Effect of flooding on annual dormancy cycles in buried seeds of two wetland Carex species

Buried seeds of Carex comosa and C. stricta were exposed to nonflooded and flooded conditions and natural seasonal temperature changes for 30.5 and 33 mo, respectively. At 1-, 2- or 6-mo intervals, exhumed seeds were tested for germination in light and darkness over a range of daily thermoperiods. Freshly-matured seeds of both species were conditionally dormant; maximum germination was at 35/20°C, in light. Dormancy decreased in nonflooded and flooded seeds of C. comosa during late autumn and winter, but the decrease was greater in flooded than in nonflooded seeds. Nonflooded and flooded seeds of C. stricta gained the ability to germinate in light during the first summer of burial and in darkness during the following winter. Seeds of neither species germinated while they were buried in pots of soil under either nonflooded or flooded conditions in the nonheated greenhouse. Nonflooded and flooded seeds of both species incubated in light and flooded seeds of C. comosa incubated in darkness had an annual conditional dormancy/nondormancy cycle, being conditionally dormant in summer and autumn and nondormant in spring. However, nonflooded seeds of C. comosa incubated in darkness remained dormant, germinating to only 1%. Most nonflooded and flooded seeds of C. stricta incubated in darkness had an annual dormancy/nondormancy cycle, being dormant in summer and nondormant in spring. Thus, flooding influenced the annual changes in dormancy states of buried seeds of C. comosa, but it had no effect on seeds of C. stricta.