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1.
Biogenic calcretes associated with a regional Cretaceous to Paleogene subaerial unconformity and an intraformational composite (polygenic) surface in Upper Cretaceous intra-platform peritidal successions in central Dalmatia and eastern Istria, Croatia (Adriatic-Dinaridic Carbonate Platform), were analyzed for their δ13C and δ18O signatures in order to provide insight into the conditions of subaerial exposure and calcrete development. The distinctly negative δ13C signatures of biogenic calcretes marking the regional subaerial unconformity differ considerably from the δ13C values of the host marine limestones. This indicates carbon isotope exchange of primary marine CaCO3 with CO2 released by root and rhizomicrobial respiration and subsequent precipitation of pedogenic calcrete. The range of δ13C (from ?13.1 to ?8.2 ‰ Vienna PeeDee Belemnite standard, VPDB) and δ18O (from ?10.1 to ?6.1 ‰ VPDB) values of calcretes are similar to those reported from calcretes elsewhere, and the δ13C values of biogenic calcretes with typical Microcodium aggregates (?13.1 to ?12.3 ‰ VPDB) at the ?ibenik locality are very close to, or at the lower limit of, values for soil carbonates formed in isotopic equilibrium with soil CO2. These values are expected for authigenic pedogenic carbonates formed under the influence of C3 plant communities, without influence from heavier carbon from pre-existing carbonate and lack of input of atmospheric CO2. Such low δ13C values support the interpretation of Microcodium aggregates as being precipitated under a direct biological control within the soil, although the relationship between formation mechanisms and stable isotope signatures of Microcodium needs further investigation. The δ13C values (?4.4 to ?3.6 ‰ VPDB) of rhizogenic calcretes formed inside firmground Thalassinoides burrows of the composite surface at the ?ibenik locality are more negative than the δ13C values of the host marine limestones, which confirms that the composite surface went through a phase of meteoric pedo(dia)genesis. However, the overall δ13C values of calcretes are less negative than expected, which might reflect contamination from associated primary marine carbonate. This study represents the first detailed stable isotope investigation of calcretes from carbonate successions of the External Dinarides, and the results may be applied to discontinuities present in other shallow-water carbonate rock successions. 相似文献
2.
The Ludfordian (Upper Silurian) succession in Podolia, western Ukraine, represents a Silurian carbonate platform developed in an epicontinental sea on the shelf of the paleocontinent of Baltica. Coeval deposits throughout this basin record a positive stable carbon isotope excursion known as the Lau excursion. The record of this excursion in Podolia exhibits an unusual amplitude from highly positive (+6.9 ‰) to highly negative (?5.0 ‰) δ13Ccarb values. In order to link δ13Ccarb development with facies, five sections in the Zbruch River Valley were examined, providing microfacies characterization and revised definitions of the Isakivtsy, Prygorodok, and Varnytsya Formations. The Isakivtsy Fm. is developed as dolosparite replacing originally bioclastic limestone. The Prygorodok Fm., recording strongly depleted (down to ?10.53 ‰) to near zero (0.12 ‰) δ13Ccarb values is developed as laminated, organic-rich dolomicrite with metabentonite and quartz siltstone beds. The Varnytsya Fm. is characterized by peritidal deposition with consistent, slightly negative δ13Ccarb values (?0.57 to ?3.20 ‰). It is proposed that dolomitization of the Isakivtsy Fm. is associated with a sequence boundary and erosional surface. The overlying Prygorodok Fm. represents the proximal part of a TST deposited in restricted and laterally extremely variable environments dominated by microbial carbonate production. The transition to the overlying Varnytsya Fm. facies is marked by a maximum flooding surface. The SB and MFS are potentially correlative within the basin and support a global rapid sea-level fall previously proposed for this interval. The interpretation of the Prygorodok Fm. as coastal lake deposits may explain the unusual δ13Ccarb values and constitute one of the few records of this type of environment identified in the early Paleozoic. 相似文献
3.
