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Relationships between different measures of succulence and Crassulacean acid metabolism (CAM; defined here as nocturnal increases in tissue acidity) were investigated in leaves of ten species of Sansevieria under greenhouse conditions. CAM was found in seven of the ten species investigated, and CAM correlated negatively with leaf thickness and leaf hydrenchyma/chlorenchyma ratio. Similarly, CAM correlated negatively with leaf water content, but only when expressed on a fresh mass basis. CAM was not correlated with "mesophyll succulence", but weakly with leaf chlorophyll concentration. These results indicate that CAM is associated more with "all-cell succulence" and not with the amount of leaf hydrenchyma in the genus Sansevieria. The findings of this study emphasize the importance of defining the nature of "leaf succulence" in studies of photosynthetic pathways and leaf morphology. Evidence is also provided that CAM and succulence arose multiple times in the genus Sansevieria.
Sansevieria pfennigii, which to date has been a doubtful species, is confirmed as extant by a recent collection from the Lindi Region in southern Tanzania. The original description of the species, which is based on herbarium material only, is here emended based on additional observations recorded from living plants, including fruits that were previously unknown. Sansevieria pfennigii distinguishes from S. canaliculata, to which it was repeatedly assigned, by its capitate instead of elongate inflorescence, rough rather than smooth leaves, non-pungent instead of pungent leaf tips, dull green leaf colour, more delicate overall appearance, alongside other traits. The difference in inflorescence architecture indicates that these species belong to different groups within Sansevieria and are not closely related; the closest relatives of S. pfennigii are probably S. fischeri and S. stuckyi. Sansevieria pfennigii occurs on well-drained soil in forests, close to S. canaliculata populations. According to the extent of the population seen and the species' overall rarity, it is tentatively assessed as critically endangered.
Molinio-Arrhenatheretea = Kulturgrasland und verwandte Vegetationstypen. Teil 2: Molinietalia
(2004)
Rivers form the most important natural corridors through the landscape. Certain plant species grow mainly or exclusively in these corridors as it has been observed for about 150 years in Central European lowlands. However, these species do not form a homogenous group in terms of biogeography, site requirements, life form, or any other feature this distribution pattern. Accordingly, first, we give a review of the various hypotheses which have been proposed to explain the river corridor distribution pattern. This includes (1) river corridors acting as routes of migration or invasion, (2) floodplain-specific disturbance providing open sites, (3) temporary anoxic conditions during floods, (4) deviating meso-climatic conditions, (5) specific substrate and nutrient supply, and (6) water supply. In particular, the above hypotheses (2-5) imply that river corridor plants may be well-adapted to specific stress and regeneration conditions in floodplains while other species may be not. This may lead to reduced competition in river corridors. We suggest this mechanism to constitute actual benefits for river corridor plants. Secondly, we present a simple model of multi-species population dynamics to show, that our competition-related framework is, in principle, able to explain river corridor plant species distribution patterns. As, however, none of the above hypotheses (1-6) have been tested experimentally we thirdly present a currently running experimental study on the river corridor plant Juncus atratus (black rush) in north- eastern Germany. We emphasize that much more experimental evidence must be gained on population ecology and meta- population dynamics to understand the distribution patterns of river corridor plants.
Aims: Factors limiting distributions of species are fundamental to ecology and evolution but have rarely been addressed experimentally for multiple species. The conspicuous linear distribution patterns of plant species confined to river corridors in the Central European lowlands constitute an especially long-standing distribution puzzle. We experimentally tested our novel hypothesis that the tolerance of species to river corridor conditions is independent of the degree of confinement to river corridor habitats, but that species not confined to river corridors are better able to take advantage of the more benign non-river corridor conditions. Methods: We grew 42 herbaceous species differing in their confinement to river corridors in a common garden experiment on loamy soil typical for river corridor areas and sandy soil typical for non-river corridor areas, and with and without a flooding period. For a subset of species, we grew plants of both river corridor and non-river corridor origin to test for adaptation to river corridor conditions. Important findings: Species more confined to river corridor areas benefited less from the more benign non-flooded and non-river corridor soil conditions than species of wider distributional range did. For subsets of 7 and 12 widespread species, the response to flooding and soil origin, respectively, did not differ between plants from river corridor sites and plants from other sites, suggesting that the habitat tolerance of widespread species is clue to phenotypic plasticity rather than to local adaptation. Overall, we found clear support for our novel hypothesis that species not confined to river corridors are more able to take advantage of the more benign non-river corridor conditions. Our study provides a general hypothesis on differences between species confined to stressful habitats and widespread species out for test in further multispecies comparative experiments.