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1.
Aims The optimal patterns of plant community for water use and nutrient utilization, the responses of soil carbon and nitrogen turnover processes to forest succession, and the mechanisms of soil organic carbon accumulation, are three critical issues in forest ecosystem study. It is difficult to accurately detect these ecological processes with conventional methodologies in the short term, yet the application of 13C and 15N natural abundance technique may yield important information about these processes. Methods This study was conducted in Dinghushan Biosphere Reserve. We investigated the natural isotopic abundance of both 13C and 15N of plant-soil continuum along a successional gradient from Pinus massoniana forest (PF) to coniferous and broad-leaved mixed forest (MF), and monsoon evergreen broad-leaved forest (BF). We also analyzed the correlations of foliar stable carbon isotope ratio ( δ13C) and stable nitrogen isotope ratio ( δ15N) with foliar elemental contents and the variations of soil δ13C and δ15N along soil profiles at different successional stages. Important findings A significant positive correlation between foliar δ13C and foliar C:N was observed. In both litter and soil, the δ13C values tended to decrease along the forest succession, with the order as PF > MF > BF. Foliar δ15N was positively correlated with foliar N content. The δ15N values of litter and upper soil (0-10 cm) increased with successional status. Both soil δ13C and δ15N values increased with increasing soil depth at all three forests. Our results imply that 1) trade-off between water use efficiency and nitrogen use efficiency did not necessarily exist in subtropical forests of China; 2) the application of isotopic technique could assist understanding of the mechanisms of soil carbon accumulation in subtropical forests, especially in old-grow forests; 3) the 15N natural abundance of plant-soil continuum could be a potential indicator of soil nitrogen availability and ecosystem nitrogen saturation status. 相似文献
2.
植物群落对水分利用和养分利用的优化策略, 土壤碳周转和氮循环过程对演替变化如何响应, 森林土壤有机碳积累机制等都是森林生态学需要解决的关键问题。然而, 这些生态学过程的变化在短时间内通过传统的研究手段难以被精确观测, 碳氮同位素( 13C、 15N)技术的应用或许能提供更多有价值的信息。该文通过对鼎湖山森林演替序列代表性群落——马尾松( Pinus massoniana)针叶林(PF)、针阔叶混交林(MF)和季风常绿阔叶林(BF)植物-土壤碳氮同位素自然丰度的测定, 分析了叶片稳定碳同位素比率( δ13C)和稳定氮同位素比率( δ15N)与其叶片元素含量的关系, 以及叶片-凋落物-土壤 δ13C、 δ15N在演替水平和垂直方向上的变化特征。结果显示: 1)主要优势树种叶片 δ13C与其C:N极显著正相关( p < 0.01), 凋落物和各层土壤 δ13C均表现为PF > MF > BF, 沿演替方向逐渐降低; 2)叶片 δ15N与叶片N含量正相关( p = 0.05), 凋落物和表层土壤(0-10 cm) δ15N沿演替方向逐渐增大; 3)不同演替阶段土壤 δ13C、 δ15N均沿垂直剖面呈现增大的趋势。结果表明: 南亚热带地区植物群落的发展并不一定受水分利用和氮素利用的补偿制约; δ13C自然丰度法的应用有助于森林土壤有机碳积累机制, 尤其有助于成熟森林土壤“碳汇”机制的阐释; 植物-土壤 δ15N值可作为评估土壤氮素有效性和生态系统“氮饱和”状态的潜在指标。 相似文献
3.
