of 13C and 15N in five epiphytic bromeliad species or morphospecies of a humid montane forest in Xalapa, Mexico. The atmospheric species Tillandsia juncea and T. butzii exhibited full crassulacean acid metabolism, with δ13C values (mean ‐ 15.3 ‰ and ‐ 14.7 ‰, respectively) independent of size. In Tillandsia species with C3 photosynthesis, δ13C decreased with increasing plant size, indicating stronger drought stress in juveniles. The increase of the C/N ratio with size suggests that, at least in heteroblastic bromeliads, the availability of water is more limiting during early growth, and that limitations of nitrogen supply become more important later on, when water stored in the tank helps to bridge dry periods, reducing water shortage. δ15N values of the two atmospheric species were very negative (‐ 12.6 ‰ and ‐ 12.2 ‰, respectively) and did not change with plant size. Tank‐forming bromeliads had less negative δ15N values (c ‐ 6 ‰), and, in species with atmospheric juveniles and tank‐forming adults, δ15N values increased significantly with plant size. These differences do not appear to be an effect of the isotopic composition of N sources, but rather reflect N availability and limitation and stress‐induced changes in 15N discrimination.  相似文献   

5.
Abstract. Woody plants are increasing in many grassland and savanna ecosystems around the world. As a case in point, the Edwards Plateau of Texas, USA, is a vast region (93 000 km2) in which rapid woody encroachment appears to be occurring. The native vegetation (prior to the Anglo‐European settlement 150–200 yr ago) and the biogeochemical consequences of woody encroachment in this region, however, are poorly understood. To assess these matters we measured plant and soil δ13C, soil organic C and soil N content from grasslands and two important woody patch types (mature Quercus virginiana clusters and Juniperus ashei woodlands) in this region. Soil δ13C values showed that relative productivity of C3 species has increased in grassland and both woody habitats in recent times. δ13C of SOC in grasslands and Q. virginiana clusters increased with depth from the litter layer to 30 cm (grasslands =?21 to ?13‰Q. virginiana clusters =?27 to ?17‰) and were significantly different between habitats at all depths, indicating that Q. virginiana has been a long‐term component of the landscape. In J. ashei woodlands, soil δ13C values (at 20–30 cm depth) near the woodland edge (‐13‰) converged with those of an adjacent grassland (‐13‰) while those from the woodland interior (‐15‰) remained distinct, indicating that the woodland has been present for many years but has recently expanded. Concentrations and densities of SOC and total N were generally greater in woody patches than in grasslands. However, differences in the amount of SOC and N stored beneath the two woody patch types indicates that C and N sequestration potentials are species dependent.  相似文献   

6.
 The origin of carbon in the spores of arbuscular mycorrhizal (AM) fungi was quantified based on their obligate symbiosis with C3 and C4 plants showing clearly different δ13C values. The δ13C values of individual spores of the AM fungus Gigaspora margarita were analyzed. In monoculture pots of a C3 or a C4 plant species, spore δ13C values were ca. 3.5‰ lower than those of host roots. In coculture pots of a C3 and a C4 plant species, spore δ13C values varied between those of the roots of C3 and C4 plants, and increased linearly from the C3 to the proximity of the C4 plant (P<0.01). This reflects the higher δ13C values in C4 plants than in C3 plants. Thus the carbon origin of G. margarita spores changed with growth state and combination of host plants. In the presence of fresh plant residue instead of living host plants, spore δ13C values did not vary with distance from the residue. This finding supports the current view that AM fungi are obligate symbionts. Accepted: 12 February 1999  相似文献   

7.
Question: The relationship between carbon‐13 in soil organic matter and C3 and C4 plant abundance is complicated because of differential productivity, litter fall and decomposition. As a result, applying a mass balance equation to δ13C data from soils cannot be used to infer past C3 and C4 plant abundance; only the proportion of carbon derived from C3 and C4 plants can be estimated. In this paper, we compare δ13C of surface soil samples with vegetation data, in order to establish whether the ratio of C3:C4 plants (rather than the proportion of carbon from C3 and C4 plants) can be inferred from soil δ13C. Location: The Tsavo National Park, in southeastern Kenya. Methods: We compare vegetation data with δ13C of organic matter in surface soil samples and derive regression equations relating the δ13C of soil organic matter to C3:C4 plant abundance. We use these equations to interpret δ13C data from soil profiles in terms of changes in inferred C3:C4 plant ratio. We compare our method of interpretation with that derived from a mass balance approach. Results: There was a statistically significant, linear relationship between the δ13C of organic matter in surface soil samples and the natural logarithm of the ratio of C3:C4 plants in the 100m2 surrounding the soil sample. Conclusions: We suggest that interpretation of δ13C data from organic matter in soil profiles can be improved by comparing vegetation surveys with δ13C of organic matter in surface soil samples. Our results suggest that past C3 plant abundance might be under‐estimated if a mass balance approach is used.  相似文献   

