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131.
云南元谋盆地西部物茂盆地的湾堡土林和虎跳滩土林的晚上新世沙沟组地层大戟科秋枫属的秋枫(Bischofia javanica BL.)化石木。化石木木材由导管、纤维、射线组成。生长轮不明显。散孔材。径列复管孔(2~6,多2~4)甚多,单管孔较少,管孔团稀见。导管端壁具单穿孔。管间纹孔式互列。导管内侵填体丰富。轴向薄壁组织未见。木纤维壁薄,分隔。射线组织异形Ⅰ及Ⅱ。射线与导管间纹孔式为横列梯形及大圆形。孢粉分析表明元谋盆地晚上新世可能存在包括大戟科草本植物,而当前秋枫化石木的发现清楚地表明大戟科乔木植物的存在。秋枫为热带和亚热带常绿季雨林中的主要树种。秋枫化石木的发现指示元谋盆地当时的环境较现今湿润。 相似文献
132.
133.
TIAN Jun WANG Pinxian CHENG Xinrong WANG Rujian & SUN Xiangjun . State Key Laboratory of Marine Geology Tongji University Shanghai China . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Institute of Botany Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2005,48(10)
The variations of the Earth’s geometry (ETP) pre-dominate climate changes such as monsoon on the Earth[1], serving as its external forcing. The loess/ paleosol sequence in Central China provides a good record of terrestrial deposition to study the evolution of the east Asian monsoon[2―4]. However, the deep sea deposition, due to its high resolution dating and abun-dant climate proxies, should be able to provide more climatic information in the geological time, such as the forcing mechanis… 相似文献
134.
We analysed vegetation data recorded in the degraded lowland grasslands in Otindag Sandland during the first 4-years of restoration (2001–2004) to investigate: (1) the contribution of individual plant functional type (PFT) to PFT diversity of community and (2) the relationships between primary productivity and biodiversity both at species and PFT levels. Sixteen PFTs were distinguished based on the following traits: (1) life-span (annual vs. perennial); (2) photosynthetic pathway (C3 vs. C4); (3) reproductive mode (clonal vs. non-clonal); and (4) growth form (grass vs. forb). Analysis of data indicates that density, coverage, number of species, phytomass, and relative importance of PFTs depended strongly on life-span, photosynthetic pathway, reproductive mode and growth form. Phytomass was significantly correlated with PFT diversity, but not species diversity. However, the relationship between phytomass and PFT diversity varied greatly with year, with a positive relationship in 2001 and 2004 and a negative one in 2002 and 2003. As the restoration proceeds, the perennial C3 clonal grass became the greatest contributor to PFT diversity. 相似文献
135.
136.
Wang Guoan Han Jiamao Zhou Liping Xiong Xiaogang Tan Ming Wu Zhenhai Peng Jun 《中国科学D辑(英文版)》2006,49(1):97-102
Carbon isotope ratios (δ
13C) of 89 C4 plant samples were determined from the loess area in North China. δ
13C values vary between −10.5‰ and −14.6‰ with a mean of −12.6‰. Along a precipitation gradient from the semi-moist area to
the semiarid area, then to the arid area, the δ
13C values of C4 plants show a slight decreasing trend. The δ
13C values of C4 plants in the dry season are found lower than those in the wet season. These trends are opposite to those observed for C3 species. 相似文献
137.
内蒙古是我国西部开发、生态环境建设、农牧业结构调整、民族团结稳定的重要区域。本 文主要运用能值理论和方法, 对其主要资源的贮存价值、总能值用量、能值的流入流出情况、能值 自给率、能值投资率、环境负载率、人口承载力、可持续发展指数等指标进行了系统研究, 并与其 他国家的有关指标进行了比较研究。结果表明内蒙古总能值用量的98.11%来自于区内, 其中 74.26%为不可更新资源。提出内蒙古地区实现可持续发展的对策为调整产业结构, 提高资源利用 效率; 努力获得更多的外部高品质的能值反馈; 加快软硬件的建设, 促进旅游业的快速发展。 相似文献
138.
