The interaction of heat and smoke in the release of seed dormancy in seven species from southwestern Western Australia

Exposure to high temperatures (40-60 degreesC) over several days to months (simulating summer soil conditions) or to extremely high temperatures (80-120 degreesC) for periods ranging from minutes to several days (simulating the heat of an extreme fire) promoted germination in five (including one legume species) of the seven species tested from southwestern Australia. Heat, a collective term for high temperature (HT) and extremely high temperature (EHT), has previously been used to promote germination in species with impermeable seed coats (many of which are legumes). If heat is found to promote germination in species with permeable seed coats, it could be of use in the release of dormancy for commercial development of native plants. Here we report that elevated storage temperatures (50 degreesC for 45 and 90 d or 60 degreesC for 45 d) and EHT (100 degreesC for 3 h and 120 degreesC for 30 min) alone, and in addition to smoke, directly promote germination of the refractory species Actinotus leucocephalus, Anigozanthos manglesii, Gompholobium knightianum, Loxocarya striatus and Stylidium affine. Germination of Sowerbaea laxiflora seed was not improved with heat alone but was improved by the combination of heat and smoke. Seed of Schoenus unispiculatus did not germinate in response to any of the treatments. Interactions between the effect of temperature, the duration of heat exposure or smoke were detected in all species. Whilst most species demonstrated an interaction between heat and time, not all species were affected by smoke alone. This was illustrated by an interaction between smoke and HT found only in Actinotus leucocephalus, Anigozanthos manglesii and Stylidium affine or smoke and EHT in A. manglesii and S. affine. Smoke and exposure time to heat influenced the germination of Actinotus leucocephalus, Anigozanthos manglesii and L. striatus in response to HT and only S. affine appeared to demonstrate an interaction between smoke and EHT. The variations found in the interactions between treatments suggest that germination events occur over a range of conditions both spatially and temporally which may facilitate seedling survival and limit competition between emergents. (C) 2001 Annals of Botany Company.