哺乳动物化石牙齿釉质的碳,氧同位素组成与古气候重建方面的研？…

哺乳动物化石牙齿釉质能有效地抵抗成岩作用的影响,并保存原始的碳、氧稳定同位素组成信息。通过对食草类哺乳动物化石牙齿釉质同位素组成的分析可以重建这些动物生存时代的古气候。釉质碳酸盐的碳同位素组成响应于取食植物的碳同位素组成,藉此可以恢复陆地生态系统中Ｃ３和Ｃ４植物的分布比例,这个比例主要受控于大气的ＣＯ２水平、气压和光照等因素,与不同的纬度带和气候带有关,釉质磷酸盐的氧同位素组成响应于饮用水的氧同位     

小哺乳动物化石牙齿釉质碳、氧同位素测试方法简介及应用前景

探讨古环境和古气候变化与哺乳动物演化之间的关系是目前古生物学研究领域中的一个热点,而哺乳动物化石牙齿釉质的碳、氧同位素分析是恢复古环境和古气候的一个重要手段。以往的哺乳动物化石牙齿釉质稳定同位素分析多集中在大哺乳动物化石,这主要是受到技术手段的限制,所需的样品量较大所决定的。但最近几年随着激光和离子显微探针技术的应用,对小哺乳动物化石(如啮齿类和兔形类)的牙齿釉质碳、氧同位素的分析和应用日趋成熟和广泛。除了传统的化学处理方法之外,对小哺乳动物化石牙齿釉质碳、氧同位素的分析还有以下三种方法:1)激光剥蚀气相色谱/同位素比值质谱分析;2)直接激光氟化技术;3)离子显微探针技术(SHRIMPII)。这些技术需要的样品量少,对标本的破损小,准确度和精密度高,所以在小哺乳动物化石和一些珍贵标本(如古人类化石)的稳定同位素分析中起到了重要作用。相对于大哺乳动物化石,小哺乳动物化石数量多、演化速度快,更能反映多个层位长时间序列的古环境和气候变化;而且小哺乳动物通常没有长距离迁徙的行为,栖息地局限,所以更能准确反映化石埋藏地点的古环境和气候状况。     

环境条件对植物稳定碳同位素组成的影响

植物稳定碳同位素技术是近年兴起的一项快速、可靠的技术。利用稳定碳同位素技术可以揭示碳同化的过程的许多方面的信息。1 3C和1 2 C同位素效应 ,使它们在进行碳循环时发生稳定碳同位素的分馏。植物光合作用过程中CO2 经气孔扩散分差和RUBPCase及PEPCase羧化分馏是造成植物稳定碳同位素比率 (R =1 3C/ 1 2 C)不同于源CO2 中碳同位素比率的主要原因。遗传因素和环境因子同时决定植物碳同位素组成。植物稳定碳同位素技术同时还是古气候重建和预测未来环境变化的理论基础。本文综述了光照、温度、水分、二氧化碳、矿质营养、盐分和大气污染物等环境因素对植物稳定碳同位素组成影响方面的研究进展。     

环境条件对植物稳定碳同位素组成的影响

植物稳定碳同位素技术是近年兴起的一项快速、可靠的技术。利用稳定碳同位素技术可以揭示碳同化的过程的许多方面的信息。13C和12C同位素效应,使它们在进行碳循环时发生稳定碳同位素的分馏。植物光合作用过程中CO2经气孔扩散分差和RUBPCase及PEPCase羧化分馏是造成植物稳定碳同位素比率(R=13C/12C)不同于源CO2中碳同位素比率的主要原因。遗传因素和环境因子同时决定植物碳同位素组成。植物稳定碳同位素技术同时还是古气候重建和预测未来环境变化的理论基础。本文综述了光照、温度、水分、二氧化碳、矿质营养、盐分和大气污染物等环境因素对植物稳定碳同位素组成影响方面的研究进展。     

