Evolution of embolism and drought resistance in the biofuel species Silphium perfoliatum- Josh Randall


The Genus Silphium is composed of two subgenera, Silphium and Composita, which are distinguished by growth habit: as either tall sunflower-like or geophytic herbs, respectively. Both groups have scleramorphic leaves as well as high densities of trichomes. Species in Composita are found in drier habitats, and the biofuel species Silphium perfoliatum is a member. The radiation of Silphium into wetter habitats with increased biomass did not come at the expense of leaf toughness, but selection for more vulnerable hydraulic traits could have potentially occurred. The anatomy of both taxa revealed that the number of vascular bundles, their size, and carbon chain accumulation differed between the two and followed the hypothesis of increased hydraulic machinery and decreased lignification in species from the subgenus Silphium. In order to determine if differences are present between the xylem vulnerability to embolism, the optical vulnerability method was performed. Results from this experiment supported the hypothesis that mesic species from the subgenus Silphium have traded embolism resistance for increased growth. Further integration of other species in the genus and carbon accumulation study will be performed to increase strength for the hypothesis that this change defines the Composita and Silphium split. Identifying apomorphies between S. perfoliatum and its closest relatives could reveal traits useful for further utilization as a biofuel or conservation species.


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    1:00 pm - 3:00 pm
    Room(s): Atrium