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1.
Tooth enamel of nine Middle Miocene mammalian herbivores from Fort Ternan, Kenya, was analyzed for δ13C and δ18O. The δ18O values of the tooth enamel compared with pedogenic and diagenetic carbonate confirm the use of stable isotope analysis of fossil tooth enamel as a paleoenvironmental indicator. Furthermore, the δ18O of tooth enamel indicates differences in water sources between some of the mammals. The δ13C values of tooth enamel ranged from −8·6–−13·0‰ which is compatible with a pure C3diet, though the possibility of a small C4fraction in the diet of a few of the specimens sampled is not precluded. The carbon isotopic data do not support environmental reconstructions of a Serengeti-typed wooded grassland with a significant proportion of C4grasses. This study does not preclude the presence of C3grasses at Fort Ternan; it is possible that C3grasses could have had a wider geographic range if atmospheric CO2levels were higher than the present values.  相似文献   

2.
The serial test dissection and sieve fraction methods for determining the pattern of size-related change in oxygen and carbon isotopic ratios are compared using four Late Cretaceous planktic foraminifer species (Racemiguembelina fructicosa, Planoglobulina acervulinoides, Planoglobulina multicamerata, and Pseudoguembelina palpebra) from a subtropical site in the North Atlantic (DSDP Hole 390A). Despite the extra labor required, we identify several clear advantages of the dissection method, including: (1) it provides a means of obtaining size-dependent changes in isotopic signatures that are unequivocally ontogenetic, whereas isotopic variation observed from sieve-separated size fractions could be ontogenetic or ecotypic; (2) the taxonomic identity of smaller sized specimens using the dissection method is unequivocal, whereas species identification is increasingly ambiguous in smaller size fractions using the sieve method; (3) it reveals a greater total range and a greater complexity in the pattern of ontogenetic change in stable isotopic values, whereas the sieve method averages the isotopic signal across the entire ontogenetic range preserved within the whole tests that are used. Our results from serial dissections demonstrate that among the species analyzed, R. fructicosa and P. acervulinoides yield relatively negative adult δ18O values, a large size-related change in δ13C values (1.32 and 2.05‰, respectively), and virtually no correlation between size-related δ13C and δ18O values. On this basis we suggest that these were photosymbiotic species that inhabited relatively shallow surface waters. Evidence for photosymbiosis is not as compelling for P. palpebra, as this species yields a 1.06‰ shift in δ13C and relatively negative δ18O values in adult chambers, but much stronger correlation between size-related δ13C and δ18O values (r2=0.40) than in R. fructicosa and P. acervulinoides. Planoglobulina multicamerata yields the most positive adult δ18O values of the species studied, a strong covariance between size-related δ13C and δ18O values (r2=0.77), and a 0.97‰ shift in δ13C composition during ontogeny. We conclude that this species lacked photosymbionts and migrated to a deeper surface water paleohabitat as it increased in size. Single specimen analyses of tightly constrained size fractions reveal a high degree of intraspecific variation. δ13C and δ18O values vary by up to 0.70 and 0.28‰ in R. fructicosa, 1.41 and 0.80‰ in P. acervulinoides, 0.66 and 0.82‰ in P. palpebra, and 0.18 and 0.33‰ in P. multicamerata, respectively. Such a range of isotopic variation has been observed in modern day planktic foraminifer assemblages, and likely results from growth of individuals during different phases of the seasonal cycle and/or the kinetic effect of intraspecific variation in shell calcification rates. As suggested by other investigators, large sample sizes should be analyzed to provide the most reliable correlation of stable isotopic stratigraphic records.  相似文献   

