The changing window of conditions that promotes germination of two fire ephemerals, Actinotus leucocephalus (Apiaceae) and Tersonia cyathiflora (Gyrostemonaceae).

BACKGROUND AND AIMS: Following a period of burial, more Actinotus leucocephalus (Apiaceae) and Tersonia cyathiflora (Gyrostemonaceae) seeds germinate in smoke water. The main aim of this study was to determine whether these fire-ephemeral seeds exhibit annual dormancy cycling during burial. This study also aimed to determine the effect of dormancy alleviation on the range of light and temperature conditions at which seeds germinate, and the possible factors driving changes in seed dormancy during burial.

METHODS: Seeds were collected in summer, buried in soil in mesh bags in autumn and exhumed every 6 months for 24 months. Germination of exhumed and laboratory-stored (15 degrees C) seeds was assessed at 20 degrees C in water or smoke water. Germination response to light or dark conditions, incubation temperature (10, 15, 20, 25 and 30 degrees C), nitrate and gibberellic acid were also examined following burial or laboratory storage for 24 months. In the laboratory seeds were also stored at various temperatures (5, 15, 37 and 20/50 degrees C) for 1, 2 and 3 months followed by germination testing in water or smoke water.

KEY RESULTS: The two species exhibited dormancy cycling during soil burial, producing low levels of germination in response to smoke water when exhumed in spring and high levels of germination in autumn. In autumn, seeds germinated in both light and dark and at a broader range of temperatures than did laboratory-stored seeds, and some Actinotus leucocephalus seeds also germinated in water alone. Dormancy release of Actinotus leucocephalus was slow during dry storage at 15 degrees C and more rapid at higher temperatures (37 and 20/50 degrees C); weekly wet/dry cycles further accelerated the rate of dormancy release. Cold stratification (5 degrees C) induced secondary dormancy. By contrast, no Tersonia cyathiflora seeds germinated following any of the laboratory storage treatments.

CONCLUSIONS: Temperature and moisture influence dormancy cycling in Actinotus leucocephalus seeds. These factors alone did not simulate dormancy cycling of Tersonia cyathiflora seeds under the conditions tested.