Qian Chen Yang Liu Wei-Tim Ho Shek Kiu Chan Qiu-hua Li Jian-Rong Huang 《Wetlands Ecology and Management》2017,25(1):59-66
In this study, components of the food-web in Macao wetlands were quantified using stable isotope ratio techniques based on carbon and nitrogen values. The δ13C and δ15N values of particulate organic matter (δ13CPOM and δ15NPOM, respectively) ranged from ?30.64 ± 1.0 to ?28.1 ± 0.7 ‰, and from ?1.11 ± 0.8 to 3.98 ± 0.7 ‰, respectively. The δ13C values of consumer species ranged from ?33.94 to ?16.92 ‰, showing a wide range from lower values in a freshwater lake and inner bay to higher values in a mangrove forest. The distinct dietary habits of consumer species and the location-specific food source composition were the main factors affecting the δ13C values. The consumer 15N-isotope enrichment values suggested that there were three trophic levels; primary, secondary, and tertiary. The primary consumer trophic level was represented by freshwater herbivorous gastropods, filter-feeding bivalves, and plankton-feeding fish, with a mean δ15N value of 5.052 ‰. The secondary consumer level included four deposit-feeding fish species distributed in Fai Chi Kei Bay and deposit-feeding gastropods in the Lotus Flower Bridge flat, with a mean δ15N value of 6.794 ‰. The tertiary consumers group consisted of four crab species, one shrimp species, and four fish species in the Lotus Flower Bridge Flat, with a mean δ15N value of 13.473 ‰. Their diet mainly comprised organic debris, bottom fauna, and rotten animal tissues. This study confirms the applicability of the isotopic approach in food web studies. 相似文献
4.
Melanie Kriszan Wulf Amelung Jürgen Schellberg Thomas Gebbing Walter Kühbauch 《Plant and Soil》2009,325(1-2):157-169
Tracing back the N use efficiency of long-term fertilizer trials is important for future management recommendations. Here we tested the changes in natural N-isotope composition as an indicator for N- management within a long-term fertilization lysimeter experiment in a low mountain range pasture ecosystem at Rengen (Eifel Mountains), Germany. Cattle slurry (δ15N?=?8.9?±?0.5‰) and mineral fertilizers (calcium ammonium nitrate; δ15N?=??1.0?±?0.2‰) were applied at a rate between 0 and 480 kg N ha?1?yr?1 throughout 20 years from 1985 onwards. In 2006, samples were taken from different grass species, coarse and fine particulate soil organic matter, bulk soil and leachates. Total soil N content hardly changed during fertilization experiment. As also N leaching has been small within the stagnant water regime, most N was lost through the gaseous phase beside plant uptake and cutting. Unlike N uptake by plants, the process of N volatilization resulted in strong discrimination against the 15N isotope. As a consequence, the δ15N values of top soil samples increased from 1.8?±?0.4‰ to 6.0?±?0.4‰ and that of the plants from ?1.2?±?1.3‰ to 4.8?±?1.2‰ with increasing N fertilizer rate. Samples receiving organic fertilizer were most enriched in δ15N. The results suggest that parts of the fertilizer N signal was preserved in soils and even discovered in soil organic matter pools with slow N turnover. However, a 15N/14N isotope fractionation of up to 1.5‰ added to the δ15N values recovered in soils and plants, rendering the increase in δ15N value a powerful indicator to long-term inefficient N usage and past N management in the terrestrial environment. 相似文献
5.
The stable isotope composition of spines produced serially from the apex of columnar cacti has the potential to be used as a record of changes in climate and physiology. To investigate this potential, we measured the δ18O, δ13C and F14C values of spines from a long-lived columnar cactus, saguaro (Carnegiea gigantea). To determine plant age, we collected spines at 11 different heights along one rib from the stem apex (3.77 m height) to the base of a naturally occurring saguaro. Fractions of modern carbon (F14C) ranged from 0.9679 to 1.5537, which is consistent with ages between 1950 and 2004. We observed a very strong positive correlation (r = 0.997) between the F14C age of spines and the age of spines determined from direct and repeated height measurements taken on this individual over the past 37 years. A series of 96 spines collected from this individual had δ18O values ranging from 38‰ to 50‰ [Vienna standard mean ocean water (VSMOW)] and δ13C values from ?11.5‰ to ?8.5‰ [Vienna Peedee belemnite (VPDB)]. The δ18O and δ13C values of spines were positively correlated (r = 0.45, P < 0.0001) and showed near-annual oscillations over the ~15-year record. This pattern suggests that seasonal periods of reduced evaporative demand or greater precipitation input may correspond to increased daytime CO2 uptake. The lowest δ18O and δ13C values of spines observed occurred during the 1983 and 1993 El Niño years, suggesting that the stable isotope composition recorded in spine tissue may serve as a proxy for these climate events. We compared empirical models and data from potted experimental cacti to validate these observations and test our hypotheses. The isotopic records presented here are the first ever reported from a chronosequence of cactus spines and demonstrate that tissues of columnar cacti, and potentially other long-lived succulents, may contain a record of past physiological and climatic variation. 相似文献
6.
