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271.
272.
一般认为植物根际微生物的生物量高于非根际,这与植物根际分泌多种物质有关。不同种类的红树林内出现不同程度的林内富营养化现象,浮游藻类生物量很高,认为这部分地与红树植物根系分泌物(Root Exudates,REs)对林内生物的调控作用有关。红树植物根系分泌物是调控红树林生态效应的关键因素之一。壬二酸(Azelaic acid)是初次在红树植物中检测到的一种二元羧酸类根泌物,选用壬二酸和海洋原甲藻(Prorocentrum micans)为代表,以不同浓度壬二酸培养藻,在藻生长周期内定期观测其密度、形态、胞内甘油含量、色素含量等指标,进行室内红树植物根系分泌物对藻类的影响作用的初步的机理实验。主要结果如下:在低浓度0.5~1.5 mg/L时,壬二酸可作为营养物质被藻细胞所吸收。而在较高浓度2和4 mg/L时,壬二酸主要起化感抑制作用。细胞膜的脂质过氧化导致胞内甘油含量上升,色素体产生应激反应,色素合成量加大,特别是多甲藻黄素含量增加。通过细胞代谢产生更多的内含物质,如淀粉粒和脂肪,导致液泡增大。色素体是应激反应和抗逆作用的重要细胞器之一。由于壬二酸可以较低浓度出现较高的抑制效应,因此对红树林内的生态效应非以营养效应而以化感效应为主。红树植物根系分泌物对林内生态具有一定的调控作用,应加强野外条件下的红树植物多种根系分泌物的混合效应原位试验。 相似文献
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274.
Crustal root beneath the highlands of southern Norway resolved by teleseismic receiver functions 总被引:1,自引:0,他引:1
L. Svenningsen N. Balling B. H. Jacobsen R. Kind K. Wylegalla J. Schweitzer 《Geophysical Journal International》2007,170(3):1129-1138
Teleseismic data have been collected with temporary seismograph stations on two profiles in southern Norway. Including the permanent arrays NORSAR and Hagfors the profiles are 400 and 500 km long and extend from the Atlantic coast across regions of high topography and the Oslo Rift. A total of 1071 teleseismic waveforms recorded by 24 temporary and 8 permanent stations are analysed. The depth-migrated receiver functions show a well-resolved Moho for both profiles with Moho depths that are generally accurate within ±2 km.
For the northern profile across Jotunheimen we obtain Moho depths between 32 and 43 km (below sea level). On the southern profile across Hardangervidda, the Moho depths range from 29 km at the Atlantic coast to 41 km below the highland plateau. Generally the depth of Moho is close to or above 40 km beneath areas of high mean topography (>1 km), whereas in the Oslo Rift the crust locally thins down to 32 km. At the east end of the profiles we observe a deepening Moho beneath low topography. Beneath the highlands the obtained Moho depths are 4–5 km deeper than previous estimates. Our results are supported by the fact that west of the Oslo Rift a deep Moho correlates very well with low Bouguer gravity which also correlates well with high mean topography.
The presented results reveal a ca . 10–12 km thick Airy-type crustal root beneath the highlands of southern Norway, which leaves little room for additional buoyancy-effects below Moho. These observations do not seem consistent with the mechanisms of substantial buoyancy presently suggested to explain a significant Cenozoic uplift widely believed to be the cause of the high topography in present-day southern Norway. 相似文献
For the northern profile across Jotunheimen we obtain Moho depths between 32 and 43 km (below sea level). On the southern profile across Hardangervidda, the Moho depths range from 29 km at the Atlantic coast to 41 km below the highland plateau. Generally the depth of Moho is close to or above 40 km beneath areas of high mean topography (>1 km), whereas in the Oslo Rift the crust locally thins down to 32 km. At the east end of the profiles we observe a deepening Moho beneath low topography. Beneath the highlands the obtained Moho depths are 4–5 km deeper than previous estimates. Our results are supported by the fact that west of the Oslo Rift a deep Moho correlates very well with low Bouguer gravity which also correlates well with high mean topography.
The presented results reveal a ca . 10–12 km thick Airy-type crustal root beneath the highlands of southern Norway, which leaves little room for additional buoyancy-effects below Moho. These observations do not seem consistent with the mechanisms of substantial buoyancy presently suggested to explain a significant Cenozoic uplift widely believed to be the cause of the high topography in present-day southern Norway. 相似文献
275.
The offset-domain prestack depth migration with optimal separable approximation, based on the double square root equation, is used to image complex media with large and rapid velocity variations. The method downward continues the source and the receiver wavefields simultaneously. The mixed domain algorithm with forward Fourier and inverse Fourier transform is used to construct the double square root equation wavefield extrapolation operator. This operator separates variables in the wave number domain and variables in the space domain. The phase operation is implemented in the wave number domain, whereas the time delay for lateral velocity variation is corrected in the space domain. The migration algorithm is efficient since the seismic data are not computed shot by shot. The data set test of the Marmousi model indicates that the offset-domain migration provides a satisfied seismic migration section on which complex geologic structures are imaged in media with large and rapid lateral velocity variations. 相似文献
276.
