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排序方式: 共有1714条查询结果,搜索用时 25 毫秒
731.
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734.
Patterns in tropical seagrass photosynthesis in relation to light, depth and habitat 总被引:1,自引:0,他引:1
Stuart J. Campbell Len J. McKenzie Simon P. Kerville Juanita S. Bit 《Estuarine, Coastal and Shelf Science》2007,73(3-4):551-562
Seagrass meadows across north-eastern Australia, survive a range of environmental conditions in coastal bays, reefs, estuarine and deepwater habitats through adaptation of a range of structural, morphological and physiological features. The aim of this study was to investigate the influence of spatial features (habitat type, site and depth) and photon flux on the photosynthetic performance of 11 tropical seagrass species. Pulse amplitude modulated (PAM) fluorometry was used to generate rapid light curves from which measures of maximal electron transport rate (ETRmax), photosynthetic efficiency (α), saturating irradiance (Ek) and effective quantum yield (ΔF/Fm′) were derived. The amount of light absorbed by leaves (absorption factor) was also determined for each population. In intertidal habitats many seagrass species exhibited typical sun-type responses with a close coupling of both ETRmax and Ek with photon flux. Photosynthetic performance ranged from minima in Thalassodendron ciliatum to maxima in Syringodium isoetifolium. The absence of a coupling between photosynthetic performance and photon flux in subtidal populations was most likely due to highly variable light climates and possible light attenuation, and hence the photo-biology of estuarine and deepwater seagrasses exhibited photosynthetic responses indicative of light limitation. In contrast seagrass species from shallow reef and coastal habitats for the most part exhibited light saturation characteristics. Of all the variables examined ETRmax, Ek and ΔF/Fm′ were most responsive to changing light climates and provide reliable physiological indicators of real-time photosynthetic performance of tropical seagrasses under different light conditions. 相似文献
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Gabriele M. Berberich Tobias Sattler Dietrich Klimetzek Simon A. Benk Martin B. Berberich Daniela Polag Heinz Friedrich Schöler Elliot Atlas 《Journal of Atmospheric Chemistry》2017,74(2):261-281
We investigated and evaluated the occurrence of fault zone tracer gases (CO2, He, Rn), volatile organohalogens (CH3Cl, CHCl3, CHBr3), alkanes and limonene in soil and nest gases of red wood ants (RWA) in comparison to ambient air, in a seismically active area. In this new approach, we compared RWA-free areas to RWA-areas by combining different investigation and analytical methods. In soil gas, the fault zone tracer gas Rn was surprisingly highly correlated to limonene, suggesting a combination of biotic production of limonene and abiotic degassing of Rn in a seismically active area; moderate correlations were found with trihalomethanes and other halocarbons. In RWA nests a variety of elevated concentrations of haloforms were found, while remaining below the atmospheric background values in RWA-free areas. The evidence of CHCl3 in RWA nests is the first record. Its average concentrations in nests of F. rufa and F. polyctena were up to 3 fold higher than atmospheric background and up to 28–70 fold higher compared to e.g. volcanic emissions being considered as one of its main geogenic sources. Thus, RWA nests could possibly be an additional source for CHCl3 liberation. Consequently, apart from RWA being bioindicators for seismically active degassing faults, they might also be used as bioindicators for CHCl3 formation in forest soils. Although we cannot yet differentiate between a geogenic/abiotic and a biotic formation. RWA nests will have to be reconsidered for halocarbon formation in future quantifications of geochemical cycles at global scale, since they impact organic soil chemistry through biotic and/or abiotic pathways. Therefore, further larger-scale research in different tectonic settings but also in well-known CHCl3 “hot spot” study areas such as the Klosterhede area (Denmark) should focus directly on gas sampling from confirmed active fault systems. Nests of other ant species should be addressed to compare seasonal, diurnal and nocturnal variations of degassing procedures in relation to earth tides, different geologic settings, and tectonic events such as earthquakes and on quantifying the fluxes to the atmosphere. 相似文献
737.
