Seed mass and plant origin interact to determine species germination patterns

Ongoing changes in temperature and precipitation regime may have strong impact on vulnerable life-history stages such as germination. Differences in germination patterns among species and populations may reflect their adaptation to conditions of their origin or may be determined by the phylogenetic constrains. These two effects are, however, rarely separated. All the germination patterns may also be modified by seed mass. We studied 40 populations of 14 species of Impatiens coming from Himalayas. Germination of seeds of different origin was tested in four target temperatures, three simulating original conditions plus a warmer climate change scenario. We also studied effect of shorter stratification and warmer temperature in combination as another possible effect of climate change. Original and target climate interacted and had strong impact on total germination, but not on germination speed and seed dormancy. Interaction between seed mass and original climate indicated different germination strategies in light and heavy seeds. Only seed mass was affected by phylogenetic relationships among the species, while germination response (with exception of T50) was driven primarily by climate of origin. This study is the first to show that the effect of seed mass interacts with original climate in determining species germination patterns under changing climate. The differences in seed mass are thus likely crucial for species ability to adapt to novel conditions as seed mass, unlike seed germination patterns, is strongly phylogenetically constrained. Further studies exploring how seed mass modifies species germination under changing climate are needed to confirm generality of these findings.