Geographical variation in predictive seedling emergence in a perennial desert grass

1 Mechanisms that link germination and emergence to environmental cues asso ciated with seedling success (predictive germination) would be expected to evolve when seedlings have a greater mortality risk than seeds, but may be less important in perennial plants than in annual plants. 2 We investigated variation in predictive seedling emergence among divergen t populations of a short-lived perennial desert grass, Digitaria californic a, from sites that differed in climatic and edaphic factors. This species i s native to environments in which the amount and duration of adequate soil moisture may control germination and seedling establishment success. 3 We utilized a special irrigation system that permits application of a ran ge of amounts of water within a single experiment in a glasshouse. Emergenc e data were subjected to probit and survival analyses to describe differenc es among the populations in response to applied water. 4 Significant variation in predictive emergence was shown to exist among po pulations of D. californica when measured as amount of water required for 5 0% emergence following 3 days of water application, or as time required to achieve this level of emergence. Both climatic and soil characteristics wer e important with populations that originated from sites with less summer pr ecipitation, and soils with higher water-holding capacity tended to have lo wer water requirements for emergence. 5 The report demonstrates the existence of subtle variation in predictive e mergence among populations of a perennial grass representing a relatively n arrow range of ecological amplitude. It also establishes the usefulness of line-source irrigation and probit analysis procedures in studying seedling emergence behaviour.