8.
Microbial mats that inhabit gypsum deposits in ponds at Guerrero Negro, Baja California Sur, Mexico, developed distinct pigmented horizons that provided an opportunity to examine the fixation and flow of carbon through a trophic structure and, in conjunction with previous phylogenetic analyses, to assess the diagenetic fates of molecular δ13C biosignatures. The δ13C values of individual biomarker lipids, total carbon, and total organic carbon (TOC) were determined for each of the following horizons: tan‐orange (TO) at the surface, green (G), purple (P), and olive‐black (OB) at the bottom. δ13C of individual fatty acids from intact polar lipids (IPFA) in TO were similar to δ13C of dissolved inorganic carbon (DIC) in the overlying water column, indicating limited discrimination by cyanobacteria during CO2 fixation. δ13CTOC of the underlying G was 3‰ greater than that of TO. The most δ13C‐depleted acetogenic lipids in the upper horizons were the cyanobacterial biomarkers C17 n‐alkanes and polyunsaturated fatty acids. Bishomohopanol was 4 to 7‰ enriched, relative to alkanes and intact polar fatty acids (IPFA), respectively. Acyclic C20 isoprenoids were depleted by 14‰ relative to bishomohopanol. Significantly, ?[δ13CTOC ? δ13C∑IPFA] increased from 6.9‰ in TO to 14.7‰ in OB. This major trend might indicate that 13C‐enriched residual organic matter accumulated at depth. The permanently anoxic P horizon was dominated by anoxygenic phototrophs and sulfate‐reducing bacteria. P hosted an active sulfur‐dependent microbial community. IPFA and bishomohopanol were 13C‐depleted relative to upper crust by 7 and 4‰, respectively, and C20 isoprenoids were somewhat 13C‐enriched. Synthesis of alkanes in P was evidenced only by 13C‐depleted n‐octadecane and 8‐methylhexadecane. In OB, the marked increase of total inorganic carbon δ13C (δ13CTIC) of >6‰ perhaps indicated terminal mineralization. This δ13CTIC increase is consistent with degradation of the osmolyte glycine betaine by methylotrophic methanogens and loss of 13C‐depleted methane from the mat.  相似文献   

9.
Photosynthetic activity in carbonate‐rich benthic microbial mats located in saline, alkaline lakes on the Cariboo Plateau, B.C. resulted in pCO2 below equilibrium and δ13CDIC values up to +6.0‰ above predicted carbon dioxide (CO2) equilibrium values, representing a biosignature of photosynthesis. Mat‐associated δ13Ccarb values ranged from ~4 to 8‰ within any individual lake, with observations of both enrichments (up to 3.8‰) and depletions (up to 11.6‰) relative to the concurrent dissolved inorganic carbon (DIC). Seasonal and annual variations in δ13C values reflected the balance between photosynthetic 13C‐enrichment and heterotrophic inputs of 13C‐depleted DIC. Mat microelectrode profiles identified oxic zones where δ13Ccarb was within 0.2‰ of surface DIC overlying anoxic zones associated with sulphate reduction where δ13Ccarb was depleted by up to 5‰ relative to surface DIC reflecting inputs of 13C‐depleted DIC. δ13C values of sulphate reducing bacteria biomarker phospholipid fatty acids (PLFA) were depleted relative to the bulk organic matter by ~4‰, consistent with heterotrophic synthesis, while the majority of PLFA had larger offsets consistent with autotrophy. Mean δ13Corg values ranged from ?18.7 ± 0.1 to ?25.3 ± 1.0‰ with mean Δ13Cinorg‐org values ranging from 21.1 to 24.2‰, consistent with non‐CO2‐limited photosynthesis, suggesting that Precambrian δ13Corg values of ~?26‰ do not necessitate higher atmospheric CO2 concentrations. Rather, it is likely that the high DIC and carbonate content of these systems provide a non‐limiting carbon source allowing for expression of large photosynthetic offsets, in contrast to the smaller offsets observed in saline, organic‐rich and hot spring microbial mats.  相似文献   

