Germination and emergence of Rumex in river flood-plains. II. The role of perianth, temperature, light and hypoxia

The germination responses of Rumex acetosa, R. crispus and R. palustris were studied in relation to perianth-imposed primary dormancy, the temperature and light control of germination and response to hypoxia. The perianth-imposed primary dormancy in R. crispus and R. palustris is related to light filtering through the perianth and/or inhibited water uptake due to a water repulsive layer around the perianths. Rumex acetosa is able to germinate at a constant rate over a wide range of temperatures, whereas both the other species are characterized by fast and maximal germination at regimes with higher upper temperatures; in this sense R. palustris was the most extreme species. In R. acetosa, germination in light and dark is independent of diurnal fluctuating temperatures. Dark germination in R. crispus is stimulated by alternating temperatures. Rumex palustris needs both light and fluctuating temperatures to induce germination. Differences in germination behaviour in relation to light and temperature are discussed in relation to the phytochrome regulation of Rumex germination. In contrast to R. acetosa, imbibed achenes of both R. crispus and R. palustris are able to survive a prolonged hypoxic incubation. The results are discussed in relation to the distribution of the three Rumex species in a flooding gradient of a river area.