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1.
Knowledge gaps regarding potential ontogeny and plant species identity effects on carbon isotope fractionation might lead to misinterpretations of carbon isotope composition (δ 13C) of respired CO 2, a widely-used integrator of environmental conditions. In monospecific mesocosms grown under controlled conditions, the δ 13C of C pools and fluxes and leaf ecophysiological parameters of seven herbaceous species belonging to three functional groups (crops, forage grasses and legumes) were investigated at three ontogenetic stages of their vegetative cycle (young foliage, maximum growth rate, early senescence). Ontogeny-related changes in δ 13C of leaf- and soil-respired CO 2 and 13C/ 12C fractionation in respiration (Δ R) were species-dependent and up to 7‰, a magnitude similar to that commonly measured in response to environmental factors. At plant and soil levels, changes in δ 13C of respired CO 2 and Δ R with ontogeny were related to changes in plant physiological status, likely through ontogeny-driven changes in the C sink to source strength ratio in the aboveground plant compartment. Our data further showed that lower Δ R values (i.e. respired CO 2 relatively less depleted in 13C) were observed with decreasing net assimilation. Our findings highlight the importance of accounting for ontogenetic stage and plant community composition in ecological studies using stable carbon isotopes. 相似文献
2.
Recent developments in (13) C NMR spectrometry have allowed the determination of intramolecular (13) C/(12) C ratios with high precision. However, the analysis of carbohydrates requires their derivatization to constrain the anomeric carbon. Fructose has proved to be particularly problematic because of a byproduct occurring during derivatization and the complexity of the NMR spectrum of the derivative. Here, we describe a method to determine the intramolecular (13) C/(12) C ratios in fructose by (13) C NMR analysis of the acetyl-isopropylidene derivative. We have applied this method to measure the intramolecular (13) C/(12) C distribution in the fructosyl moiety of sucrose and have compared this with that in the glucosyl moiety. Three prominent features stand out. First, in sucrose from both C(3) and C(4) plants, the C-1 and C-2 positions of the glucosyl and fructosyl moieties are markedly different. Second, these positions in C(3) and C(4) plants show a similar profile. Third, the glucosyl and fructosyl moieties of sucrose from Crassulacean acid metabolism (CAM) metabolism have a different profile. These contrasting values can be interpreted as a result of the isotopic selectivity of enzymes that break or make covalent bonds in glucose metabolism, whereas the distinctive (13) C pattern in CAM sucrose probably indicates a substantial contribution of gluconeogenesis to glucose synthesis. 相似文献
3.
We tested the hypothesis that the diurnal patterns of variationin lacunal gas concentrations and isotopic fractionationpreviously reported in a single plant genera ( Typha)typified the patterns of all through-flow convective plantsby extending our observations to Phragmites australisCav. In daylight, Phragmites CH 4 transport isdriven by internal pressurization which results in gas flowdown young green culms and its exit from one year old deadbrown culms. Flow rates of 10.4 ± 4.0 mL min –1 weremeasured in this study. At night, CH 4 is transportedfrom the sediments to the atmosphere via the lacunal plantspaces by molecular diffusion. Within green culms, lacunalCH 4 concentrations varied by a factor of 1000, from 3%(parts by volume) pre-dawn to lows of 25 ppmv during midday.Methane in brown culms varied by a factor of 10 diurnally,from 5% pre-dawn to 0.3% at midday. Lacunal CO 2concentrations varied similarly.Concentrations of both gases varied inversely with lacunalpressure. In green culms, large isotopic fractionations wereobserved in CH 4 and CO 2 in the morning and eveningduring transitions in gas transport mode and were associatedwith slight downward flows counter to the upward diffusionof these gases. Methane 13C as depletedas –100 was observed. In daylight, lacunal CH 4 wassimilar to or 13C depleted relative to sedimentary andemitted CH 4 isotopic values, but at night lacunalCH 4 was 13C enriched relative to sedimentarymethane. Overall, the diurnal variations of CH 4concentration and 13C value in Phragmiteswere similar to those observed in Typha andindicate that these patterns should be consistent in otherconvective-flow plants. Furthermore, our results demonstratethat the large isotopic fractionations found in aquaticplants can result solely from isotopic fractionationassociated with gas transport. 相似文献
4.