Stable isotope analyses of fossil teeth and other authigenic minerals have been used to reconstruct the paleoenvironment and paleoelevation of the Tibetan Plateau. The accuracy of such reconstructions is limited by the lack of a comprehensive modern comparative database from the region. We analyzed the carbon and oxygen isotopic compositions ( δ13C and δ18O values) of tooth enamel from modern herbivores, the δ13C values of grasses and the δ18O values of water samples collected from various elevations within the Tibetan Plateau to examine their relationships with modern environment/elevation. The δ13C values of enamel samples from horses, yaks and goats display a narrow range of variation, with a mean of − 10.7 ± 1.4‰ ( n = 301), indicating that these modern herbivores were feeding predominantly on C3 plants, consistent with the current dominance of C3 vegetation in the region. Some of the samples have δ13C values between − 7.3 and − 10‰. Although these higher δ13C values could suggest consumption of some C4 plants by the animals, the lack of significant seasonal δ13C variations within individual teeth indicates that these higher enamel δ13C values are due to consumption of C3 plants experiencing water stress and/or some CAM plants rather than C4 plants. Our data show that the conservative “cut-off” δ13C value for a pure C3 diet within the Tibetan Plateau should be − 8‰ for modern herbivores and − 7‰ (or even − 6.5‰) for fossils if the region was as arid in the past as today. In contrast to the small intra-tooth δ13C variations within individual teeth, serial enamel samples display large intra-tooth δ18O variations, reflecting seasonal variations in the δ18O of meteoric water. The mean δ18O values of tooth enamel from yaks and horses show a strong correlation with water δ18O values, confirming that the δ18O of tooth enamel from obligate drinker generally tracks the δ18O of meteoric water. Unfortunately, elevation alone cannot explain most of the variance in the δ18O of precipitation and tooth enamel, suggesting that quantitative reconstruction of the paleoelevation of the Tibetan Plateau using re-constructed δ18O values of paleo-meteoric water from fossil enamel or other oxygen-bearing minerals is not warranted. For a given environment, horses have the lowest enamel– δ18O values while goats display the highest enamel– δ18O values among the species studied. The large inter-species δ18O variations are likely due to differences in physiology and diet/drinking behavior of the animals. This underscores the importance of species-specific studies when interpreting δ18O data of fossil mammalian teeth in a stratigraphic sequence as a record of paleoclimate changes. 相似文献
4.
Aims Phragmites australis marshes in Tianjin play an important role in ecosystem functioning. Wetlands of Tianjin municipality have been suffering from serious nitrogen loading, salinization and water shortage. The foliar stable carbon isotope ratio ( δ13C) is a good parameter which records environmental change information associated with the plant growth process, and reflects physiological and ecological responses of plants to environment changes. The objective of this study is to investigate the effects of environment stress on the leaf δ13C of P. australis in marsh wetlands in Tianjin municipality. Methods This study was conducted in Qilihai, Beidagang, and Dahuangpu marsh wetlands. We investigated the foliar δ13C of P. australis and sediment properties, and evaluated the relationships between the foliar δ13C and sediment environmental factors. Important findings 1) Foliar δ13C ranged from -26.3‰ to -23.6‰, with an average value of -25.8‰. 2) Sediment water and nitrogen status were the important factors affecting reed foliar δ13C. Foliar δ13C was negatively correlated to sediment relative water content, and positively correlated to sediment total nitrogen and available nitrogen content. In contrast, foliar δ13C was not significantly correlated to sediment salinity and phosphorus content. 3) Leaf δ13C were significantly positively correlated with leaf nitrogen content, and negatively correlated with leaf carbon and nitrogen ratio across all site. However, these relationships were not detected due to the wetland drainage at Qilihai site in August. Wetland drainage changed the plant water and nitrogen balance, and further affected water and nitrogen utilization strategies of P. australis. Moreover, wetland drainage had stronger effects on these processes than nitrogen loading and salinization. 相似文献
5.
