AOBPreview originally published online on September 30, 2005
Annals of Botany 2005 96(7):1225-1236; doi:10.1093/aob/mci274
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The Changing Window of Conditions that Promotes Germination of Two Fire Ephemerals, Actinotus leucocephalus (Apiaceae) and Tersonia cyathiflora (Gyrostemonaceae)
1 School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia, 2 Alice Springs Desert Park, PO Box 2130, Alice Springs, NT 0871, Australia, 3 School of Pharmacy, Division of Health Sciences, Murdoch University, Murdoch, WA 6150, Australia and 4 Botanic Gardens and Parks Authority, Kings Park and Botanic Garden, West Perth, WA 6005, Australia
* For correspondence. E-mail katherine.baker{at}nt.gov.au
Received: 21 June 2005 Returned for revision: 2 August 2005 Accepted: 18 August 2005 Published electronically: 30 September 2005
• 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 °C) seeds was assessed at 20 °C in water or smoke water. Germination response to light or dark conditions, incubation temperature (10, 15, 20, 25 and 30 °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 °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 °C and more rapid at higher temperatures (37 and 20/50 °C); weekly wet/dry cycles further accelerated the rate of dormancy release. Cold stratification (5 °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.
Key words: Dormancy cycling, fire ephemeral, germination stimulants, scarification, smoke water, soil burial, storage temperature, Actinotus leucocephalus, Tersonia cyathiflora
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