10.
Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) is a serious worldwide pest of stored cereal grains that also has the ability to breed in non‐agricultural host plant material. Stable isotope signatures (concentrations of isotopes) were used as internal tissue markers to determine dietary differences among adult R. dominica and to make inferences about source habitats of field‐trapped insects. Adult R. dominica collected near granaries or from non‐agricultural forested sites near Stillwater, OK, USA, and insects reared on selected hosts under laboratory conditions were studied to determine the carbon and nitrogen isotope signatures. Laboratory‐reared R. dominica showed δ13C (stable isotope ratio of carbon) values similar to the host on which they developed with an enrichment of about 1 in the insect body. Insects reared on seeds of wheat and oak, which have C3 photosynthetic pathways, showed much depleted δ13C values (–23.7 and –26.2, respectively) in comparison to insects reared on seeds of corn, a C4 photosynthetic plant (–11.3). A majority of the field‐collected R. dominica showed δ13C values similar to expectations for a C3 host. However, a few field‐collected insects had δ13C signatures similar to the C4 plant‐reared insects in the laboratory experiment. Stored grain of C4 crops were lacking at many of the sample field sites. These results suggest that R. dominica occurs on either C3‐ or C4‐based hosts in the field, and point to utilization of non‐grain C4 plants as hosts. Our studies indicated that 13C isotope is a reliable marker to infer types of hosts used in the feeding history of R. dominica.  相似文献   

11.
Tooth enamel apatite carbonate carbon and oxygen isotope ratios of modern kangaroos (Macropus spp.) collected on a 900-km latitudinal transect spanning a C3–C4 transition zone were analysed to create a reference set for palaeoenvironmental reconstruction in southern Australia. The carbon isotope composition of enamel carbonate reflects the proportional intake of C3 and C4 vegetation, and its oxygen isotope composition reflects that of ingested water. Tooth enamel forms incrementally, recording dietary and environmental changes during mineralisation. Analyses show only weak correlations between climate records and latitudinal changes in δ13C and δ18O. No species achieved the δ13C values (~?1.0 ‰) expected for 100 % C4 grazing diets; kangaroos at low latitudes that are classified as feeding primarily on C4 grasses (grazers) have δ13C of up to ?3.5 ‰. In these areas, δ13C below ?12 ‰ suggests a 100 % C3 grass and/or leafy plant (browse) diet while animals from higher latitude have lower δ13C. Animals from semi-arid areas have δ18O of 34–40 ‰, while grazers from temperate areas have lower values (~28–30 ‰). Three patterns with implications for palaeoenvironmental reconstruction emerge: (1) all species in semi-arid areas regularly browse to supplement limited grass resources; (2) all species within an environmental zone have similar carbon and oxygen isotope compositions, meaning data from different kangaroo species can be pooled for palaeoenvironmental investigations; (3) relatively small regional environmental differences can be distinguished when δ13C and δ18O data are used together. These data demonstrate that diet–isotope and climate–isotope relationships should be evaluated in modern ecosystems before application to the regional fossil record.  相似文献   

12.
Southern African forests are naturally fragmented yet hold a disproportionately high number of bird species. Carbon and nitrogen stable isotopes were measured in feathers from birds captured at Woodbush (n = 27 species), a large afromontane forest in the eastern escarpment of Limpopo province, South Africa. The δ13C signatures of a range of forest plants were measured to categorise the food base. Most plants sampled, including two of five grass species, had δ13C signatures typical of a C3 photosynthetic pathway (?29.5 ± 1.9‰). Three grass species had a C4 signature (?12.0 ± 0.6‰). Most bird species had δ13C values representing a predominantly C3‐based diet (?24.8‰ to ?20.7‰). δ15N values were as expected, with higher levels of enrichment associated with a greater proportion of dietary animal matter. The cohesive isotopic niche defining most species (n = 22), where the ranges for δ13C and δ15N were 2.4‰ and 3.4‰, respectively, highlight the difficulties in understanding diets of birds in a predominantly C3‐based ecosystem using carbon and nitrogen stable isotopes. However, variation in isotopic values between and within species provides insight into possible niche width and the use of resources by different birds within a forest environment.  相似文献   

