Germination characteristics of Cakile edentula (Brassicaceae) seeds from two different climate zones

Different species have different germination strategies to cope with various climates they encounter when spreading, in which temperature and water are two of the most important factors that affect seed germination. Such differences in their coping strategies, therefore, could determine the fate of a species after its invasion into different environments. Cakile edentula is an invasive species originating from North America that invaded Australian coastlines. However, it has gradually disappeared in most of those habitats and can only be found in a few places nowadays. To explore whether germination strategy has had any contribution to such a phenomenon, we collected seeds from two populations with different climate patterns, i.e., subtropical and temperate. Germination experiments were performed using temperature and water potential hierarchies to detect differences of germination characteristics between the two populations. Based on the experimental data, a hydrothermal time model was utilized to further analyze and predict the germination characteristics of seeds from two populations. Results showed that germination percentage of C. edentula was affected by both temperature and water. The temperature and water requirements for germination of C. edentula varied significantly between populations. The population from the sub-tropical area displayed higher base water potential and base temperature for germination. However, there were a large fraction of seeds remaining dormancy, leading to a relatively low germination performance. Overall, our study has shown that C. edentula populations from subtropical and temperate climate zones differed in seed germination behavior, indicating its adaptation after invasion. Such results suggested that there was a wider environmental range than expected for seed germination in C. edentula, potentially promoting its invasion.