Seed size an important factor for the germination response of legume seeds subjected to simulated post-fire soil temperatures

Potential impacts of soil temperatures in a post-fire environment were examined for seeds of legume species with a physical seed dormancy typically found in the eucalypt communities in eastern Australia. Soil temperatures in a post-fire environment may be elevated owing to increased solar radiation and this may influence germination of species with soil-stored seed banks. Seeds were heated at 50, 60 or 70°C, with one unheated control, for 3 h per day for 5 days to simulate soil temperatures where canopy gaps existed. More germination of small-seeded species (<12.6 mg) occurred owing to changes in simulated soil temperatures than large-seeded species (>14.0 mg). Temperatures up to 70°C significantly increased the germination of species with relatively small-sized seeds than large-seeded species (>70°C). This study demonstrated that small-seeded species are able to germinate across a range of temperatures (50-70°C) and can have dormancy broken either during the passage of a fire, or after fire from increased solar radiation, potentially resulting in the decline of the post-fire residual soil seed bank. In contrast, post-fire germination of large-seeded species may be dependent solely on the degree of soil heating during the passage of fire and the species may have a relatively stable residual soil seed bank thereafter.