Germination and dormancy release of seeds of Australian native understorey species used for minesite rehabilitation

Temperature and pre-treatment effects on the germination of seven Australian native understorey species were studied to determine environmental conditions to maximise germination when broadcast to revegetate mined land. Germination responses to temperatures ranging from 5 to 40°C; transfer from the temperature extremes to 22°C; mechanical, acid and thermal (water at 80°C or 100°C) scarification; and the effect of light or dark were investigated. Seeds of Calytrix tetragona and Bursaria spinosa germinated only when placed at 15 or 22°C. In contrast, species of the Fabaceae family, Hardenbergia violacea, Kennedia rubicunda, Kennedia prostrata, Indigofera australis and Gompholobium latifolium germinated over a wider temperature range, 10 to 32°C. There was no germination of seeds of any of the seven species at 5°C. Moist incubation at 5°C for 14 days prior to seed transfer to 22°C increased the subsequent rate of seed germination at 22°C. Compared to the response of seeds kept continuously at 22°C, exposure to 5°C for 14 days prior to transfer to 22°C considerably reduced germination of K. prostrata and slightly reduced that of other species. Relatively few seeds germinated after they had been incubated at 40°C even if the seeds were transfered to 22°C after 14 days at 40°C. Unlike the low temperature 5°C treatment, exposure to 40°C killed the seeds. Light generally did not affect germination with the exception of two species, G. latifolium and K. rubicunda, which showed an interaction with scarification. Scarification generally improved both percent and rate of seed germination of most Fabaceae despite significant differences between the type and duration of the scarification treatments. Maximum germination of the smaller-seeded species, G. latifolium and I. australis, was obtained following pre-treatment with acid or hot water at 80°C. The larger seeds of H. violacea required boiling or nicking for optimum germination. The temperature requirements of these seven species indicate they have the potential to germinate on minesites in the Hunter Valley whenever moisture is available. Low temperatures will delay germination while conditions of high summer temperatures exceeding 40°C and rainfall would cause seed mortality. Seed treatments are recommended for the Fabaceae and vary depending on the species.