- • Premise of the study: The pathway of radial water movement in tree stems presents an unknown with respect to whole-tree
hydraulics. Radial profi les have shown substantial axial sap fl ow in deeper layers of sapwood (that may lack direct connection
to transpiring leaves), which suggests the existence of a radial pathway for water movement. Rays in tree stems include ray
tracheids and/or ray parenchyma cells and may offer such a pathway for radial water transport. This study investigated relationships
between radial hydraulic conductivity (k[subscript s-rad]) and ray anatomical and stem morphological characteristics in the stems of
three conifer species whose distributions span a natural aridity gradient across the Cascade Mountain range in Oregon, United
• Methods: The k [subscript s-rad] was measured with a high-pressure fl ow meter. Ray tracheid and ray parenchyma characteristics and water
transport properties were visualized using autofl uorescence or confocal microscopy.
• Key results: The k[subscript s-rad] did not vary predictably with sapwood depth among species and populations. Dye tracer did not infi ltrate
ray tracheids, and infi ltration into ray parenchyma was limited. Regression analyses revealed inconsistent relationships between
k[subscript s-rad] and selected anatomical or growth characteristics when ecotypes were analyzed individually and weak relationships
between k[subscript s-rad] and these characteristics when data were pooled by tree species.
• Conclusions: The lack of signifi cant relationships between k[subscript s-rad] and the ray and stem morphologies we studied, combined with
the absence of dye tracer in ray tracheid and limited movement of dye into ray parenchyma suggests that rays may not facilitate
radial water transport in the three conifer species studied.
- Barnard, D. M., Lachenbruch, B., McCulloh, K. A., Kitin, P., & Meinzer, F. C. (2013). Do ray cells provide a pathway for radial water movement in the stems of conifer trees? American Journal of Botany, 100(2), 322-331. doi: 10.3732/ajb.1200333
|Funding Statement (additional comments about funding)
- This work was supported
in part by the U. S. Department of Agriculture Wood Utilization Research
Special Grant to Oregon State University, by National Science Foundation
(09-19871) and Joint Venture Agreement (07-JV-468) with the U. S.
Department of Agriculture, Forest Service Pacifi c Northwest Research