We tested the reliability of herbivore faecal δ 13C and δ 15N values for reconstructing diet through review of an extensive database derived from a 3-year study of ungulates in South Africa's Kruger National Park. Faeces are a useful material for stable isotope studies of diet because they record dietary turnover at very short time scales, and because sampling is non-invasive. However, the validity of faecal isotope proxies may be questioned because they represent only undigested food remains. Results from Kruger Park confirm that free-ranging browsers have faecal δ 13C consistent with C 3 feeding, grazer faeces are C 4, and mixed-feeder faeces intermediate. Although the respective ranges do not overlap, there is significant variation in faecal δ 13C of browsers and grazers (~2.0–4.0‰) across space and through time. We demonstrate that most (~70%) of this variation can be ascribed to corresponding patterns of variation in the δ 13C of C 3 and C 4 plants, respectively, re-enforcing the fidelity of faecal isotope proxies for diet but highlighting a need for mixing models that control for variations in plant δ 13C in order to achieve accurate diet reconstructions. Predictions for the effects of climate (rainfall) and ecophysiology on 15N-abundance variations in mammals do not persist in faeces. Rather, faecal δ 15N tracks changes in plant δ 15N, with further fractionation occurring primarily due to variations in dietary protein (reflected by %N). Controlling for these effects, we show that a dual-isotope multiple source mixing model (Isosource) can extend diet reconstructions for African savanna herbivores beyond simplified C 3/C 4 distinctions, although further understanding of variations in mammal δ 15N are needed for greater confidence in this approach. 相似文献
5.
Carbon isotopic composition of predominantly marine kerogen in latest Oligocene mudstones of the Peru Margin ODP 682A Hole shows an about 3.5‰ increase with decreasing age. Py-GC and elemental (C/N ratio) analysis of the kerogen plus sulphur isotopic study together with earlier knowledge on geological setting and organic geochemistry results in a better understanding of depositionary environment and allows to separation of the influence of concentration of water dissolved carbon dioxide ( ce) on kerogen δ 13C from that of other factors (bacterial degradation, sea surface temperature, DIC δ 13C, productivity, and admixture of land plant OM). Based on this analysis, the major part of the kerogen shift is considered as a result of the latest Oligocene decrease of marine photosynthetic carbon isotopic fractionation in the Peru Margin photic zone, which in turn possibly reflects a simultaneous drop in atmospheric CO 2 level. Uncertainties in the evaluation of the factors affecting the marine photosynthetic carbon isotopic fractionation and the extent of ocean–atmosphere disequilibrium do not permit calculation of the decrease of the atmospheric CO 2. 相似文献
6.
Our objective was to evaluate the relative importance of gradients in light intensity and the isotopic composition of atmospheric
CO 2 for variation in leaf carbon isotope ratios within a Pinus resinosa forest. In addition, we measured photosynthetic gas exchange and leaf carbon isotope ratios on four understory species ( Dryopteris carthusiana, Epipactus helleborine, Hieracium floribundum, Rhamnus frangula), in order to estimate the consequence of the variation in the understory light microclimate for carbon gain in these plants.
During midday, CO 2 concentration was relatively constant at vertical positions ranging from 15 m to 3 m above ground. Only at positions below
3 m was CO 2 concentration significantly elevated above that measured at 15 m. Based on the strong linear relationship between changes
in CO 2 concentration and δ 13C values for air samples collected during a diurnal cycle, we calculated the expected vertical profile for the carbon isotope
ratio of atmospheric CO 2 within the forest. These calculations indicated that leaves at 3 m height and above were exposed to CO 2 of approximately the same isotopic composition during daylight periods. There was no significant difference between the daily
mean δ 13C values at 15 m (–7.77‰) and 3 m (–7.89‰), but atmospheric CO 2 was significantly depleted in 13C closer to the ground surface, with daily average δ 13C values of –8.85‰ at 5 cm above ground. The light intensity gradient in the forest was substantial, with average photosynthetically
active radiation (PAR) on the forest floor approximately 6% of that received at the top of the canopy. In contrast, there
were only minor changes in air temperature, and so it is likely that the leaf-air vapour pressure difference was relatively
constant from the top of the canopy to the forest floor. For red pine and elm tree samples, there was a significant correlation
between leaf δ 13C value and the height at which the leaf sample was collected. Leaf tissue sampled near the forest floor, on average, had
lower δ 13C values than samples collected near the top of the canopy. We suggest that the average light intensity gradient through the
canopy was the major factor influencing vertical changes in tree leaf δ 13C values. In addition, there was a wide range of variation (greater than 4‰) among the four understory plant species for average
leaf δ 13C values. Measurements of leaf gas exchange, under natural light conditions and with supplemental light, were used to estimate
the influence of the light microclimate on the observed variation in leaf carbon isotope ratios in the understory plants.
