Dormancy and germination in a guild of Sonoran Desert annuals

To investigate bet hedging and species coexistence in a guild of Sonoran Desert winter annuals, we subjected seeds of eight species to factorial combinations of summer treatments (varying temperature and precipitation), germination conditions (representative of early, middle, and late germination season temperatures and day lengths), and experiment trial dates (spanning the germination season). In keeping with bet hedging theory, we found that many viable seeds would not germinate in response to any combination of treatments (germination usually <50%). In keeping with the storage effect model, we found that these coexisting species differed in their germination response to our experimental manipulations and also differed in how the experimental variables interact. Field germination data from a long-term project on population and community dynamics of this guild show that germination fractions are similar between field and growth chamber and that species that tend to germinate under early season conditions in the growth chamber also tend to do so under unmanipulated field conditions. Some species are nondormant during the summer and only acquire dormancy at the onset of the autumn germination season, while others appear to have either innate or conditional dormancy until the onset of the germination season.