Bleaching and cold stratification can break dormancy and improve seed germination in Cyperaceae

Seed germination of sedges is often difficult, due to physiological dormancy and the hard seed coat. It has been proposed that chemical scarification by sodium hypochlorite (‘bleach’) and cold stratification might successfully break this type of dormancy and improve seed germination rates. Yet the choice of the dormancy-breaking conditions in previous studies appears to be arbitrary, resulting in inconsistent results when applied to the seeds of other sedges. Here, we propose and test a strategy for optimizing the dormancy-breaking treatment to achieve higher germination rates and minimize the number of damaged seeds in 16 ‘hard-to-germinate’ members of the Cyperaceae family. The seeds were soaked in 0–10% bleach solutions for different periods of time (from 1 to 120 h) followed by immediate germination tests or cold stratification for either 9 or 18 weeks. To break dormancy, we recommend pretreatment of seeds with sodium hypochlorite, possibly followed by cold stratification, but details (bleach concentration-duration and stratification duration follow each species) varied by species: Bolboschoenus glaucus, Eleocharis palustris and E. uniglumis (2–6% for 6–48 h, 9 weeks), Cladium mariscus (4–10% for 72–120 h, 18 weeks), Schoenoplectiella mucronata (2–10% for 72–120 h, 0 weeks), Schoenoplectus tabernomontani (6–10% for 24–48 h, 18 weeks), Schoenus nigricans (4–6% for 24–72 h, 0 weeks), Bleach-scarification treatment negatively affected seed germination in Eleocharis ovata, Eriophorum latifolium, Rhynchospora alba, Schoenoplectiella supina and Scirpoides holoschoenus, whereas seeds of Bolboschoenus maritimus and Rhynchospora glomerata showed no response to the treatment. We conclude that careful selection of seed dormancy-breaking conditions plays a crucial role in optimizing sedge seed germination. The proposed range-searching approach can help to detect the species-specific, in some cases very narrow, optimum for the bleaching treatment followed by cold stratification, at least in some species of the Cyperaceae family.