Zur Keimungsbiologie acht ausgewählter ephemerer Xerothermrasenarten

Abstract

Partzsch, M.: Germination biology of eight selected ephemeral xerothermic grassland species. – Hercynia N.F. 42 (2009): 93–110.The germination behaviour of plants is strongly related to the environmental conditions and the biology and life span of the species involved. In the natural-near xerothermic vegetation of the porphyry landscape around Halle, Germany (Saxony-Anhalt), we can find plant species with a very narrow seasonal dynamic. These are ephemeral plants which are annual and survive long time of the year as seeds in the soil. They can germinate in very early spring or in summer. Other species germinate in autumn und overcome winter as seedlings or juvenile individuals. Both types can be also in combination. For this study our goal was to find out whether the different types of therophytes are characterized by the same germination pattern, or if they show differences depending on their life types. For the consequent comparative studies on germination temperature, percentage germination, velocity, dormancy and viability we selected the following eight species: Cerastium semidecandrum, Erophila verna, Gypsophila muralis, Myosotis ramosissima, M. stricta, Saxifraga tridactylites, Spergula morisonii and Veronica verna.The germination experiments were carried out under varying light-dark-regimes (12/12 hrs at 8/4 °C, 20/10 °C, and 32/20 °C). The first experiment was started ca. 6 weeks after harvest. The rest of the seeds was burrowed under field conditions outdoors and exposed to a natural stratification. The second germination experiment was initiated after hibernation in the following spring. The viability of seeds was tested before and after the 1st and 2nd round of experiments. Results show that there was no complete dormancy in any of the species; a certain proportion of seeds always germinated under all conditions. For C. semidecandrum, E. verna, G. muralis, S. tridactylites and S. morisonii germination percentage and velocity was lowest in the fruiting year while after hibernation it was significantly higher and faster. In the case of M. ramosissima, M. stricta and V. verna, germination was highest in autumn while after hibernation only a small proportion of seeds germinated. The germination behaviour of the eight target species is related to the life span of the species: C. semidecandrum, E. verna, S. tridactylites and S. morisonii are summer annual as well as annual hibernating species. A small proportion of seeds already germinated in the year of harvesting; after hibernation they germinated very quickly with between 85 and 100 % germination at optimal temperature/light-conditions of 20/10 °C. In accordance with Jäger & Werner (2005), M. ramosissima, M. stricta and V. verna are just annual hibernating species. However, in our study they showed highest germination success in autumn while in the spring germination was minimal and slow, and only under cold conditions (8/4 °C). G. muralis is summer annual, but germination in the year of harvesting was low under all three temperature/ light-conditions. After hibernation, half of the seeds germinated quickly under cold and medium conditions. Also, under warm conditions (32/20 °C) she was relatively successful. The very low seed size of the eight species argued for a long-term persistent diaspore bank. Caused to the germination and dormancy pattern it was estimated differently. The results show, that C. semidecandrum, E. verna, S. tridactylites and S. morisonii almost completely germinate after hibernation, which would assign these species to the short-term persistent diaspore bank type. The low germination and the high seed viability after hibernation in M. ramosissima and M. stricta may suggest a long-term persistent diaspore bank type. However, V. verna developed a transient and G. muralis a short-term till long-term persistent seed bank.