C. Catala T. Böhm J. -F. Donati T. Simon A. Welty E. Houdebine L. Huang S. Jiang D. Zhai J. Neff B. H. Foing K. Ghosh J. Butler A. Collier-Cameron J. Baudrand J. Czarny B. Carter D. Rees M. Semel G. Cutispoto M. Rodonò 《Solar physics》1994,155(1):185-193
MUSICOS (for MUlti-SIte COntinuous Spectroscopy) is an international project to facilitate and organize world-wide multi-site campaigns in high resolution spectroscopy, in view of obtaining a complete time coverage of various types of variable stellar phenomena.In the framework of this project a vast spectroscopic campaign was organized in December 1992, involving 8 sites well distributed in longitude around the Earth. The observations concerned three scientific programs, among which was the study of azimuthal structures in the wind and chromosphere of the pre-Main-Sequence Herbig Ae star AB Aur.The Hei 5876 line of AB Aur, which is formed in the expanding chromosphere of this star, in the innermost parts of its wind, was monitored at a resolution of 30000, nearly continuously for about 4 days. A spectacular variability of this line was discovered, the profile changing from pure emission to a composite profile including a deep absorption component in the course of a few hours. This variability can be the signature of azimuthal structures in the wind of AB Aur.We present the data collected during the campaign, and discuss possible interpretations of the spectacular variations of the Hei 5876 line.ESA/VILSPAUniversity of British Columbia CanadaBased on observations obtained during the MUSICOS 92 MUlti-SIte COntinuous Spectroscopic campaign from the National Solar Observatory McMath/Pierce 1.5 m, University of Hawaii 2.2 m, Beijing Observatory Xinglong 2.16 m, La Palma 4.2 m William Herschel Telescope, and Observatoire de Haute-Provence 1.52 m telescopes.Presented at the Cosmic Winds and the Heliosphere Conference in Tucson, Arizona, U.S.A., October 18–22, 1993.Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.Visiting Astronomer National Solar Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. 相似文献
738.
The sediment–water interface is usually marked by an increase in acoustic impedance and is therefore displayed in a seismic
section as a positive polarity reflection. Here, we use the term “seabed phase reversal” to describe areas of seafloor which
are instead expressed as a negative polarity reflection in seismic data. We describe in detail a number of examples of seafloor
phase reversals and use a simple one-dimensional geophysical model to test the hypothesis that they are the result of the
presence of gas within the seafloor sediment. Our examples are all related to seismically imaged mud volcanoes located within
the South Caspian Sea. Sections of phase-reversed seafloor at the summit area of these volcanoes have been mapped to reveal
the existence of seafloor mud pools (salses) and recently erupted mud flows which show a strong similarity to smaller-scale
features at onshore volcanoes in Azerbaijan. Synthetic geophysical modelling indicates that under the physical conditions
likely to occur when the seabed sediment is gas-bearing, the seafloor will be expressed as a strong negative polarity reflection.
Unlike other indicators of seafloor gas, such as pockmarks, which merely record the transient expulsion of fluids from sedimentary
basins, seafloor phase reversals indicate the presence of gas in marine sediment at the time of survey acquisition. They therefore
are of significance to engineering and site survey operations as well as the identification of biological communities and
gas flux calculations. 相似文献
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740.
Simon Swaffield Henry Winchester 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2016,116(1):14-23
New Zealand is a food producer and exporter that combines neoliberal policy with performance-based environmental management, using ‘soft’ governance and actions where possible. Voluntary environmental farm awards are analysed to identify the landscape management activities recognised as best practice by peers at a farm level. Results highlight the importance of whole farm system management. However, the efficacy of reliance upon voluntary mechanisms is coming under increasingly critical scrutiny, as environmental conditions in intensive agricultural landscapes continue to decline. The research question this poses is whether whole farm plans can be practically and formally connected in three concurrent ways – to supply chain management, and to statutory planning frameworks and environmental regulations and to local landscape co-management – while still maintaining flexibility of action for the farmer. 相似文献