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  • 1
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The effects of the flooding-resistant plant species Rumex palustris and the non-flooding-resistant plant species Rumex acetosa on nitrification were compared. The plants were grown under drained and waterlogged conditions on a mixture of calcareous riversand and sieved grassland soil with a high potential nitrifying activity. In the shoots of R. acetosa, but not in those of R. palustris, the ratio between the amounts of accumulated carboxylates and organic nitrogen, ((CA-A)/Norg.), appeared to be a useful indicator of ammonium or nitrate consumption by tghe plant. In both plant species, the inorganic nitrogen source had no observed effect on the (C-A)/Norg. ratio in the roots.The growth of R. acetosa, but not that of R. palustris was inhibited by waterlogging of the soil. Both the activity and the growth of the ammonium-oxidizing bacteria were repressed under drained and waterlogged conditions in soils with R. palustris, a condition that was attributed to a competitive ammonium uptake by its relatively fast growing roots. In the presence of R. acetosa, the activity and growth of the ammonium-oxidizing bacteria were inhibited under waterlogged, but not under drained, conditions. he growth and activity of nitrite-oxidizing bacteria in the absence of actively ammonium-oxidizing, nitrite-producing bacteria was likely due to organotrophic growth.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Rosettes of flooding-resistant Rumex palustris plants show a submergence-induced stimulation of elongation, which is confined to the petioles of young leaves. This response increases the probability of survival. It is induced by ethylene that accumulates in submerged tissues. Flooding-intolerant Rumex acetosella plants do not show this response. We investigated whether differences in shoot elongation between the species, between old and young leaves and between the petiole and leaf blade of a R. palustris plant result from differences in internal ethylene concentration or in sensitivity to the gas. Concentrations of free and conjugated ACC in petioles and leaf blades of R. palustris indicated that ethylene is synthesized throughout the submerged shoot, although production rates varied locally. Nevertheless, no differences in ethylene concentration were found between submerged leaves of various ages. In contrast, dose-response curves showed that only elongation of young petioles of R. palustris was sensitive to ethylene. In R. acetosella, elongation of all leaves was insensitive to ethylene. We conclude that variation in ethylene sensitivity rather than content explains the differences in submergence-induced shoot elongation between the two Rumex species and between leaves of R. palustris.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5052
    Keywords: Dominant plant species ; Litter ; Ordination ; Riparian wetlands ; Zonation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In riparian wetlands total standing crop often fails to account for a significant part of the observed variation in species richness and species composition within communities. In this study, we used abundance of the dominant species instead of total standing crop as the biotic predictor variable and investigated its relationships with species composition and species richness in communities dominated by Phragmites australis (Cav.) Trin. ex Steudel. This was done by measuring soil organic matter content, litter cover and elevation, Phragmites abundance (standing crop and stem density) and species composition in 78 relevés. In addition, we tried to identify the environmental boundaries of Phragmites communities by sampling relevés in neighbouring communities. Two gradients were related to a decline in Phragmites abundance: one gradient, perpendicular to the shoreline, was mainly related to increased elevation and the second gradient ran parallel to the shoreline and was related to increased amounts of soil organic matter. Within the relevés dominated by Phragmites, stem density of Phragmites and litter cover were the only factors significantly related to species composition in the RDA solution. Litter cover and standing crop of the dominant accounted for 64% of the variation in species richness within the Phragmites-dominated community. These results show that dead and living biomass of the dominant species may account for a substantial part of the variation in species composition and species richness within a single community.
    Type of Medium: Electronic Resource
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