Lithostratigraphic analysis of a new stromatolite–thrombolite reef from across the rise of atmospheric oxygen in the Paleoproterozoic Turee Creek Group,Western Australia
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This study describes a previously undocumented dolomitic stromatolite–thrombolite reef complex deposited within the upper part (Kazput Formation) of the c. 2.4–2.3 Ga Turee Creek Group, Western Australia, across the rise of atmospheric oxygen. Confused by some as representing a faulted slice of the younger c. 1.8 Ga Duck Creek Dolomite, this study describes the setting and lithostratigraphy of the 350‐m‐thick complex and shows how it differs from its near neighbour. The Kazput reef complex is preserved along 15 km of continuous exposure on the east limb of a faulted, north‐west‐plunging syncline and consists of 5 recognisable facies associations (A–E), which form two part regressions and one transgression. The oldest facies association (A) is characterised by thinly bedded dololutite–dolarenite, with local domical stromatolites. Association B consists of interbedded columnar and stratiform stromatolites deposited under relatively shallow‐water conditions. Association C comprises tightly packed columnar and club‐shaped stromatolites deposited under continuously deepening conditions. Clotted (thrombolite‐like) microbialite, in units up to 40 m thick, dominates Association D, whereas Association E contains bedded dololutite and dolarenite, and some thinly bedded ironstone, shale and black chert units. Carbon and oxygen isotope stratigraphy reveals a narrow range in both δ13Ccarb values, from ?0.22 to 0.97‰ (VPDB: average = 0.68‰), and δ18O values, from ?14.8 to ?10.3‰ (VPDB), within the range of elevated fluid temperatures, likely reflecting some isotopic exchange. The Kazput Formation stromatolite–thrombolite reef complex contains features of younger Paleoproterozoic carbonate reefs, yet is 300–500 Ma older than previously described Proterozoic examples worldwide. Significantly, the microbial fabrics are clearly distinct from Archean stromatolitic marine carbonate reefs by way of containing the first appearance of clotted microbialite and large columnar stromatolites with complex branching arrangements. Such structures denote a more complex morphological expression of growth than previously recorded in the geological record and may link to the rise of atmospheric oxygen. 相似文献
7.
John E. Drake Catriona A. Macdonald Mark G. Tjoelker Peter B. Reich Brajesh K. Singh Ian C. Anderson David S. Ellsworth 《Biogeochemistry》2018,138(1):85-102
Large amounts of atmospheric N deposition cause negative effects on ecosystems. Effective mitigation strategies require the sources of N deposition to be identified and the contributions from individual sources to be quantified. Determination of the isotopic composition represents a useful approach in source apportionment. In this study, the δ15N-NHx of wet and dry atmospheric deposition and the main NH3 emission sources were analyzed at an urban, a suburban and a rural site in the Taihu Lake region of China. The 2-year average δ15N-\( {\text{NH}}_{4}^{ + } \) of precipitation was ? 3.0 ± 2.3, ? 3.1 ± 2.8 and ? 0.5 ± 2.8‰ for the urban, suburban and rural sites, respectively. These values were much lower than the corresponding values for particulate \( {\text{NH}}_{4}^{ + } \) (15.9, 15.2 and 14.3‰ at the urban, suburban and rural sites, respectively), and much higher than those of gaseous δ15N-NH3 (? 16.7, ? 18.2 and ? 17.4‰ at the urban, suburban and rural sites, respectively). The δ15N-NH3 of NH3 from the main emission sources ranged from ? 30.8 to ? 3.3‰ for volatilized fertilizer, from ? 35.1 to ? 10.5‰ for emissions from a pig farm, and ? 24.7 to ? 11.3‰ for emissions from a dairy farm. Temporal variations of deposition δ15N-NHx indicated that δ15N-NHx values were lower in summer and autumn, but higher in winter and spring for both precipitation \( {\text{NH}}_{4}^{ + } \)-N and gaseous NH3-N. Weather conditions such as temperature and precipitation significantly influenced the spatial and temporal distribution of isotope values of the deposition. Analysis of δ15N-NHx in deposition and emission sources identified volatilized fertilizer and livestock wastes as the origins of both gaseous NH3-N and precipitation \( {\text{NH}}_{4}^{ + } \)-N over the region. A stable isotope mixing model estimated that volatilized fertilizer and animal excreta contributed more than 65% to precipitation \( {\text{NH}}_{4}^{ + } \)-N, more than 60% to particulate \( {\text{NH}}_{4}^{ + } \)-N, and more than 75% to gaseous NH3-N. 相似文献
8.
