| Artemisia tridentata (big sagebrush) is a dominant shrub across western North America,
where it plays a critical ecological role in arid and semi-arid ecosystems increasingly threatened
by climate change. Increasing temperatures, changes in precipitation regimes, and increased fire
cycles have contributed to a decrease in A. tridentata density across its range. Intraspecific
variation is crucial for plant adaptive capacity, especially in environments with limiting
resources. Variation in plant physiology is controlled by a combination of genetic factors,
environmental factors, and interactions between the two (G x E). Understanding how genetic and
environmental factors influence drought-related traits in A. tridentata is essential for predicting
its persistence and guiding restoration strategies. However, the breadth of studies exploring
intraspecific variation and genetics in A. tridentata is limited. In this dissertation, I performed
three complementary studies using a combination of common garden experiments and fieldbased measurements to assess intraspecific variation across subspecies (ssps. tridentata and
wyomingensis), cytotypes, populations, and climate of population origin. Across studies, climate
of population origin and ploidy were stronger predictors of phenotypic variation than subspecies
identity. Common garden studies showed limited divergence between subspecies in springtime
physiological traits with late-season measurements revealing greater variation. In-field
measurements across fine-scale soil-moisture and elevation gradients suggest stomatal
mechanisms may dominate photosynthesis limitation and present population-level variation.
These results underscore the importance of fine-scale genetic and environmental variation in
shaping drought response, with implications for seed sourcing and habitat restoration under future climate scenarios. Together, these studies highlight the complex interplay of
genetics, environment, and physiology that governs drought resilience in A. tridentata.
Keywords: adaptation, diversity, drought, ecophysiology, plasticity |