一个太阳耀斑约含数千个微耀斑[1],每个微耀斑以热的,低频波和加速粒子的形式释放能量。耀斑期间大部分能量的释放是通过电子加速转移的结果,然而电子加速是在耀斑前相开始,并在整个耀斑持续期间继续保持。在耀斑发展的不同相期间伴有各种各样的射电辐射现象(及其它波段共生现象),多波段射电观测和比较可以给出有关电子加速过程和耀斑自身发展的重要信息,尤其可检测加速开始的时间和频率部位(目前仍为太阳物理的前沿)。微耀斑能量的瞬时释放可能是引起不同类型快速精细结构的原因,射电毫秒级尖峰辐射是起因于连续能量释放的证据,其辐射源位于或靠近能量释放区[2],公认射电辐射的快速结构是日冕电子束的特征信号[3,4],所以今后使用高时间和高频率分辨率的宽带频谱仪同时观测可详细地探测加速过程,从而对预耀斑的加热和初始能量释放,耀斑的逐步建立和演化都具有重要意义。本文介绍几个典型事件,包括射电尖峰脉冲辐射,类尖峰辐射和短时标漂移结构 相似文献
277.
Sensitivity of evapotranspiration E and root zone soil moisture content θ to the parameterization of soil water retention Ψ(θ) and soil water conductivity K(Ψ), as well as to the definition of field capacity soil moisture content, is investigated by comparing Psi1-PMSURF and Theta-PMSURF models. The core of PMSURF (Penman–Monteith Surface Fluxes) consists of a 3-layer soil moisture prediction module based on Richard’s equation in combination with the Penman–Monteith concept for estimating turbulent heat fluxes. Psi1- PMSURF and Theta-PMSURF differ only in the parameterization of the moisture availability function Fma. In Psi1,Fma is parameterized by using Ψ(θ) and K(Ψ) hydrophysical functions; in Theta, Fma is parameterized by using hydrophysical parameters: the field capacity θf and wilting point θw soil moisture contents. Both Psi1 and Theta are based on using soil hydrophysical data, that is, there is no conceptual difference between them in the parameterization of E even if in Psi1Fma depends on 12 parameters, while in Theta only on two soil/vegetation parameters. Sensitivity tests are performed using the Cabauw dataset. Three soil datasets are used: the vG (van Genuchten), CH/vG (Clapp and Hornberger/van Genuchten) and CH/PILPS (Clapp and Hornberger/Project for Intercomparison of Land-surface Parameterization Schemes) datasets. The vG dataset is used in van Genuchten’s parameterization, while in Clapp and Hornberger’s the CH/vG and CH/PILPS datasets are used. It is found that the consistency of soil hydrophysical data in the simulation of transpiration is quite important. The annual sum of E obtained by Psi1EPsi1, differs from the annual sum of E obtained by Theta, ETheta, because of the inconsistency between the fitting parameters of Ψ(θ) and K(Ψ) and the θf, and not because of the differencies in the parameterization of Fma. Further, θf can be estimated not only on the basis of using soil hydrophysical functions (the θf so obtained is θSoilf) but also on the basis of analysing the transpiration process (the θfso obtained is θtrf). θtrf values estimated from the condition ETheta ≈ EPsi1 are in acceptable accordance with the θSoilf values proposed by Wösten and co-workers. The results are useful in optimizing the parameterization of transpiration in land-surface schemes. 相似文献
278.
黄河干流兰州站与花园口站年径流序列协整分析研究 总被引:2,自引:0,他引:2
协整理论是经济计量学中处理非平稳经济时间序列常用的一种理论,具有模型可靠的优点。将其引入河川径流序列分析中,以黄河为例,通过单位根检验,获得平稳的河川径流序列,在此基础上,建立了误差修正模型,用于描述流域上下游径流间的协整关系。 相似文献
279.
280.
A. Gelencsér T. Mészáros M. Blazsó Gy. Kiss Z. Krivácsy A. Molnár E. Mészáros 《Journal of Atmospheric Chemistry》2000,37(2):173-183
The organic matter in tropospheric aerosol plays animportant, yet undetermined role in atmosphericprocesses. The bulk of organic carbon representing asignificant part of the fine aerosol mass is bound toa polymeric matter whose structure and properties areto date largely unknown. Here we use thefingerprinting technique of derivatization pyrolysis-gas chromatography-massspectrometry tosubstantiate that in terms of chemical structure partof this polymer in rural aerosol in summer can beregarded as natural humic matter. We suggest thatthese compounds are likely to be directly emitted bybiogenic sources. 相似文献