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
9.
Andrea Jaeschke Benjamin Eickmann Susan Q. Lang Stefano M. Bernasconi Harald Strauss Gretchen L. Früh-Green 《Extremophiles : life under extreme conditions》2014,18(3):545-560
We investigated microbial life preserved in a hydrothermally inactive silica–barite chimney in comparison with an active barite chimney and sediment from the Loki’s Castle low-temperature venting area at the Arctic Mid-Ocean Ridge (AMOR) using lipid biomarkers. Carbon and sulfur isotopes were used to constrain possible metabolic pathways. Multiple sulfur (δ34S, ?33S) isotopes on barite over a cross section of the extinct chimney range between 21.1 and 22.5 ‰ in δ34S, and between 0.020 and 0.034 ‰ in Δ33S, indicating direct precipitation from seawater. Biomarker distributions within two discrete zones of this silica–barite chimney indicate a considerable difference in abundance and diversity of microorganisms from the chimney exterior to the interior. Lipids in the active and inactive chimney barite and sediment were dominated by a range of 13C-depleted unsaturated and branched fatty acids with δ13C values between ?39.7 and ?26.7 ‰, indicating the presence of sulfur-oxidizing and sulfate-reducing bacteria. The majority of lipids (99.5 %) in the extinct chimney interior that experienced high temperatures were of archaeal origin. Unusual glycerol monoalkyl glycerol tetraethers (GMGT) with 0–4 rings were the dominant compounds suggesting the presence of mainly (hyper-) thermophilic archaea. Isoprenoid hydrocarbons with δ13C values as low as ?46 ‰ also indicated the presence of methanogens and possibly methanotrophs. 相似文献
10.
Effects of land use on sources and ages of inorganic and organic carbon in temperate headwater streams 总被引:1,自引:0,他引:1
Yue Han Lu James E. Bauer Elizabeth A. Canuel R. M. Chambers Youhei Yamashita Rudolf Jaffé Amy Barrett 《Biogeochemistry》2014,119(1-3):275-292
The amounts, sources and relative ages of inorganic and organic carbon pools were assessed in eight headwater streams draining watersheds dominated by either forest, pasture, cropland or urban development in the lower Chesapeake Bay region (Virginia, USA). Streams were sampled at baseflow conditions six different times over 1 year. The sources and ages of the carbon pools were characterized by isotopic (δ13C and ?14C) analyses and excitation emission matrix fluorescence with parallel factor analysis (EEM–PARAFAC). The findings from this study showed that human land use may alter aquatic carbon cycling in three primary ways. First, human land use affects the sources and ages of DIC by controlling different rates of weathering and erosion. Relative to dissolved inorganic carbon (DIC) in forested streams which originated primarily from respiration of young, 14C-enriched organic matter (OM; δ13C = ?22.2 ± 3 ‰; ?14C = 69 ± 14 ‰), DIC in urbanized streams was influenced more by sedimentary carbonate weathering (δ13C = ?12.4 ± 1 ‰; ?14C = ?270 ± 37 ‰) and one of pasture streams showed a greater influence from young soil carbonates (δ13C = ?5.7 ± 2.5 ‰; ?14C = 69 ‰). Second, human land use alters the proportions of terrestrial versus autochthonous/microbial sources of stream water OM. Fluorescence properties of dissolved OM (DOM) and the C:N of particulate OM (POM) suggested that streams draining human-altered watersheds contained greater relative contributions of DOM and POM from autochthonous/microbial sources than forested streams. Third, human land uses can mobilize geologically aged inorganic carbon and enable its participation in contemporary carbon cycling. Aged DOM (?14C = ?248 to ?202 ‰, equivalent14C ages of 1,811–2,284 years BP) and POM (?14C = ?90 to ?88 ‰, 14C ages of 669–887 years BP) were observed exclusively in urbanized streams, presumably a result of autotrophic fixation of aged DIC (?297 to ?244 ‰, 14C age = 2,251–2,833 years BP) from sedimentary shell dissolution and perhaps also watershed export of fossil fuel carbon. This study demonstrates that human land use may have significant impacts on the amounts, sources, ages and cycling of carbon in headwater streams and their associated watersheds. 相似文献
11.
