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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 197 (1963), S. 1026-1027 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A technique utilizing carbon-14 as a tracer was developed for assaying the in situ productivity of periphyton. The methods wore similar to those that I developed4 for submerged macrophytes. Transparent and opaque 'Plexiglas' chambers4, cylindrical, open at one end, and containing an injection port, ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 33 (1995), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Pelagic trophic structure and energy fluxes are evaluated predominantly on the basis of ingestion of particulate organic matter by living organisms and the effects of consumption on the population dynamics of trophic levels.2. Population fluxes are not representative of the material and energy fluxes of either the composite pelagic region or the lake ecosystem. Metabolism of particulate and especially dissolved organic detritus from many pelagic and non-pelagic autochthonous and from allochthonous sources dominates both material and energy fluxes. Because of the very large magnitudes and relative chemical recalcitrance of these detrital sources, the large but slow metabolism of detritus provides an inherent ecosystem stability that energetically dampens the ephemeral, volatile fluctuations of higher trophic levels.3. The annual time period is the only meaningful interval in comparative quantitative analyses of material and energy fluxes at population, community, and ecosystem levels.4. Non-predatory death and metabolism by prokaryotic and protistian heterotrophs dominate. Continued application of animal-orientated relationships to the integrated, process-driven couplings of the aquatic ecosystems impedes understanding of quantitative ecosystem pathways and control mechanisms.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 1 (1971), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A typical marl lake of the Upper Great Lakes region has very few quantitatively important aquatic macrophytes. The macrophytes, however, dominate the total primary production of the lake. Submersed vegetation is extremely sparse on the shallow (less than I m) marl bench that characterizes the littoral of these lakes, and is completely dominated by one. little-known species (Scirpus subterminalis Torr.) between 1 and 7 m.A detailed investigation of the spatial and seasonal distribution of macrophytic species and biomass showed that S. subterminalis strongly dominated the lake (79% of total biomass). S. suhterminalis represented an almost pure stand (to 200 g m−2 mean annual ash-free dry weight) at all times of the year at intermediate depths of macrophytic growth (1–6 m). Two species of Chara (of eight varieties and forms) were present in significant quantities (12% of total biomass; to 100 g m−2) but were severely limited to shallow depths (0-S-l m) and protected areas. Several annual submersed angiosperms were present (9% of total biomass), but only two species were quantitatively important. Potamogeton illinoensis Morong. and P. praelongus Wulfen formed brief summer peaks (less than 100 g m−2) at 3 and 4–6 m, respectively.A striking feature of the seasonal biomass distribution of Scirpus subterminalis was the higher, viable biomass (to 150g m−2) throughout the winter under ice cover. Cyclic fluctuations of the S. subterminalis populations were discerned at different depths, each with different periodicities. The population at 2 m exhibited a fall peak; that at 4 m had a summer maximum. The lowest overall biomass of S. subterminalis occurred in the 2 m population in June. Chara populations at 0–2 m also exhibited a relatively constant biomass throughout the year. The appearance of Nitella at 7 m in July-October and of Chara at 5 m in September-October was interpreted as an interaction between light, thermal, and carbon stratification.Estimates of macrophytic productivity of perennial (‘evergreen’) species populations whose biomass remains relatively constant throughout the year were made employing several different methods of calculation and turnover factors. All methods resulted in productivity estimates in good agreement with the conservative value of 178 g m−2 year−1 for the entire lake. In comparison to the other components (phyto-planktonic, epiphytic and epipelic algae) of the primary production of Lawrence Lake, the aquatic macrophytes constituted a major portion (anuual mean 82·77 g C m−2 year−1 or 48·3 %) of the total production of the lake.The low diversity but relatively high quantitative importance of macrophytes in marl lakes is attributed to an adverse dissolved inorganic and organic chemical milieu which inhibits phytoplanktonic production and allows only certain adapted macrophytes to develop strongly. The phenomenon of perennial biomass levels throughout the year is believed to be much more common than previously suspected and has iikely resulted from adaptations of submersed macrophytes to ameliorated conditions of water and temperatures relative to the terrestrial situation in winter.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. We examined the absorption of solar radiation by phytoplankton and chromophoric dissolved organic matter (CDOM) taking into account riparian shading in the rivers, reservoirs, swamps of the Neuse River Estuary and its drainage basin.2. In the streams, CDOM typically absorbed 55 and 64% of photons in the spectral range of 400–700 nm (photosynthetically active radiation, PAR) and 500–600 nm, respectively. The large proportion of photons absorbed by CDOM indicates high potential for abiotic photochemial reactions in the 500–600 nm region.3. Despite the high concentration of nutrients, phytoplankton contributed little (2%) to the total absorption of PAR in the streams. Small (〈30 m wide) streams typically received only 7% of incident PAR that impinged onto the more exposed reservoirs and estuary. Riparian shading and the low contribution of phytoplankton to the total absorption resulted in conditions where phytoplankton absorbed nearly two orders of magnitude less PAR in the streams than in the estuary and reservoirs.4. The results indicated that riparian shading and non-algal absorbing components can significantly restrict phytoplankton production in nutrient-rich streams with a high concentration of CDOM flowing throughout forested catchments.