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Germination Speed (germination + speed)
Selected AbstractsWelche Bedeutung hat die sexuelle Reproduktion für den Erfolg der Art Calamagrostis epigejos (L.) Roth?FEDDES REPERTORIUM, Issue 3-4 2003A. Grüttner Dr. Als Quellen der Variabilität im Potential der sexuellen Reproduktion fanden sich Unterschiede in der Keimungsgeschwindigkeit (entspelzte Karyopsen keimten rascher und synchroner), bei den Keimraten und vor allem bei der Zahl keimfähiger Diasporen pro Rispe. Von den anderen abweichend zeigten kleine isolierte Bestände geringere Keimraten und brachten , wohl bedingt durch Selbstinkompatibilität , kaum keimfähige Diasporen hervor. Bei gezielter Suche fanden sich Keimlinge auf offenen, zumindest leicht tonhaltigen Rohböden. Das Wachstum der Keimlinge stagnierte und keiner von über 6000 überlebte bis zum nächsten Jahr. Da Bewässerung die Entwicklung auf dem selben Substrat sehr förderte, war offenbar Wassermangel für das geringe Wachstum ausschlaggebend. Die erfolgreiche generative Etablierung ist also auf den Zufall günstiger Witterungsphasen oder Standorte angewiesen. Auch im Frühjahr waren noch keimfähige Diasporen in aufrechten Rispen nachweisbar, sodass sich der Diasporenfall mehr oder weniger über das gesamte Jahr erstreckt. Im Zusammenspiel mit dem Fehlen von Dormanz ermöglicht das die Nutzung nicht vorhersagbarer günstiger Witterungsphasen. Bei einem Kulturversuch kamen einzelne Individuen auch mit schwierigen Substraten gut zurecht, auf denen die Mehrzahl kümmerte. Danach ergibt sich die standörtliche Breite der Art C.,epigejos als Summe sehr unterschiedlicher Reaktionsnormen der Individuen. Die angeführten Befunde unterstreichen insgesamt die Bedeutung der sexuellen Reproduktion und der genetischen Diversität für den Erfolg der Art. Is sexual reproduction important to the success of Calamagrostis epigejos (L.) Roth? Calamagrostis epigejos is very common in Central Europe and occupies an extraordinary wide range of habitats. As up to now nearly no reports exist on spontaneous seedling emergence, we aimed to investigate several aspects of sexual reproduction, thereby refering to contrasting habitat types. Components in the variability of the potential of sexual reproduction were differences in germination speed and rates and, above all, number of germinable seeds per panicle. Unlike the others, small isolated stands produced very low numbers of germinable seeds, probably caused by selfincompatibility. Our search for seedlings was successful at several sites , all distinguished by raw soil, a certain clay content, and little cover of vegetation and plant litter. The seedlings grew very slowly and none of more than 6000 survived the first year. Additional water enabling much better growth indicates the necessity of favorable weather or favorable habitats (with constant water supply) for successful seedling establishment. Seed dispersal nearly all around the year, combined with the lack of dormancy, allows to make use of the unpredictable opportunities of suitable weather periods. A growth experiment on different substrates demonstrated: the more extreme the conditions, the more differentiated the amount of biomass achieved by each of 20 genets. Some genets grew well even on substrates where most others stagnated. This outcome suggests the wide range of habitats covered by C. epigejos to be the result of the genetic diversity, which in turn is maintained by sexual reproduction and avoidance of inbreeding. [source] Helophyte germination in a Mediterranean salt marsh: Gut-passage by ducks changes seed response to salinityJOURNAL OF VEGETATION SCIENCE, Issue 3 2004J.L. Espinar Abstract: Question: In seeds which are regularly consumed by waterbirds in the field, how does gut-passage modify their response to salinity gradients? Location: Doñana National Park salt marsh, south-west of Spain. Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non-ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0,32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed. Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut pas sage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (,2 dS/m) but decreased it at high salinities (,4 dS/m). Conclusion: Gut-passage by ducks significantly changes seed response to salinity. The outcome of plant-animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results. [source] Differential Responses of Germination and Seedling Establishment in Populations of Tragopogon pratensis (Asteraceae)PLANT BIOLOGY, Issue 1 2007L. D. Jorritsma-Wienk Abstract: The establishment phase is an important bottleneck in the life cycle of plants. It consists of two steps that are rarely separated, i.e., the germination of seeds and the establishment of seedlings. Here we report the results of two experiments in which we independently investigated germination and seedling establishment in the greenhouse, under different grass vegetation treatments representing different regeneration niches. Seeds of Tragopogon pratensis from six populations and two habitat types were studied, three from roadside verges and three from hayfields. Germination percentages and germination speed were higher for seeds from roadside verges than for seeds from hayfields, but were little affected by treatment. In contrast, seedling growth was much lower in the tall grass vegetation, than in the short grass and especially the bare soil treatment. Seedling sizes were generally similar for different populations and habitat types. Our results thus show that the two early steps in the establishment phase of plants may respond very differently to the micro-environment, and may have a different selection history. Insight into the ecology and evolution of life histories may require that germination and establishment are considered separately. [source] Fitness consequences of floral variation in Senecio jacobaea (Asteraceae): evidence from a segregating hybrid population and a resource manipulation experimentBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2001STEFAN ANDERSSON The present study examines some of the ecological factors that might exert selection on floral morphology in Senecio jacobaea, a self-sterile composite which exhibits geographic variation in the frequency of rayed and discoid individuals. Regression analyses of phenotypic data from a large, segregating hybrid population, established in a semi-natural (garden) environment and studied over a 2-year period, revealed a negative relationship between the size of the rays and the average germination rate of the maternal seed crop, a pattern that can be attributed to the reduced germination speed of achenes from ray florets. There was no effect of ray size on the amount of cross-pollination achieved, the proportion of heads infested by larvae of seed flies (Pegohylemyia) and the amount of resources retained for the next flowering season. The lack of resource costs was also apparent in a manipulation experiment with greenhouse-grown plants of the rayed phenotype: artificial removal of all rays at the early bud or flowering stage had no detectable effect on subsequent flower and fruit development, regardless of whether the plants experienced high or low water stress. Given these and other observations, I hypothesize that plant-animal interactions and resource costs sometimes play a minor role in exerting selection on flower morphology and that spatially varying selection on germination behaviour accounts for some of the morph frequency variation in S. jacobaea. [source] | ||||||||||