13.
Stable isotope natural abundance measurements integrate across several biogeochemical processes in ecosystem N and C dynamics. Here, we report trends in natural isotope abundance (δ13C and δ15N in plant and soil) along a climosequence of 33 Nothofagus forest stands located within Patagonia, Southern Argentina. We measured 28 different abiotic variables (both climatic variables and soil properties) to characterize environmental conditions at each of the 33 sites. Foliar δ13C values ranged from ?35.4‰ to ?27.7‰, and correlated positively with foliar δ15N values, ranging from ?3.7‰ to 5.2‰. Soil δ13C and δ15N values reflected the isotopic trends of the foliar tissues and ranged from ?29.8‰ to ?25.3‰, and ?4.8‰ to 6.4‰, respectively, with no significant differences between Nothofagus species (Nothofagus pumilio, Nothofagus antarctica, Nothofagus betuloides). Principal component analysis and multiple regressions suggested that mainly water availability variables (mean annual precipitation), but not soil properties, explained between 42% and 79% of the variations in foliar and soil δ13C and δ15N natural abundance, which declined with increased moisture supply. We conclude that a decline in water use efficiency at wetter sites promotes both the depletion of heavy C and N isotopes in soil and plant biomass. Soil δ13C values were higher than those of the plant tissues and this difference increased as annual precipitation increased. No such differences were apparent when δ15N values in soil and plant were compared, which indicates that climatic differences contributed more to the overall C balance than to the overall N balance in these forest ecosystems.  相似文献   

14.
This study aimed to estimate trophic discrimination factors (TDFs) and metabolic turnover rates of nitrogen and carbon stable isotopes in blood and muscle of the smallnose fanskate Sympterygia bonapartii by feeding six adult individuals, maintained in captivity, with a constant diet for 365 days. TDFs were estimated as the difference between δ13C or δ15N values of the food and the tissues of S. bonapartii after they had reached equilibrium with their diet. The duration of the experiment was enough to reach the equilibrium condition in blood for both elements (estimated time to reach 95% of turnover: C t95%blood = 150 days, N t95%blood = 290 days), whilst turnover rates could not be estimated for muscle because of variation among samples. Estimates of Δ13C and Δ15N values in blood and muscle using all individuals were Δ13Cblood = 1·7‰, Δ13Cmuscle = 1·3‰, Δ15Nblood = 2·5‰ and Δ15Nmuscle = 1·5‰, but there was evidence of differences of c.0·4‰ in the Δ13C values between sexes. The present values for TDFs and turnover rates constitute the first evidence for dietary switching in batoids based on long‐term controlled feeding experiments. Overall, the results showed that S. bonapartii has relatively low turnover rates and isotopic measurements would not track seasonal movements adequately. The estimated Δ13C values in S. bonapartii blood and muscle were similar to previous estimations for elasmobranchs and to generally accepted values in bony fishes (Δ13C = 1·5‰). For Δ15N, the results were similar to published reports for blood but smaller than reports for muscle and notably smaller than the typical values used to estimate trophic position (Δ15N c. 3·4‰). Thus, trophic position estimations for elasmobranchs based on typical Δ15N values could lead to underestimates of actual trophic positions. Finally, the evidence of differences in TDFs between sexes reveals a need for more targeted research.  相似文献   