Our data suggest that one species, Epipactus helleborine, gained a substantial fraction of carbon during sunflecks.
Received: 21 March 1996 / Accepted: 13 August 1996 相似文献
7.
Background and aimsIn forestry-drained peatlands, drying leads to changes in C cycling which could affect peat δ13C. Furthermore, the δ13C profile of the entire peat column may reveal effects of earlier climatic periods. MethodsWe measured peat δ13C and C inventories in adjacent peat profiles, two collected from undrained and two from the drained side of a bog that was partially ditch-drained 37 years earlier. The cores were sliced into 10-cm subsamples for analyses; matching of the profiles based on surface levelling, peat stratigraphic correlation and a horizontal ash layer found in both profiles. ResultsSurface subsidence of 30 cm was observed in the dried site and the uppermost 160 cm in the undrained site contained an excess of 5.9 kg m−2 of C compared with the corresponding strata of the ditch-drained site. The δ13C values increased but markedly only in the thin surface layer of the drained site, indicating low δ13C of the missing C (ca. –30‰). In the deeper strata, dating to Mid-Holocene, high dry bulk density, C%, N%, humification index and low C/N ratio were connected to low δ13C of peat. ConclusionsDrainage of 37 years increased δ13C values in the upper peat profile of the drained bog and led to the selective loss of 13C depleted C. Results indicate that C balance studies can be aided by C isotope analyses. Low δ13C values in the peat profile indicate the existence of a wet fen stage during the moist and warm period during Mid-Holocene. 相似文献
9.
We studied Holocene speleothems and tufa samples collected in numerous caves and rivers in the Dinaric Karst of Croatia, Slovenia, Bosnia and Herzegovina, as well as Serbia and Montenegro. Differences in the formation process of tufa and speleothems are discussed in the context of their isotopic composition ( 14C, 13C and 18O), as well as the chemistry of surface water (rivers, lakes) and drip water (in caves). The physical and chemical parameters monitored in the surface water (tufa precipitation) and drip water (speleothem precipitation) show that more stable conditions accompany speleothem rather than tufa formation. This is particularly obvious in the water temperature variations (2-22°C in surface water and 7-12°C in drip water) and in saturation index variation (3-11 in surface water and 1-6 in drip water). The range of 14C ages recorded by Holocene speleothems (∼12?000 yr) is wider by several thousands years than that of Holocene tufa samples (∼6000 yr). δ 13C values for tufa samples range from −12‰ to −6‰ and for speleothem samples from −12‰ to +3‰ reflecting higher soil carbon and/or vegetation impact on the process of tufa than on speleothem formation. The differences in δ 18O values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water. The study shows that speleothems from the Dinaric Karst can be used as global palaeoclimatic records, whereas tufa records changes in the local palaeoenvironment. 相似文献
10.
Stable isotope analysis of diet has become a common tool in conservation research. However, the multiple sources of uncertainty inherent in this analysis framework involve consequences that have not been thoroughly addressed. Uncertainty arises from the choice of trophic discrimination factors, and for Bayesian stable isotope mixing models (SIMMs), the specification of prior information; the combined effect of these aspects has not been explicitly tested. We used a captive feeding study of gray wolves ( Canis lupus) to determine the first experimentally-derived trophic discrimination factors of C and N for this large carnivore of broad conservation interest. Using the estimated diet in our controlled system and data from a published study on wild wolves and their prey in Montana, USA, we then investigated the simultaneous effect of discrimination factors and prior information on diet reconstruction with Bayesian SIMMs. Discrimination factors for gray wolves and their prey were 1.97‰ for δ 13C and 3.04‰ for δ 15N. Specifying wolf discrimination factors, as opposed to the commonly used red fox ( Vulpes vulpes) factors, made little practical difference to estimates of wolf diet, but prior information had a strong effect on bias, precision, and accuracy of posterior estimates. Without specifying prior information in our Bayesian SIMM, it was not possible to produce SIMM posteriors statistically similar to the estimated diet in our controlled study or the diet of wild wolves. Our study demonstrates the critical effect of prior information on estimates of animal diets using Bayesian SIMMs, and suggests species-specific trophic discrimination factors are of secondary importance. When using stable isotope analysis to inform conservation decisions researchers should understand the limits of their data. It may be difficult to obtain useful information from SIMMs if informative priors are omitted and species-specific discrimination factors are unavailable. 相似文献
11.