《Palaeoworld》2022,31(2):249-257
The early–middle Frasnian boundary interval of the northern part of the East European Platform (northwest of Russia) corresponding to the transitans-punctata isotope event is revealed by biostratigraphically constrained conodont carbon stable isotope data (δ13Ccon). The dynamics of δ13Ccon demonstrate a three-fold pattern with positive peaks at the onset of the main phase of the transitans-punctata isotope event (upper part of Montagne Noire 4 conodont Zone, MN4; up to -22.5‰ VPDB), and during the late part of the event (lower and middle parts of MN6 Zone; up to -24.0‰ VPDB and -22.1‰ VPDB). The stratigraphic level near the MN5 and MN6 boundary is marked by a prominent negative excursion in δ13Ccon (down to -31.8‰ VPDB) that resembles the negative excursion in the terminal phase of the transitans-punctata isotope event worldwide. The δ13Ccon variations in different taxa are generally consistent but demonstrate some differences in values and amplitudes. It is assumed that variations in the carbon isotopic compositions of conodonts were mainly controlled by changes in the isotope composition of the planktons as the main food source for conodonts. 相似文献
12.
Rumiko Nakashita Yuzuru Hamada Eishi Hirasaki Juri Suzuki Toru Oi 《Primates; journal of primatology》2013,54(3):271-281
We determined the magnitude of isotopic fractionation of carbon and nitrogen stable isotope ratios (as enrichment factors, Δδ13C and Δδ15N, respectively) between the tissues and diets of captive Japanese macaques (Macaca fuscata) using a controlled feeding experiment, to provide basic data for reconstructing their feeding habits. The Δδ13C and Δδ15N values, respectively, were 0.9 ± 0.2 ‰ (mean ± standard deviation, SD) and 3.0 ± 0.3 ‰ for whole blood, 1.3 ± 0.2 ‰ and 4.3 ± 0.3 ‰ for plasma, and 0.8 ± 0.2 ‰ and 3.0 ± 0.2 ‰ for red blood cells. However, the Δδ13C and Δδ15N values for hair were 2.8 ± 0.3 ‰ and 3.4 ± 0.2 ‰, respectively. No difference was detected in the δ13C and δ15N values of hair sampled from different parts of the body. We investigated the effects of diet on δ13C in growing hair by alternating the diet of the macaques each month between two diets that differed markedly in δ13C. Hair regrown after shaving repeatedly recorded the δ13C of the diet consumed during the time of hair growth. On the other hand, hair naturally grown during the diet-change experiment did not show a clear pattern. One possible reason is that the hair had grown abnormally under unnatural indoor conditions and showed complicated isotope signatures. To reconstruct the long-term feeding history of Japanese macaques, we need to further clarify the relationships between the stable isotope signature of diet and various body tissues. 相似文献
13.
The farming of shrimp is developing quickly worldwide, and recently, ingredients such as seaweeds in low proportion (25 to 4 %), incorporated into the commercial food, have been shown to improve the shrimp productive variables. The change of commercial foods to commercial feed with a proportion of natural food, and finally, to natural food has been little and simultaneously evaluated. The aim of our study was to determine the relative contribution of dietary carbon to the growth of Litopenaeus vannamei fed with a proportion of 4 % Sargassum (δ13C = ?20.9?±?0.05?‰), 4 % Ulva (δ13C = ?20.6?±?0.6?‰) meal, and a control diet (δ13C?=??22.6?±?0.2?‰) in 60-L tanks for 30 days, and finally, with the green seaweed Ulva spp. (δ13C = ?13.2?±?0.25?‰) and Ulva meal (δ13C = ?14.5?±?0.6?‰) in open-air ponds for 120 days, by measuring δ13C for each of the foods and in the muscle of shrimp. After 15 days, the rates of metabolic turnover (Δ13C = δ13Cshrimp ? δ13Cfood) were constant until the end of the experiment in the tanks. The muscle of shrimp assimilated carbon from all diets, which demonstrated the potential use of combined diets and the optimization of their use in diets containing seaweed. Our data will be useful in future interpretations of field and laboratory isotopic values for this species. 相似文献
14.
