Seed dormancy cycles and germination phenologies in sedges (Carex) from various habitats

Abstract

Seeds (nutlets) of four temperate-zone perennialCarex species from various habitats and with different growth forms were investigated to identify seasonal germination patterns. In the first experiment, freshly matured seeds were sown in summer 1994 on the soil surface and at a depth of 1 cm at a sunexposed site and under a leaf canopy in an experimental garden. In the second experiment, seeds were exhumed after various periods of burial (7-cm depth) for up to 30 months and tested for germination in both light and darkness at 15°, 25°, and 22/10°C. In the first experiment, freshly-matured seeds of the four sedges did not germinate during summer or autumn 1994. Almost all surface-sown seeds of the four species germinated from late spring to summer in 1995 at the sun-exposed site. Most buried seeds of three species germinated in the soil, but germinants died prior to emergence. InCarex flacca, however, about 50% of the buried seeds germinated and emerged until 1997, and the ungerminated seeds remained viable. At the shaded site, seeds ofC. acutiformis. andC. flacca did not germinate, whereas a small percentage of the buried and surface-sown seeds ofC. arenaria andC. extensa emerged in the second year. Seeds ofC. acutiformis andC. flacca were dormant, and those ofC. arenaria andC. extensa were conditionally dormant at the beginning of the second experiment. All four species had annual dormancy cycles at 22/10°C in light and in darkness and at 25° and 15° in light. Seeds came out of dormancy in late autumn or winter and re-entered dormancy or conditional dormancy in late spring or early summer. Very few seeds of any of the four species germinated at constant temperatures in darkness. No seeds germinated during burial in soil at a depth of 7 cm. These field germination patterns indicate that the four sedges have the potential to form a persistent seed bank but that losses due to germination in the seed bank are dependent on temperature amplitudes, mean temperatures, and red: far red ratios under a leaf canopy.