Stable carbon isotope signatures are often used as tracers for environmentally driven changes in photosynthetic δ 13C discrimination. However, carbon isotope signatures downstream from carboxylation by Rubisco are altered within metabolic pathways, transport and respiratory processes, leading to differences in δ 13C between carbon pools along the plant axis and in respired CO 2. Little is known about the within-plant variation in δ 13C under different environmental conditions or between species. We analyzed spatial, diurnal, and environmental variations in δ 13C of water soluble organic matter (δ 13C WSOM) of leaves, phloem and roots, as well as dark-respired δ 13CO 2 (δ 13C res) in leaves and roots. We selected distinct light environments (forest understory and an open area), seasons (Mediterranean spring and summer drought) and three functionally distinct understory species (two native shrubs— Halimium halimifolium and Rosmarinus officinalis—and a woody invader— Acacia longifolia). Spatial patterns in δ 13C WSOM along the plant vertical axis and between respired δ 13CO 2 and its putative substrate were clearly species specific and the most δ 13C-enriched and depleted values were found in δ 13C of leaf dark-respired CO 2 and phloem sugars, ~?15 and ~?33 ‰, respectively. Comparisons between study sites and seasons revealed that spatial and diurnal patterns were influenced by environmental conditions. Within a species, phloem δ 13C WSOM and δ 13C res varied by up to 4 ‰ between seasons and sites. Thus, careful characterization of the magnitude and environmental dependence of apparent post-carboxylation fractionation is needed when using δ 13C signatures to trace changes in photosynthetic discrimination. 相似文献
12.
The main aim of this study was to test various hypotheses regarding the changes in 13C of emitted CO 2 that follow the addition of C 4-sucrose to the soil of a C 3-ecosystem. It forms part of an experimental series designed to assess whether or not the contributions from C 3-respiration (root and microbial) and C 4-respiration (microbial) to total soil respiration can be calculated from such changes. A series of five experiments, three on sieved (root-free) mor-layer material, and two in the field with intact mor-layer (and consequently with active roots), were performed. Both in the experiments on sieved mor-layer and the field experiments, we found a C 4-sucrose-induced increase in C 3-respiration that accounted for between 30% and 40% of the respiration increase 1 h after sucrose addition. When the course of C 3-, C 4- and total respiration was followed in sieved material over four days following addition of C 4-sucrose, the initially increased respiration of C 3-C was transient, passing within less than 24 h. In a separate pot experiment, neither ectomycorrhizal Pinus sylvestrisL. roots nor non-mycorrhizal roots of this species showed respiratory changes in response to exogenous sucrose. No shift in the 13C of the evolved CO 2 after adding C 3-sucrose to sieved mor-layer material was found, confirming that the sucrose-induced increase in respiration of endogenous C was not an artefact of discrimination against 13C during respiration. Furthermore, we conclude that the C 4-sucrose induced transient increase in C 3-respiration is most likely the result of accelerated turnover of C in the microbial biomass. Thus, neither respiration of mycorrhizal roots, nor processes discriminating against 13C were likely sources of error in the field. The estimated 13C of evolved soil CO 2 in three field experiments lay between –25.2 and –23.6. The study shows that we can distinguish between CO 2 evolved from microbial mineralisation of added C 4-sucrose, and CO 2 evolved from endogenous carbon sources (roots and microbial respiration). 相似文献
13.