天津芦苇( Phragmites australis)沼泽具有重要的生态功能。目前天津地区水体咸化、氮污染和水资源短缺问题严重, 显著影响了芦苇湿地的植物生理生态过程。植物稳定碳同位素组成(碳稳定同位素比值( δ13C))能够记录与植物生长过程相关联的环境变化信息, 反映植物对环境变化的生理生态适应特性。该研究调查了天津七里海、北大港和大黄堡湿地芦苇叶片的 δ13C分布特征, 探讨了影响该地区叶片 δ13C值变化的主要因素。研究表明: 1)天津芦苇湿地植物叶片 δ13C的变化范围在-26.3‰ - -23.6 ‰之间, 平均值为-25.8‰; 2)芦苇叶片 δ13C与底泥相对含水量呈显著负相关关系, 与底泥有效氮和全氮含量呈显著正相关关系, 而与底泥盐度和磷含量没有显著相关关系; 水分条件和底泥氮营养状况是影响叶片的 δ13C值变化的主要因素; 3)淹水条件下, 芦苇叶片 δ13C与叶片质量氮含量呈显著正相关关系, 与叶碳氮比呈显著负相关关系, 8月份七里海湿地干涸打破了此相关关系。当前环境压力下, 天津沼泽湿地干涸极大地改变了芦苇的氮、水平衡和植物对水、氮资源的利用策略, 而湿地干涸对该过程的影响要高于盐度和氮负荷增加。 相似文献
6.
Five positive carbon isotope excursions are reported from Platteville–Decorah strata in the Upper Mississippi Valley. All occur in subtidal carbonate strata, and are recognized in the Mifflin, Grand Detour, Quimbys Mill, Spechts Ferry, and Guttenberg intervals. The positive carbon isotope excursions are developed in a Platteville–Decorah succession in which background δ13C values increase upward from about −2‰ at the base to about 0‰ Vienna Pee Dee belemnite (VPDB) at the top. A regional north–south δ13C gradient, with lighter values to the north and heavier values to the south is also noted. Peak excursion δ13C values of up to +2.75 are reported from the Quimbys Mill excursion, and up to +2.6 from the Guttenberg excursion, although there are considerable local changes in the magnitudes of these events. The Quimbys Mill, Spechts Ferry, and Guttenberg carbon isotope excursions occur in units that are bounded by submarine disconformities, and completely starve out in deeper, more offshore areas. Closely spaced chemostratigraphic profiles of these sculpted, pyrite-impregnated hardground surfaces show that they are associated with very abrupt centimeter-scale negative δ13C shifts of up to several per mil, possibly resulting from the local diagenetic effects of incursions of euxinic bottom waters during marine flooding events. 相似文献
7.
In order to elucidate early Aptian marine paleotemperature evolution across the period of enhanced organic carbon (C org)-burial [Oceanic Anoxic Event (OAE) 1a], stable isotope analyses were performed on pelagic limestones at Deep Sea Drilling Project Site 463, central Pacific Ocean. The δ18O data exhibit a distinct anomaly by ~ − 2‰ spanning the OAE 1a interval (i.e., a ~ 6 m-thick, phytoplanktonic C org-rich unit constrained by magneto-, bio- and δ13C stratigraphy). Elucidation of paleotemperature significance of the δ18O shift is made by taking account of recent Sr/Ca evidence at the same section, which revealed that geochemical signals in carbonate-poor lithologies are relatively unaltered against burial diagenesis. By discriminating δ18O values from carbonate-poor samples (CaCO 3 contents = 5–30 wt.%), it appears that an abrupt rise in sea-surface temperatures (SSTs) by 8 °C (= − 1.7‰ shift in δ18O) occurred immediately before OAE 1a, whereas a cooling mode likely prevailed during the peak C org-burial. In terms of its stratigraphic relationship as to the C org-rich interval and to a pronounced negative δ13C excursion, as well as its timescale, the observed SST rise resembles those associated with the Paleocene–Eocene thermal maximum and, more strikingly, Jurassic Toarcian OAE. This observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism, which was likely initiated by the greenhouse effect via massive release of CH 4 or CO 2 from the isotopically-light carbon reservoir and terminated by a negative productivity feedback. 相似文献
8.
