Diversity and zonal distribution of arbuscular mycorrhizal fungi on the northern slopes of the Tianshan Mountains     

Shi ZhaoYong  Chen ZhiChao  Zhang LiYun  Feng Gu  Christie Peter  Tian ChangYan  Li XiaoLin 《中国科学D辑(英文版)》2007,50(1):135-141

The arbuscular mycorrhizal (AM) fungal status of the 20 most common plant species distributed in 4 vegetation types (meadow steppe, desert steppe, steppe desert and typical desert) on the northern slopes of the Tianshan Mountains was investigated. Samples of the plant species and their rhizosphere soils were collected from the 4 vegetation zones and examined to compare their mycorrhizal status, AM fungal spore densities, biovolumes, and community structures. 28 AM fungal species were isolated from the rhizosphere soils: of these, 5 belonged to Acaulospora, 1 to Archaeospora and 22 to Glomus. 5 AM fungi, Glomus aggregatum, G. claroideum, G. deserticola, G. etunicatum and G. sinuosum, were observed in all 4 zonal types. No significant differences were observed in mean proportion of root length colonized by AM fungi among the plant species within each zonal type. Comparing the 4 zonal types, Plantago minuta (84.5%) in steppe desert and Eremopyrum orientale (83.1%) in typical desert showed the highest root colonizatsion rates. AM fungal spore densities and biovolumes were significantly different in the different zonal types. AM fungal spore densities and biovolumes, species richness and diversity were highest in meadow steppe and lowest in typical desert.  相似文献   

Formation of Working Surfaces in Radiatively Cooled Laboratory Jets     

D. J. Ampleford  S. V. Lebedev  A. Ciardi  S. N. Bland  S. C. Bott  J. P. Chittenden  G. Hall  C. A. Jennings  J. Armitage  G. Blyth  S. Christie  L. Rutland 《Astrophysics and Space Science》2005,298(1-2):241-246

Whilst observations provide many examples of collimated outflows or jets from astrophysical bodies, there remain unresolved questions relating to their formation, propagation and stability. The ability to form scaled jets in the laboratory has provided many useful insights. Experiments (Lebedev et al.: 2002, ApJ 564, 113) using conical arrays of fine metallic wires on the MAGPIE generator (1MA in 240 ns) have produced radiatively cooled collimated jets in vacuum using the redirection of convergent flows by a conical shock. Here we present results of a jet produced by this method propagating through a photo-ionized, quasi-stationary gas cloud. A working surface is observed at the head of the jet. The velocity of this working surface is lower than the velocity of a jet tip in vacuum.  相似文献   

Resistance of salt marsh substrates to near-instantaneous hydrodynamic forcing     

Helen Brooks  Iris Möller  Simon Carr  Clementine Chirol  Elizabeth Christie  Ben Evans  Kate L. Spencer  Tom Spencer  Katherine Royse 《地球表面变化过程与地形》2021,46(1):67-88

Salt marshes deliver vital ecosystem services by providing habitats, storing pollutants and atmospheric carbon, and reducing flood and erosion risk in the coastal hinterland. Net losses in salt marsh areas, both modelled globally and measured regionally, are therefore of concern. Amongst other controls, the persistence of salt marshes in any one location depends on the ability of their substrates to resist hydrodynamic forcing at the marsh front, along creek margins and on the vegetated surface. Where relative sea level is rising, marsh elevation must keep pace with sea-level rise and landward expansion may be required to compensate for areal loss at exposed margins. This paper reviews current understanding of marsh substrate resistance to the near-instantaneous (seconds to hours) forcing induced by hydrodynamic processes. It outlines how variability in substrate properties may affect marsh substrate stability, explores current understanding of the interactions between substrate properties and erosion processes, and how the cumulative impact of these interactions may affect marsh stability over annual to decadal timescales. Whilst important advances have been made in understanding how specific soil properties affect near-instantaneous marsh substrate stability, less is known about how these properties interact and alter bulk substrate resistance to hydrodynamic forcing. Future research requires a more systematic approach to quantifying biological and sedimentological marsh substrate properties. These properties must then be linked to specific observable erosion processes, particularly at the marsh front and along creek banks. A better understanding of the intrinsic dynamics and processes acting on, and within, salt marsh substrates will facilitate improved prediction of marsh evolution under future hydrodynamic forcing scenarios. Notwithstanding the additional complications that arise from morphodynamic feedbacks, this would allow us to more accurately model the future potential protection from flooding and erosion afforded by marshes, while also increasing the effectiveness of salt marsh restoration and recreation schemes. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Long term monitoring of photosystem II herbicides--correlation with remotely sensed freshwater extent to monitor changes in the quality of water entering the Great Barrier Reef, Australia     

Kennedy K  Schroeder T  Shaw M  Haynes D  Lewis S  Bentley C  Paxman C  Carter S  Brando VE  Bartkow M  Hearn L  Mueller JF 《Marine pollution bulletin》2012,65(4-9):292-305

