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81.
82.
Zhang Leiming Yu Guirui Sun Xiaomin Wen Xuefa Ren Chuanyou Song Xia Liu Yunfen Guan Dexin Yan Junhua Zhang Yiping 《中国科学D辑(英文版)》2006,49(2):47-62
The long-term and continuous carbon fluxes of Changbaishan temperate mixed forest (CBS), Qianyanzhou subtropical evergreen coniferous forest (QYZ), Dinghushan subtropical evergreen mixed forest (DHS) and Xishuangbana tropical rainforest (XSBN) have been measured with eddy covariance techniques. In 2003, different responses of carbon exchange to the environment appeared across the four ecosystems. At CBS, the carbon exchange was mainly determined by radiation and temperature. 0°C and 10°C were two important temperature thresholds; the former determined the length of the growing season and the latter affected the magnitude of carbon exchange. The maximum net ecosystem exchange (N EE) of CBS occurred in early summer because maximum ecosystem photosynthesis (G PP) occurred earlier than maximum ecosystem respiration (R e). During summer, QYZ experienced severe drought and N EE decreased significantly mainly as a result of the depression of G PP. At DHS and XSBN, N EE was higher in the drought season than the wet season, especially the conversion between carbon sink and source occurring during the transition season at XSBN. During the wet season, increased fog and humid weather resulted from the plentiful rainfall, the ecosystem G PP was dispressed. The Q 10 and annual respiration of XSBN were the highest among the four ecosystems, while the average daily respiration of CBS during the growing season was the highest. Annual N EE of CBS, QYZ, DHS and XSBN were 181.5, 360.9, 536.2 and ?320.0 g·C·m?2·a?1, respectively. From CBS to DHS, the temperature and precipitation increased with the decrease in latitude. The ratio of N EE/R e increased with latitude, while R e/G PP, ecosystem light use efficiency (L UE), precipitation use efficiency and average daily G PP decreased gradually. However, XSBN usually escaped such latitude trend probably because of the influence of the south-west monsoon climate which does not affect the other ecosystems. Long-term measurement and more research were necessary to understand the adaptation of forest ecosystems to climate change and to evaluate the ecosystem carbon balance due to the complexity of structure and function of forest ecosystems. 相似文献
83.
哈达门沟金矿床成岩成矿时代的定点定年研究 总被引:22,自引:3,他引:22
哈达门沟大型钾长石 -石英脉型金矿床位于华北地台北缘西段的乌拉山地区。矿区西部的大桦背花岗岩和矿区内的伟晶岩脉与金矿化均具有较为密切的空间关系 ,这导致不少研究者认为哈达门沟金矿床与大桦背岩体或伟晶岩之间也具有时间和成因联系。通过采用先进的高灵敏的高分辨率的离子探针 (SHRIMP)对大桦背岩体、伟晶岩脉和钾长石化蚀变岩进行的锆石 U- Pb定点定年研究表明 :伟晶岩脉形成于 (1836± 5)× 10 6a,属吕梁旋回 ;大桦背岩体形成于 (353± 7)× 10 6a,应为海西旋回早期产物 ;金矿化年龄小于或等于 (132± 2 )× 10 6a,应为燕山晚期。这些年龄结果说明 ,本区金矿化比大桦背岩体晚至少 2 2 0× 10 6a,这排除了金矿化与大桦背岩体和伟晶岩脉之间有任何成因联系的可能性。蚀变岩的年龄还证明 ,虽然乌拉山和胶东地区金矿床的围岩和年龄不同 ,但两地区的金矿化却几乎同时发生。此外 ,大桦背岩体的形成年龄与华北地块和蒙古古陆块碰撞作用发生的时间基本一致 ,因此大桦背岩体的 SHRIMP年龄为这一碰撞作用提供了可靠的年代学证据。 相似文献
84.
