Seed moisture content affects afterripening and smoke responsiveness in three sympatric Australian native species from fire-prone environments

Germination of freshly collected seeds of three sympatric herbaceous species native to fire-prone environments in south-western Australia was significantly improved through the application of novel combinations of dry heat, gibberellic acid, smoke water and dry afterripening. For fresh seeds, combinations of dry heat, gibberellic acid and/or smoke water resulted in > 80% germination in Austrostipa elegantissima (Poaceae) and Stylidium affine (Stylidaceae) seeds and > 60% germination in Conostylis candicans (Haemodoraceae) seeds, compared with < 10% germination of control seeds. For fresh seeds, two broad germination patterns were observed in response to smoke water: nil - low germination for both control and smoke water-treated seeds (A. elegantissima and S. affine); and a significant smoke response (35%) compared with control seeds (1%) (C. candicans). During afterripening, high germination for A. elegantissima seeds was achieved following 3 months storage of seeds at equilibrium relative humidities of 23-75%, but seeds stored at 5-13% equilibrium relative humidities took 6-36 months to achieve similar levels of germination. Germination of C. candicans seeds also increased after 3 months storage, to > 60% at each equilibrium relative humidity and further increases over time were slight. For S. affine seeds > 60% germination was achieved only after 36 months storage at 50% equilibrium relative humidity. Seeds from all three species were smoke-responsive at some point, but the interaction/effects of afterripening on the smoke response varied significantly between species. This study highlights an apparent effect of seed dormancy status on response to smoke and a surprisingly high level of ecological variation in pre-germination requirements (cues) for these co-occurring species that may relate to variation(s) in microsite selection forces operating on the soil seed bank of the different species.