宁夏同心中中新世三种植食性哺乳动物牙齿碳同位素分析

宁夏同心中中新世Platybelodondanovicheni,Amebelodontobieni和Stephanocemasthomsoni化石牙齿的δ1 3C值为 - 8.7‰～ - 1 0 .3‰ ,说明这些动物可能以δ1 3C值为 - 2 0 .7‰～ - 2 5 .3‰的C3植物作为主要食物来源。根据齿冠高低与取食嫩叶或硬草的关系 ,这三种动物的低冠齿所指示的食性支持了牙齿釉质的碳稳定同位素所指示的食性。     

青藏高原东部典型高山植物叶片δ13C的季节变化

通过对青藏高原高寒草甸生态系统28种高山植物叶片不同月份稳定碳同位素组成的测定,研究植物δ 13C值在不同季节变化及其与环境之间的关系,试图找出影响δ 13C值变化的关键环境因子.结果表明植物δ13C值在不同月份间有显著性差异(P<0.01),生长初期(6月)δ13C值明显高于生长末期(8月).植物的δ13C值变化主要是由于温度和降水引起的,随温度和降雨量降低而偏重.另外,不同生长期植物叶片的成熟度可能对植物δ13C的变化有一定的贡献.不同种植物稳定性碳同位素值变化差别很大,反应了不同植物对环境变化的不同响应.     

扫描电镜研究牙齿釉质的制样方法

<正> 釉质是动物体内最硬的组织,它被覆于几乎所有的哺乳动物牙齿冠面,由于它的硬度很高,大大提高了牙齿对食物的粉碎和咀嚼机能.多年来,人们利用各种仪器和方法对釉质的组织学结构和化学成分作了大量的分析和研究,为探讨釉质的发育,进化以及治疗牙齿疾病等方面的应用奠定了基础.扫描电镜用于牙齿微观结构的研究,扩展了人们对釉质结构的了解,越来越多的古生物学家和口腔医学专家认为釉质在动物的分类和系统发育研究中具有重要作用.扫描电镜由于其制样方法比较简单,放大倍数高、立体感强,可以直接观察样品表面结构等优点而更适合脊椎动物化石材料的研究工作.在国外,研究现生和化石脊椎动物牙齿微观结     

中国北方农牧交错带C3草本植物δ13C与温度的关系及其对水分利用效率的指示

由于植物稳定碳同位素组成(δ¹³C)综合反映了植物光合过程中C、H₂O交换的信息,因而从理论上讲它可以作为植物长期水分利用效率的潜在指标,并揭示与植物生理生态过程相联系的一系列气候环境信息。通过对中国北方农牧交错带400 mm等降水样带上28个科的118种C3草本植物叶片δ¹³C值的测定,探讨了C3草本植物δ¹³C和水分利用效率(WUE)对环境温度梯度变化的响应以及气候环境因素对其产生的影响,揭示了样带控制植物δ¹³C变化的主要环境因子。结果显示: 在400 mm降水带上C3植物δ¹³C分布区间为-31.5‰ -23.0‰,平均值为-27.6‰,分布范围与黄土区干旱-半干旱区C3草本植物一致。整体C3植物δ¹³C随年均温度和夏季均温升高分别变重0.14‰/℃和0.27‰/℃,指示植物WUE随大气温度升高而增加。但这仅是一种表象,温度与植物碳同位素的这种关系实质上是温度升高导致的土壤相对湿度(或湿润指数)降低造成水分胁迫进而影响植物碳同位素分馏的结果,植物可利用的有效水分是本样带植物碳同位素分馏的控制因子。5种C3广适性植物δ¹³C均随温度升高而变重,但变化幅度不同,而且它们之间平均δ¹³C值有显著差异,表明不同物种的水分利用状况对温度的响应不同,说明不同物种有不同适应环境变化的策略。此外,本结果还显示不同寿命的草本植物δ¹³C值以及用碳同位素表征的WUE表现出多年生草本>2年生草本>1年生草本(可能与不同寿命草本植物的根系分布和吸水能力有关),这与Ehleringer等在沙漠地区研究的结果一致,而与湿润气候区的结果相反,表明不同寿命的草本植物δ¹³C值和WUE的变化可能与当地水分条件有关。     