Edison A. Díaz-Álvarez Casandra Reyes-García Erick de la Barrera 《Journal of plant research》2016,129(5):863-872
Atmospheric nitrogen deposition poses a major threat to global biodiversity. Tropical epiphytic plants are especially at risk given their reliance on atmospheric sources of nutrients. The leaf, pseudobulb, and root carbon and nitrogen content, C:N ratio, as well as the nitrogen isotopic composition were studied for individuals of Laelia speciosa from a city and from an oak forest in Mexico. The nitrogen content of leaves was similar between the city and the oak forest, reaching 1.3 ± 0.2 % (dry mass). The δ15N of leaves, pseudobulbs, and roots reached 5.6 ± 0.2 ‰ in the city, values found in sites exposed to industrial and vehicular activities. The δ15N for plant from the oak forest amounted to –3.1 ± 0.3 ‰, which is similar to values measured from sites with low industrial activities. Some orchids such as Laelia speciosa produce a single pseudobulb per year, i.e., a water and nutrient storage organ, so the interannual nitrogen deposition was studied by considering the ten most recent pseudobulbs for plants from either site formed between 2003 and 2012. The C:N ratio of the ten most recent pseudobulbs from the oak forest, as well as that of the pseudobulbs formed before 2010 for plants in the city were indistinguishable from each other, averaging 132.4 ± 6.5, while it was lower for the two most recent pseudobulbs in the city. The δ15N values of pseudobulbs from the oak forest averaged ?4.4 ± 0.1 ‰ for the entire series. The δ15N ranged from 0.1 ± 1.6 ‰ for the oldest pseudobulb to 4.7 ± 0.2 ‰ for the pseudobulb formed in the city from 2008 onwards. Isotopic analysis and the C:N ratio for L. speciosa revealed that rates of nitrogen deposition were higher in the city than in the forest. The δ15N values of series of pseudobulbs showed that it is possible to track nitrogen deposition over multiple years. 相似文献
15.
Strahan Tucker Garry B. Stenson W. Don Bowen Sara J. Iverson 《Marine Mammal Science》2013,29(4):E428-E447
Determining how marine predators partition resources is hindered by the difficulty in obtaining information on diet and distribution. Stable isotopes (SI) of carbon (13C/12C, δ13C) and nitrogen (15N/14N, δ15N) provide a two‐dimensional estimate of the dietary space of consumers; an animal's isotopic composition is directly influenced by what they consume and where they feed. Harp (Pagophilus groenlandicus) and hooded (Cystophora cristata) seals are abundant phocid species found in the North Atlantic. We measured and contrasted SI values between seals sampled at nearshore and offshore sites to test for effects of sampling location, sex, age‐class, and body size to gain insight into how these species partition space and prey resources. In addition we contrasted previously published results for gray seals (Halichoerus grypus). Isotope values differed significantly by age class and location in harp and hooded seals. We found significant differences in SI values (mean δ13C and δ15N ± SE) between all species. Hooded seals, a continental shelf‐edge, deep‐diving species, exhibited low SI values (juveniles: ?20.9‰ ± 0.03‰, 13.36‰ ± 0.05‰; adults: ?20.41‰ ± 0.03‰, 14.81‰ ± 0.04‰) characteristic of feeding on meso‐ to bathypelagic prey. Harp seals, which dive to moderate depths primarily on the shelf had intermediate SI values (juveniles: ?20.53‰ ± 0.01‰, 13.91‰ ± 0.01‰; adults: ?20.13‰ ± 0.01‰, 14.96‰ ± 0.01‰) characteristic of feeding on epipelagic prey, whereas gray seals, which feed on or near the sea floor in shallow shelf waters, had high SI values (juveniles: ?19.74‰ ± 0.04‰, 17.51‰ ± 0.05‰; adults: ?18.86‰ ± 0.01‰, 17.23‰ ± 0.02‰) characteristic of feeding on demersal prey. In all species, δ13C values increased with body size and age in the same manner, indicating that seals exploit or forage in deeper habitats as they get larger and older. We hypothesize that the consistent ontogenetic shift in foraging niche, despite large differences between species in their diving behavior, geographic range and habitat use, not only reflects increased access to different prey due to increased diving capacity, but a progressive adjustment to balance energy budgets by reducing foraging costs. 相似文献
16.
