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 coefficients were determined for leaves from plants in native stands and reciprocal 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 differentiation, while the ecologically neutral dynamic equilibrium model predicts complete niche overlap, at least in the vicinity of the hybrid zone. The concentrations of elements in the leaves of site-indigenous sagebrush and the biological absorption coefficients differed significantly between the subspecies and between either parental taxon and hybrids. Within reciprocal transplant gardens, both the elemental concentrations and the biological absorption 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 superiority model and suggest that the big sagebrush parental taxa and their hybrids have adapted to their respective unique habitats.