Temperature and Light Effects on the Germination of Seven Native Forbs.

Abstract

Seeds of seven native herbaceous species common in natural grasslands and woodlands of south-eastern Australia were tested for germination over a range of alternating temperatures (15/5-35/25°C) with and without light. Seeds were also exposed to low (4°C) and high (50/40°C) temperatures and the addition of gibberellic acid. Tests were conducted on seeds stored for 0-15 months at room temperature.

The optimum temperature for germination differed among species, with only Helipterum albicans germinating maximally over all temperatures. Germination of Bulbine bulbosa seed was the most strongly temperature-dependent. Light and cold treatments promoted germination in Helipterum albicans and Vittadinia muelleri only. Short-term dormancy (3-4 months) was shown to occur in fresh seeds of Stylidium graminifolium, Helichrysum apiculatum and Wahlenbergia stricta, but not in seeds of the other species; addition of gibberellic acid to seeds of the two last-named species did not overcome that dormancy. Seeds of all species remained germinable after 15 months of storage. Seeds of most species germinated maximally at 20/10°C. Storage at high alternating temperatures for 1 month inhibited subsequent germination at 30/20° in Leptorhynchos squamatus and S. graminifolium but increased it in V. muelleri, H. albicans and H. apiculatum. In the last species, exposure of 1-month-old seeds to high temperature broke dormancy.

These results show that germination and dormancy of seeds of a range of native forbs vary with temperature and light regime; they provide an initial basis on which to test and interpret the effects of seasonal factors on germination and field establishment.