Background and aims
Rhizosphere effect is controlled by spatial distribution of rhizodeposits, which may be influenced by soil aggregation and soil moisture regime in relation to water uptake by roots. The objectives of this study were to measure soil organic carbon (SOC) concentration and its δ13C abundance by aggregate size in the rooted bulk soil and by distance in the root-free soil vertically and horizontally away from roots, and to measure DOC concentration and its δ13C abundance in pore water in the rooted bulk soil after a seasonal pulse labelings of 13CO2 to maize (Zea mays L.).Methods
Pulse labeling was conducted in the field once a week for 11 weeks. Soil cells (50 mm in diameter and 100 mm long) mimicking root-free soils were imbedded vertically and horizontally 25–50 mm away from the main root of a maize crop. The rooted bulk soils were sampled to extract soil pore water at different suctions and to fractionate aggregates by wet sieving. The root-free soil cells were sliced by 1 mm intervals from the root end to 20 mm away. All the sampling was 12 days after the last labeling after the crop was harvested.Results and discussion
The δ13C abundance before and after the continuous labeling was ?24.20?±?0.05?‰ and ?23.80?±?0.05?‰ in the rooted bulk soil. The labeling caused increases in δ13C abundance in all the aggregates in the rooted bulk soil and down to 14 mm away from the roots in both the root-free cells. The δ13C abundance was enriched in the >2 mm and 1–2 mm aggregates (?23.17?±?0.12?‰ and ?23.26?±?0.05?‰) though the SOC concentration was not different among the >0.25 mm aggregates, indicating that rhizodeposits or their metabolites were protected and distributed widely in whole soil through soil aggregation. The δ13C abundance in pore water (?24.0?±?0.01?‰) was much lower than those soil aggregates and greatest from the >2 μm soil pores though the DOC concentration was greater from the <20 μm soil pores. The δ13C abundance was in general greater in the horizontal cell than in the vertical cell. The δ13C abundance decreased with the increasing distance to the roots in the vertical cell and peaked at the 5 and 6 mm distance to the roots in the horizontal cell (?23.66?±?0.11?‰ and ?23.5?±?0.10?‰), possibly due to the drier condition unfavorable to microbial decomposition in the horizontal cell. The higher δ13C abundance in the horizontal cell than in the vertical cell was accompanied by a lower SOC concentration and a lower C: N ratio within 3 mm away from the roots, suggesting a stronger priming effect due to the longer residence time of rhizodeposits in the horizontal cell than in the vertical cell.Conclusions
Rhizodeposits or their metabolites were protected during soil aggregation and distributed to 14 mm beyond the rhizosphere in the natural soil-plant system. This extension is of significance in regulating the formation of soil structure and the priming of soil organic matter during the whole life cycle of plants, which needs further study. 相似文献17.
Estimating stable carbon isotope values of microphytobenthos in the Arctic for application to food web studies 总被引:1,自引:0,他引:1
Most studies on Arctic food webs have neglected microphytobenthos as a potential food source because we currently lack robust measurements of δ13C values for microphytobenthos from this environment. As a result, the role of microphytobenthos in high latitude marine food webs is not well understood. We combined field measurements of the concentration of aqueous carbon dioxide and the stable carbon isotopic composition of dissolved inorganic carbon (δ13CDIC) from bottom water in the Beaufort and Chukchi seas with a set of stable carbon isotopic fractionation factors reflecting differences in algal taxonomy and physiology to estimate the stable carbon isotope composition of microphytobenthos-derived total organic carbon (δ13Cp). The δ13Cp for Phaeodactylum tricornutum, a pennate diatom likely to be a dominant microphytobenthos taxon, was estimated to be ?23.9 ± 0.4 ‰ as compared to a centric diatom (Porosira glacialis, δ13Cp = ?20.0 ± 1.6 ‰) and a marine haptophyte (Emiliana huxleyi, δ13Cp = ?22.7 ± 0.5 ‰) at a growth rate (µ) of 0.1 divisions per day (d?1). δ13Cp values increased by ~2.5 ‰ when µ increased from 0.1 to a maximum growth rate of 1.4 d?1. We compared our estimates of δ13Cp values for microphytobenthos with published measurements for other carbon sources in the Arctic and sub-Arctic. We found that microphytobenthos values overlapped with pelagic sources, yet differed from riverine and ice-derived carbon sources. These model results provide valuable insight into the range of possible isotopic values for microphytobenthos from this region, but we remain cautious in regard to the conclusiveness of these findings given the paucity of field measurements currently available for model validation. 相似文献
18.
