GERMINATION AND SEEDLING EMERGENCE OF SCIRPUS-LACUSTRIS L AND SCIRPUS-MARITIMUS L WITH SPECIAL REFERENCE TO THE RESTORATION OF WETLANDS

Germination and seedling emergence of Scirpus lacustris L. ssp. lacustris (S.l. lacustris), S. lacustris L. ssp. tabernaemontani (C.C. Gmelin) Syme (S.l. tabernaemontani) and Scirpus maritimus L. were investigated in order to assess their ability to establish from seed in former tidal waters, where the original standing population has almost completely disappeared. Germination of 1-year-old seeds of all three taxa was improved by stratification (wet/cold storage) and in the case of S.l. lacustris and S. maritimus, by bleach-scarification (deeds pre-soaked in sodium hypochlorite). Germination of S.l. lacustris and S. maritimus was equally improved by both pretreatments. When light was supplied during daytime, the minimum stratification period required for maximum germination was lower for S. maritimus (4 weeks) than for both S. lacustris subspecies (more than 6 weeks). In continuous darkness, seeds of the three taxa hardly germinated after a stratification period of less than 6 weeks, but after 80 weeks of stratification, germination in light and darkness were almost equal. Fluctuating temperatures compared with constant temperatures improved germination of S.l. tabernaemontani and S. maritimus, but not that of S.l. lacustris. The amplitude between day and night temperature (from 5 to 25 degrees C) did not affect germination. Germination of S. maritimus increased with increasing day temperature. Generally, at constant temperatures the germination of 66-month-old seeds was reduced compared with that of 14-month-old seeds of all three taxa. At a fluctuating temperature of 30/5 degrees C, germination of old compared with young seeds of S.l. lacustris and S. maritimus was not reduced; it was halved, however, in S.l. tabernaemontani. Underwater the three Scirpus taxa were able to emerge from the substrate after being buried at substrate depths of 0.5 and 2 cm. At a burial depth of 5 cm only a small portion of the S. maritimus seeds and none of the two S. lacustris subspecies emerged. The failure to germinate and emerge at 5 cm burial depth could not be ascribed to diminishing fluctuation of temperatures with increasing burial depth.