Global patterns in the evolutionary relations between seed mass and germination traits
During stressful climatic periods, plant populations face significant challenges, especially during germination and seedling establishment. Theoretical studies present conflicting findings regarding the relationship between seed size and germination rate. Some analyses suggest that species with larger seeds should exhibit rapid germination, while others point to faster germination in smaller seeds. This discrepancy can, for example, be attributed to the higher vulnerability of larger seeds to post-dispersal seed predation. To assess the correlation between seed mass and seed germination characteristics at a global scale, we performed a rigorous meta-analysis of published data sources, covering a wide range of germination traits across 1877 species with diverse dormancy types and global distribution. Additionally, we investigated the potential relationship between seed mass and dormancy level. Our findings revealed contrasting responses of germination traits to seed mass, suggesting complex eco-evolutionary correlations among these traits. Trade-offs and corelated evolution likely played an important role in the evolutionary history of seed mass, with seed mass displaying notable trait conservation across the phylogeny. Interestingly, our study demonstrated that seed dormancy exhibited trade-offs with post-germination traits and seed mass. The meta-analysis demonstrated that any changes in the relationship between seed mass and dormancy is dependent on dormancy types with physiological dormancy showing lower seed mass while other dormancy types were has a higher seed mass. These results underscore the critical role of seed mass in shaping plant performance and provide valuable insights into plant trait evolution. Our findings clearly indicate that the hypothesis of larger seeds conferring advantages in both pre- and post-germination traits might not be empirically true in all cases as theoretical studies suggest and that this relationship is complex and varies among species and growth forms. We interpret these results within the context of germination strategies and correlated evolution between seed dormancy and seed mass. Considering these traits in future analyses of plant germination strategies and species distributions is crucial. Factors such as lifespan, seed mass, and germination-related traits should be carefully considered to gain a comprehensive understanding of plant adaptation to challenging environmental conditions.