3.
We have measured stable isotopic compositions of Miocene pelagic fine-fraction (<63 μm) carbonates from oligotrophic deep-sea sites in the Pacific and Atlantic oceans and compared them with those of coexisting foraminifers to test their utility as near sea-surface indicators. Fine-fraction carbonates (primarily polyspecific nannofossils) and surface-dwelling planktic foraminiferal (Globigerinoides) stable isotopes both have been considered to reflect surface-water hydrographic conditions. However, our results indicate that fine-fraction stable isotopes are offset from and do not correlate well with those of Globigerinoides. In contrast, stable isotopic records of the deep-dwelling planktic foraminifer Globoquadrina are in good correspondence with the fine-fraction records in terms of long-term (ca. >1 m.y.) trends and temporal variability. On the basis of a time-series hydrography and flux study site in the oligotrophic subtropical North Atlantic, we interpret the isotopic discrepancies between fine-fraction and Globigerinoides as resulting primarily from season of calcification, as well as possible vital effects. We suggest that fine-fraction stable isotope values from oligotrophic waters reflect late winter–early spring relatively cool, nutrient-rich shallow mixed-layer conditions during the time of deep mixing (i.e., spring bloom), whereas Globigerinoides stable isotope values record conditions that prevailed in the stratified surface waters in the warmer late spring–fall. This implies that paired analyses of fine-fraction and surface-dwelling planktic foraminiferal δ18O could be applied to reconstruct paleoseasonality of the open oceans. However, because the fine-fraction δ13C values are not representative of the annual mean surface-water δ13C, we recommend use of near surface-dwelling planktic foraminiferal δ13C as a proxy for δ13C of stratified surface waters that are more or less in equilibrium with the atmosphere with respect to pCO2.  相似文献   

4.
The carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep-sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water. Uvigerina, Pyrgo murrhina, and Oridorsalis tener are the closest to 18O equilibrium (with average deviations about −0.4‰), while Planulina wuellerstorfi and P. murrhina are the closest to 13C equilibrium (with average deviations about −1‰). P. wuellerstorfi shows the most systematic relationship between δ 13C and bottom water apparent oxygen utilization. The intraspecific variabilities in δ 18O and δ 13C suggest that estimates of bottom water paleotemperatures can be made to a precision of ± 0.7°C, while estimates of past apparent oxygen utilization (AOU) can be made to ± 35 μmol/kg. Based on intraspecific comparisons of the Recent samples with fossils, no temporal changes in the degree of either 18O or 13C disequilibrium have been detected for Planulina wuellerstorfi, Uvigerina, Oridorsalis tener and Globocassidulina subglobosa.  相似文献   

5.
Abundance, isotopic composition and morphological imprints of the planktonic foraminifera Globorotalia scitula (Brady) were closely examined for possible use as a novel reconstruction tool of chemical environments in sub-intermediate depth seawater in the past. Based on the MOCNES plankton tow observation of dwelling depths of G. scitula and the isotopic compositions together with hydrochemistry data, the empirical relations between isotopic disequilibria in carbon (Δδ13C=δ13CG. scitulaδ13CDIC) and oxygen (Δδ18O=δ18OG. scitulaδ18Ow) isotopes in the carbonate tests and the seawater δ18O and δ13C of dissolved inorganic carbon (DIC), respectively, are introduced. The morphological information such as pore density and porosity is also examined for significant relations to carbonate chemistry. Shell porosity is strongly correlated saturation state of calcite. The dissolution of living G. scitula tests may promote the observed isotopic differences as well as the increases in porosity. Δδ18O of G. scitula is found effectively to be linear function of both water temperature and calcite saturation state (Ω), and thereby temperature equation for G. scitula is provided, while Δδ13C of G. scitula is a linear function of only calcite saturation state.The equation was validated by using Globorotalia scitula collected by a sediment trap in intermediate water depths. Satisfactory agreements were found between observed and calculated Δδ18O from the empirical equations based on temperature and hydrochemistry data at sediment trap deployment site, indicating that the equation may be useful in paleo-environmental reconstruction of sub-intermediate water. The sediment trap observation further suggests that the abundance of G. scitula does not necessarily correspond to surface water productivity and to POC flux, but instead, it correlates well with the supply of fine organic matter, which appears to be a result of water convection. Thus, G. scitula may be an unambiguous and excellent paleo-environmental recorder for carbonate chemistry and for fine organic matter transport to the depths, if isotopic and morphological observations are combined.  相似文献   