The Late Oligocene (25.8 Ma) Enspel Fossillagerstätte in Westerwald, Germany, contains a comprehensive fossil ecosystem preserved with specimens retaining morphological detail and a concentration of organic material. Stable carbon and nitrogen isotope analyses were used to examine the lacustrine ecosystem preserved in one stratigraphic horizon. These data suggest the presence of several trophic levels, including primary producers (diatoms and higher plants), primary consumers (e.g., tadpoles and insects), and secondary consumers (e.g., the fish species Paleorutilus enspelensis). Terrigenous and aquatic plants were associated with the lowest δ13C and δ15N values (mean plant = − 26.28‰ ± 0.45, 3.18‰ ± 1.04), primary consumers such as flies are one trophic level higher, and carnivores such as fish are yet another level higher. The δ15N values for P. enspelensis also showed enrichment in 15N with increasing body length, implying a shift in diet or feeding strategy with size. P. enspelensis and tadpole ( Pelobates decheni) samples showed intraorganism fractionation between ‘muscle’ and ‘bone’ tissues. Stable carbon and nitrogen isotope data from the measurement of components (shale, leaves and seeds) common to a number of different stratigraphic horizons showed significant variation between horizons. A number of the features of the stable isotopic data are similar to those relationships seen in modern ecosystems and therefore suggest that stable isotope analyses can contribute to understanding ancient ecosystems. 相似文献
9.
A procedure, based on measurement of the stable carbon isotope 13C, has been developed for determining the extent to which petroleum carbon is incorporated into soil organic matter (SOM) by humification of biomass produced during biodegradation of the petroleum in soil. We have shown that a crude oil having a δ 13C of-27.4%, when biodegraded in a soil containing SOM with a δ 13C of-15.7%, resulted in a change of the δ 13C of the bound SOM reflecting that of petroleum carbon. Comparison of five soil biodegradation tests using different amounts and types of fertilizer to stimulate biodegradation of the oil in this soil showed that the extent of the δ 13C change in the bound SOM varied with the extent of oil biodegradation observed. To obtain 13C data on the SOM, the residual petroleum was first removed by rigorous extraction with dichloromethane using a Soxhlet apparatus. The extracted soil was then combusted to release bound carbon as CO 2, which was analyzed for 13C. Where the SOM has a δ 13C similar to that of petroleum, 14C measurements of SOM would give similar results. This type of data, referred to as the petroleum “footprint” in the SOM, could be useful in identifying or confirming intrinsic biodegradation of petroleum in contaminated soil. 相似文献
10.
Carbon isotope changes during most of Late Ordovician time (from the mid-Caradoc Kinnekulle K-bentonite until the beginning of the Silurian) were investigated. As the corresponding sequence of rocks is stratigraphically nearly complete in Estonia, an attempt was made to use it to elaborate the general pattern of carbon isotope changes in the Late Ordovician. Complications were caused by several local or regional hiatuses in the middle and late Caradoc and Hirnantian. A total of 385 whole rock samples were studied from eight drill cores in northern and central Estonia. The following positive carbon isotope events were observed: (1) the mid-Caradoc excursion (peak δ13C value 2.2‰) in the uppermost part of the Keila Stage, also known in Sweden; (2) the first late Caradoc excursion (1.9‰) in the lower part of the Rakvere Stage; (3) the second late Caradoc excursion (2.4‰) in the upper part of the Nabala Stage; (4) the early Ashgill excursion (2.5‰) in the lowermost part of the Pirgu Stage; (5) the widely known large Hirnantian excursion (in Estonia the peak value reaches 6.7‰) in the Porkuni Stage. The study interval comprises a long (10 Ma) period characterized by low-magnitude carbon isotope changes and a following brief (2 Ma) interval with large changes. No obvious lithological preference for hosting the positive shifts was recorded. In principle, the δ13C values exceeding the background values may occur in all types of rocks present in a sedimentary basin. Several δ13C positive excursions (values 1.5‰ to 3‰) in the Mohawkian of North America are evidence that the minor Caradoc and early Ashgill δ13C positive shifts in Baltoscandia may have counterparts in Laurentia. If correctly correlated, these shifts may have global significance. The Hirnantian excursion is usually linked to a major glacial event, even if some carbon cycling mechanisms are not completely understood. The environmental causes suggested for the earlier minor shifts range from global climatic and glacial events to very local changes in basin regime and sea level. Our study supports the primary role of climatic or climatically triggered oceanic processes. 相似文献
11.