Wu Jiabing Guan Dexin Sun Xiaomin Zhang Mi Shi Tingting Han Shijie Jin Changjie 《中国科学D辑(英文版)》2006,49(2):89-98
Based on the light-photosynthesis response measurement at leaf level, combined with over-and under-canopy eddy covariance measurements, research on photosynthetic characteristics of single trees and forest canopy was conducted. The relationship between light intensity and photosynthetic rates for leaves and canopy can be well fitted by a non-rectangular hyperbola model. Mongolian oak presented a high light compensation point, L cp (28 μmol·m?2·s?1), a light saturation point L sp (>1800 μmol·m?2·s?1), and a maximal net photosynthetic rate P max (9.96 μmol·m?2·s?1), which suggest that it is a typical heliophilous plant. Mono maple presented the highest apparent quantum efficiency α (0.066) but the lowest, L cp (16 μmol·m?2·s?1), L sp (≈800 μmol·m?2·s?1), and P max (4.51 μmol·m?2·s?1), which suggest that it is heliophilous plant. Korean pine showed the lowest α value but a higher P max, which suggest that it is a semi-heliophilous plant. At the canopy level, the values of both α and P max approached the upper limit of reported values in temperate forests, while L cp was within the lower limit. Canopy photosynthetic characteristics were well consistent with those of leaves. Both showed a high ability to photosynthesize. However, environmental stresses, especially high vapor pressure deficits, could significantly reduce the photosynthetic ability of leaves and canopy. 相似文献
85.
利用IPCC发布的5个全球气候模式在高(SRES A2)、低(SRES B1)两种不同排放情景下的预报集成结果,对21世纪大尺度环境进行分析,进而对西北太平洋夏季热带气旋(TC)的频数进行预估。结果表明:两种情景下热带西北太平洋均呈现500 hPa位势高度偏高、太平洋东部海表温度偏高、低层菲律宾以东为异常反气旋性环流控制的特征。这种大尺度环境不利于TC生成,在高排放情景下或21世纪中叶后该环境特征更显著。未来TC频数总体呈减少的趋势,低排放情景下的TC频数变化趋势比高排放情境下平缓,TC频数存在年代际和年际变化。 相似文献
86.
87.
采用审查回归模型,分别选取了中国东、中、西部的三个典型城市无锡、武汉和西安,计算了三城市受访者的支付意愿值,并对其影响因素进行了分析。结果表明:(1)支付意愿值与地区经济发展水平直接相关。无锡、武汉和西安受访者的支付意愿分别为21.68,17.15和10.07元/年;(2)年龄越长者,由于其天气知识更丰富、日常消费较节俭,对气象服务的支付意愿越低;(3)文化程度越高者,更能理解和支持气象服务事业,对气象服务的支付意愿越高;(4)月收入变量对气象服务的支付意愿有显著影响,但就不同城市的受访者而言,影响的方向并不一致。 相似文献
88.
夏季多年平均及个别年份低层流场的准周期扰动分析 总被引:1,自引:0,他引:1
利用ECMWF的1980 ̄1986年多年平均及1980年的低层纬、经向网络点资料对季内振荡方差进行了分析,给出了多年平均及个别年份流场中季内同斯振荡强度的对比特征及其在低伟和中高纬地区的差异。为动力学诊断和理论研究夏季风的年际差异提供线索。 相似文献
89.
Variability of soil moisture and its relationship with surface albedo and soil thermal parameters over the Loess Plateau 总被引:9,自引:0,他引:9
Data from July 2006 to June 2008 observed at SACOL(Semi-Arid Climate and Environment Observatory of Lanzhou University,35.946°N,104.137°E,elev.1961 m),a semi-arid site in Northwest China,are used to study seasonal variability of soil moisture,along with surface albedo and other soil thermal parameters, such as heat capacity,thermal conductivity and thermal diffusivity,and their relationships to soil moisture content.The results indicate that surface albedo decreases with increases in soil moisture content,s... 相似文献
90.