6.
Jun Xu  Min Zhang  Ping Xie   《Harmful algae》2007,6(5):679-685
Carbon stable isotope analysis of surface bloom scum and subsurface seston samples was conducted in shallow eutrophic lakes in China during warm seasons from 2003 to 2004. δ13C values of bloom scum were always higher (averaged 5‰) than those of seston in this study, and the possible reasons were attributed to (i) direct use of atmospheric CO2 at the air–water interface, (ii) decrease in 13C fractionation due to higher carbon fixation, (iii) active CO2 transport, and/or (iv) HCO3 accumulation. Negative correlation between δ13Cscum − δ13Cseston and pH in the test lakes indicated that phytoplankton at the subsurface water column increased isotopic enrichment under the carbon limitation along with the increase of pH, which might in turn decreased the differences in δ13C between the subsurface seston and the surface scums. Significant positive correlations of seston δ13C with total concentrations of nitrogen and phosphorus in water column suggested that the increase in δ13C of seston with trophic state was depending on nutrient (N or P, or both) supply. Our study showed that δ13C of phytoplankton was indicative of carbon utilization, primary productivity, and nutrient supply among the eutrophic lakes.  相似文献   

7.
The δ PDB13C values have been determined for the cellular constituents and metabolic intermediates of autotrophically grown Chromatium vinosum. The isotopic composition of the HCO3- in the medium and the carbon isotopic composition of the bacterial cells change with the growth of the culture. The δ PDB13C value of the HCO3- in the media changes from an initial value of −6.6‰ to +8.1‰ after 10 days of bacterial growth and the δ PDB13C value of the bacterial cells change from −37.5‰ to −29.2‰ in the same period. The amount of carbon isotope fractionation during the synthesis of hexoses by the photoassimilation of CO2 has a range of −15.5‰ at time zero to −22.0‰ after 10 days. This range of fractionation compares to the range of carbon isotope fractionation for the synthesis of sugars from CO2 by ribulose 1,5-diphosphate carboxylase and the Calvin cycle.  相似文献   

8.
We measured nitrous oxide (N2O), dinitrogen (N2), methane (CH4), and carbon dioxide (CO2) fluxes in horizontal and vertical flow constructed wetlands (CW) and in a riparian alder stand in southern Estonia using the closed chamber method in the period from October 2001 to November 2003. The replicates’ average values of N2O, N2, CH4 and CO2 fluxes from the riparian gray alder stand varied from −0.4 to 58 μg N2O-N m−2 h−1, 0.02–17.4 mg N2-N m−2 h−1, 0.1–265 μg CH4-C m−2 h−1 and 55–61 mg CO2-C m−2 h−1, respectively. In horizontal subsurface flow (HSSF) beds of CWs, the average N2 emission varied from 0.17 to 130 and from 0.33 to 119 mg N2-N m−2 h−1 in the vertical subsurface flow (VSSF) beds. The average N2O-N emission from the microsites above the inflow pipes of the HSSF CWs was 6.4–31 μg N2O-N m−2 h−1, whereas the outflow microsites emitted 2.4–8 μg N2O-N m−2 h−1. In VSSF beds, the same value was 35.6–44.7 μg N2O-N m−2 h−1. The average CH4 emission from the inflow and outflow microsites in the HSSF CWs differed significantly, ranging from 640 to 9715 and from 30 to 770 μg CH4-C m−2 h−1, respectively. The average CO2 emission was somewhat higher in VSSF beds (140–291 mg CO2-C m−2 h−1) and at the inflow microsites of HSSF beds (61–140 mg CO2-C m−2 h−1). The global warming potential (GWP) from N2O and CH4 was comparatively high in both types of CWs (4.8 ± 9.8 and 6.8 ± 16.2 t CO2 eq ha−1 a−1 in the HSSF CW 6.5 ± 13.0 and 5.3 ± 24.7 t CO2 eq ha−1 a−1 in the hybrid CW, respectively). The GWP of the riparian alder forest from both N2O and CH4 was relatively low (0.4 ± 1.0 and 0.1 ± 0.30 t CO2 eq ha−1 a−1, respectively), whereas the CO2-C flux was remarkable (3.5 ± 3.7 t ha−1 a−1). The global influence of CWs is not significant. Even if all global domestic wastewater were treated by wetlands, their share of the trace gas emission budget would be less than 1%.  相似文献   