In southern Ontario, ooids are associated with two distinct facies associations in the Queenston Formation, the final stage of Late Ordovician (Ashgill) Taconic basin fill. One facies consists of thin ooid and bioclastic grainstones interbedded with mudrock, and lies near the base of the formation, and, in southwestern Ontario, also forms a local NW-thickening wedge near the middle of the formation. Ooids have radial-fibrous and radial-concentric fabrics (Type A), with chamosite, illite, and Fe-oxide laths at intercrystalline sites. Vertical lithologic and ooid abundance patterns indicate that thresholds to carbonate production were sensitive to changes in terrigenous sediment supply, sea level, circulation, accommodation space, and tectonism. Ooids in the second facies association are admixed with abraded fragments of open-marine biota, or occur burrow fills, within a <30-cm-thick interval of mudrock near the top of the preserved Queenston succession, a few metres below the Ordovician–Silurian unconformity. Ooids have radial concentric and crosscutting patchy microcrystalline fabrics (Type B). This unit may represent a transgressive or stillstand deposit modified by bioturbation. The extent of preserved fabric suggests that both ooid types were originally magnesian calcite, but Type A ooids underwent greater burial alteration. This is shown by crystalline mosaics that cross-cut relict primary fabrics; δ13C values (−1.82‰ to +0.67‰) and δ18O values (−4.46‰ to −10.57‰) more negative than marine calcite of similar age; Mn and Fe concentrations more elevated above expected marine values; and a luminescence similar to that of intergranular cements. Burial meteoric diagenesis was likely promoted by excellent permeability of the host sand. We interpret authigenic chamosite and Fe-oxide to reflect diagenesis of iron-bearing and clay detritus trapped during ooid growth. Type B ooids suffered less alteration: δ13C (+1.1‰ to +6.64‰) and δ18O (−3.04‰ to −4.81‰) values overlap the expected marine range, including 13C enrichment that occurs within the Hirnantian (latest Ordovician) excursion. Although Mn and Fe values are still higher than those of modern calcitic ooids, negligible luminescence suggests that recrystallization occurred in the presence of marine-derived pore fluids. Further burial alteration was inhibited due to low permeability of the host mud. Type A ooid facies in the Queenston Formation forms an ancient analogue for lesser known Quaternary ooid shoals peripheral to tropical deltaic systems. The facies of Type B ooids, while more enigmatic, may preserve a geochemical herald of latest Ordovician climate change. The presence of minor chamosite in Type A ooids defines a possible distal facies of the well-known oolitic ironstones of similar age in the mid-continental USA. 相似文献
12.
The preparation of a novel mononuclear complex of zirconium having an η8-bonded pentalene ligand and two η3-allyl groups is described. Its structure has been determined by 1H and 13C NMR spectroscopy. At room temperature some of the NMR signals are broadened, revealing that the compound is structurally dynamic. It is shown that the compound has C2 symmetry with the enantiomeric forms undergoing racemisation. 相似文献
13.