Synopsis Spatial patterns of resource use by small-bodied fishes in the San Juan River were examined using stable isotopes. Using δ 15N of fishes as an index of trophic position, our data suggest both native and non-native fishes primarily consumed macro-invertebrates.
The δ 13C of these fishes further suggested a detritus-based food web, from which most species fed on chironomids in low-velocity
habitats. A two-way ANOVA revealed a significant interaction between trophic level of fish species and longitudinal position
in the river. This interaction was primarily attributed to a decline in trophic level of non-native red shiner Cyprinella lutrensis, relative to other species, in upstream reaches of the river. In addition, ANCOVA results suggest trophic position of fishes
was dependent on channel type (primary vs. secondary), as there was less variability in resource use in secondary channels.
These data provided a spatial framework of trophic interactions that can be used to predict the outcome of management actions.
Overall, we confirmed high overlap in resource used between native and non-native fishes. However, spatial variation in trophic
interactions both longitudinally and laterally in the river present a challenge to resource managers attempting to managing
entire river systems. 相似文献
14.
Summary Seedlings of two mangrove species, Avicennia marina and Aegiceras corniculatum, were grown in a range of salinities and humidities in controlled environment chambers, and Phaseolus vulgaris plants were grown in the glasshouse. The fractionation of carbon isotopes in the three species was correlated with the ratio of intercellular and ambient partial pressures of CO 2. The results are consistent with fractionation being due both to diffusion in air and to carboxylation in the leaf. It was concluded that the latter process discriminates against 13CO 2 relative to 12CO 2 by about 27. 相似文献
15.
We evaluated the effects of ecosystem composition and structure (species richness and diversity, cover and spatial attributes of vegetation), abiotic factors (climate and topographical features) and the condition of the bare-ground areas (evaluated using soil-surface indicators) on the performance of Stipa tenacissima [evaluated using foliar 13C, 15N, nitrogen concentration and the carbon-to-nitrogen (C:N) ratio] in 15 steppes of SE Spain. Foliar 13C values of S. tenacissima showed a low degree of variation in the studied steppes, with average values ranging from –24.1 to –22.9. Higher variation was found in the 15N values, which ranged from –5.5 to –2.4. The nitrogen concentration and the C:N ratio varied between 5.0 and 8.0 mg g –1, and between 55.4 and 85.3, respectively. The 13C values became less negative with increasing spatial aggregation of perennial vegetation, while the C:N values increased with increasing perennial vegetation cover. The 15N values became more negative with increasing infiltration in the bare-ground areas, but the nitrogen concentration was not related to any of the environmental variables measured. Our results suggest that the relative importance of ecosystem structure and soil-surface conditions in the bare ground areas was higher than that of abiotic factors as determinants of the performance of S. tenacissima. The results also show that even subtle changes in these ecosystem features may lead to modifications in plant performance in semiarid S. tenacissima steppes, and thus to modifications in the associated ecosystem functions in the mid- to long-term. 相似文献
16.
Skeletal δ 13C levels in symbiotic reef corals are believed to be predominantly influenced by metabolic fractionation. Therefore, environmental
variables influencing coral metabolism should also affect skeletal δ 13C levels. To test this hypothesis, we measured the effects of light (which drives photosynthesis) and relative zooplankton
levels (heterotrophy) on skeletal δ 13C values in the corals Pavona clavus and P. gigantea at two depths (1 m and 7 m). For both species, decreases in light or increases in zooplankton resulted in significant decreases
in skeletal δ 13C levels. A significant decrease in δ 13C values with depth was observed in Pavona gigantea only. Thus, light and zooplankton directly affect coral skeletal δ 13C values, supporting the hypothesis that metabolic fractionation significantly contributes to skeletal δ 13C levels. Simultaneous decreases in both light and zooplankton resulted in decreases in skeletal δ 13C values, reflecting decreases in light. In Pavona clavus, intra-annual variation in skeletal δ 13C values over one year correlated with seasonal changes in irradiance. Further study is needed to resolve how skeletal δ 13C values vary at intermediate levels of irradiance and zooplankton, and in other coral species.
Accepted: 14 July 1998 相似文献
18.
