Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata : Asteraceae). IX. Elemental uptake and niche separation

The concentrations of selected elements and their biological absorption coe fficients were determined for leaves from plants in native stands and recip rocal transplant gardens to determine whether niche differentiation occurs among the parental taxa and their hybrids in the big sagebrush hybrid zone in Utah. The bounded hybrid superiority model predicts such niche different iation, while the ecologically neutral dynamic equilibrium model predicts c omplete niche overlap, at least in the vicinity of the hybrid zone. The con centrations of elements in the leaves of site-indigenous sagebrush and the biological absorption coefficients differed significantly between the subsp ecies and between either parental taxon and hybrids. Within reciprocal tran splant gardens, both the elemental concentrations and the biological absorp tion coefficients differed among the gardens and taxa. Significant genotype -by-environment interactions were observed for several essential elements. Niche differentiation was evident as correspondence analyses ordinated the parental taxa and hybrids into separate groups even when raised in the same garden. These findings support the ecologically based bounded hybrid super iority model and suggest that the big sagebrush parental taxa and their hyb rids have adapted to their respective unique habitats.