9.
The relative composition of stable carbon isotopes, δ13C, was determined in flag leaves and grain of spring wheat (Triticum aestivum L. cv Albis) grown in open-top field fumigation chambers and exposed to different O3 levels during the growing season. The aim of the study was to establish exposure-response relationships for the radiation-weighted seasonal mean O3 concentration and δ13C (relative deviation of the 13C/12C ratio) values of the two plant parts. Samples were collected at harvest in 1986, 1987, and 1988. With increasing O3 concentration, δ13C values increased (became less negative) proportionally. Year to year δ13C differences at equivalent O3 concentrations were small. The shift in δ13C caused by O3 was more pronounced in grain than in leaves. According to models of 13C discrimination in C3 plants, these results indicate increasing limitation of photosynthesis by CO2 diffusion relative to limitation by carboxylation with increasing O3 exposure. This conclusion is not in agreement with results from gas exchange analysis. Water use efficiency in green flag leaves tended to decrease with increasing O3, indicating a dominating effect of O3 on CO2 carboxylation.  相似文献   

10.

Background

The oxygen (δ18O) and carbon (δ13C) isotope compositions of bioapatite from skeletal remains of fossil mammals are well-established proxies for the reconstruction of palaeoenvironmental and palaeoclimatic conditions. Stable isotope studies of modern analogues are an important prerequisite for such reconstructions from fossil mammal remains. While numerous studies have investigated modern large- and medium-sized mammals, comparable studies are rare for small mammals. Due to their high abundance in terrestrial ecosystems, short life spans and small habitat size, small mammals are good recorders of local environments.

Methodology/Findings

The δ18O and δ13C values of teeth and bones of seven sympatric modern rodent species collected from owl pellets at a single locality were measured, and the inter-specific, intra-specific and intra-individual variations were evaluated. Minimum sample sizes to obtain reproducible population δ18O means within one standard deviation were determined. These parameters are comparable to existing data from large mammals. Additionally, the fractionation between coexisting carbonate (δ18OCO3) and phosphate (δ18OPO4) in rodent bioapatite was determined, and δ18O values were compared to existing calibration equations between the δ18O of rodent bioapatite and local surface water (δ18OLW). Specific calibration equations between δ18OPO4 and δ18OLW may be applicable on a taxonomic level higher than the species. However, a significant bias can occur when bone-based equations are applied to tooth-data and vice versa, which is due to differences in skeletal tissue formation times. δ13C values reflect the rodents’ diet and agree well with field observations of their nutritional behaviour.

Conclusions/Significance

Rodents have a high potential for the reconstruction of palaeoenvironmental conditions by means of bioapatite δ18O and δ13C analysis. No significant disadvantages compared to larger mammals were observed. However, for refined palaeoenvironmental reconstructions a better understanding of stable isotope signatures in modern analogous communities and potential biases due to seasonality effects, population dynamics and tissue formation rates is necessary.  相似文献   

11.
Concentration and isotopic composition (δ13C and δ18O) of ambient CO2 and water vapour were determined within a Quercus petraea canopy, Northumberland, UK. From continuous measurements made across a 36-h period from three heights within the forest canopy, we generated mixing lines (Keeling plots) for δa 13CO2, δa C18O16O and δa H2 18O, to derive the isotopic composition of the signal being released from forest to atmosphere. These were compared directly with measurements of different respective pools within the forest system, i.e. δ13C of organic matter input for δa 13CO2, δ18O of exchangeable water for δa C18O16O and transpired water vapour for δa H2 18O. [CO2] and δa 13CO2 showed strong coupling, where the released CO2 was, on average, 4 per mil enriched compared to the organic matter of plant material in the system, suggesting either fractionation of organic material before eventual release as soil-respired CO2, or temporal differences in ecosystem discrimination. δa C18O16O was less well coupled to [CO2], probably due to the heterogeneity and transient nature of water pools (soil, leaf and moss) within the forest. Similarly, δa H2 18O was less coupled to [H2O], again reflecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The δ18O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO2 and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time. Received: 21 March 1998 / Accepted: 10 December 1998  相似文献   