Complete panmixia across the entire range of a species is a relatively rare phenomenon; however, this pattern may be found in species that have limited philopatry and frequent dispersal. American white pelicans ( Pelecanus erythrorhyncos) provide a unique opportunity to examine the role of long-distance dispersal in facilitating gene flow in a species recently reported as panmictic across its broad breeding range. This species is also undergoing a range expansion, with new colonies arising hundreds of kilometers outside previous range boundaries. In this study, we use a multiple stable isotope ( δ2H, δ13C, δ15N) approach to examine feather isotopic structuring at 19 pelican colonies across North America, with the goal of establishing an isotopic basemap that could be used for assigning individuals at newly established breeding sites to source colonies. Within-colony isotopic variation was extremely high, exceeding 100‰ in δ2H within some colonies (with relatively high variation also observed for δ13C and δ15N). The high degree of within-site variation greatly limited the utility of assignment-based approaches (42% cross-validation success rate; range: 0–90% success). Furthermore, clustering algorithms identified four likely isotopic clusters; however, those clusters were generally unrelated to geographic location. Taken together, the high degree of within-site isotopic variation and lack of geographically-defined isotopic clusters preclude the establishment of an isotopic basemap for American white pelicans, but may indicate that a high incidence of long-distance dispersal is facilitating gene flow, leading to genetic panmixia. 相似文献
19.
For 383 Poaceae species harvested over the Japanese islands and stored as herbarium specimens along several decades, we determined
C 3 and C 4 types of photosynthesis from leaf stable carbon isotope ratio (δ 13C). Then, we sought the relationships between C 4 species richness and climatic factors or habitat types. Except for the two Panicum species ( P. lanuginosum and P. scoparium) having the possibility of C 3–C 4 intermediate, 227 and 154 species were classified into C 3 and C 4. The C 4 species richness increased from northern to southern islands in Japan, positively correlated with mean annual air temperature.
Greater C 4 species richness in the seashore habitats, and smaller C 4 species richness in the shaded, wet and highland habitats would be related to the photosynthetic responses to local environmental
factors such as irradiance level and temperature regime. No difference of leaf δ-value of C 3 Poaceae was obtained between the habitats with different soil water availability, suggesting the less importance of soil
water availability on leaf water-use efficiency in C 3 Poaceae species in Japan having humid climate. Additionally, possible effects of human activity around the harvested time
or site on leaf δ-value were estimated, because the habitat includes the sites with high human activity. Leaf δ-value was
decreased with sampling year, and it was higher in the densely inhabited district for both C 3 and C 4. They are probably due to a historical decrease in the atmospheric δ-value via increasing human activity, and high gas emission
at the districts of high human density. 相似文献
20.
The effect of increased salinity on photosynthesis was studied in leaves of Plantago maritima L. that developed while plants were at low and high NaCl levels. In leaves that developed while plants were grown at 50 mol·m -3, exposure to 200 and 350 mol·m -3 NaCl resulted in reductions in net CO 2 assimilation and stomatal conductance. The decline in CO 2 assimilation in plants at 200 and 350 mol·m -3 NaCl occurred almost exclusively at high intercellular CO 2 concentrations. The initial slope of the CO 2 assimilation-intercellular CO 2 ( A-C
i) curve, determined after salinity was increased, was identical or very similar to that measured initially. In contrast to the reductions observed in CO 2 assimilation, there were no significant differences in O 2 evolution rates measured at 5% CO 2 among leaves from plants exposed to higher salinity and plants remaining at low salinity.Leaves that developed while plants were at increased salinity levels also had significantly lower net CO 2 assimilation rates than plants remaining at 50 mol·m -3 NaCl. The lower CO 2 assimilation rates in plants grown at 200 and 350 mol·m -3 NaCl were a result of reduced stomatal conductance and low intercellular CO 2 concentration. There were no significant differences among treatments for O 2 evolution rates measured at high CO 2 levels. The increased stomatal limitation of photosynthesis was confirmed by measurements of the 13C/ 12C composition of leaf tissue. Water-use efficiency was increased in the plants grown at high salinity.Abbreviations and symbols
A
net CO 2 assimilation rate
-
C
a
ambient CO 2 concentration
-
C
i
intercellular CO 2 concentration
- 13C
isotopic ratio ( 13C/ 12C) expressed relative to a standard
- RuBP
ribulose-1,5-bisphosphate 相似文献
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