Stable carbon isotope ratio of tree leaves, boles and fine litter in a tropical forest in Rondônia, Brazil 总被引:2,自引:0,他引:2
L. A. Martinelli S. Almeida I. F. Brown M. Z. Moreira R. L. Victoria L. S. L. Sternberg C. A. C. Ferreira W. W. Thomas 《Oecologia》1998,114(2):170-179
Leaves of 208 trees were collected for isotopic analysis together with wood from 36 tree boles and 18 samples of fine litter from a terra-firme forest located at Samuel Ecological Reserve, Rondônia State, in the southwestern Amazon region. The range of δ13C values in leaves was from ?28 to ?36‰, with an average (±1 SD) of ?32.1?±?1.5‰, which was more negative than the δ13C values of bole samples (?28.4?±?2.0‰) and fine litter (?28.7?±?2.0‰). These values are within the range found for tropical and subtropical forests. Pooling the δ13C values for leaf samples from trees of the same height gave averages which were positively correlated with plant height at a highly significant level, with a slope of 0.06 and an intercept of ?33.3‰ and a correlation coefficient r 2=0.70 (P<0.001). 相似文献
19.
Variations in nitrogen-15 natural abundance of plant and soil systems in four remote tropical rainforests, southern China 总被引:1,自引:0,他引:1
Ang Wang Yun-Ting Fang De-Xiang Chen Keisuke Koba Akiko Makabe Yi-De Li Tu-Shou Luo Muneoki Yoh 《Oecologia》2014,174(2):567-580
The foliar stable N isotope ratio (δ15N) can provide integrated information on ecosystem N cycling. Here we present the δ15N of plant and soil in four remote typical tropical rainforests (one primary and three secondary) of southern China. We aimed to examine if (1) foliar δ15N in the study forests is negative, as observed in other tropical and subtropical sites in eastern Asia; (2) variation in δ15N among different species is smaller compared to that in many N-limited temperate and boreal ecosystems; and (3) the primary forest is more N rich than the younger secondary forests and therefore is more 15N enriched. Our results show that foliar δ15N ranged from ?5.1 to 1.3 ‰ for 39 collected plant species with different growth strategies and mycorrhizal types, and that for 35 species it was negative. Soil NO3 ? had low δ15N (?11.4 to ?3.2 ‰) and plant NO3 ? uptake could not explain the negative foliar δ15N values (NH4 + was dominant in the soil inorganic-N fraction). We suggest that negative values might be caused by isotope fractionation during soil NH4 + uptake and mycorrhizal N transfer, and by direct uptake of atmospheric NH3/NH4 +. The variation in foliar δ15N among species (by about 6 ‰) was smaller than in many N-limited ecosystems, which is typically about or over 10 ‰. The primary forest had a larger N capital in plants than the secondary forests. Foliar δ15N and the enrichment factor (foliar δ15N minus soil δ15N) were higher in the primary forest than in the secondary forests, albeit differences were small, while there was no consistent pattern in soil δ15N between primary and secondary forests. 相似文献
20.
Natsuru Yasuno Shuichi Shikano Tetsuo Shimada Kentaro Shindo Eisuke Kikuchi 《Limnology》2013,14(3):239-246
Carbon and nitrogen stable isotope ratios (δ13C and δ15N) in three sympatric species of larval chironomids were analyzed in a temperate eutrophic shallow lake in Japan. Markedly lower δ13C values were reported in Chironomus plumosus (?51.2 ‰) and Tanypus sp. (?43.5 ‰) than those in photoautotrophic carbon sources [particulate organic matter (POM) and sediment]. There were positive correlations between δ13C and δ15N in the two chironomid species. These results indicated that they assimilated carbon derived from biogenic methane by exploiting methane-oxidizing bacteria (MOB). In contrast, Propsilocerus akamusi exhibited similar δ13C values to those of POM or sediment. A δ13C-based isotope mixing model was used to estimate the dietary contributions of MOB to each chironomid species. The mean contributions ranged from 11 to 15 % in C. plumosus, 13 to 19 % in Tanypus sp., but only up to 5 % in P. akamusi. In an aquarium, we observed that individuals of C. plumosus and Tanypus sp., which exhibited low δ13C values, built U-shaped larval tubes in the sediment, and an oxidized layer developed around these tubes. Propsilocerus akamusi did not exhibit this behavior. These results suggest that tube building may provide larval chironomids with greater access to methane-derived carbon through increased opportunities to feed on MOB. 相似文献