Virtual Reciprocal Garden Assessment of Germination Syndromes for Elymus elymoides ssp. brevifolius and Elymus multisetus

Bottlebrush squirreltail (Elymus elymoides) and big squirreltail (Elymus multisetus) are high-priority species for restoration of millions of hectares of rangeland in the western United States that have been degraded by accelerated wildfire and introduced annual grasses. Previous research has compared potential germination and seedling performance of these species in a common environment and noted significant genetic differentiation in characteristics that are associated with their environments of origin. In this experiment, we used wet-thermal germination models and long-term simulations of seedbed microclimate to conduct a virtual reciprocal-garden analysis of the potential germination response of these species. We confirmed significant species differentiation in germination rate that appears to confer site-specific advantages for initial seedling establishment in their respective habitats of origin. Our results specifically highlight the relative importance of late-fall seeding for the more rapidly germinating E. multisetus in order to avoid early-fall germination and post-germination seedling mortality from freezing conditions in the winter. In contrast, the slower-germinating E. elymoides ssp. brevifolius A is less likely to germinate in the fall and likely avoids inherently harsher winter temperatures in the seedbed. Virtual simulations of this type might lead to identification of complex-trait genetic markers that are associated with intraspecific and interspecific adaptations to specific environments. Identification of these traits could also inform management of plant communities that are under threat from invasive weeds and climate change.