title: Relationships among xylem transport, biomechanics and storage in stems and roots of nine Rhamnaceae species of the California chaparral.
abstract: Here, hypotheses about stem and root xylem structure and function were assessed by analyzing xylem in nine chaparral Rhamnaceae species. Traits characterizing xylem transport efficiency and safety, mechanical strength and storage were analyzed using linear regression, principal components analysis and phylogenetic independent contrasts (PICs). Stems showed a strong, positive correlation between xylem mechanical strength (xylem density and modulus of rupture) and xylem transport safety (resistance to cavitation and estimated vessel implosion resistance), and this was supported by PICs. Like stems, greater root cavitation resistance was correlated with greater vessel implosion resistance; however, unlike stems, root cavitation resistance was not correlated with xylem density and modulus of rupture. Also different from stems, roots displayed a trade-off between xylem transport safety from cavitation and xylem transport efficiency. Both stems and roots showed a trade-off between xylem transport safety and xylem storage of water and nutrients, respectively. Stems and roots differ in xylem structural and functional relationships, associated with differences in their local environment (air vs soil) and their primary functions.
authors.affiliation: Department of Biology, California State University, Bakersfield, Bakersfield, CA 93311, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Pratt
authors.affiliation: Michigan State University, Department of Plant Biology, East Lansing, MI 48824, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Jacobsen
authors.affiliation: Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768, USA.
authors.forename: F W
authors.initials: FW
authors.lastname: Ewers
authors.affiliation: Natural Science Division, Pepperdine University, Malibu, CA 90263, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Davis
mesh_terms: D002140:California; D002980:Climate; D005843:Geography; D018517:Plant Roots / Q000502:physiology*; D018547:Plant Stems / Q000502:physiology*; D027823:Rhamnaceae / Q000145:classification / Q000502:physiology*; D052584:Xylem / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*