Zur Keimungsbiologie ausgewählter Xerothermrasenarten: Teil 1

Abstract

Partzsch, M.: Germination biology of eight selected xerothermic grassland species – Part 1. – Hercynia N.F. 42 (2009): 239 –254.The species-rich dry grassland communities of the porphyry landscape near Halle/Saale host a number of rare dicotyledonous hemicryptophytes. In open fields the species usually flower abundantly and produce many fruits and seeds during the summer. The purpose of this study was to determine whether such germination behaviour represents a cause for same of the species’ apparent rarity. Seed of eight distinct dry grassland species (Astragalus danicus Retz, Carlina vulgaris L., Erysimum crepidifolium Rchb., Hypochaeris radicata L., Leontodon hispidus L., Prunella grandiflora (L.) Scholler, Pulsatilla vulgaris Mill., Stachys recta L.) were collected and their germination behaviour following harvesting and hibernation under field conditions was monitored in order to determine their optimal germination conditions and seed bank type. Seeds were collected from semi-dry grassland near Halle/Saale. The conditions in the climate chamber were as follows: 8/4 °C at 12 hours light / 12 hours dark; 20/10 °C at 12 hours light / 12 hours dark; 32/20 °C at 12 hours light / 12 hours dark. Thirty batches of seeds (n = 4) were put on filter paper in Petri dishes and were kept permanently moist with de-ionized water. All germinated seeds (radicula being visible) were counted every two to three days and the duration of the experiment was 45 days. The same procedure was repeated in spring of the following year after seed hibernation in the field. For data analyses were calculated the percentage of final germination and germination velocity using the modified Timson´s Index. Multiple comparisons were performed using a parametric one-way ANOVA along with Tukey`s post hoc test (p<0.05) and a two way ANOVA. Percentages were arcsin-transformed prior to analysis. The results showed that germination of Astragalus danicus after harvest was generally low, but was highest under hot conditions. Following hibernation, germination was similarly low under all three temperature/ light conditions. Carlina vulgaris seed germination after harvest was highest under warm and hot conditions; after hibernation all seeds germinated completely under all temperature conditions. Seeds of Erysimum crepidifolium all germinated under warm conditions after harvest while after hibernation germination was greatly reduced. Hypochaeris radicata germinated highest under warm conditions after harvest and after hibernation the seeds germinated to a greater extent, but also highest under 20/10 °C. The germination of Leontodon hispidus seeds increased with increasing temperature after harvest, after hibernation germination was a little higher. Prunella grandiflora seeds germinated highest under warm und hot conditions after harvest while after hibernation germination was greatly reduced. Pulsatilla vulgaris seeds germinated highest under warm und hot conditions after harvest, but after hibernation germination was reduced. Very few of the Stachys recta seeds germinated after harvest as well as after hibernation. The germination biology of the perennial hemicryptophytes of dry grassland communities is very different. I conclude that six species build up a transient (Carlina vulgaris, Erysimum crepidifolium) or shortterm persistent (Hypochaeris radicata, Leontodon hispidus, Prunella grandiflora, Pulsatilla vulgaris) seed bank, whereas two species (Astragalus danicus, Stachys recta) belong to the long-term persistent seed bank type. This implies that a lot of dry grassland species are endangered to isolation in space and time as well as changing environmental conditions.