影响C₄草本植物C/N比值变化的因素与土壤有机C积累的关系   总被引：6，自引：1，他引：6       下载免费PDF全文

朴河春  朱建明  余登利  冉景丞 《第四纪研究》2004,24(6):621-629

文章对采自贵州从低海拔的东部到高海拔的西部且大致平行的石灰岩和砂岩两地带均生长的3种C₄草本植物,即巴茅(Miscanthusfloridulus)、白茅(Imperatacylindrica)和类芦(Neyraudiareynaudiana),以及相对应的土壤表层样品,进行了营养元素和C同位素组成分析;研究营养元素含量随着海拔的不同而出现的变化趋势,以及这些元素之间的相互协变作用,尤其是Ca和N之间的相互协变作用对植物的N含量、C/N比值和^δ13C值的影响,以了解植物的C/N比值(指示植物残留物质量的一种标志)与土壤有机C积累的关系。研究结果表明,植物的N含量和^δ13C值具有随海拔的上升而显著增大趋势,而植物的C/N比值在砂岩地区虽有减小的趋势,在石灰岩地带则没有。对所研究的C4草本植物来说,在土壤pH值为5.8的中性条件下显示出Ca的最大吸收,因此,Ca与其他营养元素之间的协变模式在两种土壤类型中表现出相反的倾向,并存在土壤交换性Ca的边界浓度:当土壤可交换性Ca的含量为2.24mg/g,相应土壤的pH值在5.8以下时,随着土壤可交换性Ca浓度的增大,植物的N含量上升,而植物的C/N比值会显著降低;当Ca在边界浓度以上时,随着土壤可交换性Ca浓度的增大,植物的N含量下降,而植物的C/N比值有增加的趋势。由此可见,植物残留物的N含量和C/N比值受Ca元素含量的相  相似文献   

Late Holocene δC and pollen records of paleosalinity from tidal marshes in the San Francisco Bay estuary, California     

Frances Malamud-Roam  B. Lynn Ingram 《Quaternary Research》2004,62(2):134-145

Records of stable carbon isotopes (δ¹³C) are presented from cores collected from four San Francisco Bay marshes and used as a proxy for changes in estuary salinity. The δ¹³C value of organic marsh sediments are a reflection of the relative proportion of C₃ vs. C₄ plants occupying the surface, and can thus be used as a proxy for vegetation change on the marsh surface. The four marshes included in this study are located along a natural salinity gradient that exists in the San Francisco Bay, and records of vegetation change at all four sites can be used to infer changes in overall estuary paleosalinity. The δ¹³C values complement pollen data from the same marsh sites producing a paleoclimate record for the late Holocene period in the San Francisco Bay estuary. The data indicate that there have been periods of higher-than-average salinity in the Bay estuary (reduced fresh water inflow), including 1600-1300 cal yr B.P., 1000-800 cal yr B.P., 300-200 cal yr B.P., and ca. A.D. 1950 to the present. Periods of lower-than-average salinity (increased fresh water inflow) occurred before 2000 cal yr B.P., from 1300 to 1200 cal yr B.P. and ca. 150 cal yr B.P. to A.D. 1950. A comparison of the timing of these events with records from the California coast, watershed, and beyond the larger drainage of the Bay reveals that the paleosalinity variations reflected regional precipitation.  相似文献   

Holocene calcrete crust deposits on the moraine of Batura Glacier, northern Pakistan     

Tetsuya  Waragai 《Island Arc》2005,14(4):368-377

Abstract   Calcretes can be observed on the surface of old moraines around Batura Glacier in the upper Hunza Valley, Karakoram Mountains, Pakistan. They develop as a calcareous crust cementing small gravels under boulders. In order to understand the genesis of the calcrete crust, a variety of methods were employed: (i) study of mineralogy and geochemistry of a calcrete crust precipitated on the lateral moraine using X-ray diffractometer and electron probe microanalysis; (ii) analysis of solute chemistry of surface water and ice bodies around the Batura Glacier; and (iii) accelerator mass spectrometry ¹⁴C dating of the crust itself. The results indicate that the calcrete crust has definite laminated layers composed of a fine-grain and compact calcite layer, and a mineral fragment layer. The chemical composition of the calcite layer is approximately 60% CaO and 1% MgO. The mineral fragment layer consists of rounded grain materials up to 0.2 mm in diameter. It shows a graded bedding structure with fine grains of quartz, albite and muscovite. Meanwhile, as the Paleozoic Pasu limestone is distributed around the terminal of Batura Glacier, Ca cations dissolve in the melt water of the glacier. Accordingly, the calcrete crust is precipitated by decreases in CO₂ partial pressure from glacier ice and evaporation of the melt water, including high concentration of Ca²⁺ at ephemeral streams and small ponds stagnating between the moraine and glacial ice. On the basis of the AMS ¹⁴C age, the calcrete is considered to have formed approximately 8200 calibrated years bp under the Batura glacial stage.  相似文献   

Characterizing the properties of dissolved organic matter isolated by XAD and C-18 solid phase extraction and ultrafiltration   总被引：1，自引：0，他引：1  

Sara B. Schwede-Thomas  Yu-Ping Chin  Karl J. Dria  Patrick Hatcher  Edith Kaiser  Barbara Sulzberger 《Aquatic Sciences - Research Across Boundaries》2005,67(1):61-71

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长江口沉积物210Pb分布及沉积环境解释   总被引：19，自引：0，他引：19  

