Variation in seed germination of 86 subalpine forest species from the eastern Tibetan Plateau: phylogeny and life-history correlates

We have examined the seed germination strategy of 86 subalpine woody species from the eastern part of the Tibetan Plateau and assessed correlations between seed germination and phylogeny, life-history attributes, habitat, and altitude using stepwise analyses of variance (ANOVAs) and phylogenetically independent contrasts (PICs). A series of ANOVAs revealed that the total amount of variance in the arcsine-transformed value of germination percentage among species could be accounted for by phylogeny (19.2%) and dispersal mode (14.3%) in seeds incubated in the light and by phylogeny (29.3%) and dispersal mode (11.0%) in those incubated in the dark. In addition, the total amount of variance in T50 (days to half of the final germination) can be accounted for by phylogeny (22.7%) and dispersal mode (17%) in seeds incubated in the light and by phylogeny (32.1%) and dispersal mode (9.9%) in those incubated in the dark. PICs indicated a significant correlation between germination percentage and dispersal mode and a positive correlation between T50 and seed mass, showing that wind-dispersed seeds had higher germination percentages than both unassisted and vertebrate-dispersed seeds and that small seeds germinated faster than large ones. We suggest that phylogeny and dispersal mode may constrain variation in seed germination across species and that the speed of germination and seed mass may co-vary to adapt to a variable environment. Therefore, from an evolutionary perspective, seed germination might be the result of both selective pressures over long-term ecological time and phylogenetic constraints over the long-standing evolutionary history of the phylogenetic group.