Germination ecology of Leptochloa panicoides, a summer annual grass of seasonally dewatered mudflats

Leptochloa panicoides is one of many summer annuals that grows on mudflats formed when water levels in Lake Barkley, an impoundment on the Cumberland River in W middle Tennessee and W-central Kentucky, are lowered in late summer-autumn. Seeds were dormant at maturity in autumn, and dormancy break occurred over a range of temperatures, with 30/50°C being optimal. Seeds required light for germination. Seeds were buried in flooded and nonflooded soil in October and exposed to natural seasonal temperature changes. Seeds reach minimal dormancy by the following June or July. Some dormancy losses occurred during winter, but the remainder took place as temperatures increased from February through May or June. After the initial (primary) dormancy was broken, exhumed seeds germinated to 80-100% at 35/20°C and to 40-100% at 30/15°C in all seasons of the year, while germination at 25/15°C reached a maximum (20-100%) in summer and a minmum (0%) in winter. Thus, seeds exhibited an annual nondormancy/conditional dormancy cycle. Seeds can germinate at any time during summer, whenever water levels drop and the mud is exposed. -from Authors