SANDQUIST, DARREN. Department of Biological Science, California State University, Fullerton, CA 92834 U.S.A.. - Integrated physiological, morphological and phenological responses to drought associated with “adaptive” leaf pubescence in a desert perennial shrub.
Putative phylogenetic constraint of plasticity for physiological and
morphological traits in the genus Encelia (Asteraceae)
appears to have resulted in strong selection for plasticity of leaf
pubescence within at least one species, Encelia farinosa. Leaf
pubescence is a crucial component of the energy balance, water
relations and photosynthetic physiology of this drought-deciduous
desert shrub, but pubescence development is also irreversible and thus
prevents adaptive responses under certain conditions such as
mid-drought rainfall. Carbon-gain and water-use tradeoffs associated
with these developmental responses play a complex role in adaptation
of this species across a broad environmental matrix. I will discuss
how a combination of population genetic and ecophysiological studies
has been used to elucidate these complex relationships and relate them
to the environmental heterogeneity of this species’ range. Of these
analyses, one (carbon isotope ratio) provides an integrated
measurement of multiple physiological responses (photosynthesis and
water-use). Due to the unique but fairly well understood interplay of
phenotypic limitations and plasticity in this species, Encelia
farinosa provides a model system for the study of phenotypic
integration and adaptation in plants.
Key words: drought, Encelia, leaf pubescence, photosynthesis, plasticity, water-use