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  • 1
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. The elemental composition, the proportion of living organic carbon and the carbon stable isotope signatures of particulate organic matter (POM) were determined in a large river floodplain system in order to elucidate the major carbon sources in relation to the hydrological conditions over a 13-month period.2. Two floodplain segments and the main channel of the River Danube downstream of Vienna (Austria), were compared on the basis of discharge and water age estimations. The more dynamic floodplain was connected to the main channel for 46% of the study period and drained up to 12% of total discharge at high water.3. The mean C : N ratio and δ13C signature of the POM increased from the floodplain site that was more isolated from the river (6.6; −33‰) to the main channel (8.4; −25‰). At the dynamic floodplain site, the C : N ratio and the δ13C signature of the POM increased with hydrological connectivity (expressed as water age).4. Only during flood events (4% frequency of occurrence), a considerable input of riverine POM was observed. This input was indicated by a C : N ratio of the POM pool of more than 10, the amount of detrital carbon (〉80% of the total POM pool) and a δ13C signature of POM of more than −25‰ in the dynamic floodplain.5. Plankton derived carbon, indicated by C : N ratios less than eight and δ13C values lower than −25‰, dominated the particulate organic carbon (POC) pool at both floodplain sites, emphasising the importance of local (autochthonous) production. Phytoplankton was the major plankton compartment at the dynamic site, with highest biomasses at medium water ages.6. At the dynamic floodplain site, the Danube Restoration Project has enhanced the duration of upstream surface connection with the main channel from 4 to 46% frequency of occurrence. Therefore, the export of living POC to the main channel is now established during phases of maximum phytoplankton production and doubled the estimated total export of non-refractory POM compared with prerestoration conditions.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 54 (2003), S. 0 
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We compared functional diversity in 6- to 150-year-old sites on two primary successional glacier forelands (Ödenwinkelkees and Rotmoosferner, Austria) and related these changes to properties of their habitat in the soil (pH, soil organic matter, mineral nitrogen, phosphorus). Comparisons were made with land undisturbed for 9500 years immediately outside the glacier foreland. The functional diversity of the soil microflora was assessed based on microbial processes (N mineralization, ammonium oxidation, arginine deaminase) as well as on the activities of soil enzymes (protease, urease, xylanase, phosphatase, arylsulphatase). On both chronosequences, functional diversity (Shannon diversity index and evenness) and enzyme activity increased up to an age of 50 years, while older soils appeared to have reached a temporary steady state. The values of microbial biomass and enzyme activity were generally smaller in the Ödenwinkel soils than in the Rotmoos sequence, indicating that primary input of carbon from plant growth was less. Functional diversity increased with increasing plant development and organic matter accumulation, explaining similarities in enzyme activity patterns in the sequences. The local climates might also have contributed to the magnitude of the changes. Our data suggest that microbial functional diversity reached stability within 50 years' succession.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Foliar carbon isotope discrimination (Δ) of C3 plants decreases in water-deficit situations as discrimination by the photosynthetic primary carboxylation reaction decreases. This diminished Δ in leaves under water deficit can be used as a tracer to study whole plant carbon allocation patterns. Carbon isotope composition (δ13C value) of leaf hot water extracts or leaf tissue sap represents a short-term integral of leaf carbon isotope discrimination and thus represents the δ13C value of source carbon that may be distributed within a plant in water-deficit situations. By plotting the δ13C values of source carbon against the δ13C values of sink tissues, such as roots or stems, it is possible to assess carbon allocation to and incorporation into sink organs in relation to already present biomass. This natural abundance labelling method has been tested in three independent experiments, a one-year field study with the fruit tree species Ziziphus mauritiana and peach (Prunus persica), a medium-term drought stress experiment with Ziziphus rotundifolia trees in the glasshouse, and a short-term drought stress experiment with soybean (Glycine max). The data show that the natural abundance labelling method can be applied to qualitatively assess carbon allocation in drought-stressed plants. Although it is not possible to estimate exact fluxes of assimilated carbon during water deficit the method represents an easy to use tool to study integrated plant adaptations to drought stress. In addition, it is a less laborious method that can be applied in field studies as well as in controlled experiments, with plants from any developmental stage.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 22 (1999), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The foliar content of nitrogen and the relative abundances of 13C and 15N were analysed in vascular epiphytes collected from six sites along an altitudinal gradient from tropical dry forests to humid montane forests in eastern Mexico. The proportion of epiphyte species showing crassulacean acid metabolism (CAM) (atmospheric bromeliads, thick-leaved orchids, Cactaceae, and Crassulaceae) decreased with increasing elevation and precipitation from 58 to 6%. Atmospheric bromeliads, almost all of which had δ13C values indicating CAM, were more depleted in 15N (x=−10·9‰± 2·11) than the C3 bromeliads which form water-storing tanks (−6·05‰± 2·26). As there was no difference in δ15N values between C3 and CAM orchids, the difference in bromeliads was not related to photosynthetic pathways but to different nitrogen sources. While epiphytes with strong 15N depletion appear to obtain their nitrogen mainly from direct atmospheric deposition, others have access to nitrogen in intercepted water and from organic matter decomposing on branches and in their phytotelmata. Bromeliads and succulent orchids had a lower foliar nitrogen content than thin-leaved orchids, ferns and Piperaceae. Ground-rooted hemi-epiphytes exhibited the highest nitrogen contents and δ15N values.
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