碳稳定同位素技术在植物水分胁迫研究中的应用

植物体的碳稳定同位素组成主要由植物本身的生物学特性决定 ,但环境胁迫对其影响也十分明显。综述了碳稳定同位素技术在研究植物水分利用效率、生物量高低及判断历史气候依据等研究领域的进展 ,阐明了植物体的 δ1 3C值对干旱、盐分及其它环境因素的变化所引起的水分胁迫的响应 ,并对碳稳定同位素对水分胁迫的响应机理进行了归纳和推断     

用天然13C丰度法评估贵州茂兰喀斯特森林区玉米地土壤中有机碳的来源

当森林生态系统转变成农田生态系统时,会把C4植物有机质导入到曾在C3植被下发育的土训中去,使土壤中含有来源不同的土壤有机质,引起碳同位素组成变化。因此,可以利用碳同位素来区分土壤有机质来源,实验结果表明,耕作几十年后原森林土壤有机质的含量仍占有主要地位,来源于原始C3植被的有机碳的比例为66.7％,但容易矿化的、对植物营养有效的有机质含量较低,这与当地的耕作方式有关,需要加强对植物残留物返回土壤工作的管理。     

Paleoenvironmental reconstruction of the Asbole fauna (Busidima Formation, Afar, Ethiopia) using stable isotopes

The Middle Pleistocene environmental and climatic conditions at Asbole, lower Awash Valley, Ethiopia were reconstructed using stable carbon and oxygen isotopic composition (¹³C, ¹⁸O) of fossil tooth enamel coupled with faunal abundance data. We analyzed the isotopic composition of a total of 80 herbivorous tooth enamel samples from 15 mammalian taxa, which archive the dietary preferences and drinking behavior from the “Asbole faunal zone”. The carbon isotopic data signify a wide range of foraging strategies, across the entire spectrum of pure C4 to C4-dominated diet, mixed C3/C4 diet and C3-dominated diet. The oxygen isotopic enrichment between evaporation sensitive and insensitive taxa (?_ES-EI) is 3.7‰ which provides an estimate of the mean annual water deficit of the Middle Pleistocene at Asbole of 1470 mm, a value characteristic of modern arid landscapes in this part of the Awash Valley. The isotopic data coupled with faunal abundance data indicate an arid C4-dominated open-vegetated region, with an abundance of forest-dwelling primates that identify the presence of gallery forests flanking tributary streams to the paleo-Awash River. Thus, with these combined methodologies, it is possible to explicate a more detailed character of the “mosaic” of environments characteristic of Neogene savanna ecosystems. These findings, clearly indicate the importance of avoiding oversimplification of Pleistocene environmental reconstructions, based on single proxies at isolated localities.     

