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John D. Aplin D.E. Brooks Charles F.A. Culling Laurance D. Hall Philip E. Reid 《Carbohydrate research》1979
A new, mild method is described for spin-labelling sialic acid residues in situ. The procedure involves the formation of C-1 sialamides and has been applied to a serum glycoprotein, a mucin, tissue sections from human colon, and erythrocyte membrane components. The selectivity of the method and its possible applicability to other types of labelling are discussed. 相似文献
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Lourens Poorter Lucy Amissah Frans Bongers Iris Hordijk Jazz Kok Susan G. W. Laurance Madelon Lohbeck Miguel Martínez-Ramos Tomonari Matsuo Jorge A. Meave Rodrigo Muñoz Marielos Peña-Claros Masha T. van der Sande 《Biological reviews of the Cambridge Philosophical Society》2023,98(6):2049-2077
Succession is a fundamental concept in ecology because it indicates how species populations, communities, and ecosystems change over time on new substrate or after a disturbance. A mechanistic understanding of succession is needed to predict how ecosystems will respond to land-use change and to design effective ecosystem restoration strategies. Yet, despite a century of conceptual advances a comprehensive successional theory is lacking. Here we provide an overview of 19 successional theories (‘models’) and their key points, group them based on conceptual similarity, explain conceptual development in successional ideas and provide suggestions how to move forward. Four groups of models can be recognised. The first group (patch & plants) focuses on plants at the patch level and consists of three subgroups that originated in the early 20th century. One subgroup focuses on the processes (dispersal, establishment, and performance) that operate sequentially during succession. Another subgroup emphasises individualistic species responses during succession, and how this is driven by species traits. A last subgroup focuses on how vegetation structure and underlying demographic processes change during succession. A second group of models (ecosystems) provides a more holistic view of succession by considering the ecosystem, its biota, interactions, diversity, and ecosystem structure and processes. The third group (landscape) considers a larger spatial scale and includes the effect of the surrounding landscape matrix on succession as the distance to neighbouring vegetation patches determines the potential for seed dispersal, and the quality of the neighbouring patches determines the abundance and composition of seed sources and biotic dispersal vectors. A fourth group (socio-ecological systems) includes the human component by focusing on socio-ecological systems where management practices have long-lasting legacies on successional pathways and where regrowing vegetations deliver a range of ecosystem services to local and global stakeholders. The four groups of models differ in spatial scale (patch, landscape) or organisational level (plant species, ecosystem, socio-ecological system), increase in scale and scope, and reflect the increasingly broader perspective on succession over time. They coincide approximately with four periods that reflect the prevailing view of succession of that time, although all views still coexist. The four successional views are: succession of plants (from 1910 onwards) where succession was seen through the lens of species replacement; succession of communities and ecosystems (from 1965 onwards) when there was a more holistic view of succession; succession in landscapes (from 2000 onwards) when it was realised that the structure and composition of landscapes strongly impact successional pathways, and increased remote-sensing technology allowed for a better quantification of the landscape context; and succession with people (from 2015 onwards) when it was realised that people and societal drivers have strong effects on successional pathways, that ecosystem processes and services are important for human well-being, and that restoration is most successful when it is done by and for local people. Our review suggests that the hierarchical successional framework of Pickett is the best starting point to move forward as this framework already includes several factors, and because it is flexible, enabling application to different systems. The framework focuses mainly on species replacement and could be improved by focusing on succession occurring at different hierarchical scales (population, community, ecosystem, socio-ecological system), and by integrating it with more recent developments and other successional models: by considering different spatial scales (landscape, region), temporal scales (ecosystem processes occurring over centuries, and evolution), and by taking the effects of the surrounding landscape (landscape integrity and composition, the disperser community) and societal factors (previous and current land-use intensity) into account. Such a new, comprehensive framework could be tested using a combination of empirical research, experiments, process-based modelling and novel tools. Applying the framework to seres across broadscale environmental and disturbance gradients allows a better insight into what successional processes matter and under what conditions. 相似文献
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A Fourier-transform method has been used to measure the spin-lattice relaxation-times (T1 values) of the anomeric protons of a selection of oligo- and poly-saccharide derivatives. Although systematic variations are found for the substances of lower molecular weight, these variations are essentially non-existent at higher molecular weights. Data for the disaccharides cellobiose, maltose, lactose, gentiobiose, and melibiose demonstrate that proton T1-values may provide a powerful method for evaluating conformations of oligosaccharides. 相似文献
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A survey has been made of the spin-lattice relaxation-rates at 100 MHz of the ring protons of all eight of the d-pentopyranose tetra-acetates and of methyl α-d-xylopyranoside triacetate. Qualitative intercomparisons clearly demonstrate the diagnostic utility of these R1-values for configurational assignments. 相似文献
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Laurance WF 《Trends in ecology & evolution》2005,20(12):56-648
The rate of forest destruction has accelerated sharply in Brazilian Amazonia, but there are also vital conservation opportunities with the ongoing designation of important new protected areas. In a timely paper, Carlos Peres argues that an extensive network of mega-reserves, operationally defined as those exceeding 1 million ha in area, is needed to ensure the long-term persistence of Amazonian species and ecological processes. Although such protected areas might seem excessively large to some, disparate lines of evidence suggest that mega-reserves are vital for the future of Amazonian biodiversity. 相似文献