Germination characteristics of lakeshore plants under an artificially stabilized water regime

Abstract

To examine the possibility of the failure of lakeshore plants to germinate under an anthropogenically controlled water regime, we investigated physiological germination responses to temperature and inundation among 25 lakeshore plant species from Lake Kasumigaura, Japan. The requirement of low temperature for dormancy breakage, which is common in spring-germinators, was seen in 14 species. Eight species showed sensitivity to temperature fluctuation, which is thought to be relevant to bare ground detection for germination. Seed germination of most species was significantly reduced under inundation. Seedling emergencies under outdoor conditions in which the wet and inundated conditions of the natural lakeshore habitat were simulated showed that the timing of all species was concentrated in spring. A significant reduction of emergence in the inundated condition was observed in 19 species. Therefore, most of the lakeshore plant species are adapted to germinate in spring on exposed bare ground during low-water periods. The recent imposition of water level control with a winter-spring elevation possibly prevents regeneration of most common lakeshore plants through the loss of seasonal safe sites for germination.