Heat shock, smoke and darkness: partner cues in promoting seed germination in Epacris tasmanica (Epacridaceae)

The Epacridaceae is one of the families that dominate Australian heathlands, environments prone to disturbance events such as fire and seasonal drought. To investigate the role of fire-related cues in breaking seed-dormancy mechanisms in the Epacridaceae, the influences of heat shock, darkness, direct smoke and varying concentrations of aqueous smoke solutions (5, 10 and 100%) on seed germination of the Tasmanian endemic Epacris tasmanica were examined. A small fraction (5.3%) of non-dormant E. tasmanica seed could germinate in the absence of fire-related cues. The most effective treatment for promoting seed germination was direct smoke (74.67%); however, germination with direct smoke was delayed by about two weeks when compared to other significant treatments, suggesting an initial inhibitory effect. Significant interactions were recorded between all classes of treatments (heat shock, darkness and smoke solutions), with treatments acting sequentially and additively to promote germination. The most effective combinatory treatment tested was 5% smoked water (5%S) in conjunction with darkness (D) and heat-shock (H) treatments (5%SDH), which raised germination levels to 49%. In the absence of heat shock, darkness and various concentrations of smoked water had no significant effect on seed germination. The 5%SDH treatment promoted seed germination significantly also in two wet-heathland (E. lanuginosa (42.7%) and E. obtusifolia (64.7%)) and two dry-heathland Epacris species (the Tasmanian endemic E. apsleyensis (72.7%) and the rare mainland Australian E. purpurascens (75%)). The results of this study indicate that fire-related dormancy-breaking cues act synergistically in promoting seed germination in E. tasmanica and suggesting that their level of influence may reflect the ecology of Epacris species.