Germination strategies of annual forbs from south-eastern Australian semiarid grasslands

Abstract

Germination is a key process driving the composition and dynamics of annual-forb communities and soil seed banks. We tested the germination biology of 20 annual forbs from semiarid grasslands in southern Australia, under a single temperature regime (20/10°C) in either constant darkness or 12-h diurnal light, to assess whether their laboratory germination responses are consistent with transient seed banks and rapid field emergence. Germination in the light was generally moderate to high, with most (70%) species achieving >35% final germination. Additionally, most (90%) species began germinating within 5 days, and all species achieved at least 50% of final germination within 10 days, suggesting that rapid and synchronous germination is the main strategy of annual forbs in this region. However, several species had seeds that continued to germinate for a prolonged period, and in most species, a fraction of seeds did not germinate, demonstrating risk-spreading strategies. Additionally, the germination of most (79%) species was significantly inhibited by continuous darkness. Despite the potential for the formation of large persistent seed banks through low germination in some species and dark inhibition in most, rapid germination and prevailing environmental conditions apparently prevent this in the field.