15.
Abstract We used differences in soil carbon δ13C values between forested sites and grasslands dominated by the C4 grass Schizachyrium scoparium (little bluestem) to detect the presence of former grasslands in the historical landscape of the coastal sand plain of Martha's Vineyard, Massachusetts, U.S.A. Soil δ13C was measured at (1) sites with long‐term forest or grassland vegetation and (2) sites with known histories where forest vegetation invaded grassland and where forest converted to grassland. The δ13C of soil under long‐term grassland was –24.1‰ at 0 to 2 cm depth and –23.4‰ at 2 to 10 cm and was enriched by 3.4‰ and 2.8‰ compared with soil under long‐term forest. In forests that invaded grasslands dominated by S. scoparium, soil δ13C decreased as C derived from trees replaced C from S. scoparium. This decline occurred faster in surface soils and in the light soil organic matter fraction than in the mineral soil. In forests that converted to grasslands, soil δ13C increased and the rate of increase was similar in surface and mineral soil and in the different soil organic matter fractions. Rates of change indicated that soil δ13C could be used to detect changes in vegetation involving the presence or absence of S. scoparium during the last 150 years. Application of this model to a potential grassland restoration site on Martha's Vineyard where the landscape history was not known indicated that the site was previously unoccupied by S. scoparium during this time. The δ13C of surface mineral soil can be useful for detecting the presence of historic S. scoparium grasslands but only in the period well after European settlement of these coastal sand plain landscapes.  相似文献   

16.
Stable carbon isotope analyses of vertebrate hard tissues such as bones, teeth, and tusks provide information about animal diets in ecological, archeological, and paleontological contexts. There is debate about how carbon isotope compositions of collagen and apatite carbonate differ in terms of their relationship to diet, and to each other. We evaluated relationships between δ13Ccollagen and δ13Ccarbonate among free‐ranging southern African mammals to test predictions about the influences of dietary and physiological differences between species. Whereas the slopes of δ13Ccollagen–δ13Ccarbonate relationships among carnivores are ≤1, herbivore δ13Ccollagen increases with increasing dietary δ13C at a slower rate than does δ13Ccarbonate, resulting in regression slopes >1. This outcome is consistent with predictions that herbivore δ13Ccollagen is biased against low protein diet components (13C‐enriched C4 grasses in these environments), and δ13Ccarbonate is 13C‐enriched due to release of 13C‐depleted methane as a by‐product of microbial fermentation in the digestive tract. As methane emission is constrained by plant secondary metabolites in browse, the latter effect becomes more pronounced with higher levels of C4 grass in the diet. Increases in δ13Ccarbonate are also larger in ruminants than nonruminants. Accordingly, we show that Δ13Ccollagencarbonate spacing is not constant within herbivores, but increases by up to 5 ‰ across species with different diets and physiologies. Such large variation, often assumed to be negligible within trophic levels, clearly cannot be ignored in carbon isotope‐based diet reconstructions.  相似文献   

17.
Abstract The diet of the harvester termite Hodotermes mossambicus was investigated at two sites with distinct dietary components: C4 grasses (δ13C isotope values, ?13.8‰ to ?14.0‰) and C3 plants (δ13C isotope values, ?25.6‰ to ?27.1‰). By comparing observations of food items carried into the colony by the termites and carbon isotope ratios of whole termites (that determined assimilated carbon), the relative proportion of the C3 and C4 plant food components of the termite diet was estimated. There was agreement between the observational data and stable carbon isotopic data, with grass representing approximately 93% of the diet of H. mossambicus at two study sites (urban and rural) on the South African highveld. However, when correcting for mass of food items, that is, C3 and C4, carried by termites, the proportion of grass (C4) in the diet may be underestimated.  相似文献   

18.
Using bulk tissue and fatty acid 13C analysis we investigated major trophic pathways from soil microorganisms to microbial consumers to predators in conventional versus organic farming systems planted for the first time with maize. Organic farming led to an increase in microbial biomass in particular that of fungi as indicated by phospholipid fatty acids (PLFAs). Microbial PLFAs reflected the conversion from C3 to C4 plants by a shift in δ13C of 2‰, whereas the isotopic signal in fatty acids (FAs) of Collembola was much more pronounced. In the euedaphic Protaphorura fimata the δ13C values in maize fields exceeded that in C3 (soybean) fields by up to 10‰, indicating a close relationship between diet and vegetation cover. In the epedaphic Orchesella villosaδ13C values shifted by 4‰, suggesting a wider food spectrum including carbon of former C3 crop residues. Differences in δ13C of corresponding FAs in consumers and resources were assessed to assign food web links. P. fimata was suggested as root and fungal feeder in soybean fields, fungal feeder in conventional and leaf consumer in organically managed maize fields. O. villosa likely fed on root and bacteria under soybean, and bacteria and fungi under maize. Comparison of δ13C values in FAs of the cursorial spider Pardosaagrestis and O. villosa implied the latter as important prey species in soybean fields. In contrast, the web‐building spider Mangora acalypha showed no predator–prey relationship with Collembola. The determination of δ13C values in trophic biomarker FAs allowed detailed insight into the structure of the decomposer food web and identified diet‐shifts in both consumers at the base of the food web and in top predators in organic versus conventional agricultural systems. The results indicate changes in major trophic links and therefore carbon flux through the food web by conversion of conventional into organic farming systems.  相似文献   

