ON THE ECOLOGY OF SHORT-LIVED FORBS IN CHALK GRASSLANDS: SEMELPARITY AND SEED OUTPUT OF SOME SPECIES IN RELATION TO VARIOUS LEVELS OF NUTRIENT SUPPLY.

An experiment was set up in order to investigate semelparity and seed output of Daucus carota L., Linum catharticum L., Picris hieracioides L. and Scabiosa columbaria L. in relation to various levels of nutrient supply. Some plants of Daucus carota and Scabiosa columbaria were found to flower within one growing season, when nutrient supply was at its highest, whereas the other species did not flower. In the second growing season almost all plants receiving a maximum supply of nutrients flowered and produced seeds. In Linum catharticum flowering plants were recorded in all treatments. The reproductive plants of all species died after seed shedding, except those of Picris hieracioides and Scabiosa columbaria under high nutrient conditions which formed lateral shoots. These plants survived and were iteroparous. Seeds produced early in the fruiting period were most numerous and heaviest in the treatments with highest levels of fertilization. In Daucus and Scabiosa a positive linear relationship between seed weight and germination success was found. Thus, the plants grown under the highest nutrient supply conditions showed the highest seed output in all species, although this was less clear in Linum. The significance of these results for the field situation is discussed. [ABSTRACT FROM AUTHOR]