Photosystem II (PSII) herbicides are used in large quantities on agricultural lands adjoining the Great Barrier Reef (GBR). Routine monitoring at 14 sites in inshore waters of the GBR using passive sampling techniques detected diuron (32-94% of sampling periods) at maximum concentrations of 1.7-430ng L(-1) in the relatively pristine Cape York Region to the Mackay Whitsunday Region, respectively. A PSII herbicide equivalent (PSII-HEq) index developed as an indicator for reporting was dominated by diuron (average contribution 89%) and typically increased during the wet season. The maximum PSII-HEq indicates the potential for photosynthetic inhibition of diatoms, seagrass and coral-symbionts. PSII herbicides were significantly positively correlated with remotely sensed coloured dissolved organic matter, a proxy for freshwater extent. Combining these methods provides for the first time the potential to cost-effectively monitor improvements in water quality entering the GBR with respect to exposure to PSII herbicides.  相似文献   

Comments on the interpretation of deformation textures in rocks   总被引：4，自引：0，他引：4  

H.-R. Wenk  J.M. Christie 《Journal of Structural Geology》1991,13(10)

In rocks that undergo ductile deformation, preferred orientation develops as a result of intracrystalline slip and mechanical twinning. The orientation distribution is a consequence of the microscopic mechanisms and of the strain path. It can be used to get some insight into the deformation history; however it is never unique. The interpretation relies largely on polycrystal plasticity theory. The concepts of stress equilibrium and strain compatibility, which are two extreme assumptions made to model deformation, are discussed. New approaches such as the viscoplastic self-consistent theory are a compromise and may be applicable to mineral systems which display a high degree of plastic anisotropy. Important extensions allow for heterogeneous deformation in the polycrystal from grain to grain and even within grains in correspondence with microstructural observations. All these theories defy the popular notion which is becoming entrenched in the geological literature, that the microscopic slip plane normal aligns with the axis of maximum principal compressive stress, and that in simple shear the crystallographic slip plane rotates into the macroscopic shear plane and the slip direction into the macroscopic shear direction, an orientation referred to by geologists as ‘easy glide’. It is emphasized that future work on texture development of rocks should be based on rigorous physics rather than ingenious intuition, in accordance with an old recommendation of Walter Schmidt.  相似文献   

Subsolidus reactions in lunar pyroxenes: An electron petrographic study     

J. S. Lally  A. H. Heuer  G. L. Nord Jr.  J. M. Christie 《Contributions to Mineralogy and Petrology》1975,51(4):263-281

Zoned lunar pyroxenes have been examined by high voltage (800–1000 kV) transmission electron microscopy and electron diffraction, with the particular aim of providing information on the cooling history of individual pyroxenes. Microstructures resulting from composition discontinuities occurring during continuous crystallization, exsolution lamellae of pigeonite and augite and the development of denuded zones, and anti-phase domains (APD's) in pigeonite have been studied with respect to their scale, morphology and micro-structural evolution. These features have been further interpreted with respect to a proposed pseudobinary phase diagram of constant En/Fs.Information found to be the most useful for determining cooling rates in pyroxenes are: for quickly cooled rocks; microstructural evolution and APD size for moderately cooled rocks; and denuded zone widths and APD morphology for slowly cooled rocks.Now at U.S. Geological Survey, 959 National Center, Reston, Virginia 22092.  相似文献   

Shock processes in porous quartzite: Transmission electron microscope observations and theory     

Susan Werner Kieffer  Prem P. Phakey  John M. Christie 《Contributions to Mineralogy and Petrology》1976,59(1):41-93

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Secular or cyclic change in ozone     

Christie  A. D. 《Pure and Applied Geophysics》1973,106(1):1000-1009

Pure and Applied Geophysics -  相似文献   

Data laundering leading to meaningful principal component classification criterion and map attribute in surface geochemistry     

Olav H. J. Christie 《Aquatic Sciences - Research Across Boundaries》1995,57(3):242-254

Principal components classification based on geochemical data from sea bed samples offers a discriminant methodology for assignment of sea bed core location to defined types of hydrocarbon seep characteristics. Significant contributions to the geochemical fingerprint of the samples, like influence of sediment nature and biogenic input, are considered bias effects by oil explorationists and may be removed by aid of the method of principal components target rotation. This removal is called data laundering, and map attributes representing known hydrocarbon accumulations can be constructed from laundered data sets. Signatures of the Draugen (Haltenbanken, Norway) sea bed type occur over the Heidrun and Smørbukk fields and points out regions of interest to exploration in unexplored areas.  相似文献   

Ecological monitoring strategy with special reference to a rocky subtidal programme     

Hartvig Christie 《Marine pollution bulletin》1985,16(6):232-235

Excluding the most polluted areas, a general problem to handle in an ecological monitoring context is the recognition of pollution-induced changes as opposed to natural variations always occurring in marine communities. In the search for solutions to this problem, a combination of different methods is suggested. The use of basic ecological community studies, comparison of common patterns on a broad geographical scale, and making predictions from short and long term trend models are the methods that have been tried and discussed. Ecological knowledge and comparison of common patterns are here suggested as the most fruitful tools in an ecological monitoring programme.  相似文献