Effect of flooding on the annual dormancy cycle and on germination of seeds of the summer annual Schoenoplectus purshianus (Cyperaceae)

Seeds of Schoenoplectus purshianus were dormant at maturity in early autumn and thus did not germinate in light or darkness at 15/6, 20/10, 25/15, 30/15 or 35/20°C. Seeds buried in either flooded or nonflooded soil and exposed to natural seasonal temperature changes for 32 months exhibited an annual dormancy/nondormancy cycle each year when tested in light under either flooded or non flooded conditions. That is, seeds came out of dormancy during autumn and winter and could germinate to high percentages in spring. Burial prevented seeds from germinating, thus they re-entered dormancy by summer and could not germinate at any temperature. Seeds buried in flooded soil and tested in darkness on wet sand (=nonflooded) also exhibited an annual dormancy/nondormancy cycle, but those buried in non flooded soil and tested in darkness on wet sand never germinated to more than 2%. Optimum habitat conditions for high year-to-year germination are a regime of nonflooding in winter and flooding in spring. (C) 2000 Elsevier Science B.V.