12.
Open-top chambers were used to estimate the possible effects of global warming on δ13C of seven plant species grown in alpine meadow ecosystem. The δ13C values of plant species were lower after long-term growth in open-top chambers. In the course of experiment, temperature significantly increased inside the chambers by 4°C. Plant species grown at a lower elevation above sea level had higher δ13C values as compared to those grown at a higher elevation. This was in accordance with the effect of open-top chamber on δ13C values in plants. Greater availability of CO2 and lower water vapor pressure at higher temperature inside the chambers, as indicated by an increase in discrimination against 13CO2, probably result in more negative δ13C values of plants because higher stomatal conductance increases availability of CO2 and causes greater discrimination against 13CO2. The plant species studied could be the indicator species for testing global warming by the change in carbon isotope ratios at the two growth temperatures. This text was submitted by the authors in English.  相似文献   

13.
Kellomäki  S.  Wang  Kai-Yun  Lemettinen  M. 《Photosynthetica》2000,38(1):69-81
A closed CO2 and temperature-controlled, long-term chamber system has been developed and set up in a typical boreal forest of Scots pine (Pinus sylvestris L.) near the Mekrijärvi Research Station (62°47N, 30°58E, 145 m above sea level) belonging to the University of Joensuu, Finland. The main objectives of the experiment were to provide a means of assessing the medium to long-term effects of elevated atmospheric CO2 concentration (EC) and temperature (ET) on photosynthesis, respiration, growth, and biomass at the whole-tree level and to measure instantaneous whole-system CO2 exchange. The system consists of 16 chambers with individual facilities for controlling CO2 concentration, temperature, and the combination of the two. The chambers can provide a wide variety of climatic conditions that are similar to natural regimes. In this experiment the target CO2 concentration in the EC chambers was set at a fixed constant of 700 µmol mol–1 and the target air temperature in the ET chambers to track the ambient temperature but with a specified addition. Chamber performance was assessed on the base of recordings covering three consecutive years. The CO2 and temperature control in these closed chambers was in general accurate and reliable. CO2 concentration in the EC chambers was within 600–725 µmol mol–1 for 90 % of the exposure time during the "growing-season" (15 April – 15 September) and 625–725 µmol mol–1 for 88 % of the time in the "off-season" (16 September – 14 April), while temperatures in the chambers were within ±2.0 °C of the ambient or target temperature in the "growing season" and within ±3.0 °C in the "off season". There were still some significant chamber effects. Solar radiation in the chambers was reduced by 50–60 % for 82 % of the time in the "growing season" and 55–65 % for 78 % of the time in the "off season", and the relative humidity of the air was increased by 5–10 % for 72 % of the time in the "growing season" and 2–12 % for 91 % of the time in the "off season". The crown architecture and main phenophase of the trees were not modified significantly by enclosure in the chambers, but some physiological parameters changed significantly, e.g., the radiant energy-saturated photosynthesis rate, transpiration rate, maximum photochemical efficiency of photosystem 2, and chlorophyll content.  相似文献   

14.
N2O gas is involved in global warming and ozone depletion. The major sources of N2O are soil microbial processes. Anthropogenic inputs into the nitrogen cycle have exacerbated these microbial processes, including nitrification. Ammonia-oxidizing archaea (AOA) are major members of the pool of soil ammonia-oxidizing microorganisms. This study investigated the isotopic signatures of N2O produced by soil AOA and associated N2O production processes. All five AOA strains (I.1a, I.1a-associated and I.1b clades of Thaumarchaeota) from soil produced N2O and their yields were comparable to those of ammonia-oxidizing bacteria (AOB). The levels of site preference (SP), δ15Nbulk and δ18O -N2O of soil AOA strains were 13–30%, −13 to −35% and 22–36%, respectively, and strains MY1–3 and other soil AOA strains had distinct isotopic signatures. A 15N-NH4+-labeling experiment indicated that N2O originated from two different production pathways (that is, ammonia oxidation and nitrifier denitrification), which suggests that the isotopic signatures of N2O from AOA may be attributable to the relative contributions of these two processes. The highest N2O production yield and lowest site preference of acidophilic strain CS may be related to enhanced nitrifier denitrification for detoxifying nitrite. Previously, it was not possible to detect N2O from soil AOA because of similarities between its isotopic signatures and those from AOB. Given the predominance of AOA over AOB in most soils, a significant proportion of the total N2O emissions from soil nitrification may be attributable to AOA.  相似文献   