Stable carbon isotope analysis has become a key tool in functional ecology, yet considerable natural variability often limits the interpretations. In this study we document the spatial, taxonomic, temporal and tissue-specific δ13C variability in 10 tree species of a temperate European forest. The Swiss Canopy Crane provided access to the three dimensional space within 55 trees 30–35 m high representing the genera Acer, Carpinus, Fagus, Prunus, Quercus, Tilia, Abies, Larix, Picea and Pinus. The results from six broad-leaved and four conifer species (seven deciduous, three evergreen) documented that the species effect was not significant in contrast to tissue-specific and spatial differences in the canopy. Year-to-year differences were not large but still significant. Our analysis confirmed a significant difference between δ13C of foliage collected in the upper and lower canopy, but revealed no systematic differences with respect to azimuthal directions in tree crowns of the broad-leaved trees, as opposed to the conifers, which show clear differences between the sun-exposed and the shaded side. Tissue-specific differences were significant, despite surprisingly similar mean values for most tissue types. Such tissue effect was largely due to young branch xylem, which exhibited a systematic less negative deviation from the other tissue types. These findings were consistent across the species tested and provided some guidelines towards a representative sampling strategy for 13C analysis. 相似文献
14.
哈民忙哈遗址是迄今为止内蒙古乃至东北地区发现面积最大的一处史前聚落遗址,为重建当时的生产和生活情况、文化习俗甚至思想观念等都提供了弥足珍贵的实物资料。其中,重建该遗址先民的食物结构和生业经济,有助于揭示哈民忙哈遗址产生和兴盛的动因及科尔沁沙地史前文化的变迁过程。目前,多学科的研究成果已经初步显示哈民忙哈遗址先民的生业经济具有多样性,但各种生业模式的比重以及是否存在家畜饲养等问题还缺乏相应的了解。本文对该遗址87例人骨与18例动物骨骼进行了C、N稳定同位素分析,还原了人和动物的食物结构及生业经济面貌。结果显示,陆生野生动物的食物结构主要基于C 3植物类食物和少量的C 4农作物,而犬科动物则体现出家养动物的食谱特性:食物主要依赖C 4食物和人类食物残羹。C 4类粟黍农作物和以此饲喂的动物是该遗址先民的主要食物来源,其中粟黍农作物在食物结构中的地位尤其重要。在该遗址中,女性摄入相对较多的粟黍和相对较少的肉类,与男性在食物结构上存在显著差异。农耕、家畜饲养是先民最重要的经济行为,狩猎、渔猎和采集是生业的重要补充。 相似文献
15.
Octahedral tetraammineosmium(II) species are generated from their Os III precursors containing an amine ligand cis to a labile alcohol or triflate. These compounds undergo reversible β-hydride eliminations resulting in the formation of cis-η2-iminium hydride complexes. Judging from NMR data, the η2-iminium group in these products lies parallel to the osmium-hydride bond with the iminium carbon eclipsing the hydride. Attempts to form η2-arene complexes of an Os II ammine system bearing a stereogenic carbon are also described. 相似文献
16.
The sand dollar Dendraster excentricus is a facultative suspension feeder, which is relatively rare within the Order Clypeasteroida. Field studies of regulation of its feeding mode have been mostly conducted in exposed coastal habitats, where they are typically observed in an inclined position and oriented parallel to each other during suspension feeding. Physical (current speed and direction, reduction of drag and lift) and biological factors (increased efficiency of capture of particulates, and density) have been associated with regulation of its feeding mode in exposed coastal systems. We simultaneously measured the role of physical and biological factors in regulating the selection mode for feeding under varying tidal conditions in a shallow estuary in Baja California, Mexico. We used photographic records and direct sampling in fixed plots to determine the relationship between feeding behavior and environmental conditions. Current direction and speed, tidal level, density and content of organic matter in the water column and sediments were measured with respect to feeding mode (prone or inclined) and orientation relative to prevailing currents during spring and neap tides. Multiple regression analysis indicated that the percentage of inclined sand dollars was strongly and positively correlated only with tidal level at the densities found in the estuary (mean < 180 individuals m − 2); there was no relationship with current velocity, density, and organic matter content of the water. The prone position, indicative of deposit feeding, was largely limited to low tidal levels. We used circular statistics to determine whether the orientation of inclined sand dollars was correlated with current direction and speed. Sand dollars were only oriented parallel to the prevailing currents during the strongest currents of spring tides (> 20 cm s − 1). We did not observe the predominant oral:aboral configuration found in exposed coastal systems, which may be attributed to the relatively low densities of sand dollars in the exposed coastal environment (30-180 individuals m − 2), compared to protected coastal habitats (up to 1000 individuals m − 2). Our results suggest that regulation of the feeding mode of sand dollars in shallow and hydrodynamically complex estuarine systems differs from the feeding mode found in exposed coastal environments. 相似文献
17.
Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources. 相似文献
18.
Axial variation of latewood-widths and -stable isotopes ( δ13C and δ18O) of a single sessile oak tree ( Quercus petraea (Matt.) Liebl.) was analyzed. The influence of sampling height was found to be weak for both, latewood-widths and -stable isotopes in the latewood. The observed trends with stem-height show clearly that possible effects due to cambial aging are overrated by annual effects. In addition, relations between samples from different stem-heights are strong for identical calendar years while they are poor for identical cambial age. This indicates that samples from both, living trees and historical wood can be taken from any height position of a trunk or beam as long they are free from anatomical abnormities. Simple correlation and Gleichläufigkeit were used for validation. 相似文献
19.
Summary Subtidal sand dollars, Dendraster excentricus, assume an inclined posture under conditions of moderate water flow (10 cm s -1 to 2 m s -1). In this posture, when the test is in the usual position parallel to the water flow, the test acts as a lifting body. Analysis of the hydrodynamic characteristics of the sand dollar test was accomplished by slender body theory. Streamline curvature due to lift moves food particles in the direction of the feeding surface and enhances feeding efficiency. The position parallel to water flow is most advantageous to sand dollars in reversing flows, such as wave surge, whereas sand dollars in unidirectional flows can place the test at a slight angle to the water flow to increase lift. The high camber of sand dollars from a bay habitat characterized by low water velocities was interpreted as an adaptation allowing efficient lift production in low velocity flows; sand dollars from a protected outer coast location characterized by higher water velocities were significantly less cambered.Within sand dollar beds, the animals alter their spacing as a function of the water velocity. This movement is construed as a method for maintaining the optimal gap between sand dollars. Sand dollar tests induce mutual interference effects which vary with the configuration of the animals. In the prevalent configuration, sand dollars are able to take advantage of the streamline curvature induced by neighboring animals. The optimal gap increases as the square of the water velocity. At distances grater than or less than the optimal gap, feeding efficiency was shown to decrease from that at the optimal gap. 相似文献
20.
A small pond containing the charophyte Chara hispida was monitored over a one-year period for changes in growth, water chemistry, water level and stable isotopic composition. Chara growth was found to be seasonal, with maximum growth occurring from late April to July. During this period, pH rose to > 10 while the dissolved inorganic carbon (DIC) and calcium fell as a result of photosynthesis and calcification. Large gradients in pH, water temperature and irradiance were found within the Chara sward and measurements showed that most growth and photosynthesis occurred within the upper 20 cm of the water column. Chara oospore formation was also found to be seasonal but dependent upon environmental conditions. δ18Ow rose rapidly during summer as evaporation progressed and this was correlated with the δ18ODIC, and to some extent with δ18Oc of the Chara encrusted calcite. However, extreme isotopic disequilibrium was observed between the δ18Oc and the δ18Ow and also between the δ13Cc and the δ13CDIC. This arose from the high pH allowing atmospheric CO2 to enter the water and combine directly with OH−. It is concluded that, within shallow eutrophic lakes containing Chara swards, inferences of climate (e.g. air temperature) cannot be made from observations of the isotopic composition of Chara carbonates. However in combination with other geochemical data, disequilibrium events may be identifiable in ancient lake basins and taken as evidence for lake shallowing and/or eutrophication. 相似文献
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