Dormancy release in Australian fire ephemeral seeds during burial increases germination response to smoke water or heat

Abstract

Fire ephemerals are short-lived plants that primarily germinate after fire. Fresh and laboratory-stored seeds are difficult to germinateex situ, even in response to fire-related cues such as heat and smoke. Seeds of eight Australian fire ephemeral species were buried in unburnt and recently burnt sites of natural bushland during autumn. Seeds were exhumed after 6 and 12 months and incubated in water and smoke water, either with or without a heat treatment at 70°C for 1 h. Generally, germination did not increase after 6 months of burial, but after 12 months of burial germination was enhanced in seven of the eight species.Actinotus leucocephalusproduced higher germination following 12 months of burial without any further treatment, and smoke water and heat further improved germination. The fourGyrostemonaceaespecies,Codonocarpus cotinifolius,Gyrostemon racemiger,Gyrostemon ramulosusandTersonia cyathiflora, only germinated in the presence of smoke water, and their germination was enhanced by burial. Burial improved germination in response to a heat treatment inGrevillea scapigeraandAlyogyne huegeliiseeds, but did not enhanceAlyogyne hakeifoliagermination. During concurrent dry laboratory storage of seeds at 15°C, onlyActinotus leucocephalusproduced increased germination in response to smoke water and heat over time. In summary, soil burial can alter the dormancy status of a number of Australian fire ephemeral seeds, rendering them more responsive to germination cues such as smoke water and heat. The requirement for a period of burial before seeds become responsive to smoke and/or heat would ensure that seeds persist in the soil until a subsequent fire, when there is an increase in nutrients available for growth and reduced competition from other plants.