GERMINATION ECOLOGY OF LEPTOCHLOA-PANICOIDES, A SUMMER ANNUAL GRASS OF SEASONALLY DEWATERED MUDFLATS

Leptochloa panicoides is one of many summer annuals that grows on mudf lats formed when water levels in Lake Barkley, an impoundment on the C umberland River in western middle Tennessee and western central Kentuc ky, USA, are lowered in late summer-autumn. Seeds were dormant at matu rity in autumn, and dormancy break occurred over a range of temperatur es (5, 15/6, 20/10, 25/15 and 30/15-degrees-C), with 30/15-degrees-C b eing optimal. Seeds required light for germination. Seeds were buried in flooded and nonflooded soil in October and exposed to natural seaso nal temperature changes. Seeds reach minimal dormancy (i. e., germinat ed over the widest range of temperatures) by the following June or Jul y. Some dormancy loss occurred during winter, but the remainder took p lace as temperatures increased from February through May or June. Afte r the initial (primary) dormancy was broken, exhumed seeds germinated to 80-100 % at 35/20-degrees-C and to 45-100 % at 30/15-degrees-C in a ll seasons of the year, while germination at 25/15-degrees-C reached a maximum (20-100 %) in summer and a minimum (0 %) in winter. Thus, see ds exhibited an annual nondormancy/conditional dormancy cycle. The tem peratures required for germination of nondormant seeds overlap with th ose in the habitat from mid-May to mid- to late September. Consequentl y, seeds can germinate at any time during summer, whenever water level s drop and the mud is exposed.