《Earth and Planetary Science Letters》2007,253(3-4):389-401
The time at which the Tibetan Plateau rose to its present high elevation remains controversial, with estimates ranging from 40 Ma to more recent than 7 Ma. New stable isotope analyses of modern and accurately dated ancient paleosol carbonate in the Nima basin of central Tibet point to an arid climate and high paleoelevation (4.5–5 km, comparable to today's setting) by 26 Ma. Oxygen isotope values of ancient (26 Ma) soil carbonate are both very negative and indistinguishable–after modest corrections for changes in global climate–from the lowest (least evaporated) oxygen isotope values of modern soil carbonates in the area. Substantial enrichments in oxygen-18 in paleolacustrine carbonates, as well as high carbon isotope values from paleosol carbonates, indicate considerable lake evaporation and low soil respiration rates, respectively, and both are consistent with the present arid climate of the Nima area. Blockage of tropical moisture by the Himalaya and perhaps the Gangdese Shan probably has contributed strongly to the aridity and very negative oxygen isotope values of soil carbonate and surface water in the Nima area since at least the Late Oligocene. The maintenance of high elevation since at least 26 Ma suggests that any flow of lower crust from beneath central Tibet must have been balanced by coeval northward insertion of Indian crust beneath the Plateau. 相似文献
139.
Grassland is one of the most widespread vegetation types worldwide and plays a significant role in regional climate and global
carbon cycling. Understanding the sensitivity of Chinese grassland ecosystems to climate change and elevated atmospheric CO2 and the effect of these changes on the grassland ecosystems is a key issue in global carbon cycling. China encompasses vast
grassland areas of 354 million ha of 17 major grassland types, according to a national grassland survey. In this study, a
process-based terrestrial model the CENTURY model was used to simulate potential changes in net primary productivity (NPP)
and soil organic carbon (SOC) of the Leymus chinensis meadow steppe (LCMS) under different scenarios of climatic change and elevated atmospheric CO2. The LCMS sensitivities, its potential responses to climate change, and the change in capacity of carbon stock and sequestration
in the future are evaluated. The results showed that the LCMS NPP and SOC are sensitive to climatic change and elevated CO2. In the next 100 years, with doubled CO2 concentration, if temperature increases from 2.7-3.9˚C and precipitation increases by 10% NPP and SOC will increase by 7-21%
and 5-6% respectively. However, if temperature increases by 7.5-7.8˚C and precipitation increases by only 10% NPP and SOC
would decrease by 24% and 8% respectively. Therefore, changes in the NPP and SOC of the meadow steppe are attributed mainly
to the amount of temperature and precipitation change and the atmospheric CO2 concentration in the future. 相似文献
140.
Tree rings and climate for the last 680 years in Wulan area of northeastern Qinghai-Tibetan Plateau 总被引:3,自引:0,他引:3
A 680-year ring-width chronology of Sabina przewalskii Kom. was developed for Wulan area of northeastern Qinghai-Tibetan Plateau, China. Response function and correlation analyses
showed that spring precipitation (May–June) is the critical limiting factor for tree-ring growth, and temperature in prior
November may also play a role in affecting tree-ring growth. Excessive spring precipitation occurred during AD 1380s–1390s,
1410s–1420s, 1520s–1560s and 1938 to present. Dry springs occurred during AD 1430s–1510s, 1640s–1730s and 1780s–1890s most
of which generally coincided with cold intervals of the Little Ice Age (LIA) on the plateau, suggesting that the LIA climate
on the northeastern Qinghai-Tibetan Plateau might be characterized by three episodes of dry spring and cold autumn. The relatively
driest spring and probably coldest autumn occurred in AD 1710s–1720s, 1787–1797, 1815–1824, 1869–1879 and 1891–1895. The extreme
drought in AD 1787–1797 might result from little monsoon precipitation due to the failure of Asian monsoon in this period.
The tree-ring data produced in this study contribute to the spatial expansion of proxy climate records for the Qinghai-Tibetan
Plateau. 相似文献