PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Interspecific variation in hydraulic architecture in Juniperus (Cupressaceae) species in a phylogenetic context.

Willson, Cynthia^*,1, Maherali, Hafiz², Manos, Paul¹, Jackson, Robert¹, ¹ Duke University, Durham, North Carolina² University of Guelph, Guelph, Ontario, Canada

ABSTRACT- A range of resistance to drought-induced xylem cavitation exists among species. In interspecific comparisons, correlations among xylem cavitation and other hydraulic traits can identify potentially adaptive relationships or tradeoffs. We constructed a molecular phylogeny for 14 Juniperus species to investigate adaptive hypotheses relating interspecific variation in hydraulic architectural traits to each other and to climatic variables and to examine tradeoffs between cavitation resistance and such variables as hydraulic conductivity and wood density. Stem and shallow root (n=4-6) samples were collected in the summers of 2000, 2001, and 2002. Vulnerability curves were constructed using the centrifugal force method to generate cavitation at known tensions. The P₅₀ value is a useful comparative value that represents the tension inducing a 50% loss in hydraulic conductivity. A phylogeny based on sequence variation of the internal transcribed spacer (ITS) of the 18S-26S nuclear ribosomal DNA (rDNA) repeat supports the subdivision of Juniperus section Sabina into species with and without serrate leaf margins. The serrate-margin group, which is roughly composed of the junipers in the western U. S., was more cavitation-resistant, with a mean stem P₅₀ of -10.3 MPa and mean annual precipitation (MAP) approximately half that of the non-serrate group. The non-serrate-margin group, which is roughly composed of the junipers in the eastern U. S. and the Caribbean, was less cavitation-resistant, with a mean stem P₅₀ of -7.2 MPa. Across species, the P₅₀ of both stems and roots showed a significant linear relationship with MAP and a moisture index. Exploring the effects of environment and phylogenetic history on interspecific variation in hydraulic architecture in Juniperus species offers insight into adaptation, tradeoffs, and the factors important in determining their distributions.

Key words: hydraulic conductivity, Juniperus, cavitation, hydraulic architecture