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Populus tremuloides leaf litter was produced under elevated (ELEV = 720 ppm) and ambient (AMB = 360 ppm) atmospheric CO2 conditions. Leaf chemical quality was significantly altered by CO2 enrichment. ELEV leaves had significantly higher concentrations of phenolic compounds and lignins, and higher C : N ratios than AMB.2. Leaf litter was incubated in a headwater stream for 14 days to become colonised by microorganisms; aquatic bacterial productivity was significantly lower on ELEV than on AMB leaf litter. Colonised leaves were fed to four species of detritivorous mosquito larvae to assess their survivorship and development rates.3. Larval mortality was 2.2 times higher for Aedes albopictus fed ELEV litter when compared with AMB. Although mortality of A. triseriatus, A. aegypti and Armigeres subalbatus was not affected by treatment, larval development rate was delayed by 78, 25 and 27%, respectively, when fed ELEV litter.4. Increased mosquito mortality and/or delayed larval development rates are more likely to have negative implications for food web structure and productivity in ecosystems where immature stages of mosquitoes are an important food source of predators.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Up to 99% of the carbon fuelling the food webs of temperate woodland streams is derived from inputs of terrestrial leaf litter. Aquatic bacteria, fungi, and detritivore invertebrates directly utilize these inputs, transferring this energy to other components of the food web. Increases in atmospheric CO2 could indirectly impact woodland stream food webs by chemically altering leaf litter. This study evaluated CO2-induced chemical changes in aspen (Populus tremuloides) leaf litter, and the corresponding effects on stream bacteria, fungi and leaf-shredding cranefly larvae (Tipula abdominalis: Diptera). Leaf litter from plants grown under elevated CO2 had decreased nutritional value to aquatic decomposers and detritivores because of higher levels of structural compounds and lower nitrogen content. Consequently, elevated CO2-grown leaf litter supported 59% lower bacterial production in a stream than litter grown at ambient CO2 levels, while not affecting fungal biomass. Larval craneflies fed elevated CO2-grown microbially colonized leaves consumed less, assimilated less, and grew 12 times slower than their ambient fed counterparts.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 49 (1980), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Cellular and extracellular levels of cAMP were analyzed in the blue-green algae Microcystis aeruginosa, Anabaena flos-aquae, and Synechococcus leopoliensis and the green algae Chlorella pyrenoidosa, Cosmarium botrytis, Pandorina morum, Scenedes-mus communis, and Pediastrum biradiatum. On the basis of chromatographic analyses, and several biochemical assays, each alga produced cAMP and released it into the medium. Cellular cAMP (92–394 pmol g−1) and extracellular cAMP (8–440 pmol liter−1) varied greatly among species.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 52 (1981), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Tissues from the aquatic macrophyte species Scirpus subterminalis, Najas flexilis, Ceratophyllum demcrsum, Potamogeton zosteriformis, and Nuphar advena contain cAMP in quantities similar to those reported in algae. Scirpus, Najas, and Ceratophyllum released cAMP into the extracellular media in quantities which varied interspecifically and intraspecifically in differing media. Macrophytic release of cAMP may be an important source of dissolved cAMP in lakewater.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An annual investigation of rates of photolithotrophy, photoheterotrophy, and chemoheterotrophy utilizing glucose and bicarbonate was made within the pelagic zone of a small, hardwater, southwestern Michigan lake. Sampling proceeded on a monthly, diurnal, and depth-wise basis. Annual mean photoheterotrophic uptake was estimated at 2.6μg C m−3h−1. Two periods of relatively high activity were observed: one during spring overturn and the second during the late summer period. In general, greatest contributions to overall carbon cycling occurred during morning to midday incubation periods and at intermediate depths within the water column. Rates of chemoheterotrophy averaged 6.9μg C m−3h−1 and were relatively uniform throughout the annual period. Greatest overall chemoheterotrophic activity was associated with periods of overturn. In general, this activity increased throughout the day and with increasing depth within the water column. The annual mean for photolithotrophic fixation was 1.33 mg C m−3h−1. Greatest contributions to rates of photosynthesis were associated with epilimnetic waters during early morning and midday incubations. Relatively minor contributions to inorganic fixation were made by waters below the 6-meter contour. Spring overturn and late summer represented periods of particularly great photolithotrophic activity. Quantitative comparisons among carbon pathways indicate that rates of pelagic heterotrophy, both photo- and chemoheterotrophy combined, contribute small quantities of carbon to overall carbon metabolism in this oligotrophic system. Qualitative comparisons among pathways indicate strong spatial and temporal separation. The late summer period showed greatest seasonal separation of the three pathways. Spring values represented a period of relatively high activity for all three pathways. On a depth-wise basis, photolithotrophic activity was greatest near the surface and chemolithotrophic activity greatest near the bottom. Photoheterotrophy took an intermediate position between the two. Diurnally, photoheterotrophy and photolithotrophy showed greatest activity during midday and early morning periods, whereas chemoheterotrophy increased throughout the daylight period and reached maximal values in sunset incubations.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 50 (1981), S. 158-161 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The objective of this study was to separate the effects of plant biomass and growth rate on vegetative reproduction in two species of cat-tail, Typha latifolia and T. angustifolia. Replicate clones of both species were grown under conditions of 100%, 42%, 24%, and 9% full sunlight with harvests at 41, 70, and 91 days after shading. T. angustifolia produced most of its vegetative offspring before the first harvest and increased biomass over the remainder of the experiment by increasing the size of its ramets. In contrast, T. latifolia produced vegetative offspring gradually throughout the experiment adding new ramets only after existing clones were of mature size. As a result of these differences in the cloning process, T. angustifolia showed little correlation between vegetative reproduction and clone size while T. latifolia showed a strong correlation between gegetative reproduction and clone size at the three highest light intensities. Growth rates, average clone size and vegetative reproduction were all reduced by reductions in light intensity for both species. However, no effect of growth rate on the relationship between clone size and vegetative reproduction in T. latifolia could be detected. T. latifolia showed greater survivorship and more biomass production under 9% light than T. angustifolia indicating a greater shade tolerance.
    Type of Medium: Electronic Resource
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