Treat seeds of non-woody plants with chemicals before sowing: freshwater wetlands

Supporting evidence from individual studies

1. A replicated, randomized, controlled study in 1994–1996 in greenhouses in Florida, USA (Ponzio 1998) found that soaking sawgrass Cladium jamaicense seeds in gibberellic acid had no significant effect on their germination rate. Germination rates did not significantly differ between seeds soaked in water then gibberellic acid (48–49% germinated) and seeds soaked in water only (44–51% germinated). For reference, seeds that were not soaked in gibberellic acid or water had a germination rate of 55–57%. Methods: Across September 1994 and 1995, sawgrass seeds (either freshly collected or three years old) were sprinkled onto 30 trays of sterilized soil (100 seeds/tray). Ten trays were planted with seeds soaked in water for 24 h then a gibberellic acid solution for 12 h. Ten trays were planted with seeds soaked in water for 24 h. Ten trays were planted with untreated seeds (left dry at room temperature). The trays were placed in random positions in greenhouses and watered daily until no more germination occurred.

   Study and other actions tested

   Referenced paper

   Ponzio K.J. (1998) Effects of various treatments on the germination of sawgrass, Cladium jamaicense Crantz, seeds. Wetlands, 18, 51-58.

2. A replicated, randomized, controlled study in 1994–1996 in greenhouses in Florida, USA (Ponzio 1998) found that soaking sawgrass Cladium jamaicense seeds in potassium nitrate either increased or had no significant effect on their germination rate. For 3-year-old seeds planted in 1994, seeds soaked in water then potassium nitrate had a higher germination rate (53%) than seeds soaked only in water (44%). For freshly-collected seeds planted in 1995, the germination rate did not significantly differ between seeds soaked in water then potassium nitrate (55%) and seeds soaked only in water (51%). For reference, seeds that were not soaked in potassium nitrate or water had a germination rate of 55–57%. Methods: Across September 1994 and 1995, sawgrass seeds were sprinkled onto 30 trays of sterilized soil (100 seeds/tray). In 10 trays, the seeds had been soaked in water for 24 h then potassium nitrate for 24 h. In 10 trays, the seeds had been soaked in water only. The final 10 trays were planted with untreated seeds (left dry at room temperature). The trays were placed in random positions in greenhouses and watered daily until no more germination occurred.

   Study and other actions tested

   Referenced paper

   Ponzio K.J. (1998) Effects of various treatments on the germination of sawgrass, Cladium jamaicense Crantz, seeds. Wetlands, 18, 51-58.

3. A replicated, randomized, controlled study in 1994–1996 in greenhouses in Florida, USA (Ponzio 1998) found that soaking sawgrass Cladium jamaicense seeds in nitric acid increased their germination rate. In two of two comparisons, germination rates were higher for seeds soaked in nitric acid then water (55–56%) than for seeds soaked in water only (44–51%). For reference, seeds that were not soaked in nitric acid or water had a germination rate of 55–57%. Methods: Across September 1994 and 1995, sawgrass seeds (either freshly collected or three years old) were sprinkled onto 30 trays of sterilized soil (100 seeds/tray). Ten trays were planted with seeds soaked in nitric acid for 12 h then water for 24 h. Ten trays were planted with seeds soaked in water only. Ten trays were planted with untreated seeds (left dry at room temperature). The trays were placed in random positions in greenhouses and watered daily until no more germination occurred.

   Study and other actions tested

   Referenced paper

   Ponzio K.J. (1998) Effects of various treatments on the germination of sawgrass, Cladium jamaicense Crantz, seeds. Wetlands, 18, 51-58.

4. A replicated, randomized, controlled study in 1995–1996 in a greenhouse in Florida, USA (Ponzio 1998) found that soaking sawgrass Cladium jamaicense seeds in bleach increased their germination rate. The germination rate was significantly higher for seeds that had been soaked in bleach (79% germinated) than for seeds that had only been soaked in water (51% germinated) or had been left dry at room temperature (57% germinated). Methods: In September 1995, freshly-collected sawgrass seeds were sprinkled onto 12 trays of sterilized soil (100 seeds/tray). In four trays, the seeds had been soaked in bleach (2–3% sodium hypochlorite) in a refrigerator for 72 h, then rinsed with tap water. In four trays, the seeds had been soaked in water at 25°C for 24 h. The final four trays were planted with unsoaked seeds. All trays were placed in random positions in a greenhouse and watered daily until no more germination occurred.

   Study and other actions tested

   Referenced paper

   Ponzio K.J. (1998) Effects of various treatments on the germination of sawgrass, Cladium jamaicense Crantz, seeds. Wetlands, 18, 51-58.

5. A replicated, controlled study in 1999 in a laboratory in Alabama, USA (Ervin & Wetzel 2002) found that sterilizing common rush Juncus effusus seeds before sowing increased their germination rate. In three of three comparisons, the germination rate was higher for sterilized seeds (93–96% germinated) than unsterilized seeds (53–81% germinated). Methods: In June 1999, common rush seeds were added to nutrient medium in 24-well cell culture plates. In 74 wells, the seeds had been sterilized before sowing, i.e. rinsed in deionized water, ethanol and bleach (5.25% sodium hypochlorite). In the other 74 wells, seeds had not been sterilized (presumably subjected to none of the rinsing treatments, although this was not clearly reported). Each well contained 5–10 field-collected seeds, stored for two days, two weeks or one year before sowing. Germination was monitored for 2–3 weeks.

   Study and other actions tested

   Referenced paper

   Ervin G.N. & Wetzel R.G. (2002) Effects of sodium hypochlorite sterilization and dry cold storage on germination of Juncus effusus L. Wetlands, 22, 191-195.

6. A replicated, randomized, controlled study in 2015 in a greenhouse in Utah, USA (Marty & Kettenring 2017) found that soaking seeds of three bulrush species in acid or bleach typically increased or had no significant effect on their germination rate, with the precise effect depending on factors such as the chemical used, whether seeds were chilled after soaking, bulrush species and source site. Seeds that had been soaked in bleach before sowing had a higher germination rate than unbleached seeds in 9 of 20 comparisons (for which bleached: 32–74%; unbleached: 2–25%). This included 9 of 10 comparisons involving seeds that were kept at room temperature (not chilled) before planting. Bleached and unbleached seeds had statistically similar germination rates in 8 of the 20 comparisons (for which bleached: 39–68%; unbleached: 27–58%). Seeds that had been soaked in acid before sowing had a statistically similar germination rate to unsoaked seeds in 20 of 20 comparisons (for which acid-soaked: 2–88%; unsoaked: 2–88%). Methods: Field-collected seeds of three bulrush species were sown onto sand in the greenhouse (36–72 sets of seeds/species; ≥100 seeds/set). There were 12–24 sets/species for each of three pre-sowing chemical treatments: soaking in 3% diluted household bleach for 48 h, soaking in 2.7% sulfuric acid for 40 min, or none. Some sets were also chilled and/or soaked in water after chemical treatments. After sowing, seeds were kept saturated and at 28–35°C. Germination rates for each set were recorded five weeks after sowing.

   Study and other actions tested

   Referenced paper

   Marty J.E. & Kettenring K.M. (2017) Seed dormancy break and germination for restoration of three globally important wetland bulrushes. Ecological Restoration, 35, 138-147.