段凌云  王张华  李茂田  潘建明  陈中原  Yishiki Saito  Yutaka kanai 《沉积学报》2005,23(3):514-522

在长江河口潮滩、分流河道和水下三角洲共获得18个柱样,进行沉积学分析和210Pb测定,并对其中6根柱样进行137Cs测定。经研究发现,长江口外在水深25～30m,122°30′N,31°00′E附近存在一个泥质沉积中心,沉积速率达2.0～6.3cm/yr。另外,在潮滩和涨潮槽也获得较高沉积速率,其中南汇和横沙岛潮滩沉积速率(1.03～1.94cm/yr)高于崇明东滩(0.51～0.76cm/yr),涨潮槽沉积速率也达0.86cm/yr。此外,在石洞口、南汇、九段沙潮滩和三角洲前缘有部分柱样未获沉积速率,推测为沉积环境不稳定或沉积速率过快所致。  相似文献   

Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America     

Bruce J. MacFadden 《Quaternary Research》2005,64(2):113-124

The toxodont megaherbivores Toxodon and Mixotoxodon were endemic to South and Central America during the late Quaternary. Isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat. Tooth enamel carbon isotope data from six regions of South and Central America indicate significant differences in toxodont diet and local vegetation during the late Quaternary. Toxodonts ranged ecologically from C₃ forest browsers in the Amazon (mean δ¹³C = −13.4‰), to mixed C₃ grazers and/or browsers living either in C₃ grasslands, or mixed C₃ forested and grassland habitats in Honduras (mean δ¹³C = −9.3‰), Buenos Aires province, Argentina (δ¹³C = −8.7‰), and Bahia, Brazil (mean δ¹³C = −8.6‰), to predominantly C₄ grazers in northern Argentina (δ¹³C = −4.4‰), to specialized C₄ grazers in the Chaco of Bolivia (δ¹³C = −0.1‰). Although these toxodonts had very high-crowned teeth classically interpreted for grazing, the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation. In the ancient Amazon region, carbon isotope data for the toxodonts indicate a C₃-based tropical rainforest habitat with no evidence for grasslands as would be predicted from the Neotropical forest refugia hypothesis.  相似文献   

A shift towards wetter and windier conditions in southern Sweden around the prominent solar minimum 2750 cal a BP          下载免费PDF全文

ANETTE MELLSTRÖM  NATHALIE VAN DER PUTTEN  RAIMUND MUSCHELER  RIXT DE JONG  SVANTE BJÖRCK 《第四纪科学杂志》2015,30(3):235-244

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Glacial landforms and their implications for glacier dynamics in Rijpfjorden and Duvefjorden,northern Nordaustlandet,Svalbard     

《第四纪科学杂志》2017,32(3):437-455

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Conceptualizing multiple clusters in mega-city regions: The case of the biomedical industry in Beijing     

《Geoforum》2016

This paper introduces a unique industrial configuration that has emerged in Beijing, where three economic clusters in the biomedical industry, originally established as industrial/research parks, have developed parallel to each other. This configuration of multiple co-located clusters of the same industry, which has not been discussed before, raises the question of whether the industrial/research parks are competing for the same resources, or whether they are complementary to each other and can collectively be viewed as a new type of industrial configuration. The paper conceptualizes a framework of multiple clusters in mega-city regions that distinguishes between collaborating and competing clusters and presents initial empirical evidence for the Beijing case. As such, this research aims to unravel the phenomenon of multiple clusters in mega-city regions and to understand the complex spatial interrelationships that exist within and beyond multiple co-located clusters in the same industry.  相似文献   

Early Albian marine environments in Madagascar: An integrated approach based on oxygen,carbon and strontium isotopic data     

《Cretaceous Research》2016

New palaeotemperature reconstructions have been obtained on the basis of oxygen isotopic analysis of 178 aragonitic shell samples taken from specimens of three ammonoid orders (and some corresponding families): Phylloceratida (Phylloceratidae), Lytoceratida (Tetragonitidae) and Ammonitida (Oppeliidae, Desmoceratidae, Silesitidae, Cleoniceratidae and Douvilleiceratidae). Those obtained from aragonite shells, secreted in the lower epipelagic and in the middle mesopelagic zones during coolest season (winter), range from 15.4 to 16.8 °C, and from 11.8 to 12.0 °C, respectively. Presumed spring/autumn palaeotemperatures obtained from aragonite shells, secreted apparently in the upper and lower epipelagic, upper and middle mesopelagic zones, are somewhat higher. Presumed summer palaeotemperatures, calculated apparently for the upper and lower epipelagic, and upper mesopelagic zones range from 19.4 to 21.7 °C, from 17.7 to 19.4 °C, and from 14.4 to 16.1 °C, respectively. The predominant part of investigated ammonoids from Madagascar inhabited the epipelagic zone, but some phylloceratid, tetragonitid and silesitid ammonoids preferred deeper, cooler conditions (upper-middle mesopelagic zone). The study supports the hypothesis that Madagascar was located in middle latitudes within the tropical-subtropical climatic zone during the early Albian. Available carbon and strontium isotope data allow us to assume a more or less expressed carbon and strontium isotope stratification of the water column in this region in the early Albian. On the basis of the stable isotope data, following partly Lukeneder (2015), two large ethological groups can be recognised mainly in mid-aged and adult ammonoids. Some ammonoids (group 1) preferred apparently mesopelagic conditions, and to a lesser degree the epipelagic zone, being mainly cool-requiring animals. However, a significant part of the isotopically investigated ammonoids (group 2) preferred, on the contrary, only epipelagic conditions, being mainly thermophilic dwellers.  相似文献