Seed germination ecophysiology of four summer annual mudflat species of Cyperaceae

Cyperus erythrorhizos Muhl., C. flavicomus Michx., Fimbristylis autumnalis (L.) R.&S. and F. vahlii (Lam.) Link are characteristic summer annuals on mudflats that appear every late summer-autumn when water levels in Lake Barkley, an impoundment on the Cumberland River in Tennessee and Kentucky USA, are lowered. Seeds of each species were buried under nonflooded conditions and exposed to natural seasonal temperature changes for 28 months. Each month, exhumed seeds were tested for germination in light and darkness at 12 12 h daily thermoperiods of 15 6, 20 10, 25 15, 30 15 and 35 20°C. At maturity in autumn, seeds of C. flavicomus were dormant, while those of C. erythrorhizos, F. autumnalis and F. vahlii germinated to high percentages, but only at high temperatures. Seeds of the four species after-ripened during winter and germinated to 93-100% in light at 25 15, 30 15 and 35 20°C by February. During the remaining 25 months of burial, seeds germinated to 91-100% in light at simulated May ( 25 15°C), June ( 30 15°C), July ( 35 20°C), August ( 35 20°C) and September ( 30 15°C) temperatures in each respective month; exhumed seeds of C. erythrorhizos, C. flavicomus, F. autumnalis and F. vahlii germinated to a maximum of 7%, 4%, 73% and 0%, respectively, in darkness. Seeds flooded from October to April or May came out of dormancy during winter, and those flooded from February to August did not re-enter dormancy. Thus, the major effect of flooding is prevention of germination while mudflats are under water. Since seeds do not enter dormancy in spring or summer, they can germinate any time during the growing season if the mudflats become exposed.