Climatic significance of isotope ratios

The hydrogen and oxygen isotope ratios of water, which can be measured by Isotope Ratio Mass Spectrometry (IRMS), exhibit climatic dependencies and are commonly exploited in hydrogeology. More generally, the overall carbon or hydrogen isotope ratios of plant organic matter, and in particular of tree-ring cellulose, have been frequently used for climatic reconstruction. However, since many physicochemical and biochemical fractionation phenomena are likely to contribute to the isotopic values, the interpretation of the climatic significance of isotopic parameters is not always straightforward. In the case of hydrogen and oxygen for instance, the climatic profile of the source meteoric water is not simply transferred to leaf water and many steps of the biosyntheses are accompanied by kinetic and thermodynamic isotope effects that depend on the individual mechanistic pathways. The information brought about by overall isotope ratios determined by IRMS is averaged over all fractionation effects undergone at the different molecular positions. In contrast, the NMR investigation of Site-specific Natural Isotope Fractionation (SNIF-NMR) gives simultaneous access to isotope ratios specific to individual positions in the molecule. Since the different atoms do not necessarily exhibit the same climatic dependency, the method provides complementary responses to the environmental conditions. In particular, the isotopic parameters of ethanol and water obtained by fermenting sugars in standardized conditions reflect climatic influences which took place at different periods of plant growth. As a consequence, statistical analyses based on multi-site isotopic variables provide powerful criteria for distinguishing geographical regions of cultivation characterized by different climatic features. Although the sensitivity to climatic variations is the most pronounced for plant water and for sugars formed at the first step of photosynthesis, other components such as lipids or minor metabolites also exhibit climatic dependencies. The combination of isotopic values pertaining to different atomic species and either averaged over the whole molecule (IRMS) or associated with different molecular sites (SNIF-NMR), provides complementary criteria, which can be exploited in terms of both climatic significance and mechanistic pathways of the individual atoms.     

Effects of Global Warming on Ancient Mammalian Communities and Their Environments

Background

Current global warming affects the composition and dynamics of mammalian communities and can increase extinction risk; however, long-term effects of warming on mammals are less understood. Dietary reconstructions inferred from stable isotopes of fossil herbivorous mammalian tooth enamel document environmental and climatic changes in ancient ecosystems, including C₃/C₄ transitions and relative seasonality.

Methodology/Principal Findings

Here, we use stable carbon and oxygen isotopes preserved in fossil teeth to document the magnitude of mammalian dietary shifts and ancient floral change during geologically documented glacial and interglacial periods during the Pliocene (∼1.9 million years ago) and Pleistocene (∼1.3 million years ago) in Florida. Stable isotope data demonstrate increased aridity, increased C₄ grass consumption, inter-faunal dietary partitioning, increased isotopic niche breadth of mixed feeders, niche partitioning of phylogenetically similar taxa, and differences in relative seasonality with warming.

Conclusion/Significance

Our data show that global warming resulted in dramatic vegetation and dietary changes even at lower latitudes (∼28°N). Our results also question the use of models that predict the long term decline and extinction of species based on the assumption that niches are conserved over time. These findings have immediate relevance to clarifying possible biotic responses to current global warming in modern ecosystems.     

Small‐mammal isotope ecology tracks climate and vegetation gradients across western North America

Stable carbon, nitrogen, hydrogen and oxygen isotopes have been used to infer aspects of species ecology and environment in both modern ecosystems and the fossil record. Compared to large mammals, stable isotopic studies of small‐mammal ecology are limited; however, high species and ecological diversity within small mammals presents several advantages for quantifying resource use and organism–environment interactions using stable isotopes over various spatial and temporal scales. We analyzed the isotopic composition of hair from two heteromyid rodent species, Dipodomys ordii and Perognathus parvus, from localities across western North America in order to characterize dietary variation in relation to vegetation and climatic gradients. Significant correlations between the carbon isotopic composition (δ¹³C) of these species and several climatic variables imply that seasonal temperature and precipitation control the composition and distribution of dietary resources (grass seeds). Our results also suggest a moisture influence on the nitrogen isotopic composition (δ¹⁵N) of heteromyid diets. Population‐ and species‐level variation in δ¹³C and δ¹⁵N values record fine‐scale habitat heterogeneity and significant differences in resource use between species. Using classification and regression‐tree techniques, we modeled the geographic variation in heteromyid δ¹³C_diet values based on 10 climatic variables and generated an isotope landscape model (‘isoscape’). The isoscape predictions for δ¹³C_diet differ from expectations based on observed C₄ distributions and instead indicate that D. ordii and P. parvus record seasonally abundant grass resources, with additional model deviations potentially attributed to geographic variation in dietary selection. The oxygen and hydrogen isotopic composition of D. ordii is enriched relative to local meteoric water and suggests that individuals rely on highly evaporated water sources, such as seed moisture. Based on the climatic influences on vegetation and diet documented in this study, the isotopic composition of small mammals has high potential for recording ecological responses to environmental changes over short and long time scales.     