19.
An isotopic reconstruction of human dietary patterns and livestock management practices (herding, grazing, foddering, etc.) is presented here from the sites of Düzen Tepe and Sagalassos in southwestern Turkey. Carbon and nitrogen stable isotope ratios were determined from bone collagen extracted from humans (n = 49) and animals (n = 454) from five distinct time periods: Classical‐Hellenistic (400–200 BC), Early to Middle Imperial (25 BC–300 AD), Late Imperial (300–450 AD), Early Byzantine (450–600 AD), and Middle Byzantine (800–1200 AD). The humans had protein sources that were based on C3 plants and terrestrial animals. During the Classical‐Hellenistic period, all of the domestic animals had δ13C and δ15N signatures that clustered together; evidence that the animals were herded in the same area or kept in enclosures and fed on similar foods. The diachronic analysis of the isotopic trends in the dogs, cattle, pigs, sheep, and goats highlighted subtle but distinct variations in these animals. The δ13C values of the dogs and cattle increased (reflecting C4 plant consumption) during the Imperial and Byzantine periods, but the pigs and the goats displayed little change and a constant C3 plant‐based diet. The sheep had a variable δ13C pattern reflecting periods of greater and lesser consumption of C4 plants in the diet. In addition, the δ15N values of the dogs, pigs, cattle, and sheep increase substantially from the Classical‐Hellenistic to the Imperial periods reflecting a possible increase in protein consumption, but the goats showed a decrease. Finally, these isotopic results are discussed in the context of zooarcheological, archeobotanical, and trace element evidence. Am J Phys Anthropol 149:157–171, 2012. © Wiley Periodicals, Inc.  相似文献   

20.
Carbon isotopic abundances have been measured for more than one hundred samples of fossil plants ranging in age from middle Triassic to late Tertiary. Most of the plant fossils were identified at the specific or generic level and were selected as representing a variety of continental environments, including xeric and humid habitats. Material analysed included numerous fragments of flowers, seeds, fruits, leaves and wood, as well as a single amorphous lignite sample. The analyses performed for the plant fragments indicate relatively constant isotopic compositions during this time interval, with plant δ13C values ranging between -28 and -20%. These values are within the range for living terrestrial plants with C3, photosynthesis, although values more positive than -23% are rare in C3 plants and typically found in plants growing under environmental stress. Lower δ13C values might have been expected owing to the much higher CO2, levels of the Cretaceous atmosphere that have been inferred from marine carbonates. No fossils with values indicating C4, photosynthesis were discovered. Fossil plants from inferred mesic environments showed δ13C values ranging between -26.7 and -24.1%. Highest δ13C values in angiosperms (up to -20.1%) were measured for Late Cretaceous combretaceous flowers from Portugal. Some cheirolepidiaceous conifers from the Early Cretaceous also showed high δ13C values. Values measured for Pseudofrenelopsis varians and Glenrosa taxensis were -21.9%, and values of gymnosperm wood, probably of cheirolepidiaceous affinity, were -19.0%. These high values are in accordance with inferred ecological conditions for the fossil plants. They may suggest a tendency for C4,-like photosynthesis, although the data are equivocal. Higher values (-17.3%) clearly falling outside the C3, range were, however, obtained from a single lignite fragment of Late Cretaceous (Maastrichtian) age. The nature of this plant fragment is unknown, but the result suggests that C4-like photosynthesis was present at least in some latest Cretaceous vegetation. A hadrosaurian dinosaur with well-preserved collagen-like organic matter from the same deposit showed δ13C values around-16%, which also suggests the presence of CAM or even C4 plants in the latest Cretaceous. □Carbon isotopic abundances, δ13C values, dinosaurs, plants, photosynthetic pathways, Mesozoic.  相似文献   

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