15.
Changes in intrinsic water use efficiency (iWUE) were investigated in Fagus sylvatica and Nothofagus spp. over the last century. We combined dendrochronological methods with dual-isotope analysis to investigate whether atmospheric changes enhanced iWUE of Fagus and Nothofagus and tree growth (basal area increment, BAI) along latitudinal gradients in Italy and Chile. Post-maturation phases of the trees presented different patterns in δ13C, Δ13C, δ18O, Ci (internal CO2 concentration), iWUE, and BAI. A continuous enhancement in isotope-derived iWUE was observed throughout the twentieth century, which was common to all sites and related to changes in Ca (ambient CO2 concentration) and secondarily to increases in temperature. In contrast to other studies, we observed a general increasing trend of BAI, with the exception of F. sylvatica in Aspromonte. Both iWUE and BAI were uncoupled with the estimated drought index, which is in agreement with the absence of enduring decline in tree growth. In general, δ13C and δ18O showed a weak relationship, suggesting the major influence of photosynthetic rate on Ci and δ13C, and the minor contribution of the regulation of stomatal conductance to iWUE. The substantial warming observed during the twentieth century did not result in a clear pattern of increased drought stress along these latitudinal transects, because of the variability in temporal trends of precipitation and in specific responses of populations.  相似文献   

16.
Winter CO2 CH4 and N2O fluxes on some natural and drained boreal peatlands   总被引:7,自引:0,他引:7  
CO2 and CH4 fluxes during the winter were measured at natural and drained bog and fen sites in eastern Finland using both the closed chamber method and calculations of gas diffusion along a concentration gradient through the snowpack. The snow diffusion results were compared with those obtained by chamber, but the winter flux estimates were derived from chamber data only. CH4 emissions from a poor bog were lower than those from an oligotrophic fen, while both CO2 and CH4 fluxes were higher in theCarex rostrata- occupied marginal (lagg) area of the fen than in the slightly less fertile centre. Average estimated winter CO2-C losses from virgin and drained forested peatlands were 41 and 68 g CO2-C m–2, respectively, accounting for 23 and 21% of the annual total CO2 release from the peat. The mean release of CH4-C was 1.0 g in natural bogs and 3.4 g m–2 in fens, giving rise to winter emissions averaging to 22% of the annual emission from the bogs and 10% of that from the fens. These wintertime carbon gas losses in Finnish natural peatlands were even greater than reported average long-term annual C accumulation values (less than 25g C m–2). The narrow range of 10–30% of the proportion of winter CO2 and CH4 emissions from annual emissions found in Finnish peatlands suggest that a wider generalization in the boreal zone is possible. Drained forested bogs emitted 0.3 g CH4-C m–2 on the average, while the effectively drained fens consumed an average of 0.01 g CH4-C m–2. Reason for the low CH4. efflux or net oxidation in drained peatlands probably lies in low substrate supply and thus low CH4 production in the anoxic deep peat layers. N2O release from a fertilized grassland site in November–May was 0.7 g N2O m–2, accounting for 38% of the total annual emission, while a forested bog released none and two efficiently drained forested fens 0.09 (28% of annual release) and 0.04 g N2O m–2 (27%) during the winter, respectively.  相似文献   

17.
The CO2- and H2O-exchange rates between soybean canopies and the atmosphere were measured in three mobile chambers (4 m3). Each chamber stopped at 8 or 9 plots (3.1-m2 ground area) every 25 min. Diurnal and seasonal CO2-exchange rates (CER) of 13 soybean (Glycine max (L.) Merr.) cultivars are summarized here. The oldest two cultivars, released in 1927 and 1932, had the lowest CER values. The CER usually decreased in the afternoon (23.4 vs 27.8 mol CO2 m-2 s-1 at 1.6 mmol photons m-2 s-1), except shortly after rainfall. During a drought, these reductions occurred earlier in the day and were more pronounced. We present evidence for a nonstomatal component of the CO2 flux-reaction system causing CER reductions during a water stress. Daytime CER values were not correlated with temperature (24–34° C), but nighttime values were (15–25° C, r=0.85,* n=41).  相似文献   

