Diversity and adaptation along altitudinal gradients in three wild Allium spp. native to Utah and implications for horticultural practices

The propagation of some native plant species can be problematic due to localized adaptation resulting in diverse genotypes and phenotypes. Geophytic species in particular have distinct life history traits that complicate the development of efficient propagation methods. In the Intermountain West, seed and bulb dormancy mechanisms in geophytes must be understood before effective propagation methods can be developed. These dormancy characteristics influence crucial life history events such as germination, growth, and reproductive development. This study explores the diversity, both genetic and physiological, along an altitudinal gradient in three Allium species native to Utah: Allium acuminatum, A. brandegei, and A. passeyi. Three wild stands of each species were selected to represent within-species habitat differences. Individuals from two additional A. acuminatum as well as one additional A. passeyi site were included in an amplified fragment length polymorphism (AFLP) study designed to investigate patterns of genetic diversity within and among the three species. Genetic divergence (ΦST) was detected between collection sites, indicating genetically distinct populations, and was lower in the rare species, A. passeyi, suggesting that inter-population gene flow may be correlated with range size. Laboratory and field germination and growth studies confirmed the presence of divergent adaptation in seed germination behavior, seedling growth characteristics, summer dormancy traits, and reproduction. All species required stratification for optimal seed germination, and the duration of the stratification was strongly correlated with altitudinal variation among species. Seedling growth trends were taxon-dependent, and the narrowly restricted species, A. passeyi, exhibited more habitat-specific seedling growth characteristics than the more common species. Bulb dormancy release in all three species occurred at moderate temperatures after exposure to moist conditions. Allium acuminatum bulb dormancy release showed little variation among treatments, suggesting a high level of plasticity for this trait. Only A. brandegei demonstrated a clear habitat-correlated temperature preference. It achieved a significantly higher proportion of bulb regrowth at the temperature most likely to exist at high elevations in the fall. Patterns of demography were linked to yearly climate variation, and differed between the rare species and the more common species. Field observations indicate that temperature is likely the key environmental cue inducing summer dormancy. Differences in the timing of dormancy induction were associated with the climatic trends at the collection site.