Natural deuterium and oxygen-18 enrichment in leaf water of cotton plants grown under wet and dry conditions: evidence for water compartmentation and its dynamics

Abstract. Significant differences in leaf water oxygen and hydrogen isotopic composition were observed between cotton plants grown under wet and dry conditions. The magnitude of the differences could be fully explained by the conventional model that describes the isotopic composition of an evaporating water pool under steady state conditions. The results indicate that leaf water isotopic composition is strongly influenced by transpiration rate via its effects on relative humidity adjacent to the leaf surface and on the isotopic composition of the air moisture. Our application of the model, however, provides evidence that leaf water must consist of a mixture of several isotopically distinct pools. These pools are suggested to reside in the symplast, in the cell walls and intercellular spaces and in the veins. A model is proposed suggesting that only the water residing in the cell walls and the intercellular spaces (the transpiration pool) interacts directly with the external environment. The large symplastic pool responds to the external environment to a limited extent via its relatively slow exchange with water in the transpiration pool. It is likely that the isotopic composition of water in the symplastic pool is strongly buffered against shortterm environmental variations, a possibility that would have important implications for the isotopic conditions under which organic matter biosynthesis occurs.     

Pedogenic carbonate cutans on clasts in soils as a record of history of grassland ecosystems

Pedogenic carbonate cutans (coatings, pendants, rinds) on coarse clasts are common in stony soils of arid and semi-arid regions dominated by open vegetation. This paper gives an overview of the potential of the carbonate cutans for paleograssland research using data from literature and personal observations. Carbonate coatings are stratified into distinct microlamina, which can provide a record of local environmental changes. Lamina made of a rather pure calcium carbonate with better formed and parallel oriented crystals seem to be indicative of relatively dry phases that were less favorable for biological activity. A high content of admixtures, poorer formed and randomly oriented calcite crystals presumably mark wetter periods characterized by climatic amelioration. At a most general level, δ¹³C of the cutan carbonate can provide information on the type of photosynthesis of local vegetation, whereas δ¹⁸O in carbonate material of the coatings correlates with oxygen isotopic composition of precipitation water at the site and is sensitive to fluctuations in temperature. To obtain chronological evidence on cutan formation the ¹⁴C and Th/U methods can be applied with certain limitations. Additionally, cutan growth rates can be used to evaluate the age of these features.     

Stable isotopes data (delta13C, delta15N) from the cave bear (Ursus spelaeus): a new approach to its palaeoenvironment and dormancy

Palaeoclimatic data that can be extracted from the isotopic signatures of delta13C and delta15N, which are found in fossil bone collagen, should be analysed according to the specific metabolism of each species. Although Ursus spelaeus is an extinct species, its metabolism is assimilated to current, closely related species of bear. In this study, bone collagen isotopic signatures (delta13C and delta15N) of cave bears from Late Pleistocene Alpine sites were compared to those that have already been documented. The delta13C signature did not seem to follow a systematic trend according to climatic conditions, probably as a consequence of the high variability present in the values of C3 plants, which were the basis of feeding. On the contrary, the delta15N signature displayed higher values in sites corresponding to colder periods in which the delta15N signature appeared to be dominated by the physiology of dormancy. Then, due to the reuse of urea in synthesizing amino acids, the delta15N signature systematically increased along with dormancy duration. This was related to the length of winter and, in turn, depended on climate.     

