Cyclic dormancy, temperature and water availability control germination of Carrichtera annua, an invasive species in chenopod shrublands

Abstract

We studied the germination of seeds of Carrichtera annua L. from a single cohort, stored in the field for up to 18 months, when retrieved at different times and subject to different combinations of temperature and water availability. Germination was affected by season of retrieval, and temperature and water availability in a complex interactive way. Germination rates were lowest when seeds were retrieved during summer or spring, but seeds germinated readily when retrieved during autumn and winter, if exposed to temperatures simulating autumn or winter conditions, and provided water equivalent to at least 50% field capacity. High temperatures and low water availability reduced germination substantially. The results indicate that this species has a combination of cyclic dormancy and germination requirements that minimizes the risk of germination during periods when the risk of prereproductive mortality is high. Given the short life of the seeds of this species, these mechanisms may be essential for the persistence of the species in the highly unpredictable arid lands of southern Australia.