Seed mass and plant home site environment interact to determine alpine species germination patterns along an elevation gradient

Ongoing changes in temperature and precipitation regime may have a strong impact on vulnerable life-history stages such as germination, especially in alpine regions. Differences in germination patterns among species and populations may reflect their adaptation to conditions of their origin or may be determined by the phylogenetic constraints. 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 different elevations in the Himalayas. Three home site temperatures were simulated and one warmer temperature according to a climate change scenario were used. We also studied the combined effect of shorter stratification and warmer temperature as another possible effect of climate change. Interactions of home site and germination conditions affected total germination and germination speed, but not seed dormancy. Seed mass and home site conditions’ interaction indicated different germination strategies in light and heavy seeds. Only seed mass was affected by phylogenetic relationships among the species, while germination response (except T30) was driven primarily by home site conditions. This study is the first to show that the effect of seed mass interacts with home site conditions 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 since 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 generalisability of these findings.