18.
The metabolism of melondialdehyde (MDA) by male and female Swiss mice was investigated. Distribution of an i.p. dose of MDA is rapid and uniform throughout the body. Conversion of 14C-labeled MDA to CO2 is complete 4 hours after an i.p. dose of 5 μmol to 200 μmol with no signs of short term toxicity. The yields of CO2 from [1-14C]-β-alanine, [3-14C]-β-alanine, [1-14C]-sodium acetate, and [2-14C]-sodium acetate were also determined. Comparison of the yields of CO2 from this series of compounds suggests the intermediacy of malonic semialdehyde in the metabolism of MDA. High doses (600 μmol) of β-alanine or acetate given prior to 14C-MDA reduced the yield of 14CO2. Ethanol and disulfiram were both inhibitors of MDA metabolism, indicating the involvement of aldehyde dehydrogenase in the oxidation of MDA.These data demonstrate the ability of animal tissues to rapidly remove exogeneously administered MDA. They also have implications with respect to the possible pathological consequences of MDA generation.  相似文献   

19.
This study tests the hypothesis that vertical habitat preferences of different monkey species inhabiting closed canopy rainforest are reflected in oxygen isotopes. We sampled bone from seven sympatric cercopithecid species in the Taï forest, Côte d''Ivoire, where long-term study has established taxon-specific patterns of habitat use and diet. Modern rib samples (n = 34) were examined for oxygen (δ18Oap) and carbon (δ13Cap) from bone apatite (‘bioapatite’), and carbon (δ13Cco) and nitrogen (δ15Nco) from bone collagen. Results are consistent for C3 feeders in a closed canopy habitat. Low irradiance and evapotranspiration, coupled with high relative humidity and recycled CO2 in forest understory, contribute to observed isotopic variability. Both δ13Cco and δ13Cap results reflect diet; however, δ13C values are not correlated with species preference for canopy height. By contrast, δ18Oap results are correlated with mean observed height and show significant vertical partitioning between taxa feeding at ground, lower and upper canopy levels. This oxygen isotope canopy effect has important palaeobiological implications for reconstructing vertical partitioning among sympatric primates and other species in tropical forests.  相似文献   

20.
Soil CO2 flux can contribute as much as 60–80% of total ecosystem respiration in forests. Although considerable research has focused on quantifying this flux during the growing season, comparatively little effort has focused on non-growing season fluxes. We measured soil CO2 efflux through snow in 50 and ~300 year old subalpine forest stands near Fraser CO. Our objectives were to quantify seasonal patterns in wintertime soil CO2 flux; determine if differences in soil CO2 flux between the two forest ages during the growing season persist during winter; and to quantify the sample size necessary to discern treatment differences. Soil CO2 flux during the 2002–2003 and 2003–2004 snow season averaged 0.31 and 0.35 μmols m−2 s−1 for the young and old forests respectively; similar to the relative difference observed during summer. There was a significant seasonal pattern of soil CO2 flux during the winter with fluxes averaging 0.22 μmols m−2 s−1 in December and January and increasing to an average of 0.61 μmols m−2 s−1 in May. Within-plot variability for measurements used in calculating flux was low. The coefficients of variation (CV) for CO2 concentration, snowpack density, and snow depth were 17, 8 and 14%, respectively, yielding a CV for flux measurements within-plot of 29%. A within plot CV of 29% requires 8 sub-samples per plot to estimate the mean flux with a standard error of ±10% of the mean. Variability in CO2 flux estimates among plots (size = 400 m2) was similar to that within plot and was also low (CV = ~28%). With a CV of 28% among plots, ten plots per treatment would have a 50% probability of detecting a 25% difference in treatment means for α = 0.05.  相似文献   

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