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  • 1
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Thirty-six species of macrophytes (fourteen flowering plants, two quillworts, sixteen mosses and liverworts, and two algae) were collected in an extensive survey of 116 high mountain lakes in the eastern Pyrenees. Seventy per cent of the lakes showed macrophyte development.2. The isoetids (Isoetes lacusiris, Isoetes setacea and Subularia aquatica) were the dominant growth form, although the natopotamid Sparganium angusifolium was the most widespread species. Potamids (Potamogeton spp., Ranunculus spp.), the alga Nitella gr. opaca and some mosses (Warnstorfia exannulata, Sphagnum denticulatum) were often present.3. A multivariate ordination analysis (RDA-redundancy analysis) revealed that water chemistry, altitude and vegetation cover of the catchment, and nutrient availability are major environmental factors associated with macrophyte distribution along the eastern Pyrenean lakes. Isoetids prevailed in softwater oligotrophic lakes, potamids in relatively hardwater oligotrophic lakes, and Potamogeton natans and Callitriche palustris in small and eutrophic water bodies affected by the presence of cattle.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Littorella uniflora ; Terrestrial isoetids ; Carbon uptake ; Sediment CO2 utilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Submerged macrophytes of the isoetid life form derive the majority of their CO2 for photosynthesis from the sediment. The experiments described here were designed to test the hypothesis that root uptake of CO2 is important also in the terrestrial form of Littorella uniflora. The results of 14CO2 experiments showed that sediment CO2 contributed 56% of the total fixation at 0.1mm CO2 in the rhizosphere, 83% at 0.5mm and 96% at 2.5mm. Sediment CO2 in emergent Littorella stands ranged from 0.1 to 1.0mm and averaged 0.5mm. Measurements of the net CO2 exchange over the leaves showed an even higher dependence of the sediment as CO2 source. Littorella leaves had no stomata at the base and densities (ca. 100 mm−2) typical of terrestrial plants at the tip, allowing sediment-derived CO2 to be supplied along the length of the leaf. The stomata permit supply of CO2 from the air during periods of reduced sediment CO2 concentrations (e.g. if the sediment dries up) and regulate transpiration.
    Type of Medium: Electronic Resource
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