Isotopologue distributions of peptide product ions by tandem mass spectrometry: quantitation of low levels of deuterium incorporation

Protonated molecular peptide ions and their product ions generated by tandem mass spectrometry appear as isotopologue clusters due to the natural isotopic variations of carbon, hydrogen, nitrogen, oxygen, and sulfur. Quantitation of the isotopic composition of peptides can be employed in experiments involving isotope effects, isotope exchange, and isotopic labeling by chemical reactions and in studies of metabolism by stable isotope incorporation. Both ion trap and quadrupole-time of flight mass spectrometry are shown to be capable of determining the isotopic composition of peptide product ions obtained by tandem mass spectrometry with both precision and accuracy. Tandem mass spectra of clusters of isotopologue ions obtained in profile mode are fit by nonlinear least squares to a series of Gaussian peaks which quantify the Mn/M0 values which define the isotopologue distribution (ID). To determine the isotopic composition of product ions from their ID, a new algorithm that predicts the Mn/M0 ratios and obviates the need to determine the intensity of all of the ions of an ID is developed. Consequently a precise and accurate determination of the isotopic composition of a product ion may be obtained from only the initial values of the ID, however, the entire isotopologue cluster must be isolated prior to fragmentation. Following optimization of the molecular ion isolation width, fragmentation energy, and detector sensitivity, the presence of isotopic excess (2H, 13C, 15N, 18O) is readily determined within 1%. The ability to determine the isotopic composition of sequential product ions permits the isotopic composition of individual amino acid residues in the precursor ion to be determined.     

Temperature effect on leaf water deuterium enrichment and isotopic fractionation during leaf lipid biosynthesis: results from controlled growth of C3 and C4 land plants

The hydrogen isotopic ratios ((2)H/(1)H) of land plant leaf water and the carbon-bound hydrogen of leaf wax lipids are valuable indicators for climatic, physiological, metabolic and geochemical studies. Temperature will exert a profound effect on the stable isotopic composition of leaf water and leaf lipids as it directly influences the isotopic equilibrium (IE) during leaf water evaporation and cellular water dissociation. It is also expected to affect the kinetics of enzymes involved in lipid biosynthesis, and therefore the balance of hydrogen inputs along different biochemical routes. We conducted a controlled growth experiment to examine the effect of temperature on the stable hydrogen isotopic composition of leaf water and the biological and biochemical isotopic fractionations during lipid biosynthesis. We find that leaf water (2)H enrichment at 20°C is lower than that at 30°C. This is contrary to the expectation that at lower temperatures leaf water should be more enriched in (2)H due to a larger equilibrium isotope effect associated with evapotranspiration from the leaf if all other variables are held constant. A hypothesis is presented to explain the apparent discrepancy whereby lower temperature-induced down-regulation of available aquaporin water channels and/or partial closure of transmembrane water channel forces water flow to "detour" to a more convoluted apoplastic pathway, effectively increasing the length over which diffusion acts against advection as described by the Péclet effect (Farquhar and Lloyd, 1993) and decreasing the average leaf water enrichment. The impact of temperature on leaf water enrichment is not reflected in the biological isotopic fractionation or the biochemical isotopic fractionation during lipid biosynthesis. Neither the biological nor biochemical fractionations at 20°C are significantly different from that at 30°C, implying that temperature has a negligible effect on the isotopic fractionation during lipid biosynthesis.     

Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Paleosol carbonates from trenches excavated as part of a landscape-scale project in Bed I of Olduvai Gorge, Tanzania, were analyzed for stable carbon and oxygen isotopic composition. The approximately 60,000-year interval ( approximately 1.845-1.785 Ma) above Tuff IB records evidence for lake and fluvial sequences, volcanic eruptions, eolian and pedogenic processes, and the development of a fluvial plain in the western margin of the basin. Significant temporal variation in the carbonate delta(18)O values records variation of local precipitation and supports the shifts in climatic conditions interpreted from the lithologic record. During this period, carbonate delta(13)C values varied between depositional facies indicating that the paleolandscape supported a local biomass of about 40-60% C(4) plants within a mosaic of grassy woodlands and wooded grasslands. The lithologic and stable isotope record in this small lake basin indicates the area was much wetter, with more woody C(3) plants, during this interval than is the semi-arid area today. The record also reflects the variation in climatic conditions (wet/dry) documented by other global climate proxies for this time.